6 ms·

Should you wash your solar panels?

247 points by surprisetalk 3mo ago

walrus01 3mo ago
It's a bit worrying the author is asking chatgpt about the tingle rather than making sure there's a grounding lug on all the panels and they're all bonded to a grounding rod. The rudimentary nature of the setup makes me think there isn't something like a single conductor 12awg (or euro equivalent) copper wire that bonds to all panels and a basic $30 rod.
- quickthrowman 3mo ago
  The system in question does not have a transformer so a grounding rod is not required as it is not a separately derived system. The equipment grounds should be tied together to prevent any difference in potential though.
  - amluto 3mo ago
    There are many different ways to connect solar panels to the inverter. Usually the exposed metallic parts will be “grounded” (bonded to the ground / protective earth / equipment grounding conductor / whatever your jurisdiction calls it at the inverter). But this is an array that looks a bit remote from any structure, and even if the electronics themselves are utterly, perfectly safe, the bonding wire will cause the panel frames to be at the potential of the inverter’s ground, and the soil will be at whatever its local potential is, and this may be different, resulting in a “touch potential”. You can mitigate this with a supplemental ground (or whatever your jurisdiction calls it) closer to the panels. There are fancy ways to do this particularly well to improve safety in the event of a fault. If you are contacting the actual power wiring of the solar array, something is wrong. If you are feeling capacitive coupled current from the power wiring of the array, then I imagine this means your inverter has crappy filtering, and again the only way you would feel it is if the panel frame isn’t at the same potential as the local soil. Oh, and if you live somewhere prone to lightning, you probably want to give a possible lightning strike to the panel a better route to a high quality ground than through the bonding wire to your house. (In fact, in many parts of the world, including IIRC 48 US states, the power utilities may operate their distribution networks with a current carrying wire (combined neutral and ground) that is grounded at multiple points along its route, which will generate substantial leakage current through the ground. The exceptions are IIRC California and Wisconsin, and IIRC those states have their rules to help protect cattle from becoming part of an undesirable circuit while being milked. In CA at least, all the distribution transformers on the poles have at least two bushings on the primary side, and this is why. I believe this is California General Order 95, rule 33 [0].) [0] https://ia.cpuc.ca.gov/gos/go95/go_95_rule_33.html https://ia.cpuc.ca.gov/gos/go95/go_95_rule_33.html
    - deleted 3mo ago
      [deleted]
    - quickthrowman 3mo ago
      > Usually the exposed metallic parts will be “grounded” (bonded to the ground / protective earth / equipment grounding conductor / whatever your jurisdiction calls it at the inverter). It’s not usually, all of the panels and also the metal racking must be bonded and grounded. Supplementary grounds are allowed by the NEC, article 250.54 There are zero requirements for supplemental grounds, you could use a single 24AWG conductor bonded to a brad nail or a #6 bare copper conductor bonded to (3) 5/8” dia’ 10’ ground rods. The fact that there are no requirements should tell you something about the necessity of supplemental grounds. > 250.54 Auxiliary Grounding Electrodes. One or more grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 or 250.53(C) or the resistance requirements of 250.53(A)(2) Exception, but the earth shall not be used as an effective ground-fault current path as specified in 250.4(A)(5) and 250.4(B)(4).
      - amluto 3mo ago
        The OP is pretty clearly not in the US and is not subject to the NEC. And just because the NEC doesn’t say you need to mitigate touch potentials for a specific installation doesn’t mean that you shouldn’t. The NEC is just a bunch of requirements, not a complete guide to building safe, high quality electrical installations. And there appears to be plenty of guidance from IEEE about this if you feel like paying for a copy of the standard: https://store.accuristech.com/ecia/products/preview/2085911 https://store.accuristech.com/ecia/products/preview/2085911 The NEC does have plenty to say about grounding for purposes of reducing potential differences in other (non-solar) installations, though. Swimming pools are a notable example (with no specific requirement IIRC to connect the fancy bonding to the Earth at the pool, but a typical concrete pool with NEC-mandated bonding is likely an excellent connection to the local soil). Amusingly, an inspector could plausibly require an “equipotential plane” per NEC 547.44 if the solar array is accessible to livestock. Alternatively, from first principles: suppose you are standing with bare feet on wet soil 100 meters from a building. That building has a very nice ground rod array, giving an impedance of 50 ohms from the building’s ground to your feet. Now take a long wire that is insulated except at the ends, connect one end to the building ground, and firmly hold the other end in your hand. How do you feel about this situation? You have a nice wire loop, potentially with area on the order of 100m^2, containing your heart. It can inductively couple to time-varying magnetic fields (e.g. the fields around nearby transmission lines) and it can capacitively couple to other conductors. It can resistively couple to power lines with multiply grounded neutral or to electrified railways or to nearby buildings with old-style (earlier NEC revisions) shared neutral/ground feeds And lightning can strike the array. I think it would be wise to ground the array to earth to reduce the potential difference between the frame and earth.
  - deleted 3mo ago
    [deleted]
  - aetherspawn 3mo ago
    I’m an electrical engineer. I just want to explain the hazard with panels. They are DC, and the voltage is usually very high, between 300V and 600V. At this voltage you will get a burn, like touching a hot kettle, but because it is DC you will be able to easily “untouch” it. Yes, the panel frames should all be grounded to each other, and also to Earth in one spot along the chain, as this makes it more difficult to be electrocuted by them because the resistance of the grounding wire is much lower than the resistance of your body, and electricity takes the shortest path.
    - quickthrowman 3mo ago
      I was just pointing out that a solar installation with only an inverter and no transformer does not need a separate ground since it’s not a separately derived system. An auxiliary/supplementary ground rod is allowed by the NEC (250.54) but it is not required.
      - aetherspawn 3mo ago
        Well, this is US code which is fairly lax and has a ludicrously low voltage grid, but in virtually every other country it is required
- tclancy 3mo ago
  Eh, compared to what though? Compared to speaking to licensed electrician, definitely. But compared to doing a raw web search and trying to put the information in the right order for the application you’re currently working on, I think it’s at worst a wash.
  - bityard 3mo ago
    > a wash Well done on this cleanly-executed pun.
    - tclancy 3mo ago
      Took four open weight models to land it. And you are giving me way more credit than I am due.
      - vermilingua 3mo ago
        This comment made me very sad
1123581321 3mo ago
Appreciate the attempts to quantify it. I haven't tried to quantify washing, but I do look at mine regularly. I doubt anything accumulates that rain doesn't handle well enough. Messing around with ground panels is lower risk and safer than roof panels where tool extenders and ladders start to become involved. If you have roof panels, you are the biggest danger to your panels (and yourself.) Don't try to clean them, spray them, knock snow off of them. I was told this multiple times by my installer. :)
- msdz 3mo ago
  As another anecdata-point, when we did this for a now already fairly old roof installation of about 15kWp, it was more than “just about worthwhile”, since the panel area is contiguous: cost seemed to scale up less quickly than the wattage/theoretical maximum output, and the cleaning guy (solo company, IIRC) even told us it wasn’t necessary to do this every year (we hadn’t had it done even once the first decade+ of the installation’s lifetime). So, at least in our case, definitely worth it.
  - 1123581321 3mo ago
    Interesting; what was on the panels? What was the ROI on paying the guy?
    - msdz 3mo ago
      Unfortunately I don’t recall anymore, since this took place at my father’s PV installation. I’ll try to post an update when/if I get exact numbers, though!
- varispeed 3mo ago
