Solar panels for charging car: PVs for EVs?

Has anyone looked into using solar panels to generate electricity to fuel their car?

We have been thinking of getting solar water-heating panels but wonder whether we should get PV panels instead which can heat water and generate power.

unkel

I have both. Hoping to extend my Solar PV system in the next few weeks, so I can effectively charge my car from it.

Solar PV is very inefficient for heating water. Unless you are getting a very large solar PV system, it is cheaper to give your excess solar PV production back to the grid for free rather than heat your water with it. This is discussed regularly in the Renewable Energies forum

Linky

Thanks Unkel, much appreciated.

Beginning to think solar water heating is the way to go for now. Maybe add PV at a later stage - looks as though the cost of having enough to power the car could be quite high?

KCross

Deleted User wrote: »

Maybe add PV at a later stage - looks as though the cost of having enough to power the car could be quite high?

The first question is.... is your car at home and likely to be plugged in for several hours during the day to take the available Solar energy?

You'll also get little or nothing to the car during the winter months as the background load of the house will consume everything your panels will produce.

And finally you'd need to buy a smart charge point like the Zappi to manage it becuase your average dumb charge point will just take max available power and dump it to the car regardless of whether its solar generated or not, so factor that into any calculations you make.

Thanks KCross, I have a relatively new - but fairly unsophisticated - home charger. The car is often parked at home for much of the day (I work from home a lot) so it could suit us in that sense.

Maybe if we go the PV route we'd just charge the car at night on the night rate (as we do now) and use the solar energy for electricity when it's there.

I started down this road just thinking about hot water: we need a bigger water cylinder and I want a cheap way to heat it. Could use solar collectors in summer and the heating in the winter.

Leaning away from PV for the moment. Just wanted to check with people here in case I was missing an EV-related trick.

daheff

I think whats really the way forward is to have a battery that you charge during the day, and charge off that at night time (until its empty and switch over to night rate to finish charging the car). But is that really economical? A half decent PV array/ battery is going to be about 10k. Whats the payback on that?

Realistically, if you think the newer cars are 40-60 kWh batteries, you would need an enormous PV array to charge a meaningful amount during the day.

unkel

Solar thermal (hot water) works very well and it attracts a decent SEAI subsidy, but your payback time will be long, unless you use a lot of hot water. We are a family of 5 with 4 females who use lots and lots of hot water

Like yourself, we were about to change the hot water cylinder anyway, so we did this as part of the solar thermal install. 360l cylinder (instead of the standard Irish 120l one installed when the house was new in 2000) and 40 tubes Kingspan Thermomax

unkel

daheff wrote: »

A half decent PV array/ battery is going to be about 10k.

Again, check the renewables forum I linked to

With the new PV subsidies, you can have a large PV system (>4kwp) with a battery installed for about €5.5k incl. VAT after subsidies

Bixler3

unkel wrote: »

I have both. Hoping to extend my Solar PV system in the next few weeks, so I can effectively charge my car from it.

Solar PV is very inefficient for heating water. Unless you are getting a very large solar PV system, it is cheaper to give your excess solar PV production back to the grid for free rather than heat your water with it. This is discussed regularly in the Renewable Energies forum

Linky

Can't find the specific discussion you mention. I have a diverter in my PV system which takes any excess power and directs it to the immersion, as a result of which we generally have to do very little water heating during the summer.

unkel

Bixler3 wrote: »

Can't find the specific discussion you mention. I have a diverter in my PV system which takes any excess power and directs it to the immersion, as a result of which we generally have to do very little water heating during the summer.

Have a good read of this thread:

Linky


Or a very brief summary of the argument against a small PV setup with immersion diverter: instead of using the diverter to part heat the water, you could have used gas (or oil), which costs about 4c/kWh. The diverter costs about EUR500 installed, give it a lifespan of 10 years, and spread its cost over the kWh it sent to the immersion and you'll find it is cheaper not to have installed the diverter at all (and just give away your excess for free to the grid)

If you have a large PV install (say over 3-4kWp) a diverter is starting to make sense. And if you do not have any gas or oil boiler in your house, it makes more sense again.

Calahonda52

Deleted User wrote: »

....

Beginning to think solar water heating is the way to go for now. Maybe add PV at a later stage - looks as though the cost of having enough to power the car could be quite high?

There are a couple of points to consider when comparing HW panels vs PV panels.

