Solar for EVs

[RivAW]

Wondering if anyone has invested in a minimal (residential) solar power system solely for the purpose of powering EVs. Perhaps a few panels over the garage or elsewhere in an area where the cost/benefit doesn’t make sense for system large enough to go “off grid” or power the whole house…

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[whiskeyfarmer]

I have a roof mounted solar array on my house. Nominal output is a bit over 6kW (19 panels). Installed a couple years prior to purchasing my R1T. On a sunny, summer day I generate around 40kWh. Grid tied. So basically enough to cover roughly 80 miles of daily driving in my truck. Almost all my driving is local and averages less than that. Also, my utility (ComEd) allowed me to enroll in hourly pricing which varies throughout the day based on grid demand. Generally this is good as peak summer solar generally dovetails with peak electrical demand (daytime temps and a/c useage). So as a rule i provide excess solar energy to grid at higher prices than I draw off the grid to charge my truck overnight. I have truck set up to charge between 11pm and 5am when hourly rates are typically lower. Working good so far.

 

[Whataboykie!]

I just moved to Florida in 2022 (retired) and bought a new house. I have a large solar system with 31 panels producing, on a full sunshine day, about 9kW/hr. I also have two 10kW backup batteries, that I charge fully almost every day.
With my Enlighten app, I can track my charging and usage instantly. Works like a charm and I virtually drive my R1T for free!
Here's the rub. My system costs $73,000! Luckily I got back $20,000 from the Taxman.
So, this obviously is beyond most people's budgets.
All I can say is, do something. Electric pricing can only go up, and does.
I can also tell you not to worry about "Pay Back". This is where most people get miss informed.
Supposedly my system will pay for itself in 20 years! BS. If I ever sell my house, you can rest assured that I will add the $50,000 cost of my system to my asking price.
So payback is a non issue. Your System adds to the value of your house.
Unfortunately my electric provider here charges me .12c per kW/hr and only gives me back .05c per kW/hr I send back to the grid, and I send back a lot. This will vary depending on your provider.
That said, I still pay my electric utility every month, around $80.00. About the same as filling the tank on a big Dually Diesel truck, that you might have to do 4 times a month!
How much do you spend on gas every month? Think about it, I spend nothing!
Why do I still have to pay in? My house is 2,800sf and I have a pool and a pool heater, as well as the AC, and all the other appliances that everybody has. So, I consume a lot.
Good luck and start looking for a system.

 

[usulio]

Timing is the question if, like most people, you drive when it's sunny and charge at night. Like whiskeyfarmer, you can offset by selling energy to the grid during the day and buying it back at night. Or you can get a house battery, charge it during the day, and use it to charge the car at night. Wonder if anyone does that?

 

[JeremyP]

It depends on your state net metering rules, but I can generate extra power during the summer and use it during the winter (or any time in the future). If the interconnection rules and installation cost are favorable, then you should put on as large a system as you can, because having your own powerplant on your roof is great. I installed my own system and I'm 3 years into a 4 year return on investment, and it's powering our house (heating and cooling), hot tub, pool, and about 15k miles a year of ev driving.

 

[Zoidz]

It depends on your state net metering rules, but I can generate extra power during the summer and use it during the winter (or any time in the future). If the interconnection rules and installation cost are favorable, then you should put on as large a system as you can, because having your own powerplant on your roof is great. I installed my own system and I'm 3 years into a 4 year return on investment, and it's powering our house (heating and cooling), hot tub, pool, and about 15k miles a year of ev driving.

Regarding installing the largest system you can, you need to check your utility's net metering agreement. In some areas, like where I live, if you use generate more power than you use over the net metering period (1 year), the excess power is "paid" to you at wholesale generation rate, not market use rate. As an example, if you use 10,000 kwh over the agreement year, and generate 14,000 kwh, you will be paid market rate (let's say 14 cents/kwh) for 10,000 kwh you generate, and wholesale rate (let's say 6 cents) for 4,000 kwh.

The reason you should be aware of this is the return on investment. Those extra panels that you install beyond your consumption will have more than twice as long ROI period.

 

[racekarl]

Regarding installing the largest system you can, you need to check your utility's net metering agreement. In some areas, like where I live, if you use generate more power than you use over the net metering period (1 year), the excess power is "paid" to you at wholesale generation rate, not market use rate. As an example, if you use 10,000 kwh over the agreement year, and generate 14,000 kwh, you will be paid market rate (let's say 14 cents/kwh) for 10,000 kwh you generate, and wholesale rate (let's say 6 cents) for 4,000 kwh.

The reason you should be aware of this is the return on investment. Those extra panels that you install beyond your consumption will have more than twice as long ROI period.

To further this point: again depending on the area you may be charged separate generation and distribution fees as part of your rate. You will pay both for the power you consume from the grid but may be paid only the generation fee for the power you sell back to the grid.