  In many countries it is actually illegal to use tall ladder etc. owners would have to erect a scaffolding to make access for work people to clean it safely.
  - dd8601fn 3mo ago
collabs 3mo ago
Maybe the thing to do is to NOT upgrade existing working panels but rather set up a different/separate entity with completely different accounts and new panels? And about the washing, I wonder if it would be worth it to automate the process with a spray of water periodically? You can still wash the panels but I suspect it won't be necessary if there isn't too much dust accumulation? Isn't rain supposed to wash away the dust? What am I missing here?
- ido 3mo ago
  Some places don't get much rain (and these are the places that tend to get even more dust - e.g. deserts).
- rjmunro 3mo ago
  It may also be worth spraying them with water when they are too hot. As they get hotter the efficiency drops a little. It's only a few percent, and usually it happens at the time you need the efficiency the least because it's sunny, but if you can combine cleaning and cooling and get a few extra w out if it, why not.
  - collabs 3mo ago
    Yes, I meant I can get on board with automatically (periodically or based on some trigger or sensor) spraying the panels with water but I was hoping it isn't necessary to use Windex® or even dish soap on the panels themselves.
  - Tade0 3mo ago
    Solar panels are increasingly being oriented east or west instead of south, as while it reduces overall yield, it maximises power when it's needed the most - during morning and evening peaks. I don't have numbers, but I suspect it alleviates issues with dust buildup and temperature.
    - sluongng 3mo ago
      isn't that more of a storage issue, which a home battery would solve?
bebe8393jrir 3mo ago
> If I increase the power output of the system then the additional capacity will not be eligible for the feed-in tariff and will revert to present-day prevailing tariff which is about 4x worse before you even consider that I currently get to use electricity and still get paid for generating it. > This is the yin and yang of market-distorting incentives. Today's incentive to install solar becomes tomorrow's disincentive to upgrading it. I am not sure what author is trying to hint. But solar does not need artificial subsidies, and can pay for itself! There are no subsidies in UK! Homeowners get so much money, because of all that sunshine and wind energy, their house generates! UK goverment just run out of money, when energy got expensive! UK goverment needs to step up, to replace gaz with renewables! You can not expect homeowners to sell energy bellow market price!
- philipallstar 3mo ago
  Solar gets lots of subsidies in the UK. Homeowners who installed it 10 years ago get a ridiculous payment for generating excess, even if the grid doesn't use it.
- rjmunro 3mo ago
  > solar does not need artificial subsidies, and can pay for itself That's true now, but wasn't true when those panels were installed. There were subsidies available to get the market kick-started. They consist of an extra payment for every kwh you generate on top of the payment for delivering the power to the grid. The amount varied depending on when you signed up to the scheme, but at certain points it was as much as 50p/kwh (+ inflation, so more than that now).
- otherme123 3mo ago
  > I am not sure what author is trying to hint. But solar does not need artificial subsidies, and can pay for itself! I think he is describing a subside that some governments gave years ago: you installed for example 5K, and get paid for whatever they generate at 300% market price, for a long time (25 years?). Today you find out that upgrading panels would made perfect financial sense, if you were selling at 100% and are going to sell electricity at 100% (you will be doubling the output for a tenth of the inversion 15 years ago), but as the subsides of 300% no longer exist, you will be actually losing money by upgrading.
wodenokoto 3mo ago
> why would you clean them when you're about to sell the house? So they look good and the potential buyer sees something that looks to be in good condition and working well.
- engineer_22 3mo ago
  I agree. Doesn't matter what you sell, you will get a higher price if it is cleaned and tidy when presented to the market - because the kinds of people who pay higher prices are looking for clean and tidy things.
  - throw0101d 3mo ago
    See also "staging": * https://en.wikipedia.org/wiki/Home_staging https://en.wikipedia.org/wiki/Home_staging
    - saagarjha 3mo ago
      Why is it written like that lmao
      - blitzar 3mo ago
        Its been "staged"
      - Nzen 3mo ago
        Wikipedia is written by various people, but likely someone with interest in a given topic. One or more realtors probably wrote or edited this post. Actually, the history of edits shows that this is contested territory where people regularly remove what they term as spam links. So, while a disinterested editor might remove a link to a listicle about how to stage your home, they might leave in the breathless tone as harmless. The drive by editors probably feel that they have no more time to rewrite it than we do, given that they watch over many articles, not just this one.
  - namdnay 3mo ago
hgomersall 3mo ago
Our peak daily export energy jumped by about 35%-40% when we had our panels cleaned for the first time in 8 years. They _look_ much cleaner, and the measured export shows it.
- trimethylpurine 3mo ago
  If export energy is 10% of your total output, and it jumped 35% then you got a ~3.5 - 4% gain in total output, not far from the author's experience. Of course, you can math that any way you like to make the numbers bigger or smaller, depending on whether you're representing the buyer or the seller of the system.
  - hgomersall 3mo ago
    It's not 10%, it's much more than that. I'm obviously comparing the peak values, which tend to be days when we don't consume much, which might mean a background 100W vs a couple of kW peak generation. I can dig deeper into the per hour generation and it's similar.
    - trimethylpurine 3mo ago
      I'd just measure total output and don't bother looking at export output. More variables and conversions in the experiment will tend to reduce the accuracy of the results.
infecto 3mo ago
Nobody can answer this. It simple depends on each setup. Some panels will get incredibly dirty quick like those in the south west where there may be a lack of rain and lots of dust but in other regions you may never need to.
z2 3mo ago
Given the angle of a panel should match its latitude and average sun angle, the panels might generate noticeably more by being pitched steeper at over 30 degrees. Eyeballing this, it appears closer to 25 degrees right now which doesn't even make sense for the summer sun in the UK. I could be wrong as it also appears these are on a slope!
ape4 3mo ago
I imagine rain will clean them. In most places it rains every so often.
- namdnay 3mo ago
  my experience is that unless you get some really torrential rain, it's not enough to clean the sand/dust/grime
  - left-struck 3mo ago
    Can confirm, my car doesn’t get cleaner unless there’s a downpour
- mywittyname 3mo ago
  Rain usually just cakes the dirt. Unless it's a downpour, it doesn't move with enough velocity or volume to remove the dirt. So the dirt just gets damp, maybe moves a few cm with gravity, then dries as a mud cake.
  - coredog64 3mo ago
    See this all the time in Phoenix metro: A light rain just pulls down all the dust in the air and deposits it on the car. It has to be fairly sustained to wash away the initial dust collection, and even then you can still see dust on the paint.
rcxdude 3mo ago
Re: the slightly strange shape of the curve. The drop at the beginning could be due to the matching between the panels getting worse. Solar panels in a bank don't like being in different conditions. As a rule of thumb they will all perform at about the same level as the worst in the bank but at the finer levels you could get less straightforward interactions. The drop off after cleaning could well be because some of the initial boost could come from the water cooling off the panels: solar panels become less efficient at higher temperatures so the drop of after they're all cleaned could be them warming up again after the water has evaporated.
- kurthr 3mo ago
  Yeah, came here to say this. There are a lot of things that will affect efficiency and how clean your panels are is only one of them. How dirty your panels get is also highly sensitive to both location and installation. All of this gets horribly confounded by string inverters (especially if they're clipping the peak, which they often are). I easily see 5% increases in efficiency after cleaning (with micro inverters), but also see ~3% increase in output on a hot day from just spraying the panels with water to cool them off, which goes away in 15-20min. If you're going to clean once a year, do it after the "last" rain of the year before summer peak solar output. If you live somewhere rural with summer thunderstorms, with high angle panels, and without a lot of pollen (or dust storms), you may not need to clean them much at all. If you're going to climb on a roof, do it safely! A 10' fall can kill or maim you.
