3 ms·

2kw draw for 24h is actually quite substantial. Don't forget regardless of how sunny it is in Africa, You will still need to have enough stored power to make it

2kw draw for 24h is actually quite substantial. Don't forget regardless of how sunny it is in Africa, You will still need to have enough stored power to make it through the night. I'm not saying it is impossible but suspect it will cost more in fuel to transport the batteries and panels than it would to just run a small inverter genset instead. If your device doesn't need to be constantly powered then I would suggest bringing pre charged batteries and not bothering with the panels.

ClumsyPilot 6y ago
A generator will consume roughly a liter of diesel per hour at this load. For a stationary installation, a diesel generator would be a terrible idea.
- lazide 6y ago
  As with many things - ‘it depends’. You’ll certainly crank up some terrible hour counts running purely off a generator, but for only 2kw continuous you can size a generator that will sip fuel. Depending on local fuel prices, it could take many many years before solar would be even close cost wise. If only 2kw peak, a common strategy is generator to charge a battery bank, also charge when possible the bank with solar, and run inverters off the batteries (or switchover to the generator when charging the bank). Some people just skip the solar panels. Solar has many problems with unpredictability, and if you need to be sure you’ll have power year round, it isn’t a good idea to rely on it 100% without some other way to charge or supplement it. Dedicated off grid folks always have a generator in my experience, even if it rarely has to get fired up. Sizing a battery bank to give you enough excess to not worry about a freak 2 weeks of bad weather in winter is extremely expensive and has other issues (like not being able to properly cycle or maintain all the batteries due to lack of peak power)
  - ClumsyPilot 6y ago
    The claim of 'you'll spend more fuel transporting panels' is a total fantasay "generator that will sip fuel." For this discussion to be usefull, you have to provide some numbers. From generator efficiency I was able to find, you need to consume roughly 1 liter of fuel to create 2 KWh of electricity. Playing around with batteries won't change that. If you look at my calculation above, a single solar panel produces the equivalent of half a ton of diezel. There is no possibility anywhere outside the arctic that a solar installation won't pay for itself.
    - lazide 6y ago
      Using battery banks helps quite a bit, as you can use a larger, more efficient generator to charge the banks quickly and can size it perfectly to do so, then shut it off. So you might only be running the generator for 4-5 hrs a day or less. This helps with wear and tear, lets you be more efficient, etc. How efficient you can get depends a lot on the specific battery chemistry (columb efficiency), bank voltage, max charge rate (C rate, which is very high for lithium, less high for lead/acid), etc. so hard to calculate here. I personally use a small inverter generator to power ~ 2kw (1.8 specifically) loads for long periods of time off grid. I don't bother with a battery pack in this case, though eventually I will. I also use propane (since I can store/refill a 1000 gallon tank with no worries about it going bad - it will be fine for a decade or more, it's easy to transfer to portable bbq size containers, etc), and propane is $2.4/gal where I'm at in bulk. It supports that 1.8~kw/h load continuously, and burns ~ a 5 gallon propane tanks worth in 10 hours at that load. Lower loads, it will go as long as 18. This is at altitude (4500 ft), no supercharging or anything, so you'd get ~ 30% more efficiency at sea level. That is roughly half a gallon of propane for 1.8kw/h, or about $1.50/kwh - pretty much the most expensive and inefficient way to generate