Opinions on Used Solar Equipment

boondox

Chief Engineer, RedNeckTech Industries
I was in a similar situation. Cost of bringing power in way exceeded cost of solar. Makes the choice easy.

For starters, do a good solar survey. Figure out where the best sun summer and winter. Winter is more important than summer so if you have to compromise make the winter the better half. With any luck it is not in the same spot you want to build your house. I opted for a shipping container to mount my solar on and put equipment inside. This allowed me to put it in an optimum sun spot while keeping the trailer I was working out of in the shade. I just run the AC to wherever I need it. As long as it isn't really far from the sun spot this works well. It also gave me locked storage and a shop as well as storage which was really great for me. Built a small generator shed outside right by the power center. Very convenient to work with and in and makes it easy to start small and grow as you need it.
 

Hedges

Photon Sorcerer
A transformer is just two coils of wire, magnetically coupled. It takes in AC of one voltage & current, outputs a different voltage and current of same power. For instance 120V 10A in, 240V 5A out.

Inverter takes DC (like from battery) and produces AC that can run your appliances (off-grid inverter). Or shoves current into grid (grid-tie inverter.)

I put the cost of power from PV panels and inverter at about $0.05/kWh, amortized over 10 years. Lead-acid batteries $0.50/kWh, amortized over their cycle life. Commercial lithium batteries are coming down, were close to lead-acid in cost when I checked, but 5x the price and 5x the life. DIY LiFePO4 is about $0.05/kWh.

The combination of PV, DIY LiFePO4, charge controller (or AC coupled inverter) and battery inverter varies a bit depending on quality/capability of the battery inverter. Better ones can start large induction motors like well pumps. Cheap end system cost might approach $0.10/kWh if the cheap inverter lasts. High-end may run $0.25/kWh or more.

What really costs is expensive capital equipment that is used occasionally. Like batteries sized for 3 days without sun but normally only cycled 15%. Inverters able to start a 5HP motor but powering an average of 500W most of the time.

If you can get a utility hookup at the edge of your property without large upfront or monthly cost, that would be good to do.

Here's 1000' of 12 awg UF for $660. $2000 would feed a modest amount of power to a grid/backup system and keep batteries charged. (How you protect the wire from damage is left as an exercise for the reader.)

 

Catsassend

New Member
I was in a similar situation. Cost of bringing power in way exceeded cost of solar. Makes the choice easy.

For starters, do a good solar survey. Figure out where the best sun summer and winter. Winter is more important than summer so if you have to compromise make the winter the better half. With any luck it is not in the same spot you want to build your house. I opted for a shipping container to mount my solar on and put equipment inside. This allowed me to put it in an optimum sun spot while keeping the trailer I was working out of in the shade. I just run the AC to wherever I need it. As long as it isn't really far from the sun spot this works well. It also gave me locked storage and a shop as well as storage which was really great for me. Built a small generator shed outside right by the power center. Very convenient to work with and in and makes it easy to start small and grow as you need it.
That sounds like an amazing setup, and we are planning to get a sea can anyways... We should seriously consider this. Thanks for sharing your idea.
 

Catsassend

New Member
A transformer is just two coils of wire, magnetically coupled. It takes in AC of one voltage & current, outputs a different voltage and current of same power. For instance 120V 10A in, 240V 5A out.

Inverter takes DC (like from battery) and produces AC that can run your appliances (off-grid inverter). Or shoves current into grid (grid-tie inverter.)

I put the cost of power from PV panels and inverter at about $0.05/kWh, amortized over 10 years. Lead-acid batteries $0.50/kWh, amortized over their cycle life. Commercial lithium batteries are coming down, were close to lead-acid in cost when I checked, but 5x the price and 5x the life. DIY LiFePO4 is about $0.05/kWh.

The combination of PV, DIY LiFePO4, charge controller (or AC coupled inverter) and battery inverter varies a bit depending on quality/capability of the battery inverter. Better ones can start large induction motors like well pumps. Cheap end system cost might approach $0.10/kWh if the cheap inverter lasts. High-end may run $0.25/kWh or more.

What really costs is expensive capital equipment that is used occasionally. Like batteries sized for 3 days without sun but normally only cycled 15%. Inverters able to start a 5HP motor but powering an average of 500W most of the time.

If you can get a utility hookup at the edge of your property without large upfront or monthly cost, that would be good to do.

Here's 1000' of 12 awg UF for $660. $2000 would feed a modest amount of power to a grid/backup system and keep batteries charged. (How you protect the wire from damage is left as an exercise for the reader.)

Yikes! Why does anyone go solar then?! Maybe a diesel or propane generator might be worth looking into, though I don't look forward to the noise.
 

Hedges

Photon Sorcerer
Yikes! Why does anyone go solar then?! Maybe a diesel or propane generator might be worth looking into, though I don't look forward to the noise.

Short term use with high loads, generator is the way to go.

For a decade of usage, PV is cheaper than grid or generator. But if grid is available, we recommend using that (hopefully net metering) rather than batteries. Without net metering, I think zero export PV (use it or lose it) is cheaper than adding batteries.

Operating a diesel generator probably costs $0.50/kW. Plus maintenance. I think that's the price one user here documented.
If you need heat, "co-generation" where you also capture exhaust/coolant heat for domestic use changes the equation.