- lelanthran 3mo ago
  > The drop off after cleaning could well be because some of the initial boost could come from the water cooling off the panels: solar panels become less efficient at higher temperatures so the drop of after they're all cleaned could be them warming up again after the water has evaporated. This was almost certainly the case. AIUI, that cooling still makes a large difference. Makes me wonder if it is worth it having a small esp32 or similar control a sprinkler system for the panels. Keep them cool during high ambient temps by spraying a litre of water on each panel every 30m. An idea I had a while back (when I was considering panels) was running my mains water through the back of each panel (before the mains got to the hose) in a sort of radiator pattern.
carloseduardopx 3mo ago
There’s this viral video on X of a guy at an Alex Hormozi talk saying he makes money cleaning solar panels… and it’ll probably turn into a whole market. If he’s getting 2% to 5% gains, I can already see marketing blowing that way out of proportion
jpgvm 3mo ago
Definitely wash the panels. However if you are using a string inverter you will want to wash all the ones on the same string in one go if you can, you don't really want them generating different voltage or you will miss out on a lot of power.
tombert 3mo ago
I haven't noticed too much of a power increase in my backyard solar farm after cleaning, but I do notice a very significant increase by weeding the surrounding stuff. Even a pretty small amount of shade will very significantly reduce your yield, like seriously 20-30%. Oh, also, I've noticed that at least with my panels, bird poop seems to be particularly bad. The dust that accrues doesn't seem to do much, but even a relatively small bit of bird poop will be almost as bad as weeds. Fortunately it's not terribly difficult to clean once it's dried.
- scarecrowbob 3mo ago
  Yeah, the one tree branch that hits my array until 10a prevents it from charging at all even though it only obscures 1/4 of one panel in the 10-panel set. But I like the branch and have plenty of full sun, so I haven't cut it.
ChrisMarshallNY 3mo ago
I know that dust on the panels is one of the reasons that one of the Mars rovers eventually croaked.
- ButlerianJihad 3mo ago
  On Mars, the wind storms and dust devils are so fearsome that some of the robots there could rely on dust being blown clean off all the solar panels on a regular basis. Spirit and Opportunity benefited the most from these effects. InSight was stationary and not so fortunate. But, the ground team got quite creative with its robotic arm to try and manipulate the sand that had accumulated on the solar panel, and gained a little bit more power. https://en.wikipedia.org/wiki/InSight#Surface_operations https://en.wikipedia.org/wiki/InSight#Surface_operations https://en.wikipedia.org/wiki/Martian_regolith https://en.wikipedia.org/wiki/Martian_regolith
LogicFailsMe 3mo ago
So if it's a 2-5% increase, barely break even, it more than breaks even during an extended power failure if you live somewhere this is likely. There are a lot of things I choose to do to avoid future timelines where 'sus appliances break at the worst possible moment. This would be along the same lines to me. Your mindset may vary YMMV. But if cash is tight, yeah, not so much.
jillesvangurp 3mo ago
Was just watching a video about a guy who has a boat that runs on solar power that he drove all the way from Finland to the Mediterranean in Winter. Obviously in the winter he was charging his batteries using shore power. But since spring he's been running on solar power doing long journeys and maxing out at 5-8 knots. He just cleaned his panels. Lots of salt, dust and sea gull shit. Also a few kids dropped a rock on one of his panels. Cleaning them improved performance by about 10%. Not nothing. But they were really dirty. https://www.youtube.com/watch?v=FhBBUFuTwR4 https://www.youtube.com/watch?v=FhBBUFuTwR4
- bergie 3mo ago
  Yes, on a boat you have to wash the panels periodically to get rid of salt and bird poop. The latter can be a surprisingly big problem. Southeast of Galapagos we had a booby sit on our spreader for a day, and it managed to cover our two 100Wp panels in the bow almost completely.
turtlebits 3mo ago
It totally depends on your area. In the PNW I get sap and conifer tree pollen all over my panels and have to wash them at least twice a year.
the_sleaze_ 3mo ago
Question for people here: my local power company charges a fee if solar is attached to the grid and is high enough to make installing residential solar impractical. I'm thinking the best thing to do would be put a large battery in between the grid and my home and selectively recharge the battery with the solar. I believe that setup circumvents the fee since the only thing using energy is the battery, as though it were an off grid setup. I might consider not putting the entire home behind the battery but just the largest energy hogs, like the HVAC or others. Does this make sense, are there existing setups like this and what are thoughts about something like this? Thanks
- inigyou 3mo ago
  Ask a lawyer about the law.
  - the_sleaze_ 3mo ago
    Why would I ask a lawyer for advice about whole home battery solar setups with a grid backup?
    - inigyou 3mo ago
      Because you're asking legal question about what the law allows, not a technical question about how to exchange voltage and current.
    - sudobash1 3mo ago
      Because often the law cares about intent, not technicalities. Technically you could argue that this is a "whole home battery solar setups with a grid backup", but clearly the intent is as a workaround. I'm not saying this is bad. I love a good workaround for onerous laws & fees, but random Internet commenters aren't the best at determining what workaround will or will not pass muster if a judge gets involved. Like someone said in another recent thread: "U.S. law though is highly non-autistic and what you were trying to do is just as important as what you superficially did." https://news.ycombinator.com/item?id=49064242 https://news.ycombinator.com/item?id=49064242
Aurornis 3mo ago
Washing solar panels is one of the current popular business ideas on social media. It’s an easy pivot for anyone who already has some experience with much harder home repair handiwork involving a ladder. The reason it’s popular is because most people don’t understand the economics at all. Someone can go door-to-door in a neighborhood offering to clean solar panels and making huge claims about improving efficiency so much that you can’t afford not to do it. Homeowners who invested $30K in solar panels think of a $300-600 charge as an easy choice to keep their investment producing money. My parents had someone going around their neighborhood trying to charge $50/panel for cleaning. They didn’t even climb a ladder. They sprayed washing solution from the ground. Most neighbors declined, but you could see the guy spraying down a couple roofs. Easy way to clear $1000+ per day for knocking on some doors and pointing a hose at a couple rooftops, at least until the public figures out the scam.
- JamesSwift 3mo ago
  Its an easy value add for a pressure-wash / soft-wash business
- jhot 3mo ago
  I asked a friend with a window cleaning business and they charge about $10 a panel. At that rate I'm tempted to try it but I'm not sure if it's even worth that.
  - xandrius 3mo ago
    $10/panel to go on top of a roof with the possibility of braking s leg or worse? I'll keep my coding job from my couch :O
- rsynnott 3mo ago
  Funnily enough, there was a thread a while ago here where people were fixated on the idea that you had to wash solar panels, and thus proponents are underestimating maintenance costs. I had wondered where that idea had come from, as I thought it was fairly well understood that even quite dirty panels once much of an efficiency drop…
- 3mo ago
kjjohnsen 3mo ago
Of course washing them makes sense, physics-wise. As others have pointed out, you are almost certainly seeing a rise due to cooling off the panels (this would not make economic sense to do all of the time). Temperature has a pretty dramatic effect on solar panel output. Cooling a panel can boost production by 10% or more. Do not polish them. Solar panels are designed to be anti-reflective. You don't want a shiny surface. But, the real factor in all of this is how valuable the time required to clean the panel is.
0xbadcafebee 3mo ago
If you feel "a tingle" when touching solar panels, that means there's a ground fault, a wiring short, or a missing ground wire. This is incredibly dangerous as solar arrays carry hundreds of volts.
