Two approaches to solar install. Thoughts appreciated!

[MattyS]

I am currently speaking to a couple of potential installers of a solar array and battery.

One installer suggested 12 440w panels with a 3.68 inverter and a 9.5kwh battery.
The other has suggested 15 460w panels, a 5kw inverter with a 10kw battery.(Edited due to slight mistake. 6.9kwp proposed system Vs 5.2kwp)

I'm erring towards more panels, however the two companies had differing opinions on what to do with my EV charger.

One company suggests making sure my zappi is battery and solar aware, and the other suggests the opposite and avoiding using the battery/solar to charge the car.

I must admit the latter idea doesn't really make sense, but it's my first foray into all this and I'm curious as to everyones thoughts?

Thanks!

 

[Bam Bam]

I am currently speaking to a couple of potential installers of a solar array and battery.

One installer suggested 12 440w panels with a 3.68 inverter and a 9.5kwh battery.
The other has suggested 14 460w panels, a 5kw inverter with a 10kw battery.

I'm erring towards more panels, however the two companies had differing opinions on what to do with my EV charger.

Yes, go for the larger inverter.

The other company are under sizing your system so they don't have to do as much paperwork.

Max out your roof is my advice. Wish we had got a few more up there as it is too difficult to add more on now.

One company suggests making sure my zappi is battery and solar aware, and the other suggests the opposite and avoiding using the battery/solar to charge the car.

Hmm, this seems to relate to the longstanding discussions between Rolfe and someone (perhaps John) about how to set up solar to avoid unwanted discharge into the car.

I guess the concern is that you will either...
1. Have the car and home battery fighting each other...
This might end up draining the home battery into the car and thus having none available for the house after sundown.
Or, similarly, failing to top up the home battery because the car takes it.
Or, having some sort of clash between the two so they are constantly adjusting to account for each other.
2. End up exporting power when you might have wanted it in the car.

Lately the solar export payments have been higher than the overnight import on an EV tariff so it was really important to avoid scenario 1.

However, those tariffs will change and at some point you might want to put any surplus solar into the car.

I think the Zappi is pretty clever so there might be a way of getting it all set up satisfactorily. One suggestion I've seen is to have the solar export 'kick-in' rate higher for the zappi, so it would only redirect to the car when there is a lot of solar export.

I must admit the latter idea doesn't really make sense, but it's my first foray into all this and I'm curious as to everyones thoughts?

My guess is that one installer is worried about one potential problem and the other is concerned with another potential problem.

One solution is to have an EVSE that is part of the same ecosystem but last I checked the myenergy (Zappi) battery system wasn't competitive with rivals. And the Givenergy EVSE isn't compatible with Intelligent Octopus Go so that isn't ideal either.

 

[MattyS]

Just for clarification, the company who've suggested more panels and a higher rate inverter are the ones who suggested not making the charger aware of the solar system.

I like the idea of charging the car from solar, but if I could charge it at the same time as the battery in the cheap rate that'd make sense too, however we do 4000 miles or less each year, so not sure if that changes things.

Many thanks for the reply

 

[Everest]

One installer suggested 12 440w panels with a 3.68 inverter and a 9.5kwh battery.

AVOID. That is underpowered and rubbish installers avoiding a (small) amount of approval work. Wouldn't touch them with a bargepole.

The other has suggested 14 460w panels, a 5kw inverter with a 10kw battery.

BETTER: But, you could do better still by having a larger inverter. With only 5kW, you'll be drawing from grid if you put the kettle on when either the dishwasher or oven is on. Go for max possible, min 6kW, IMHO. Even if that means restricting export power if the DNO limits your back-feed, you'll be able to make better use of it for the house load.

I'm erring towards more panels, however the two companies had differing opinions on what to do with my EV charger.

As @Bam Bam said above, go for max panels possible. 450W panels are only a tad over £50 trade price these days, so maximise what will fit - you can never have too many panels.

it's my first foray into all this and I'm curious as to everyones thoughts?

