EV running off solar? - Page 1
Forum section: electronics / general

author: paulca
author_rank: Super Contributor
timestamp: May 30, 2019, 11:57:21 am
content: I tried to calculate how much solar panel would be needed to charge an EV for a determined number of miles per day or week. I ended up with different figures depending on how I did it, but mostly they didn't sound right.For example:A Renault Zoe (used as a basic example) claims 255Wh per mile.My daily commute is 15 miles each way, giving 30 mile round trip.30 miles per day * 255Wh = 7.6KwhNow normally I would convert this to a constant load and then multiple it by 10. However when you do this you get:7.6Kwh / 24 hours = 318 Watts * 10 = 3.1KwActually that sounds plausible. 3Kw of solar panels and a battery capable of storing several days worth of car usage. A 15Kwh battery for example.Does this sound reasonable to you guys? I wouldn't expect it to be full proof, I would envision the charge station would run from battery and when they got low continue to charge from the mains.

author: Audioguru
author_rank: Super Contributor
timestamp: May 30, 2019, 03:58:36 pm
content: Those tiny little cars are not available over here. If your huge solar panel charges a huge battery then will you use an inverter to produce the 230VAC for the car's battery charger?What will shut off the inverter?

author: Seekonk
author_rank: Super Contributor
timestamp: May 30, 2019, 04:08:00 pm
content: So, how do you charge when at work? The panels aren't where you drive the car to. Divide 7.6KWH by the number of hours you have to charge and that gives the array size. But, that is only good for about 2 hours a day in peak sun. It takes the whole rest of the day to make up the other half. And will the car accept lower charge currents or need a battery buffer.

author: paulca
author_rank: Super Contributor
timestamp: May 30, 2019, 06:42:39 pm
content: Quote from: Seekonk on May 30, 2019, 04:08:00 pmIt was only really an finger in the air question, but yes, the plan was for a battery buffer. So the buffer is charged while you are out at work, you come home, plug in and drain that buffer into the car.Running it off an inverter using a normal 3kw charger is an option, but there are other options. People apparently make DC-DC charge points so avoiding the DC-AC-DC steps.A few google search suggest it's more than doable but currently expensive. For 15Kwh battery there is the Tesla PowerWall2, but at £6500+extras+install, (there are cheaper alternatives), then a DC based charge point + 3Kw of panels is going to cost half as much as the car itself!I wonder what the ROI would be though. Petrol (gas) is currently about £1.30 a litre here. Circa $6.20 a US gallon.I burn roughly 1 (UK)gallon a day to do those 30 miles. (I do have a 2.0 litre sports car and not a tiny hatch back though). The Zoe however was able to keep up with me on times I have met them and tested them by putting my foot down.So for my commute I get 10 days (it's usually less) for a tank and a tank costs between £55 and £60. That's roughly £2500-3000 in fuel a year, adjusted for holidays etc. for just commuting.If done right, not including the price of the car (or the battery lease if it has one), the solar charge system could see an ROI of 3-4 years... which does sound awfully to good to be true... is 7 years not the more expected figure (or is that for virtually-scam feed in tarifs?)

author: Someone
author_rank: Super Contributor
timestamp: May 30, 2019, 11:11:05 pm
content: http://www.withouthotair.com/c6/page_40.shtmlMost people don't have the space for a solar array to support their entire households energy use.Don't bother with storage at home, if you plug in the car at work the grid can carry the electrons for you (at a cost, but its still cheaper than storage for most people).

author: notsob
author_rank: Frequent Contributor
timestamp: May 31, 2019, 12:53:18 am
content: this may be worth watching for an actual install and discussion

author: paulca
author_rank: Super Contributor
timestamp: May 31, 2019, 02:21:46 pm
content: Quote from: Someone on May 30, 2019, 11:11:05 pmYes, but at present in the UK this cost is significant. Like a factor of 5!You generate a Kwh, you get given about 3.5p. You pull a Kwh you get charged 17.5p!

author: paulca
author_rank: Super Contributor
timestamp: May 31, 2019, 02:30:31 pm
content: Quote from: Someone on May 30, 2019, 11:11:05 pmWanted to deal with this separately. I have dipped into that book a few times.I just found it interesting that you could run the car on solar, for limited miles. This is very much about making an electric car both properly "green" which otherwise they are not that green and much more importantly making the car effectively "FREE" fuelled.At local prices the example car would cost about 4.2p per mile in electric. Including the up front (and recurring battery costs) this would fall significantly to half of that (maybe) with a solar rig.... and as mentioned make the car properly green (asides the battery/panel toxicity issues).