ynac 3mo ago
There are at least a couple of outfits claiming a nano coating or a nano glass surface for solar panels that are so smooth as to not collect dusts. Their other claim is greatly improved angular photon capture since the panel is just that flat. The two companies I've seen claim ~20% improvement - and less maintenance.
- bityard 3mo ago
  20% seems high enough that if it was really _that_ effective, the companies making the panels would be tripping over themselves to buy this coating to apply it to the panels right in their factories. (And charge a premium for it.)
- rconti 3mo ago
  My solar panels are leaning in stacks in my yard, as our house is currently being removed with a new roof, etc. I'm planning on cleaning them while they're "loose", but I wonder if it also makes sense to apply a(n automotve-style) ceramic coating to them.
CrzyLngPwd 3mo ago
I clean my solar panels, 7kwh, every monmth or two. When I check on the VRM portal it makes a difference, and since I am so dependent on them all year round, I have no problem giving them some attention from time to time. Ten mins well spent.
- jader201 3mo ago
  > I clean my solar panels, 7kwh, every monmth or two. This honestly sounds like a non-trivial strike against installing solar panels, especially if they’re installed on tall roofs. I definitely wouldn’t want to have to clean them that often, or pay to have them cleaned that often. If you’re spending only 10 minutes on them, then maybe you don’t have that many, and they’re not up high.
  - bityard 3mo ago
    Roof-mounted solar panels are a necessity in urban situations but they are a maintenance nightmare compared to a ground-mounted array. That has to be accepted as "the cost of doing solar" when there is no other alternative.
  - metadat 3mo ago
    On tall roofs there tends to not be much dust.
  - CrzyLngPwd 3mo ago
    Mine are not on a roof.
  - tensor 3mo ago
    I never cleaned mine. Rain does enough. It's still plenty valuable without minmaxing them.
- scarecrowbob 3mo ago
  I am curious how much of a difference it makes. I have 4kw of panels and 15kwh of storage. I only get down to about 80% most nights (I heat with wood and propane). But my system will charge completely in about 2 hours of full sun. If it took 3 hours it wouldn't make a difference. So I generally don't clean them (well, the rain and snow do that work). I do remove snow, because that has a very noticeable impact. Is the difference that you are pushing back to a grid (I am not), so the power all gets used regardless of you being the one to use it?
HumanAgent 3mo ago
[dead]
rconti 3mo ago
> This is the yin and yang of market-distorting incentives. Today's incentive to install solar becomes tomorrow's disincentive to upgrading it. Facing this as well. We've got our 5.2kW system in a pile in our yard as the house is being enlarged, new roof going on, etc. We're switching from a gas furnace to a heat pump system, and will also be installing a hot tub. I'm sure our annual power bill will double from say $1k to $2k, but it doesn't make sense to enlarge our system. I'm 8 years into a 20 year net metering scheme (NEM2.0 in CA), and any changes I make will kick me off the plan. In theory I am allowed to add up to 10% or 1kW, but in practice my solar company keeps telling me it's not worthwhile. I think the paperwork and administrative burden of even adding the amount I'm "allowed" to add just means it's not cost-effective. Whether or not the utility actually would notice that I'm mysteriously getting 1kW additional generation (if no paperwork was filed) is another story.
scarecrowbob 3mo ago
Horses for courses. My system is off grid, so any extra power is just not used, and its designed in a way that a 2-5% change doesn't do anything. That might be a more meaningful change if I were selling power to other folks. Kind of off topic, but I see a lot of folks proximate to me have built systems to turn panels so they face the sun more closely. I can see the use in that if you don't have much space or if you have a large commercial operation, but this area is very rural. My array (4kw) which I built myself has 10 400W panels. The panels cost me $1200 because the minimum order is 12 and the supplier suggested buying extras; shipping large panels one at a time isn't cheap. In fact, the shipping for the entire system (about $5000 worth of equipment) was almost $1000. But my feeling is that for the cost of a moving array that tracks the sun / time of year would have cost quite a lot more and have involved construction that I personally wasn't comfortable with. The conclusion I came to is that it would cost about the same to build a second array, angle it for "summer" (mine is angled to be most efficient in winter), and hook it to the other MPPT on my controller. That would take up a lot of space, but a) I am 40 acres and b) then I could run a mig welder with impunity during the day...
- rsynnott 3mo ago
  Are these older systems? The panels are cheap now but they used to be quite expensive, which would’ve changed the economics a bit.
- CapitalistCartr 3mo ago
  It does no longer pay to be clever with solar panels; they're too cheap. Angle not quite right? Add a couple extra. Summer vs. Winter? Add a couple extra.
  - cyberpunk 3mo ago
    Except in germany where if you install too many you get classed as an energy company and have to pay extra tax. yay.
    - majso 3mo ago
tpoindex 3mo ago
I have a 19 year-old, roof mounted, 6.3 kW nominal system in two arrays (east/west facing), 40 deg. north. I've never washed the panels outside of rain and occasional hail storm "scrubbing". Replaced a failed inverter two years ago. My peak summer output is basically the same as when installed, making 36-38 kWh on a cloudless day. I'm actually impressed my panels haven't really degraded in performance over those 19 years.
- deepsun 3mo ago
  What the panels' technology / manufacturer?
  - tpoindex 3mo ago
    SolarWorld, 175 watt, polycrystalline. I don't recall any model number (paper work is filed away somewhere.) ISTR mine were made in Germany. I think at the time my system was installed, there where some 225 watt panels available, but the 175 ones were a better price point per watt. [edit - added technology]
    - deepsun 3mo ago
      The SolarWorld company is no more :( Which means your experience is irreplicable, other companies' solar panels may be crap.
      - asdff 3mo ago
        Prices per watt of solar have fallen by so much over 20 years its absurd. You can probably buy the best and/or most costly residential panel on the market and still come well under whatever the median was 20 years ago. Probably well under a few standard deviations below the old median I'm guessing.
- sgt 3mo ago
  That's really impressive and well built solar system, for it to last thta long. It shows how durable quality panels are. I have a 6 month old ~3.7kW system (6 panels in total), planning on installing another 6 very soon. My house is surrounded by trees so it's been a bit of a struggle in the winter.
citizenpaul 3mo ago
I'm surprised that the outcome was not much greater improvement. I'm glad though it removed one of my concerns about solar. I'm glad cleaning maintenance really is not really needed.
nrjames 3mo ago
In the southeast states in the US, we experience "the pollening" each Spring, which can leave 1/8" or more of thick crusted pollen on solar panels. I wash ours at least monthly March through May. They're at least 15-20% more efficient, if not more, without the pollen crusted on them.
dev_l1x_be 3mo ago
Should we include this is the cost?
billbrown 3mo ago
Dust can reduce capacity by 40% in the desert. https://link.springer.com/article/10.1186/s40807-017-0043-y https://link.springer.com/article/10.1186/s40807-017-0043-y
jdblair 3mo ago
Last summer, I washed the single 220W module on the top of my campervan. It definitely improved the yield, but I suspect a vehicle can pick up a lot more dirt than a stationary install.
bluehatman 3mo ago
it's simply common sense. of course cleaning them would make a difference....duh Talk about "overthinking"...nerds!
jujube3 3mo ago
Are people really not aware that you have to wash your solar panels every few months? Your installer should have told you that much.
justatdotin 3mo ago
I lose about 25% if I do not clean during bushfire season
gamblor956 3mo ago
It depends. In my mom's part of SoCal, it's extremely dusty. Without bi-annual cleaning a solar panel's output will drop by over 25%. On the other hand, where my brother lives up in Norcal, an annual cleaning is overkill.
lgcmo 3mo ago
I have worked in the solar industry, and "soiling" is highly dependent on soil, weather, proximity to roads, etc. And I've seen cases where it made a 30% impact. In other locations, it is a non-issue, but vegetation was a hassle.

