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I'm in Germany and keep seeing these, I always wonder what a 400w poorly oriented panel getting like 3 hours of sun a day is good for. If they weren't basically

I'm in Germany and keep seeing these, I always wonder what a 400w poorly oriented panel getting like 3 hours of sun a day is good for. If they weren't basically free thanks to tax reduction and other tricks I assume no one would get them

eliaspro 1y ago
The tax-credit (there are no other "tricks") just shortens the pay-off time of 3-5 years by 19%, that's all!
ViewTrick1002 1y ago
Ensuring no one buys expensive thermal power when the grid is flooded with zero marginal costs renewables and near zero marginal cost storage.
- lucb1e 1y ago
  Rephrasing that to be more understandable because I didn't get this as it was: "Making sure no one buys expensive electricity from coal or gas plants when the grid is full of cheap renewable energy and almost-free stored energy." I'm frankly still not sure what you're trying to say even if I understand the sentence now, e.g.: what free storage?! Isn't germany's projected storage capacity by 2050 somewhere between negligible and tiny?
  - ViewTrick1002 1y ago
    Storage isn’t free. But when you have it the marginal cost of an extra cycle is very low. Germany’s battery storage-related grid connection requests swell beyond 500 GW https://www.ess-news.com/2025/09/01/germanys-battery-storage-related-grid-connection-requests-swell-beyond-500-gw/ https://www.ess-news.com/2025/09/01/germanys-battery-storage...
    - lucb1e 1y ago
      That's like saying the cost of taking an additional bite from your food is very low once you have already bought it, if I'm understanding the continued use of marginal correctly in context?
      - ViewTrick1002 1y ago
        Assuming you have an endless supply of food but can only take one bite per day and it means tomorrows bite will be a bit smaller. These storage systems are generally warrantied as 5000-10000 cycles with 85% capacity remaining in 20 years time. Guaranteed money today is better than saving a few cycles to maybe make money in 20 years time. Now also factor in discounting the risk etc. and the calculation is given. But the business case is of course calculated on having the entire construction cost be amortized with profit over a chosen period. With some days making more money than other. What batteries do are extending the time renewables flood the grid with cheap electricity and thus force nuclear reactors to throttle down, gas peakers to shut down etc. Or these thermal plants can bid negative ensuring they don’t have to turn off while hurrying on their own demise.
        lucb1e 1y ago
        Okay, I can follow that. I've noticed on electricitymaps.com that, for Germany, the coal component never disappears, no matter if you have optimal wind+solar conditions near the summer solstice and prices are far into the negatives. Apparently it's cheaper to let it run the power plant at negative prices for days, than to make it stop burning coal for those days. That renewables with storage would make that finally go away stands to reason But that fully relies on storage. The person you were responding to was asking whether small-scale solar panels make sense. As it is, during those hours where your solar panel is most effective, you can sign up to receive money for drawing electricity from the grid (if prices are negative enough that it outbids even the transportation costs and taxes). Having a solar panel at that time... you might as well turn it off and get a price that's better than free. Storage would be what we need much more urgently than an extra 800Wp solar per household, then we could already turn off those coal plants for probably weeks at a time during summer
monero-xmr 1y ago
Maybe these can pull 700 watts on a sunny day? And you’d need a battery to store it. Would likely make 50 cents a day or less in electricity, on perfect days. The cost for a battery, panels, and install would be ~1000 euro (or more if it’s a bureaucratic mess).
- geor9e 1y ago
  They don't use a battery; they just supplement your apartment so you use less grid.
  - brucehoult 1y ago
    I use a battery -- 6kWh, 3600W inverter, with 6x 440W panels -- and don't feed power into the house wiring, but simply power the appliances in the same room as the equipment: Starlink, Mac Mini with 32" monitor, 16" i9-13900HX laptop, half a dozen small SBCs (5-15W each), fridge, espresso machine, air fryer, microwave, toaster, kettle, 4kW (output, 900W electricity) portable air conditioner, dehumidifier (250W). some LED lighting. At the moment (spring) in half-decent weather all the above stuff is 100% off-grid. I'm still using grid power for hot water heating, dish washer, clothes washer -- all of which I do for free in my daily "Free Hour of Power" -- and for intermittent incidentals such as the water pump (e.g. runs for 15 seconds when I flush the toilet) and lighting in usually non-occupied rooms such as toilet, bathroom, and bedroom -- which together means I'm paying around 10c-20c per day over and above the fixed daily charge.
- Kim_Bruning 1y ago
  I just did some modelling with the help of claude (which can write 200LOC+ numpy code faster than I can) 300 Euros crappy setup, 600 euros mid-range setup, 1200 with storage. (Extra) regulations is zilch, it's legal to plug and play these things up to 800W nameplate capacity. I went with numbers for mid-range, vertical south orientation and offsetting 200W (without battery, any overproduction is wasted). This nets you an avarage of €0.32 per day - With practically nothing in winter, and maybe up to €1 per day on a PARTICULARLY nice summer day. But altogether, that still adds up to something like Eur 116 per year, so your midrange system earns itself back in 5-6 years. Not great, not terrible. Nothing to write home about, but free money is free money.
