need help with designing an off grid system

[JOELANCASTER]

Hi,

We are looking to build an off-grid 65kw solar array using used solar panels and home made ground mounts. This is still in the drawing phase. The caveat is that the solar array is 650ft away from the house. We have some 350 copper wire but only enough for 1 pair for 1 run. The panels will be in series and parallel to achieve 450vdc, 150amps and approximately 65kw. Any suggestion as how we can connect to a single phase house? I have seen 50kw inverter out there but mostly 3 phases. Any suggestions or help are welcome. Please let me know more info is needed.

Thanks in advance.

JL

[organic farmer]

We were looking at that scenario at one point.

Line losses for running DC are high. But the alternative would have been to install our charge-controller at a location mid-array, along with our battery-bank. And the battery-bank must be in a climate-controlled enclosure. But at least then the long run to the house would have been using VAC, with much lower line losses.

In our region we normally expect to see -20F temps plus with winds. We played with a number of designs, but in each case, it would have been easier to simply build a house.

And I did not want to deal with two separate heated structures.

Our final solution was to have a 75-foot run using MC-4 cables into our house, with the charge-controller and battery-bank and invertor all in our house.

[Ampster]

This is a complex issue with the distance between the array and the home coupled with unknowns about whether this is 230 volt single phase or North American 120/240 Volt split phase. Availability of equipment in a specific market may influence alternatives.

[JOELANCASTER]

thank you for the replies so far. With the 350 single stranded wire, there should be minimal loss even with that distance (according to one electrician). Is he wrong? The house is 120/240 volt split phase. We are looking for equipments that can handle that load or a way to split into several inverters?

[bcroe]

I do not understand, title says off grid, but you have single phase power.
Just where do you put 65Kw, the 200A 240VAC service at my house could
not take it? At 400-500V voltage loss is minimized, but you need a big
combiner to bring the strings together. Trouble is, that class usually is 3
phase, maybe that is what you need.

Using single phase inverters limits you to more like 10Kw each, so the DC
source must be broken into multiple systems, then inverter outputs combined
at the AC side. With only one feed your inverters would need to be at the
source, then combined with more loss at lower AC voltage. Do look up wire
resistance and calculate your losses, ability to cary the current does not
guarantee efficient operation. Bruce Roe

[JOELANCASTER]

Hi Bruce,

Thank you for your input. The house is currently connected to the grid but the plan is be off grid in the future. A chunk of the 65kw is for charging the EV car each night. We only need about 20kw for daily use. is there a way to use the DC from the panels to charge the battery directly to battery directly?

[Ampster]

Hi Bruce,

Thank you for your input. The house is currently connected to the grid but the plan is be off grid in the future. A chunk of the 65kw is for charging the EV car each night. We only need about 20kw for daily use. is there a way to use the DC from the panels to charge the battery directly to battery directly?

Nothing concrete has developed yet on the DC side. Charging an EV may be a reason to maintain a grid connection. I have two EVs and use Self Consumption Mode on my hybrid inverter. I mostly charge the EVs from available solar during the day using traditional AC charging. DC fast charging is of no interest to me at home since I can top off easily overnight if needed. In my opinion, using batteries to charge batteries is sub optimal.

[JOELANCASTER]

Nothing concrete has developed yet on the DC side. Charging an EV may be a reason to maintain a grid connection. I have two EVs and use Self Consumption Mode on my hybrid inverter. I mostly charge the EVs from available solar during the day using traditional AC charging. DC fast charging is of no interest to me at home since I can top off easily overnight if needed. In my opinion, using batteries to charge batteries is sub optimal.

I agree that using batteries to charge batteries is sub optimal but I can only charge at night due to my schedule.

[JOELANCASTER]

We talked to several inverter manufacturer support representatives. It's a hit and miss on their knowledge. One technician said split the voltage down. What does that mean? We keep asking if it's possible to split one source wire into several lower power inverters.

[Ampster]

I agree that using batteries to charge batteries is sub optimal but I can only charge at night due to my schedule.

Do you have a Net Metering option with your utility? That may be more cost effective than using batteries in that fashion. Have you costed out any alternative inverter configurations including batteries? How does that translate into a cost per kWh of stored energy compared to buying energy from the grid?

[JOELANCASTER]

Do you have a Net Metering option with your utility? That may be more cost effective than using batteries in that fashion. Have you costed out any alternative inverter configurations including batteries? How does that translate into a cost per kWh of stored energy compared to buying energy from the grid?

No Net Metering option. Cost-wise, it's doesn't make sense for this state (TN 10.79¢ / kWh). I just want to be off-grid. I am still trying to figure out everything and there are so much to learn. I am thankful for forum like this and you guys. Any input is appreciated!!

[Whalepod]

Hi Bruce,

Thank you for your input. The house is currently connected to the grid but the plan is be off grid in the future. A chunk of the 65kw is for charging the EV car each night. We only need about 20kw for daily use. is there a way to use the DC from the panels to charge the battery directly to battery directly?

Ok I know this post is old as dirt, but in case anyone else is still listening... are you talking about generating 65kwH per day, or building a 65kw solar array? The way you're talking about 20kw base load makes me think that when you look at your bill you see that 20kwH is probably for your home use, and another 45 to the EV. Those are VERY different propositions. A system capable of generating 65kwH in the winter is more like 20kW DC, and MUCH more approachable.

All that being said, bcroe is right. The volume, and the hours in which you use your power don't make a lot of sense for Solar + Storage to even come close to ever penciling out. Unless you're wanting to disconnect from the grid purely because you're cranky, it's going to cost you.