247 points by surprisetalk 3mo ago

It's a bit worrying the author is asking chatgpt about the tingle rather than making sure there's a grounding lug on all the panels and they're all bonded to a grounding rod. The rudimentary nature of the setup makes me think there isn't something like a single conductor 12awg (or euro equivalent) copper wire that bonds to all panels and a basic $30 rod.

quickthrowman 3mo ago
The system in question does not have a transformer so a grounding rod is not required as it is not a separately derived system. The equipment grounds should be tied together to prevent any difference in potential though.
- amluto 3mo ago
  There are many different ways to connect solar panels to the inverter. Usually the exposed metallic parts will be “grounded” (bonded to the ground / protective earth / equipment grounding conductor / whatever your jurisdiction calls it at the inverter). But this is an array that looks a bit remote from any structure, and even if the electronics themselves are utterly, perfectly safe, the bonding wire will cause the panel frames to be at the potential of the inverter’s ground, and the soil will be at whatever its local potential is, and this may be different, resulting in a “touch potential”. You can mitigate this with a supplemental ground (or whatever your jurisdiction calls it) closer to the panels. There are fancy ways to do this particularly well to improve safety in the event of a fault. If you are contacting the actual power wiring of the solar array, something is wrong. If you are feeling capacitive coupled current from the power wiring of the array, then I imagine this means your inverter has crappy filtering, and again the only way you would feel it is if the panel frame isn’t at the same potential as the local soil. Oh, and if you live somewhere prone to lightning, you probably want to give a possible lightning strike to the panel a better route to a high quality ground than through the bonding wire to your house. (In fact, in many parts of the world, including IIRC 48 US states, the power utilities may operate their distribution networks with a current carrying wire (combined neutral and ground) that is grounded at multiple points along its route, which will generate substantial leakage current through the ground. The exceptions are IIRC California and Wisconsin, and IIRC those states have their rules to help protect cattle from becoming part of an undesirable circuit while being milked. In CA at least, all the distribution transformers on the poles have at least two bushings on the primary side, and this is why. I believe this is California General Order 95, rule 33 [0].) [0] https://ia.cpuc.ca.gov/gos/go95/go_95_rule_33.html https://ia.cpuc.ca.gov/gos/go95/go_95_rule_33.html
  - deleted 3mo ago
    [deleted]
  - quickthrowman 3mo ago
    > Usually the exposed metallic parts will be “grounded” (bonded to the ground / protective earth / equipment grounding conductor / whatever your jurisdiction calls it at the inverter). It’s not usually, all of the panels and also the metal racking must be bonded and grounded. Supplementary grounds are allowed by the NEC, article 250.54 There are zero requirements for supplemental grounds, you could use a single 24AWG conductor bonded to a brad nail or a #6 bare copper conductor bonded to (3) 5/8” dia’ 10’ ground rods. The fact that there are no requirements should tell you something about the necessity of supplemental grounds. > 250.54 Auxiliary Grounding Electrodes. One or more grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 or 250.53(C) or the resistance requirements of 250.53(A)(2) Exception, but the earth shall not be used as an effective ground-fault current path as specified in 250.4(A)(5) and 250.4(B)(4).
    - amluto 3mo ago
      The OP is pretty clearly not in the US and is not subject to the NEC. And just because the NEC doesn’t say you need to mitigate touch potentials for a specific installation doesn’t mean that you shouldn’t. The NEC is just a bunch of requirements, not a complete guide to building safe, high quality electrical installations. And there appears to be plenty of guidance from IEEE about this if you feel like paying for a copy of the standard: https://store.accuristech.com/ecia/products/preview/2085911 https://store.accuristech.com/ecia/products/preview/2085911 The NEC does have plenty to say about grounding for purposes of reducing potential differences in other (non-solar) installations, though. Swimming pools are a notable example (with no specific requirement IIRC to connect the fancy bonding to the Earth at the pool, but a typical concrete pool with NEC-mandated bonding is likely an excellent connection to the local soil). Amusingly, an inspector could plausibly require an “equipotential plane” per NEC 547.44 if the solar array is accessible to livestock. Alternatively, from first principles: suppose you are standing with bare feet on wet soil 100 meters from a building. That building has a very nice ground rod array, giving an impedance of 50 ohms from the building’s ground to your feet. Now take a long wire that is insulated except at the ends, connect one end to the building ground, and firmly hold the other end in your hand. How do you feel about this situation? You have a nice wire loop, potentially with area on the order of 100m^2, containing your heart. It can inductively couple to time-varying magnetic fields (e.g. the fields around nearby transmission lines) and it can capacitively couple to other conductors. It can resistively couple to power lines with multiply grounded neutral or to electrified railways or to nearby buildings with old-style (earlier NEC revisions) shared neutral/ground feeds And lightning can strike the array. I think it would be wise to ground the array to earth to reduce the potential difference between the frame and earth.
- deleted 3mo ago
  [deleted]
- aetherspawn 3mo ago
  I’m an electrical engineer. I just want to explain the hazard with panels. They are DC, and the voltage is usually very high, between 300V and 600V. At this voltage you will get a burn, like touching a hot kettle, but because it is DC you will be able to easily “untouch” it. Yes, the panel frames should all be grounded to each other, and also to Earth in one spot along the chain, as this makes it more difficult to be electrocuted by them because the resistance of the grounding wire is much lower than the resistance of your body, and electricity takes the shortest path.
  - quickthrowman 3mo ago
    I was just pointing out that a solar installation with only an inverter and no transformer does not need a separate ground since it’s not a separately derived system. An auxiliary/supplementary ground rod is allowed by the NEC (250.54) but it is not required.
    - aetherspawn 3mo ago
      Well, this is US code which is fairly lax and has a ludicrously low voltage grid, but in virtually every other country it is required
tclancy 3mo ago
Eh, compared to what though? Compared to speaking to licensed electrician, definitely. But compared to doing a raw web search and trying to put the information in the right order for the application you’re currently working on, I think it’s at worst a wash.
- bityard 3mo ago
  > a wash Well done on this cleanly-executed pun.
  - tclancy 3mo ago
    Took four open weight models to land it. And you are giving me way more credit than I am due.
    - vermilingua 3mo ago
      This comment made me very sad

1123581321 3mo ago

Appreciate the attempts to quantify it. I haven't tried to quantify washing, but I do look at mine regularly. I doubt anything accumulates that rain doesn't handle well enough. Messing around with ground panels is lower risk and safer than roof panels where tool extenders and ladders start to become involved. If you have roof panels, you are the biggest danger to your panels (and yourself.) Don't try to clean them, spray them, knock snow off of them. I was told this multiple times by my installer. :)

msdz 3mo ago
As another anecdata-point, when we did this for a now already fairly old roof installation of about 15kWp, it was more than “just about worthwhile”, since the panel area is contiguous: cost seemed to scale up less quickly than the wattage/theoretical maximum output, and the cleaning guy (solo company, IIRC) even told us it wasn’t necessary to do this every year (we hadn’t had it done even once the first decade+ of the installation’s lifetime). So, at least in our case, definitely worth it.
- 1123581321 3mo ago
  Interesting; what was on the panels? What was the ROI on paying the guy?
  - msdz 3mo ago
    Unfortunately I don’t recall anymore, since this took place at my father’s PV installation. I’ll try to post an update when/if I get exact numbers, though!
varispeed 3mo ago
In many countries it is actually illegal to use tall ladder etc. owners would have to erect a scaffolding to make access for work people to clean it safely.
- dd8601fn 3mo ago

collabs 3mo ago

Maybe the thing to do is to NOT upgrade existing working panels but rather set up a different/separate entity with completely different accounts and new panels? And about the washing, I wonder if it would be worth it to automate the process with a spray of water periodically? You can still wash the panels but I suspect it won't be necessary if there isn't too much dust accumulation? Isn't rain supposed to wash away the dust? What am I missing here?