When we had our rooftop PV system installed 5 years ago (in MA), the rule of the thumb the installer gave us was to size your grid-connected system at 80-90% of your historical power usage. The idea being your usage may fall over time as you replace systems with more energy efficient ones, but you never really want to go into a long-term surplus with the utility.

To return to the OP's question: I would say I am not sure that makes sense. There are going to be fixed costs that do not vary much with array size (permits, interconnect, inverter, etc.) so a smaller array will take longer to recover those costs if the only offsetting benefit is EV charging.

 

[LivingInKaos]

If your only purpose is to charge your truck, don't bother imo. It's not worth the investment. In order to charge with solar, you'll have to utilize an inverter capable of powering your charger plus you'll have to utilize a battery system to store the energy in a way that can supply the charger with a steady amount of energy at whatever setting your charger/truck is set for. The battery costs can be the limiting factor here. The easiest method is to grid tie and just hope to offset your charging costs if not going large enough to off grid.

I live off grid with a 9kw system. I cannot use any of that to charge the truck really. You never generate what it is rated and only for specific times of day, v especially depending on your location.

 

[the_mace]

I have a 17.6kW system installed back in 2014. Originally for a Tesla + house stuff. Now it does Tesla + Rivian + House stuff. Tesla was just short of 20% of my total power use. Now Rivan + Tesla are about 50% of my total power use.

Depending on where you live your power can vary a lot. Here in New England there's a lot less sun in the Winters, snow on the panels etc. Weather varies year to year etc.

The short part is, you could get more EVs, your house uses electric and everything varies. Dont try to perfectly size it to what you think the use is.

 

[SRO]

Timing is the question if, like most people, you drive when it's sunny and charge at night. Like whiskeyfarmer, you can offset by selling energy to the grid during the day and buying it back at night. Or you can get a house battery, charge it during the day, and use it to charge the car at night. Wonder if anyone does that?

I have a Tesla powerwall it stores about 15kwh. Not much compared to a 135kwh Rivian battery.

 

[SRO]

Regarding installing the largest system you can, you need to check your utility's net metering agreement. In some areas, like where I live, if you use generate more power than you use over the net metering period (1 year), the excess power is "paid" to you at wholesale generation rate, not market use rate. As an example, if you use 10,000 kwh over the agreement year, and generate 14,000 kwh, you will be paid market rate (let's say 14 cents/kwh) for 10,000 kwh you generate, and wholesale rate (let's say 6 cents) for 4,000 kwh.

The reason you should be aware of this is the return on investment. Those extra panels that you install beyond your consumption will have more than twice as long ROI period.

Does your ROI include fuel savings assuming you previously had an ICE. I put my solar in and bought an EV at the same time for example. In the summer it costs me about 5 dollars a month to fuel my Rivian and $50 a month in winter.

 

[Zoidz]

Does your ROI include fuel savings assuming you previously had an ICE. I put my solar in and bought an EV at the same time for example. In the summer it costs me about 5 dollars a month to fuel my Rivian and $50 a month in winter.

Good point. No, I was referring to ROI as a solar project just on the electrical generation side.

 

[Donald Stanfield]

I really don't understand solar well enough. We had a quote here and it was like 80K dollars to get a system installed. With the costs of installation vs power it would take us 20-30 years to get the pay off which is the rated life of the system. In other words I'd be much better putting that same 80K into an investment vehicle if saving money was my goal.

Is it a hedge assuming sky rocketing future energy costs? Is electricity that much more expensive where everyone else is? Or am I just getting scalped with an installation quote?

 

[logan]

I have a Tesla powerwall it stores about 15kwh. Not much compared to a 135kwh Rivian battery.

Likewise I have 23.5kWh house batteries. It's enough to get me past the peak hours when the net meter exchange rate is lower and more importantly, for me, it gets me through power outages both at night and during the day when the solar can recharge even if the grid is down. Definitely recommend solar. I've very happy with batteries too but harder to justify from an ROI point of view. Anyway, point being batteries can provide value even if they are smaller than Rivian's for a grid tied system.

Since I work mostly from home I do try to do my occasional 45% -> 85% charge in the afternoon when I have excess solar generation and am working anyway but don't sweat it if it is easier to just plug in the evening before a longer commute.

 

[logan]

I really don't understand solar well enough. We had a quote here and it was like 80K dollars to get a system installed. With the costs of installation vs power it would take us 20-30 years to get the pay off which is the rated life of the system. In other words I'd be much better putting that same 80K into an investment vehicle if saving money was my goal.

Is it a hedge assuming sky rocketing future energy costs? Is electricity that much more expensive where everyone else is? Or am I just getting scalped with an installation quote?

I'm guessing the latter but it really depends on your usage since at least in some areas the residential rates go up fast as you move up tiers of usage. I use a lot of power even before having EVs due to servers and such. I was paying ~$400 and sometimes double that. So, my solar paid itself off in just a few years. Also, it is worth getting multiple quotes including big and local installers. My highest quote was twice my lowest quote. For example, I got 40 panels for less than half the quote you mentioned.

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