power using a generator I imagine. Diesel generators are far more efficient for the power they produce, but generally also output much more power and idle burns more fuel, but fuel is less stable - important for me in this case, not if you're running it a lot. If I was using diesel, I'd be charging a battery bank. In general, larger generators are more efficient (often MUCH more efficient) per unit power produced, as long as you can sustain load within their sweet spot. An over provisioned generator will waste a lot of fuel idling, and an overloaded generator will burn fuel inefficiently. This 'small' commercial generator [https://www.ckpower.com/what-you-need-to-know-about-fuel-efficient-generators-which-fuel-to-use-and-what-products-to-choose/ https://www.ckpower.com/what-you-need-to-know-about-fuel-eff...] (CK300VM-T4 Final) outputs 225kW, and puts out 14.25 kwH per gallon of fuel (rated capacity). If diesel was $3 a gallon like it is here, thats $.21 per kWh - damn cheap! So, assuming our friend here is running 24/7 at 2kw continuous using my terribly inefficient setup, he'd be going through 72 dollars a day in fuel. Quite a bit! But let's compare to solar! A 48kwh system is non-trivial in size and expense. A system rated to produce ~ 40kWh/day in winter (wholesale, DIY installation, no racking or batteries) is ~ 36k, and has 54 large panels. [https://unboundsolar.com/1891324/unbound-solar/solar-kits/17.55-kw-54-panel-mission-solar-off-grid-solar-system https://unboundsolar.com/1891324/unbound-solar/solar-kits/17...] Battery option price varies. Lead acid is cheap, but needs to be over provisioned to avoid stupid short cell life (> 50% discharge will severely shorten cell life), and even overprovisioned if you're actually drawing down the cells much every day, you'll be lucky to get 3-5 years out of them. To have a day buffer (essential, even if you get perfect sunny weather 99% of the time) and not kill your cells quickly, you're looking at ~ $30k worth of batteries on top of that, at nnearly wholesale prices [https://unboundsolar.com/1891324/unbound-solar/solar-kits/17.55-kw-54-panel-mission-solar-off-grid-solar-system https://unboundsolar.com/1891324/unbound-solar/solar-kits/17...] Lithium allows faster charging, deeper discharging, and longer cell life, but is expensive. A ~ 45-50kwh usable battery bank is going to run you an additional $60k at current market prices [https://unboundsolar.com/shop/solar-batteries-backup/battery-banks/lithium-ferro-phosphate-battery-banks https://unboundsolar.com/shop/solar-batteries-backup/battery...], and might not give you an actual full day buffer, depending on how much charge you got in the prior day. So let's assume we can do free racking somehow (racking and installation costs are often almost as much as a normal system), etc. We're looking at about 66k for a bare bones 'works when everything is perfect' system without much redundancy or backup. If you split that out over two years, you are paying $91/day, or $19/day more than if you were using that woefully inefficient generator, with a woefully expensive/inefficient fuel, at altitude with all it's associated losses. If you amortize it further over 5 years AND ignore maintenance, racking costs, battery wear, it starts to look like it would win. The reality is, you can't ignore those though. Unlike the generator, you're also stuck in place (those panels are huge and need to be very solidly anchored), and also unlike the generator the capex is all spent up front. You can't change plans a week in and do something else, you're out that money. Did I mention that the generator I'm talking about cost $850? Solar has it's place - mainly when you can predict the usage far in advance and can amortize the cost over many, many years (a decade or more). I get the impression you've never actually had to provision or budget a system like this? I've had to several times.