ido 3mo ago
Some places don't get much rain (and these are the places that tend to get even more dust - e.g. deserts).
rjmunro 3mo ago
It may also be worth spraying them with water when they are too hot. As they get hotter the efficiency drops a little. It's only a few percent, and usually it happens at the time you need the efficiency the least because it's sunny, but if you can combine cleaning and cooling and get a few extra w out if it, why not.
- collabs 3mo ago
  Yes, I meant I can get on board with automatically (periodically or based on some trigger or sensor) spraying the panels with water but I was hoping it isn't necessary to use Windex® or even dish soap on the panels themselves.
- Tade0 3mo ago
  Solar panels are increasingly being oriented east or west instead of south, as while it reduces overall yield, it maximises power when it's needed the most - during morning and evening peaks. I don't have numbers, but I suspect it alleviates issues with dust buildup and temperature.
  - sluongng 3mo ago
    isn't that more of a storage issue, which a home battery would solve?

bebe8393jrir 3mo ago

> If I increase the power output of the system then the additional capacity will not be eligible for the feed-in tariff and will revert to present-day prevailing tariff which is about 4x worse before you even consider that I currently get to use electricity and still get paid for generating it. > This is the yin and yang of market-distorting incentives. Today's incentive to install solar becomes tomorrow's disincentive to upgrading it. I am not sure what author is trying to hint. But solar does not need artificial subsidies, and can pay for itself! There are no subsidies in UK! Homeowners get so much money, because of all that sunshine and wind energy, their house generates! UK goverment just run out of money, when energy got expensive! UK goverment needs to step up, to replace gaz with renewables! You can not expect homeowners to sell energy bellow market price!

philipallstar 3mo ago
Solar gets lots of subsidies in the UK. Homeowners who installed it 10 years ago get a ridiculous payment for generating excess, even if the grid doesn't use it.
rjmunro 3mo ago
> solar does not need artificial subsidies, and can pay for itself That's true now, but wasn't true when those panels were installed. There were subsidies available to get the market kick-started. They consist of an extra payment for every kwh you generate on top of the payment for delivering the power to the grid. The amount varied depending on when you signed up to the scheme, but at certain points it was as much as 50p/kwh (+ inflation, so more than that now).
otherme123 3mo ago
> I am not sure what author is trying to hint. But solar does not need artificial subsidies, and can pay for itself! I think he is describing a subside that some governments gave years ago: you installed for example 5K, and get paid for whatever they generate at 300% market price, for a long time (25 years?). Today you find out that upgrading panels would made perfect financial sense, if you were selling at 100% and are going to sell electricity at 100% (you will be doubling the output for a tenth of the inversion 15 years ago), but as the subsides of 300% no longer exist, you will be actually losing money by upgrading.

wodenokoto 3mo ago

> why would you clean them when you're about to sell the house? So they look good and the potential buyer sees something that looks to be in good condition and working well.

engineer_22 3mo ago
I agree. Doesn't matter what you sell, you will get a higher price if it is cleaned and tidy when presented to the market - because the kinds of people who pay higher prices are looking for clean and tidy things.
- throw0101d 3mo ago
  See also "staging": * https://en.wikipedia.org/wiki/Home_staging https://en.wikipedia.org/wiki/Home_staging
  - saagarjha 3mo ago
    Why is it written like that lmao
    - blitzar 3mo ago
      Its been "staged"
    - Nzen 3mo ago
      Wikipedia is written by various people, but likely someone with interest in a given topic. One or more realtors probably wrote or edited this post. Actually, the history of edits shows that this is contested territory where people regularly remove what they term as spam links. So, while a disinterested editor might remove a link to a listicle about how to stage your home, they might leave in the breathless tone as harmless. The drive by editors probably feel that they have no more time to rewrite it than we do, given that they watch over many articles, not just this one.
- namdnay 3mo ago

hgomersall 3mo ago

Our peak daily export energy jumped by about 35%-40% when we had our panels cleaned for the first time in 8 years. They _look_ much cleaner, and the measured export shows it.

trimethylpurine 3mo ago
If export energy is 10% of your total output, and it jumped 35% then you got a ~3.5 - 4% gain in total output, not far from the author's experience. Of course, you can math that any way you like to make the numbers bigger or smaller, depending on whether you're representing the buyer or the seller of the system.
- hgomersall 3mo ago
  It's not 10%, it's much more than that. I'm obviously comparing the peak values, which tend to be days when we don't consume much, which might mean a background 100W vs a couple of kW peak generation. I can dig deeper into the per hour generation and it's similar.
  - trimethylpurine 3mo ago
    I'd just measure total output and don't bother looking at export output. More variables and conversions in the experiment will tend to reduce the accuracy of the results.

infecto 3mo ago

Nobody can answer this. It simple depends on each setup. Some panels will get incredibly dirty quick like those in the south west where there may be a lack of rain and lots of dust but in other regions you may never need to.

z2 3mo ago

Given the angle of a panel should match its latitude and average sun angle, the panels might generate noticeably more by being pitched steeper at over 30 degrees. Eyeballing this, it appears closer to 25 degrees right now which doesn't even make sense for the summer sun in the UK. I could be wrong as it also appears these are on a slope!

ape4 3mo ago

I imagine rain will clean them. In most places it rains every so often.

namdnay 3mo ago
my experience is that unless you get some really torrential rain, it's not enough to clean the sand/dust/grime
- left-struck 3mo ago
  Can confirm, my car doesn’t get cleaner unless there’s a downpour
mywittyname 3mo ago
Rain usually just cakes the dirt. Unless it's a downpour, it doesn't move with enough velocity or volume to remove the dirt. So the dirt just gets damp, maybe moves a few cm with gravity, then dries as a mud cake.
- coredog64 3mo ago
  See this all the time in Phoenix metro: A light rain just pulls down all the dust in the air and deposits it on the car. It has to be fairly sustained to wash away the initial dust collection, and even then you can still see dust on the paint.

rcxdude 3mo ago

Re: the slightly strange shape of the curve. The drop at the beginning could be due to the matching between the panels getting worse. Solar panels in a bank don't like being in different conditions. As a rule of thumb they will all perform at about the same level as the worst in the bank but at the finer levels you could get less straightforward interactions. The drop off after cleaning could well be because some of the initial boost could come from the water cooling off the panels: solar panels become less efficient at higher temperatures so the drop of after they're all cleaned could be them warming up again after the water has evaporated.

kurthr 3mo ago
Yeah, came here to say this. There are a lot of things that will affect efficiency and how clean your panels are is only one of them. How dirty your panels get is also highly sensitive to both location and installation. All of this gets horribly confounded by string inverters (especially if they're clipping the peak, which they often are). I easily see 5% increases in efficiency after cleaning (with micro inverters), but also see ~3% increase in output on a hot day from just spraying the panels with water to cool them off, which goes away in 15-20min. If you're going to clean once a year, do it after the "last" rain of the year before summer peak solar output. If you live somewhere rural with summer thunderstorms, with high angle panels, and without a lot of pollen (or dust storms), you may not need to clean them much at all. If you're going to climb on a roof, do it safely! A 10' fall can kill or maim you.
lelanthran 3mo ago
> The drop off after cleaning could well be because some of the initial boost could come from the water cooling off the panels: solar panels become less efficient at higher temperatures so the drop of after they're all cleaned could be them warming up again after the water has evaporated. This was almost certainly the case. AIUI, that cooling still makes a large difference. Makes me wonder if it is worth it having a small esp32 or similar control a sprinkler system for the panels. Keep them cool during high ambient temps by spraying a litre of water on each panel every 30m. An idea I had a while back (when I was considering panels) was running my mains water through the back of each panel (before the mains got to the hose) in a sort of radiator pattern.