lucb1e 1y ago
Article cites manufacturers as saying that > installing a couple of 300-watt panels will give savings of up to 30% on a typical household’s electricity bill, but there are lots of variables that come with that claim. It depends on which direction the balcony faces and whether the panels are shaded part of the day. My german electricity bill is around 1200 euros a year. Sign me up for a one-time purchase of 426€ to save ~360€ every year if I had optimal conditions -- call it 50% effective and it's still earned back in under 3 years. The thing lasts, what, a decade? More? (Price taken from https://kleineskraftwerk.de/products/kleines-kraftwerk-gitterbalkon-single https://kleineskraftwerk.de/products/kleines-kraftwerk-gitte... for 450W, first one I could find from some review site.) Edit: figure corrected for not using the tax rebate that it apparently advertised with
- blackjack_ 1y ago
  Yeah so depends on your cost per kWh, and usage time versus production time. My 800W of balcony panels can theoretically produce 3-4 kWh per day (they peak at about 550w of actual production), but they generally produce a lot less than that. This is because my usage during production time is both less than that and also very spiky (my power usage is often 0w or 100-200w base load, with 2kw spikes as the compressor in the refrigerator kicks on, or some other device kicks on). So the savings for me isn't 3 years payoff, it's probably more like 6. But yes, these panels will product for 25-30 years. So yeah, they can pay for themselves very quickly depending on your usage patterns. I'm in the US, and over here we also have some other complicating factors (here we have 2 sets of breakers that are 180 degrees out of phase and so the solar panels can only feed into one half of the breakers without extra complications. I only sort of understand this, someone else can explain better), so solar panels plugged into the balcony that don't backfeed straight to the grid can only cover a subset of the usage. In Germany you have 240v power so I would assume you would hit payoff very quickly.
- lucb1e 1y ago
  (I'm too late and can't edit anymore, but I just noticed upon re-rereading that it says "couple of 300W panels" in the quote and not just "a 300W panel". My math (though done with a 450W panel for an example sales price) is likely off in the wrong direction. Sorry about that.)
colechristensen 1y ago
Solar is cheap, non-peak-efficiency installs get to be the priority once you get the first 40% or so of production in solar. This kind of thing just knocks the edges off of production and transmission costs. You get to the point where you're not trying to squeeze peak efficiency any more and you're just trying to fill in spaces wherever works reasonably well.
danielheath 1y ago
"Poorly oriented panel" can equally well be described as "generates most of its power in the evening, when you have gotten home from work and want to use electricity". It's better to get power at a useful time, even if that means the panel only generates half as much as it could, because storage costs far more than panels.
dzhiurgis 1y ago
It's 800 watts or about 570 KWh per year in berlin, assuming balcony points directly south. At 0.2 euro, that's about 114 euros per year. Percent-wise I'd guess it's less than 10% of yearly total? Overall it's OK payback, but mostly penny pinching in grand scheme of things. https://globalsolaratlas.info/map?c=48.886392,9.470215,6&s=52.522906,13.425293&m=site&pv=small,180,90,0.8 https://globalsolaratlas.info/map?c=48.886392,9.470215,6&s=5...
valenterry 1y ago
A 400W half decently oriented panel (i.e. south facing balcony, 60 degree angle) is sufficient to run your AC to cool your 50sqrm apartment during summer for free.
- brucehoult 1y ago
  In the summer the optimal angle where I live (35.5º S) is 12º. Panels lying flat on the lawn are losing only 2% from that. Just now, near the equinox, panels lying flat on the lawn lose around 18% at noon. I'll find a way to prop them up at 50º for winter when the time comes for that (April or May), though that's for sunny conditions. In our typical overcast in winter flat on the ground is probably still fine to catch the most diffuse light. I'll experiment when the time comes.
  - valenterry 1y ago
    Right. I mentioned the suboptimal 60 degrees because many people hang it from the balcony (90 degrees) and the tilt it a bit, but usually not too much. From what I've seen 60 degrees seems like a good average number.
    - brucehoult 1y ago
      Yeah, in northern Germany vertical and 60º are pretty much equally good/bad in winter (75º would be ideal), but 60º will be getting 70% more power in summer than vertical, and is near ideal in spring/autumn.
kragen 1y ago
That's mostly true, but you're mistaken about the reason they're basically free: it's because the costs of manufacturing them have been dropping dramatically for 20 years, thanks to (in large part Chinese) manufacturing innovations, not because of things like tax reduction.
jansan 1y ago
[flagged]

eliaspro 1y ago

The tax-credit (there are no other "tricks") just shortens the pay-off time of 3-5 years by 19%, that's all!