1. maintenance
2. dumping excess hot water.
3. HW system is designed, generally, on house occupancy, so once demand goes down you can't do much else with hot water other than re-wash the dog.
4. electricity is much more versatile.
5. PV can be expanded once the planning rules get relaxed
6. Limited roof space

daheff

unkel wrote: »

Again, check the renewables forum I linked to

With the new PV subsidies, you can have a large PV system (>4kwp) with a battery installed for about €5.5k incl. VAT after subsidies

my bad...i read the quotes of 10-12k, but these are ex subsidies (about 4k).


So over a 10 year life span (I understand they'll last longer)- the cost is 600EUR a year. Are the savings that high?

unkel

Calahonda52 wrote: »

There are a couple of points to consider when comparing HW panels vs PV panels.

1. maintenance
2. dumping excess hot water.
3. HW system is designed, generally, on house occupancy, so once demand goes down you can't do much else with hot water other than re-wash the dog.
4. electricity is much more versatile.
5. PV can be expanded once the planning rules get relaxed
6. Limited roof space

maintenance - needs fresh coolant every 5 years or so, that's the only maintenance (cheap job)

dumping excess hot water - not needed with a modern system like Kingspan Thermomax

HW house occupancy. Sure, thermal hot water only works out for large household using lots of hot water. That said, with a modern cylinder, heat loss is very low. Mine loses 1C per 24h. So even if you're not there for a few days, or even a week, the water stays hot

electricity is more versatile, but it also disappears quickly with no gain if you don't use it (hot water keeps hot)

PV expanded. Yes but you need planning permission for anything beyond a small system (7 panels)

Limited roof space: you get many times more energy per m2 from thermal than you get from PV

unkel

daheff wrote: »

So over a 10 year life span (I understand they'll last longer)- the cost is 600EUR a year. Are the savings that high?

Nope. Not even if the house is occupied 24/7 and you charge your EV from it

Payback times are still bad, even with the very generous subsidy. If you are going to stay in your house a long time, it will pay for itself and you will have "free" electricity after

Also you are doing yourself, your family, everyone else and the generations that come after us a big favour by going solar

daheff

I'm conscious we're slightly pulling this thread off topic but....

unkel wrote: »

Nope. Not even if the house is occupied 24/7 and you charge your EV from it

I think thats the rub of it. If you cant save money (above and beyond the cost) from it then most people cant even think about getting it in. Its a large outlay for a lot of people. Especially if you are doing so to charge an EV thats probably not there most of the time when the sun is shining.

unkel wrote: »

Payback times are still bad, even with the very generous subsidy. If you are going to stay in your house a long time, it will pay for itself and you will have "free" electricity after

Maybe, but lifespans are circa 20 years...and you'll have some degradation over that period. And then you are exposed to how much sunlight you experience over that time.

unkel wrote: »

Also you are doing yourself, your family, everyone else and the generations that come after us a big favour by going solar

Unfortunately most people only look at the 'nice to haves' when other parts of their needs are satisfied. Similarily they probably have more urgent'needs' than solar panels.

unkel

daheff wrote: »

Maybe, but lifespans are circa 20 years...and you'll have some degradation over that period.

Design lifespan of an inverter is 20 years. Solar panels themselves should last many, many decades with only very little degradation

Battery lifespan is not so good. Personally I would probably opt for a small battery (cost €900 + install + VAT) to claim the €1000 subsidy and add batteries later when they are a lot cheaper

Bixler3

I installed a 2kWh PV system in 2015 and, having kept a record of the power generated and the savings obtained, the payback (for me) is circa 17 years.
2018 was a great year for sun and I generated 2000 units but the overall payback period remains unless the cost of electricity goes up significantly in future years. At this stage it's a sunk cost and I charge my Zoe on sunny days using a 10amo plug/cable.

unkel

How did you calculate the savings obtained, Bixler3?

Bixler3

unkel wrote: »

How did you calculate the savings obtained, Bixler3?

I just keep a record of the units generated each month & the prevailing price in a spreadsheet. My estimate of the payback period is based on current electricity prices.

unkel

Yeah, you see that's where your savings are getting too optimistic I'm afraid. And your payback period look a lot shorter than it really is

First of all, did you use all the electricity you generated or did some go back to the grid (for free)?