carloseduardopx 3mo ago

There’s this viral video on X of a guy at an Alex Hormozi talk saying he makes money cleaning solar panels… and it’ll probably turn into a whole market. If he’s getting 2% to 5% gains, I can already see marketing blowing that way out of proportion

jpgvm 3mo ago

Definitely wash the panels. However if you are using a string inverter you will want to wash all the ones on the same string in one go if you can, you don't really want them generating different voltage or you will miss out on a lot of power.

tombert 3mo ago

I haven't noticed too much of a power increase in my backyard solar farm after cleaning, but I do notice a very significant increase by weeding the surrounding stuff. Even a pretty small amount of shade will very significantly reduce your yield, like seriously 20-30%. Oh, also, I've noticed that at least with my panels, bird poop seems to be particularly bad. The dust that accrues doesn't seem to do much, but even a relatively small bit of bird poop will be almost as bad as weeds. Fortunately it's not terribly difficult to clean once it's dried.

scarecrowbob 3mo ago
Yeah, the one tree branch that hits my array until 10a prevents it from charging at all even though it only obscures 1/4 of one panel in the 10-panel set. But I like the branch and have plenty of full sun, so I haven't cut it.

ChrisMarshallNY 3mo ago

I know that dust on the panels is one of the reasons that one of the Mars rovers eventually croaked.

ButlerianJihad 3mo ago
On Mars, the wind storms and dust devils are so fearsome that some of the robots there could rely on dust being blown clean off all the solar panels on a regular basis. Spirit and Opportunity benefited the most from these effects. InSight was stationary and not so fortunate. But, the ground team got quite creative with its robotic arm to try and manipulate the sand that had accumulated on the solar panel, and gained a little bit more power. https://en.wikipedia.org/wiki/InSight#Surface_operations https://en.wikipedia.org/wiki/InSight#Surface_operations https://en.wikipedia.org/wiki/Martian_regolith https://en.wikipedia.org/wiki/Martian_regolith

LogicFailsMe 3mo ago

So if it's a 2-5% increase, barely break even, it more than breaks even during an extended power failure if you live somewhere this is likely. There are a lot of things I choose to do to avoid future timelines where 'sus appliances break at the worst possible moment. This would be along the same lines to me. Your mindset may vary YMMV. But if cash is tight, yeah, not so much.

jillesvangurp 3mo ago

Was just watching a video about a guy who has a boat that runs on solar power that he drove all the way from Finland to the Mediterranean in Winter. Obviously in the winter he was charging his batteries using shore power. But since spring he's been running on solar power doing long journeys and maxing out at 5-8 knots. He just cleaned his panels. Lots of salt, dust and sea gull shit. Also a few kids dropped a rock on one of his panels. Cleaning them improved performance by about 10%. Not nothing. But they were really dirty. https://www.youtube.com/watch?v=FhBBUFuTwR4 https://www.youtube.com/watch?v=FhBBUFuTwR4

bergie 3mo ago
Yes, on a boat you have to wash the panels periodically to get rid of salt and bird poop. The latter can be a surprisingly big problem. Southeast of Galapagos we had a booby sit on our spreader for a day, and it managed to cover our two 100Wp panels in the bow almost completely.

turtlebits 3mo ago

It totally depends on your area. In the PNW I get sap and conifer tree pollen all over my panels and have to wash them at least twice a year.

the_sleaze_ 3mo ago

Question for people here: my local power company charges a fee if solar is attached to the grid and is high enough to make installing residential solar impractical. I'm thinking the best thing to do would be put a large battery in between the grid and my home and selectively recharge the battery with the solar. I believe that setup circumvents the fee since the only thing using energy is the battery, as though it were an off grid setup. I might consider not putting the entire home behind the battery but just the largest energy hogs, like the HVAC or others. Does this make sense, are there existing setups like this and what are thoughts about something like this? Thanks

inigyou 3mo ago
Ask a lawyer about the law.
- the_sleaze_ 3mo ago
  Why would I ask a lawyer for advice about whole home battery solar setups with a grid backup?
  - inigyou 3mo ago
    Because you're asking legal question about what the law allows, not a technical question about how to exchange voltage and current.
  - sudobash1 3mo ago
    Because often the law cares about intent, not technicalities. Technically you could argue that this is a "whole home battery solar setups with a grid backup", but clearly the intent is as a workaround. I'm not saying this is bad. I love a good workaround for onerous laws & fees, but random Internet commenters aren't the best at determining what workaround will or will not pass muster if a judge gets involved. Like someone said in another recent thread: "U.S. law though is highly non-autistic and what you were trying to do is just as important as what you superficially did." https://news.ycombinator.com/item?id=49064242 https://news.ycombinator.com/item?id=49064242

Aurornis 3mo ago

Washing solar panels is one of the current popular business ideas on social media. It’s an easy pivot for anyone who already has some experience with much harder home repair handiwork involving a ladder. The reason it’s popular is because most people don’t understand the economics at all. Someone can go door-to-door in a neighborhood offering to clean solar panels and making huge claims about improving efficiency so much that you can’t afford not to do it. Homeowners who invested $30K in solar panels think of a $300-600 charge as an easy choice to keep their investment producing money. My parents had someone going around their neighborhood trying to charge $50/panel for cleaning. They didn’t even climb a ladder. They sprayed washing solution from the ground. Most neighbors declined, but you could see the guy spraying down a couple roofs. Easy way to clear $1000+ per day for knocking on some doors and pointing a hose at a couple rooftops, at least until the public figures out the scam.

JamesSwift 3mo ago
Its an easy value add for a pressure-wash / soft-wash business
jhot 3mo ago
I asked a friend with a window cleaning business and they charge about $10 a panel. At that rate I'm tempted to try it but I'm not sure if it's even worth that.
- xandrius 3mo ago
  $10/panel to go on top of a roof with the possibility of braking s leg or worse? I'll keep my coding job from my couch :O
rsynnott 3mo ago
Funnily enough, there was a thread a while ago here where people were fixated on the idea that you had to wash solar panels, and thus proponents are underestimating maintenance costs. I had wondered where that idea had come from, as I thought it was fairly well understood that even quite dirty panels once much of an efficiency drop…
3mo ago

kjjohnsen 3mo ago

Of course washing them makes sense, physics-wise. As others have pointed out, you are almost certainly seeing a rise due to cooling off the panels (this would not make economic sense to do all of the time). Temperature has a pretty dramatic effect on solar panel output. Cooling a panel can boost production by 10% or more. Do not polish them. Solar panels are designed to be anti-reflective. You don't want a shiny surface. But, the real factor in all of this is how valuable the time required to clean the panel is.