ViewTrick1002 1y ago

Ensuring no one buys expensive thermal power when the grid is flooded with zero marginal costs renewables and near zero marginal cost storage.

lucb1e 1y ago
Rephrasing that to be more understandable because I didn't get this as it was: "Making sure no one buys expensive electricity from coal or gas plants when the grid is full of cheap renewable energy and almost-free stored energy." I'm frankly still not sure what you're trying to say even if I understand the sentence now, e.g.: what free storage?! Isn't germany's projected storage capacity by 2050 somewhere between negligible and tiny?
- ViewTrick1002 1y ago
  Storage isn’t free. But when you have it the marginal cost of an extra cycle is very low. Germany’s battery storage-related grid connection requests swell beyond 500 GW https://www.ess-news.com/2025/09/01/germanys-battery-storage-related-grid-connection-requests-swell-beyond-500-gw/ https://www.ess-news.com/2025/09/01/germanys-battery-storage...
  - lucb1e 1y ago
    That's like saying the cost of taking an additional bite from your food is very low once you have already bought it, if I'm understanding the continued use of marginal correctly in context?
    - ViewTrick1002 1y ago
      Assuming you have an endless supply of food but can only take one bite per day and it means tomorrows bite will be a bit smaller. These storage systems are generally warrantied as 5000-10000 cycles with 85% capacity remaining in 20 years time. Guaranteed money today is better than saving a few cycles to maybe make money in 20 years time. Now also factor in discounting the risk etc. and the calculation is given. But the business case is of course calculated on having the entire construction cost be amortized with profit over a chosen period. With some days making more money than other. What batteries do are extending the time renewables flood the grid with cheap electricity and thus force nuclear reactors to throttle down, gas peakers to shut down etc. Or these thermal plants can bid negative ensuring they don’t have to turn off while hurrying on their own demise.
      - lucb1e 1y ago
        Okay, I can follow that. I've noticed on electricitymaps.com that, for Germany, the coal component never disappears, no matter if you have optimal wind+solar conditions near the summer solstice and prices are far into the negatives. Apparently it's cheaper to let it run the power plant at negative prices for days, than to make it stop burning coal for those days. That renewables with storage would make that finally go away stands to reason But that fully relies on storage. The person you were responding to was asking whether small-scale solar panels make sense. As it is, during those hours where your solar panel is most effective, you can sign up to receive money for drawing electricity from the grid (if prices are negative enough that it outbids even the transportation costs and taxes). Having a solar panel at that time... you might as well turn it off and get a price that's better than free. Storage would be what we need much more urgently than an extra 800Wp solar per household, then we could already turn off those coal plants for probably weeks at a time during summer

monero-xmr 1y ago

Maybe these can pull 700 watts on a sunny day? And you’d need a battery to store it. Would likely make 50 cents a day or less in electricity, on perfect days. The cost for a battery, panels, and install would be ~1000 euro (or more if it’s a bureaucratic mess).

geor9e 1y ago
They don't use a battery; they just supplement your apartment so you use less grid.
- brucehoult 1y ago
  I use a battery -- 6kWh, 3600W inverter, with 6x 440W panels -- and don't feed power into the house wiring, but simply power the appliances in the same room as the equipment: Starlink, Mac Mini with 32" monitor, 16" i9-13900HX laptop, half a dozen small SBCs (5-15W each), fridge, espresso machine, air fryer, microwave, toaster, kettle, 4kW (output, 900W electricity) portable air conditioner, dehumidifier (250W). some LED lighting. At the moment (spring) in half-decent weather all the above stuff is 100% off-grid. I'm still using grid power for hot water heating, dish washer, clothes washer -- all of which I do for free in my daily "Free Hour of Power" -- and for intermittent incidentals such as the water pump (e.g. runs for 15 seconds when I flush the toilet) and lighting in usually non-occupied rooms such as toilet, bathroom, and bedroom -- which together means I'm paying around 10c-20c per day over and above the fixed daily charge.
Kim_Bruning 1y ago
I just did some modelling with the help of claude (which can write 200LOC+ numpy code faster than I can) 300 Euros crappy setup, 600 euros mid-range setup, 1200 with storage. (Extra) regulations is zilch, it's legal to plug and play these things up to 800W nameplate capacity. I went with numbers for mid-range, vertical south orientation and offsetting 200W (without battery, any overproduction is wasted). This nets you an avarage of €0.32 per day - With practically nothing in winter, and maybe up to €1 per day on a PARTICULARLY nice summer day. But altogether, that still adds up to something like Eur 116 per year, so your midrange system earns itself back in 5-6 years. Not great, not terrible. Nothing to write home about, but free money is free money.