Secondly, was the electricity that you used really worth the full day rate? In many cases it isn't as you could have used night rate (switch on dishwasher late at night) or you could have used gas / oil

daheff

Bixler3 wrote: »

the payback (for me) is circa 17 years.

a 17 Year payback is an implied ROI of around 5.9%. Thats a decent return. You wouldn't get that in the bank (but you would still have your capital). It would take over 25 years to be ahead of a 2% interest return.

unkel wrote: »

First of all, did you use all the electricity you generated or did some go back to the grid (for free)?

Secondly, was the electricity that you used really worth the full day rate? In many cases it isn't as you could have used night rate (switch on dishwasher late at night) or you could have used gas / oil

They are surely opportunity costs? The best way (in my opinion, and not to seem argumentative) is to compare vs your normal behaviour (ie usually charge EV on night rate, then use that rate for comparison). So if Bixler usually uses the dishwasher during the day, then the relevant price would be the day rate.

unkel

daheff wrote: »

They are surely opportunity costs?

Nope. Opportunity costs are what your money would have made you had you invested it elsewhere (not in a PV setup)

Largely irrelevant these days as the best rates you can get on a savings account are 2%, and then you have to pay a lot of that in DIRT

daheff

unkel wrote: »

Nope. Opportunity costs are what your money would have made you had you invested it elsewhere (not in a PV setup)

Largely irrelevant these days as the best rates you can get on a savings account are 2%, and then you have to pay a lot of that in DIRT

Sorry -yes opportunity cost is the wrong phrase. Cant really think of the correct phrase, but basically you cant have all options -they are mutually exclusive.


You are absolutely correct on 2% return (less dirt) being your return. But even at 1% return after tax, its still 20+ years before breakeven.

Bixler3

unkel wrote: »

Yeah, you see that's where your savings are getting too optimistic I'm afraid. And your payback period look a lot shorter than it really is

First of all, did you use all the electricity you generated or did some go back to the grid (for free)?

Secondly, was the electricity that you used really worth the full day rate? In many cases it isn't as you could have used night rate (switch on dishwasher late at night) or you could have used gas / oil

There is no power going back to the grid, any excess power is diverted to the immersion which can take a variable amperage.

Based on my typical use I do believe I am getting full value on the day rate.
Is it the case that if you opt for a night rate then your day rate goes up?

unkel

On a typical small system, installed in 2015 for the then going rate, a typical payback of 30+ years is more likely. I don't want to be a spoil sport and I'm a big fan of renewables, but we have to stay realistic and honest about pay back periods.

unkel

Bixler3 wrote: »

There is no power going back to the grid, any excess power is diverted to the immersion which can take a variable amperage.

How big is your system? With a smallish system (under 3kwp / 10-12 panels or so), it is cheaper to send the excess electricity back to the grid for free than having an immersion diverter installed and heating your water...

Bixler3

It's a 2kWh 8 panel installation with a diverter for excess generated power, I take your point about not recovering the cost of the inverter vs gas/oil but I'm including that in the overall costs when calculating my cost recovery timescale. I'm not going to argue with you about the method of calculation as a number of different scenarios could apply as you have pointed out. At this stage its a sunk cost and im just enjoying the 'free?' electricity to charge my EV.

unkel

Can't argue with that Bixler3. Enjoy your free electricity

How do you charge your EV, with a Zappi charger or just plugging it in when the sun shines? If the latter, do you switch off the immersion diverter?

Bixler3

I just use a standard 13amp socket with a granny cable which draws 10amps (or 2200 watts). So if the sun is shining the panels are generating up to 2000 watts and that more or less feeds the car for a couple of hours. There is no switching on/off required for the diverter, it simply draws any excess from the fuse board, of which there is none when the Zoe is charging. Hopefully that explains it.

slave1

Probably above average user, apart from the EV have the usual array of white goods, electric shower going the same time as gravity pumped shower (via nightime immersion), storage heater in converted garage and a pretty demanding home cinema in constant use so would love to go for panels and battery but only when I can plaster the entire roof as no doubt we will be a double EV family when the like of the Niro64 reach second hand values....
Just can't see a decent payback at the minute and I would not do it with just 50% of roof as we'd need more that than (not exactly south facing).....

unkel

unkel wrote: »

Hoping to extend my Solar PV system in the next few weeks, so I can effectively charge my car from it.

Done. Just under 4kwp up and running since today