0xbadcafebee 3mo ago

If you feel "a tingle" when touching solar panels, that means there's a ground fault, a wiring short, or a missing ground wire. This is incredibly dangerous as solar arrays carry hundreds of volts.

ynac 3mo ago

There are at least a couple of outfits claiming a nano coating or a nano glass surface for solar panels that are so smooth as to not collect dusts. Their other claim is greatly improved angular photon capture since the panel is just that flat. The two companies I've seen claim ~20% improvement - and less maintenance.

bityard 3mo ago
20% seems high enough that if it was really _that_ effective, the companies making the panels would be tripping over themselves to buy this coating to apply it to the panels right in their factories. (And charge a premium for it.)
rconti 3mo ago
My solar panels are leaning in stacks in my yard, as our house is currently being removed with a new roof, etc. I'm planning on cleaning them while they're "loose", but I wonder if it also makes sense to apply a(n automotve-style) ceramic coating to them.

CrzyLngPwd 3mo ago

I clean my solar panels, 7kwh, every monmth or two. When I check on the VRM portal it makes a difference, and since I am so dependent on them all year round, I have no problem giving them some attention from time to time. Ten mins well spent.

jader201 3mo ago
> I clean my solar panels, 7kwh, every monmth or two. This honestly sounds like a non-trivial strike against installing solar panels, especially if they’re installed on tall roofs. I definitely wouldn’t want to have to clean them that often, or pay to have them cleaned that often. If you’re spending only 10 minutes on them, then maybe you don’t have that many, and they’re not up high.
- bityard 3mo ago
  Roof-mounted solar panels are a necessity in urban situations but they are a maintenance nightmare compared to a ground-mounted array. That has to be accepted as "the cost of doing solar" when there is no other alternative.
- metadat 3mo ago
  On tall roofs there tends to not be much dust.
- CrzyLngPwd 3mo ago
  Mine are not on a roof.
- tensor 3mo ago
  I never cleaned mine. Rain does enough. It's still plenty valuable without minmaxing them.
scarecrowbob 3mo ago
I am curious how much of a difference it makes. I have 4kw of panels and 15kwh of storage. I only get down to about 80% most nights (I heat with wood and propane). But my system will charge completely in about 2 hours of full sun. If it took 3 hours it wouldn't make a difference. So I generally don't clean them (well, the rain and snow do that work). I do remove snow, because that has a very noticeable impact. Is the difference that you are pushing back to a grid (I am not), so the power all gets used regardless of you being the one to use it?

HumanAgent 3mo ago

[dead]

rconti 3mo ago

> This is the yin and yang of market-distorting incentives. Today's incentive to install solar becomes tomorrow's disincentive to upgrading it. Facing this as well. We've got our 5.2kW system in a pile in our yard as the house is being enlarged, new roof going on, etc. We're switching from a gas furnace to a heat pump system, and will also be installing a hot tub. I'm sure our annual power bill will double from say $1k to $2k, but it doesn't make sense to enlarge our system. I'm 8 years into a 20 year net metering scheme (NEM2.0 in CA), and any changes I make will kick me off the plan. In theory I am allowed to add up to 10% or 1kW, but in practice my solar company keeps telling me it's not worthwhile. I think the paperwork and administrative burden of even adding the amount I'm "allowed" to add just means it's not cost-effective. Whether or not the utility actually would notice that I'm mysteriously getting 1kW additional generation (if no paperwork was filed) is another story.

scarecrowbob 3mo ago

Horses for courses. My system is off grid, so any extra power is just not used, and its designed in a way that a 2-5% change doesn't do anything. That might be a more meaningful change if I were selling power to other folks. Kind of off topic, but I see a lot of folks proximate to me have built systems to turn panels so they face the sun more closely. I can see the use in that if you don't have much space or if you have a large commercial operation, but this area is very rural. My array (4kw) which I built myself has 10 400W panels. The panels cost me $1200 because the minimum order is 12 and the supplier suggested buying extras; shipping large panels one at a time isn't cheap. In fact, the shipping for the entire system (about $5000 worth of equipment) was almost $1000. But my feeling is that for the cost of a moving array that tracks the sun / time of year would have cost quite a lot more and have involved construction that I personally wasn't comfortable with. The conclusion I came to is that it would cost about the same to build a second array, angle it for "summer" (mine is angled to be most efficient in winter), and hook it to the other MPPT on my controller. That would take up a lot of space, but a) I am 40 acres and b) then I could run a mig welder with impunity during the day...

rsynnott 3mo ago
Are these older systems? The panels are cheap now but they used to be quite expensive, which would’ve changed the economics a bit.
CapitalistCartr 3mo ago
It does no longer pay to be clever with solar panels; they're too cheap. Angle not quite right? Add a couple extra. Summer vs. Winter? Add a couple extra.
- cyberpunk 3mo ago
  Except in germany where if you install too many you get classed as an energy company and have to pay extra tax. yay.
  - majso 3mo ago

tpoindex 3mo ago

I have a 19 year-old, roof mounted, 6.3 kW nominal system in two arrays (east/west facing), 40 deg. north. I've never washed the panels outside of rain and occasional hail storm "scrubbing". Replaced a failed inverter two years ago. My peak summer output is basically the same as when installed, making 36-38 kWh on a cloudless day. I'm actually impressed my panels haven't really degraded in performance over those 19 years.

deepsun 3mo ago
What the panels' technology / manufacturer?
- tpoindex 3mo ago
  SolarWorld, 175 watt, polycrystalline. I don't recall any model number (paper work is filed away somewhere.) ISTR mine were made in Germany. I think at the time my system was installed, there where some 225 watt panels available, but the 175 ones were a better price point per watt. [edit - added technology]
  - deepsun 3mo ago
    The SolarWorld company is no more :( Which means your experience is irreplicable, other companies' solar panels may be crap.
    - asdff 3mo ago
      Prices per watt of solar have fallen by so much over 20 years its absurd. You can probably buy the best and/or most costly residential panel on the market and still come well under whatever the median was 20 years ago. Probably well under a few standard deviations below the old median I'm guessing.
sgt 3mo ago
That's really impressive and well built solar system, for it to last thta long. It shows how durable quality panels are. I have a 6 month old ~3.7kW system (6 panels in total), planning on installing another 6 very soon. My house is surrounded by trees so it's been a bit of a struggle in the winter.

citizenpaul 3mo ago

I'm surprised that the outcome was not much greater improvement. I'm glad though it removed one of my concerns about solar. I'm glad cleaning maintenance really is not really needed.

nrjames 3mo ago

In the southeast states in the US, we experience "the pollening" each Spring, which can leave 1/8" or more of thick crusted pollen on solar panels. I wash ours at least monthly March through May. They're at least 15-20% more efficient, if not more, without the pollen crusted on them.

dev_l1x_be 3mo ago

Should we include this is the cost?

billbrown 3mo ago

Dust can reduce capacity by 40% in the desert. https://link.springer.com/article/10.1186/s40807-017-0043-y https://link.springer.com/article/10.1186/s40807-017-0043-y

jdblair 3mo ago

Last summer, I washed the single 220W module on the top of my campervan. It definitely improved the yield, but I suspect a vehicle can pick up a lot more dirt than a stationary install.

bluehatman 3mo ago

it's simply common sense. of course cleaning them would make a difference....duh Talk about "overthinking"...nerds!

jujube3 3mo ago

Are people really not aware that you have to wash your solar panels every few months? Your installer should have told you that much.

justatdotin 3mo ago

I lose about 25% if I do not clean during bushfire season

gamblor956 3mo ago

It depends. In my mom's part of SoCal, it's extremely dusty. Without bi-annual cleaning a solar panel's output will drop by over 25%. On the other hand, where my brother lives up in Norcal, an annual cleaning is overkill.

lgcmo 3mo ago

I have worked in the solar industry, and "soiling" is highly dependent on soil, weather, proximity to roads, etc. And I've seen cases where it made a 30% impact. In other locations, it is a non-issue, but vegetation was a hassle.