ClumsyPilot 6y ago

A generator will consume roughly a liter of diesel per hour at this load. For a stationary installation, a diesel generator would be a terrible idea.

lazide 6y ago
As with many things - ‘it depends’. You’ll certainly crank up some terrible hour counts running purely off a generator, but for only 2kw continuous you can size a generator that will sip fuel. Depending on local fuel prices, it could take many many years before solar would be even close cost wise. If only 2kw peak, a common strategy is generator to charge a battery bank, also charge when possible the bank with solar, and run inverters off the batteries (or switchover to the generator when charging the bank). Some people just skip the solar panels. Solar has many problems with unpredictability, and if you need to be sure you’ll have power year round, it isn’t a good idea to rely on it 100% without some other way to charge or supplement it. Dedicated off grid folks always have a generator in my experience, even if it rarely has to get fired up. Sizing a battery bank to give you enough excess to not worry about a freak 2 weeks of bad weather in winter is extremely expensive and has other issues (like not being able to properly cycle or maintain all the batteries due to lack of peak power)
- ClumsyPilot 6y ago
  The claim of 'you'll spend more fuel transporting panels' is a total fantasay "generator that will sip fuel." For this discussion to be usefull, you have to provide some numbers. From generator efficiency I was able to find, you need to consume roughly 1 liter of fuel to create 2 KWh of electricity. Playing around with batteries won't change that. If you look at my calculation above, a single solar panel produces the equivalent of half a ton of diezel. There is no possibility anywhere outside the arctic that a solar installation won't pay for itself.
  - lazide 6y ago
    Using battery banks helps quite a bit, as you can use a larger, more efficient generator to charge the banks quickly and can size it perfectly to do so, then shut it off. So you might only be running the generator for 4-5 hrs a day or less. This helps with wear and tear, lets you be more efficient, etc. How efficient you can get depends a lot on the specific battery chemistry (columb efficiency), bank voltage, max charge rate (C rate, which is very high for lithium, less high for lead/acid), etc. so hard to calculate here. I personally use a small inverter generator to power ~ 2kw (1.8 specifically) loads for long periods of time off grid. I don't bother with a battery pack in this case, though eventually I will. I also use propane (since I can store/refill a 1000 gallon tank with no worries about it going bad - it will be fine for a decade or more, it's easy to transfer to portable bbq size containers, etc), and propane is $2.4/gal where I'm at in bulk. It supports that 1.8~kw/h load continuously, and burns ~ a 5 gallon propane tanks worth in 10 hours at that load. Lower loads, it will go as long as 18. This is at altitude (4500 ft), no supercharging or anything, so you'd get ~ 30% more efficiency at sea level. That is roughly half a gallon of propane for 1.8kw/h, or about $1.50/kwh - pretty much the most expensive and inefficient way to generate power using a generator I imagine. Diesel generators are far more efficient for the power they produce, but generally also output much more power and idle burns more fuel, but fuel is less stable - important for me in this case, not if you're running it a lot. If I was using diesel, I'd be charging a battery bank. In general, larger generators are more efficient (often MUCH more efficient) per unit power produced, as long as you can sustain load within their sweet spot. An over provisioned generator will waste a lot of fuel idling, and an overloaded generator will burn fuel inefficiently. This 'small' commercial generator [https://www.ckpower.com/what-you-need-to-know-about-fuel-efficient-generators-which-fuel-to-use-and-what-products-to-choose/ https://www.ckpower.com/what-you-need-to-know-about-fuel-eff...] (CK300VM-T4 Final) outputs 225kW, and puts out 14.25 kwH per gallon of fuel (rated capacity). If diesel was $3 a gallon like it is here, thats $.21 per kWh - damn cheap! So, assuming our friend here is running 24/7 at 2kw continuous using my terribly inefficient setup, he'd be going through 72 dollars a day in fuel. Quite a bit! But let's compare to solar! A 48kwh system is non-trivial in size and expense. A system rated to produce ~ 40kWh/day in winter (wholesale, DIY installation, no racking or batteries) is ~ 36k, and has 54 large panels. [https://unboundsolar.com/1891324/unbound-solar/solar-kits/17.55-kw-54-panel-mission-solar-off-grid-solar-system https://unboundsolar.com/1891324/unbound-solar/solar-kits/17...] Battery option price varies. Lead acid is cheap, but needs to be over provisioned to avoid stupid short cell life (> 50% discharge will severely shorten cell life), and even overprovisioned if you're actually drawing down the cells much every day, you'll be lucky to get 3-5 years out of them. To have a day buffer (essential, even if you get perfect sunny weather 99% of the time) and not kill your cells quickly, you're looking at ~ $30k worth of batteries on top of that, at nnearly wholesale prices [https://unboundsolar.com/1891324/unbound-solar/solar-kits/17.55-kw-54-panel-mission-solar-off-grid-solar-system https://unboundsolar.com/1891324/unbound-solar/solar-kits/17...] Lithium allows faster charging, deeper discharging, and longer cell life, but is expensive. A ~ 45-50kwh usable battery bank is going to run you an additional $60k at current market prices [https://unboundsolar.com/shop/solar-batteries-backup/battery-banks/lithium-ferro-phosphate-battery-banks https://unboundsolar.com/shop/solar-batteries-backup/battery...], and might not give you an actual full day buffer, depending on how much charge you got in the prior day. So let's assume we can do free racking somehow (racking and installation costs are often almost as much as a normal system), etc. We're looking at about 66k for a bare bones 'works when everything is perfect' system without much redundancy or backup. If you split that out over two years, you are paying $91/day, or $19/day more than if you were using that woefully inefficient generator, with a woefully expensive/inefficient fuel, at altitude with all it's associated losses. If you amortize it further over 5 years AND ignore maintenance, racking costs, battery wear, it starts to look like it would win. The reality is, you can't ignore those though. Unlike the generator, you're also stuck in place (those panels are huge and need to be very solidly anchored), and also unlike the generator the capex is all spent up front. You can't change plans a week in and do something else, you're out that money. Did I mention that the generator I'm talking about cost $850? Solar has it's place - mainly when you can predict the usage far in advance and can amortize the cost over many, many years (a decade or more). I get the impression you've never actually had to provision or budget a system like this? I've had to several times.