lucb1e 1y ago

Article cites manufacturers as saying that > installing a couple of 300-watt panels will give savings of up to 30% on a typical household’s electricity bill, but there are lots of variables that come with that claim. It depends on which direction the balcony faces and whether the panels are shaded part of the day. My german electricity bill is around 1200 euros a year. Sign me up for a one-time purchase of 426€ to save ~360€ every year if I had optimal conditions -- call it 50% effective and it's still earned back in under 3 years. The thing lasts, what, a decade? More? (Price taken from https://kleineskraftwerk.de/products/kleines-kraftwerk-gitterbalkon-single https://kleineskraftwerk.de/products/kleines-kraftwerk-gitte... for 450W, first one I could find from some review site.) Edit: figure corrected for not using the tax rebate that it apparently advertised with

blackjack_ 1y ago
Yeah so depends on your cost per kWh, and usage time versus production time. My 800W of balcony panels can theoretically produce 3-4 kWh per day (they peak at about 550w of actual production), but they generally produce a lot less than that. This is because my usage during production time is both less than that and also very spiky (my power usage is often 0w or 100-200w base load, with 2kw spikes as the compressor in the refrigerator kicks on, or some other device kicks on). So the savings for me isn't 3 years payoff, it's probably more like 6. But yes, these panels will product for 25-30 years. So yeah, they can pay for themselves very quickly depending on your usage patterns. I'm in the US, and over here we also have some other complicating factors (here we have 2 sets of breakers that are 180 degrees out of phase and so the solar panels can only feed into one half of the breakers without extra complications. I only sort of understand this, someone else can explain better), so solar panels plugged into the balcony that don't backfeed straight to the grid can only cover a subset of the usage. In Germany you have 240v power so I would assume you would hit payoff very quickly.
lucb1e 1y ago
(I'm too late and can't edit anymore, but I just noticed upon re-rereading that it says "couple of 300W panels" in the quote and not just "a 300W panel". My math (though done with a 450W panel for an example sales price) is likely off in the wrong direction. Sorry about that.)

colechristensen 1y ago

Solar is cheap, non-peak-efficiency installs get to be the priority once you get the first 40% or so of production in solar. This kind of thing just knocks the edges off of production and transmission costs. You get to the point where you're not trying to squeeze peak efficiency any more and you're just trying to fill in spaces wherever works reasonably well.

danielheath 1y ago

"Poorly oriented panel" can equally well be described as "generates most of its power in the evening, when you have gotten home from work and want to use electricity". It's better to get power at a useful time, even if that means the panel only generates half as much as it could, because storage costs far more than panels.

dzhiurgis 1y ago

It's 800 watts or about 570 KWh per year in berlin, assuming balcony points directly south. At 0.2 euro, that's about 114 euros per year. Percent-wise I'd guess it's less than 10% of yearly total? Overall it's OK payback, but mostly penny pinching in grand scheme of things. https://globalsolaratlas.info/map?c=48.886392,9.470215,6&s=52.522906,13.425293&m=site&pv=small,180,90,0.8 https://globalsolaratlas.info/map?c=48.886392,9.470215,6&s=5...

valenterry 1y ago

A 400W half decently oriented panel (i.e. south facing balcony, 60 degree angle) is sufficient to run your AC to cool your 50sqrm apartment during summer for free.

brucehoult 1y ago
In the summer the optimal angle where I live (35.5º S) is 12º. Panels lying flat on the lawn are losing only 2% from that. Just now, near the equinox, panels lying flat on the lawn lose around 18% at noon. I'll find a way to prop them up at 50º for winter when the time comes for that (April or May), though that's for sunny conditions. In our typical overcast in winter flat on the ground is probably still fine to catch the most diffuse light. I'll experiment when the time comes.
- valenterry 1y ago
  Right. I mentioned the suboptimal 60 degrees because many people hang it from the balcony (90 degrees) and the tilt it a bit, but usually not too much. From what I've seen 60 degrees seems like a good average number.
  - brucehoult 1y ago
    Yeah, in northern Germany vertical and 60º are pretty much equally good/bad in winter (75º would be ideal), but 60º will be getting 70% more power in summer than vertical, and is near ideal in spring/autumn.

kragen 1y ago

That's mostly true, but you're mistaken about the reason they're basically free: it's because the costs of manufacturing them have been dropping dramatically for 20 years, thanks to (in large part Chinese) manufacturing innovations, not because of things like tax reduction.

jansan 1y ago

[flagged]