Store Daily Solar to Charge EV

[ChrisYXE]

New here and just taking in info....I would like to store the over production of solar during the day to change my car at night as my utility only pass half of what I buy at. So today I sent 34kWh back to the grid and got paid $2.55 and when I charge my car tonight and use 25kWh i'll pay $3.69. Would be nice to store and use it just for charging my car.

Maybe I'm out to lunch on whats possible but I guess thats why I'm here.

 

[italianuser]

7,5c/KW. That's why I'm not keen on grid-tied systems. So your plan would be to go offgrid.

I have no idea of he capabilities of grid-tied inverters, I'd have to do my research here, so my first questions would be:
- Can my inverter do offgrid? If yes -> make a plan for adding battery storage; if no -> make a plan for adding a new hybrid inverter plus storage;
- What does my contract with the energy company state? Should I close the contract or may I keep it even if I won't be transferring anything.

Surely you can start seeing battery packs, prices and features. Your plan could be to have a storage for 2 or 3 days.

 

[ChrisYXE]

Not even off grid, but if I could store enough power to recharge my car at home in the evenings that would be ideal. What I would in vision would be to monitor extra production and if I'm making more than I'm using charge the storage pack until full and then send the rest back to the grid. Then I can use the extra to charge my car without pulling from the grid at night.

 

[100kwh-hunter]

7.5c...in dolar...that is a bargain, we pay 40c in euro because our roberment has "enough" wind and solar.
When they dont have enough we pay up to 1,40 euro a kwh....
Stay as much as you can off grid, expand your system, lifepo4 cells are getting cheaper.

 

[harrisonpatm]

@italianuser is spot on with checking to see whether your current equipment can handle battery backup. If it can, that's great, now you need to consider the cost of a battery backup system. Rough estimate: $75-500$ per KWH of storage. At the budget end, a lot of DIY is involved, sourcing the cells, connecting them yourself safely and up to code, ect. At the expensive end is an off-the-shelf product like a Tesla powerwall, which also is probably going to cost to be installed by a professional. Where along that spectrum you can afford is up to you.

As a side now, my much much smaller system does exactly what you are thinking about doing: 500-800w of solar, feeding into a DIY 9kwh powerwall, which only powers 400-800kwh per day... so excess solar is always stored, then used to charge my EV, a motorcycle. It's a lovely system, I can highly recommended it, if that's what you consider doing. Yours will need to be much bigger than mine, of course, at 25-35kwh of storage!

 

[ChrisYXE]

@italianuser is spot on with checking to see whether your current equipment can handle battery backup. If it can, that's great, now you need to consider the cost of a battery backup system. Rough estimate: $75-500$ per KWH of storage. At the budget end, a lot of DIY is involved, sourcing the cells, connecting them yourself safely and up to code, ect. At the expensive end is an off-the-shelf product like a Tesla powerwall, which also is probably going to cost to be installed by a professional. Where along that spectrum you can afford is up to you.

As a side now, my much much smaller system does exactly what you are thinking about doing: 500-800w of solar, feeding into a DIY 9kwh powerwall, which only powers 400-800kwh per day... so excess solar is always stored, then used to charge my EV, a motorcycle. It's a lovely system, I can highly recommended it, if that's what you consider doing. Yours will need to be much bigger than mine, of course, at 25-35kwh of storage!

I'm fine with staying on grid as my solar offsets most. Yea I'd like to upscale your EV motorcycle setup. Even if I could store 10-15kWh that would allow me to top up every day and add 100-150km of range over night.

I'm a mechanic by trade and done all my own home electrical so DIY and following safety and code is up my ally. What voltage do you charge your motorcycle at? I would imagine there is a convertor/transformer to up the voltage to 240V AC? I have much to learn.

 

[harrisonpatm]

What voltage do you charge your motorcycle at? I would imagine there is a convertor/transformer to up the voltage to 240V AC? I have much to learn.

Ah, there's the rub. It's DIY 24s LFP, so top voltage of 83-84v. This keeps it in the range of off-the-shelf components. I use a cheap aliexpress DC-DC boost converter to bring the 14s Li-Ion powerwall (48ish volts) up to 84v, and it also has current limiting, all for under 20 bucks. This works great for me, I love that everything is kept in DC, less losses.

It'll be less straightforward for your car, EV's can be anywhere from 200-600v. Can you share what model of car you have?

Without knowing anything else, off the top of my head, my first idea for what you could build is:

PV -> 14s Li-ion 25-35kWh -> 240v 6000w DCtoAC inverter -> AC car charger compatible with your EV. I wouldn't bet on being able to find a reliable direct DC charging device for your vehicle, and even if you could, most EV's aren't setup for you doing that at home.

As @italianuser said, check to see if your current equipment can support battery charging. If so, it wouldn't be too difficult to direct PV to a powerwall, and wire an output solely for an inverter, from which you can run your car charger. I'm assuming you already have a car charger installed that's pulling power from your electrical panel. If you installed it yourself, it wouldn't be too difficult to wire it to pull from an inverter instead.

It's a good idea. Looking forward to seeing what you come up with.

 

[cak]

34kWh back to the grid and got paid $2.55 and when I charge my car tonight and use 25kWh i'll pay $3.69

Great idea and lots of different ways you could design it to work the biggest challenge is car batteries are huge and so having an additional battery to charge the car would have to be even bigger to account for losses and batteries are expensive and a wear component. So all that to say your return on investment will be LONG based on those small dollar/day prices. The good news is batteries are getting cheaper fast and so especially if you DIY you could probably build a system for around $200/kwh. And if you don't need to size it for an empty car battery but maybe just your regular commute needed charge a 25kwh system is about the same size as I run my whole off grid house on so not so crazy large as say a full tesla which can be 70kwh. plus the new battery technologies have really long cycle counts so they should last awhile even if you cycle them daily. Main factors you will want to consider is round trip efficiency since every DC-AC and such use some power and then also consider how long the batteries will last to figure weather the cost is worthwhile. As an example I charge an electric tractor off my home battery but the tractor battery is bigger than my house battery so it only works to charge it when the sun is out and for short periods of time so I still have power to run the house. I also only get about 60-70% efficiency in my current setup which is not ideal. My power to tractor is(estimated energy loss) Solar-MPPT(2-5%)-Batteries In(4%)-Batteries Out(2%)-Inverter(12%)-AC Charger(15%)-Tractor Battery In plus all the combined losses from the various wires(2-5%).