Off-Grid Solar System for EV Charging (~Cost and Panel Requirements)?

[Calothrix]

I have been considering building or purchasing an off-grid solar system for charging two plug-in hybrid vehicles for some time now and the recently announced Chinese tariffs on panels, batteries, etc. has prompted me to start researching the matter (hopefully I have time before they are enacted!). Before I dive all-in into the research, I thought I would ask two questions to see if it is worth proceeding. The two vehicle's battery capacities combined is 20 kWh and on a typical weekday we utilize about 80% of that capacity. I live in Iowa and would install the panels on my roof which faces SSW (205 degrees). What would be a good cost estimate for a system that would charge both vehicles to 80% capacity on a typical day and how much square footage of roof area would be required for solar panels (of a wattage that would give me the most bang for the buck)? I understand there are a lot of variables involved but just trying to get a general feeling for total cost and roof area impacted.....if all sounds good, then I dive down the rabbit hole!

 

[MichaelK]

First, you need to look into the standard EV charging levels, L1, L2, and L3.

L1: 12A at 120VAC, 1440W
L2: 10-50A at 240VAC, 2400W-12,000W
L3: ?A at 480VDC

Level one is easily attainable with a 120V inverter, level two with a split-phase 120/240V inverter, but level three is most likely never going to be available to most DIY mavens.

So, let's start out at reading level one, and go from there. With two EVs, and having to replace 20kWh X 80% = 16kWh each and every day. Assuming you get maybe 6 sunhours (sh) of light during the summer, and maybe 3 in winter, you need to scale your system for the worst day in December. So, to make 16kWh of power on a day with 3 sh, you'll need 16,000Wh/3sh = 5400W of panels. That assumes you get any sunny weather in December.

To handle 5400W of power, you'd need a 48V system. It will be just too many amps for a 24V system. For a system that can handle that many watts, you'd need a charge controller that can handle 100+A, so maybe two 2700W arrays wired to two parallel charge controllers, charging a 48V battery in the 500Ah range.

Assuming you want to charge two batteries at 1440W each, that's 2880W total. Don't plan on running your inverter at more than 50% capacity, so a 6000W sine-wave inverter would work nicely here. Most of the good 6000W+ inverters are split-phase 120/240VAC, so you might reach a modest level 2 charge with an inverter in that size. Schneider's XW-Pro and Outback's Radian 8048 would be two very good choices.

Now whether or not 5400W of panels can put out what you need over the course of a December's day is hard for me to say. My panels are on rotating mounts that can turn East to West over the course of the day. I know that I can make 1440W from ~8:30am till about 2:30pm in December, but that is only ~ half of what you need. Maybe others here working with fixed arrays only can pipe in how many practical watts you'd need. But, the amount needed will definately be lower if you can mount them on rotating arrays.

 

[Calothrix]

Thanks Michael, that's a great start! I will start looking into building/purchasing a ~16kWh, 48V, L2 system with a split-phase inverter because I would want the choice of being able to charge the vehicles via 120 or 240V. What are folks general thoughts on building a DIY system vs purchasing an all-in-one system? Could someone provide links for a well-built DIY system and a decent quality all-in-one system that would meet my needs. With help from this forum I was able to construct a DIY LiFePO4 battery for my camper van a few years ago, and I would be willing to go the DIY route if it means getting decent components for less money than the all-in-one route.