author: Someone
author_rank: Super Contributor
timestamp: June 01, 2019, 07:34:23 am
content: Quote from: paulca on May 31, 2019, 02:21:46 pmTime to shop around, there are companies out there vying for your account:https://octopus.energy/go/Even if you could use the full capacity of a 10kWh battery pack every single day of the year, and your solar generation was enough to fill it. Thats a bit over 500 pounds per year in expense to use the grid as storage on your current rates. Now figure how much a battery costs to have installed. Still cheaper to use the grid.

author: paulca
author_rank: Super Contributor
timestamp: June 01, 2019, 08:42:24 am
content: Quote from: Someone on June 01, 2019, 07:34:23 amI'm in Northern Ireland most of those providers don't offer services here. Their 5p night rate sounds good, but without them accepting my post code I don't get to see their day/peak rates. They also claim 100% renewable energy sources which sounds fishy even on an rolling offset basis. I don't trust the regulation in that space is tight enough and I don't know how long the energy retailers are allowed to run a deficit for.You are right about the grid cost though. It just feels less of an achievement if you are "offsetting" the car with solar rather than running it directly off solar.Still cheaper than buying a Tesla power wall though.

author: bdunham7
author_rank: Super Contributor
timestamp: June 02, 2019, 01:19:16 am
content: Quote from: paulca on May 30, 2019, 11:57:21 amI'm not understanding your math. If you had 10 hours of even sunlight (you don't, but just to start simply) you would need 760W of constant generation to get your 7.6Kwh. In the UK, I would guess you would need double that in solar panel capacity if you can optimize the mounting angle, more if you can't. There are plenty of on-line calculators that can assist you, but for way of comparison I run my entire house and an EV on 30 240-watt panels, so 7.2kW of "nameplate" capacity, with a somewhat but not totally optimized mounting angle. The actual maximum output of the system is about 6.6kW and the daily energy output averages a bit over 30 kWh/day.The main difference between your location and mine (Southern California) is insolation--I get 5 to 5.5 'sun hours per day', while you likely get 3.5 to 4.5 depending on location.

author: paulca
author_rank: Super Contributor
timestamp: June 02, 2019, 06:50:54 am
content: Quote from: bdunham7 on June 02, 2019, 01:19:16 amSo pivoting your figures.7.2kW gives you 30kWh with an insolation of 5.5 hours.So factoring in the insolutation hours ( 30kWh / 5.5 ) * 3.5 hours = 19kWh, I would get from your panels.I need 7.5 kWh (say). So, ( 7.2kW / 19Kwh ) = 2.638 Kwh per Kw of panels.7.5kWh / 2.638kWh/Kw = 2.843kW required to produce 7.5kWh.The average load times 10 is just a cheat, but I believe it works fairly well for the UK. It's not about 10 hours of sunlight. It's 10 times the average load. So on average through the year you lose exactly half, a it's night time, leaving your with 5 times the average load which is account for weather, it only sunny about 20% of the time here. Actually probably less, but there is some generation on bright overcast days.Also, unlike California, where I am we get 16 hours of daylight in peak summer. Granted you still get the same peak solar time as the sun moves 15* per hour everywhere, but my little hobby panel starts making something from as early as 8am and as late at 8pm in June. Our sun is lower, even in summer, but our roofs are steeper due to more weather, including snow.The downside is in winter there are days when it generates absolutely nothing, that's more to do with our weather and the amount of heavy overcast and raining days we get and the mere 8 hours of daylight in late December.

author: f4eru
author_rank: Super Contributor
timestamp: June 03, 2019, 04:18:41 pm
content: QuoteIt´s a compromise between availability (working in bad weather) and price/size of the array. If you want nearly year round availability, even in bad weather, using only scattered light, you probably have to put a factor 5-10 on your "sunny day" calculation.Choose your overengineering factor 1-10xKeep in mind that if you overdimension significantly the array, it will probably be economically vital to use the surplus of production in some meaningful way to make the bigger panels economically useful, which probably means grid feedingThere are specialized solutions for that, for example :https://www.e3dc.com/en/

author: Seekonk
author_rank: Super Contributor
timestamp: June 03, 2019, 06:01:13 pm
content: Anytime you use batteries, the operating cost per KWH approaches grid rates. That is even ignoring panel cost and electronics.

author: f4eru
author_rank: Super Contributor
timestamp: June 03, 2019, 11:50:38 pm
content: YMMV. An example :In Germany:1kWh from the grid costs 0.29€1kWh from a PV costs 0.13€ to produce (very variable)1kWh to the grid is paid back 0.12€1kWh stored in a battery costs approx 0.05€ more ( basis LifePo4 with 5000 cycles lifetime, 250€/kWh)So using a storage battery is much cheaper than grid "storage" in this case.