Audit/add up your loads, and maybe a hybrid system of PV for light use and fire up generator for one hour a week to run laundry? (just as an example of a heavy load, could be well pump.)

Once you have the cash to burn, an oversized 100% PV system would be nice.
If you find a bargain on used/surplus equipment that work together as a system, you can save a lot.
Those four Sunny Island in my picture cost me twenty five cents on the dollar, new in the box.
 

toms

Solar Addict
In Australia, used Sunnyboy 5000 and 5kw of PV (and racking/wiring) sells for less than 1k. Add a Sunny Island, 20kwh LiFePO4 battery and BMS, and a quality diesel generator and you can have a 20kwh/day power system for approx 40c/kwh.

Where i live it was going to cost over $250k to connect a single line mains power line.

I have helped set up dozens of systems using second hand SMA inverters and good quality panels over the last decade, i think it’s a fantastic way to go.
 

Hedges

Photon Sorcerer
In Australia, used Sunnyboy 5000 and 5kw of PV (and racking/wiring) sells for less than 1k. Add a Sunny Island, 20kwh LiFePO4 battery and BMS, and a quality diesel generator and you can have a 20kwh/day power system for approx 40c/kwh.

How long do you go without sun? How much do you need to run the generator?
What do you spend on those other things? Retail, Sunny Island is $5k, DIY battery of that capacity might be $3k to $5k, is generator $5k?
Before fuel costs that brings me to $0.22/kWh over a decade. But fuel isn't cheap. Do you do CHP for winter heating?

I think you use 230V 50 Hz single phase, so one Sunny Island produces that without needing a transformer.
I would used two GT PV Sunny Boy and 15kW or so of PV (multiple angles so 10kW peak but more hours.)
Sunny Island can control twice as much GT PV as its rating, so lots of power available during the day. Helps make up for poor sun days.
With many hours to charge, LiFePO4 could be charged at about 0.12C, which it good even in fairly cold and hot weather.
This way generator would rarely be needed.

With no generator and using 40 kWh/day, $0.09/kWh. But of course that is only if you use more power when available in the summer, less in winter. Practically speaking, you'll always either be short on power or you'll have more power than you need, so cost per kWh is higher. Summer vs. winter PV production can vary 2.5 or 5 to 1. Might balance well if you operate A/C.

Any of these is still a moderately large investment, costs up-front half what OP would have to pay for grid brought to his site. I think he wants to go smaller.
 

Catsassend

New Member
Short term use with high loads, generator is the way to go.

For a decade of usage, PV is cheaper than grid or generator. But if grid is available, we recommend using that (hopefully net metering) rather than batteries. Without net metering, I think zero export PV (use it or lose it) is cheaper than adding batteries.

Operating a diesel generator probably costs $0.50/kW. Plus maintenance. I think that's the price one user here documented.
If you need heat, "co-generation" where you also capture exhaust/coolant heat for domestic use changes the equation.

Audit/add up your loads, and maybe a hybrid system of PV for light use and fire up generator for one hour a week to run laundry? (just as an example of a heavy load, could be well pump.)

Once you have the cash to burn, an oversized 100% PV system would be nice.
If you find a bargain on used/surplus equipment that work together as a system, you can save a lot.
Those four Sunny Island in my picture cost me twenty five cents on the dollar, new in the box.

OOooh. :🤦: I understand what you are saying! It never occurred to me that grid tie meant that you don't need the batteries too. So for the totally ignorant - grid tie essentially is a storage bank so you withdraw power when you require it.
 

Hedges

Photon Sorcerer
Yup.

My system has grown from grid tie to grid-backup by the addition of Sunny Island battery inverter. I had to replace my original GT PV Sunny Boys because they didn't play nice, but was able to buy new-old-stock replacements for a discount.

Newer model Sunny Boy offer PV direct backup (no batteries) during daylight hours, a good option for grid-tie users but not your off-grid application.

Originally, we simply spun our meter backwards (some mechanical meters actually did that.)
With utility company permission and a meter calibrated for that purpose we "sold" and bought power at the same price. Free, 100% efficient storage.
No cash payment to us, and credit balance on bill zeroed once each year (I would have preferred it carried forward.)
With time-of-use meter, some hours I might deliver power at 3x price, other hours get back at 1x the price so 3x the kWh. In the beginning I estimate around 1.5x my production on average.

Now with higher market penetration, utility company resents losing us as customers buying power for a 10x markup from wholesale to retail so they seek to change the financial arrangement.

The grid tie equipment is lighter weight and economical because it uses 200V to 600V PV at 7A and only has to handle peak PV watts.
A battery system handles 5x to 20x higher current due to 48V or 12V battery, and maybe 10x that due to peak household power consumption vs. low PV production. Many more MOSFETs inside.

A robust battery inverter like Sunny Island (5.75 kW continuous) costs around $5000, and a GT PV inverter like Sunny Boy (7.7 kW) costs around $2000.
There are cheap lightweight hybrid (battery/PV) inverters, one was priced at $800 for 5kW. But the forum member reported it failed after a couple months.
A more well regarded one SolArk is about $7000 - $8000 and 8kW or 9kW. (the 12kW PV one has 9kW inverter)


I think smaller units from MPP might give you moderate wattage and price with acceptable quality. I've never touched one, but I think a number of people here use them.
 
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