If you can share some more info, it will be easier to advise. Is the EV at home with you in the day? How much energy do you need to put in it per day/week. Have you done a power audit on your house to determine your typical and maximum daily / weekly energy (kWh) and peak power (kW) usage? Do you use electricity for heating etc.

I like the idea of charging the car from solar, but if I could charge it at the same time as the battery in the cheap rate that'd make sense too, however we do 4000 miles or less each year, so not sure if that changes things.

There are going to be more factors needed to consider. If your DNO will allow you to export all you can produce then - at the moment - it is more cost-effective to export solar and charge at cheap rate overnight. If you can't export all that you produce, then obviously it is better to dump spare solar into an EV. In our case, we charge our EV totally from spare solar for 8 months of the year, but then we do have quite a few panels.

Further thought - if you can get a bigger battery (having done your energy audit) that would be good. 16kWh battery packs are available for around £2000.

 

[MattyS]

There are going to be more factors needed to consider. If your DNO will allow you to export all you can produce then - at the moment - it is more cost-effective to export solar and charge at cheap rate overnight. If you can't export all that you produce, then obviously it is better to dump spare solar into an EV. In our case, we charge our EV totally from spare solar for 8 months of the year, but then we do have quite a few panels.

Further thought - if you can get a bigger battery (having done your energy audit) that would be good. 16kWh battery packs are available for around £2000.

Thank you for your comprehensive response!

I've just looked at leaving the car charging out, max usage over the last year for a day was 18 KW, we have a combi boiler, and we are very limited on space, with a max width of 700mm and height of 1380mm with which to work. This unfortunately means we are a bit stuck by what will fit . I was looking at the fox EVO system , but that's only gota choice of 5kw or 8kw inverter. The alpha smile will fit just about. I was considering a powerwall but it's too expensive unfortunately.

I charge the car on average once a month, from around 20% upto 80% unless we're going further. I've used 1100 kW in my mg4 in the year.

In terms of average daily usage, I've calculated over a year it's around 11kw per day.

I've just realised actually that I mistyped and the company have suggested 15 not 14 460w panels.

Having done so calculating, the 5kw inverter would have a potential max 6.6kw output/ input so id only lose around 350w or so even on the sunniest of days ( PV quoted at 6.9kwp)

 

[JohnV6]

I would go s big as you can ref apenels & batteries. I'm just doubling my batteries to 8.4kWh which sould be enough as I have a BEV so charge them at night.

My Ohme charge point come off directly after the meter on a separate circut the Octopus installer told me otherwise the smart chargers get confused.

I can still solar charge but I pay 7p a unit at night & export at 15p so why would I charge the car on solar?

 

[MattyS]

I would go s big as you can ref apenels & batteries. I'm just doubling my batteries to 8.4kWh which sould be enough as I have a BEV so charge them at night.

My Ohme charge point come off directly after the meter on a separate circut the Octopus installer told me otherwise the smart chargers get confused.

I can still solar charge but I pay 7p a unit at night & export at 15p so why would I charge the car on solar?

This is very true. That makes sense. Hasn't the rate be adjusted to 12p now or are you on a different tariff?

 

[MattyS]

Absolute max I can possibly fit is 15 panels and that's really tight, so well done to that company for shoe horning in 3 landscape instead of all portrait. I'm pretty sure I'll go with them honestly.

Just thinking about battery options that'll fit and inverter sizes hmmm

 

[Giller]

We installed solar last May, being in Northern Ireland we are limited to a 3.68 KWh inverter, roof wise maximum panels se facing was 12, and we went with a 10.2 KWh battery, added a Zappi last September, change the settings on the inverter to charge the battery overnight at the cheap rate, during summertime have settings changed not to charge battery but not charge car, all just works.

 

[Everest]

Thank you for your comprehensive response!

YW.

I've just looked at leaving the car charging out, max usage over the last year for a day was 18 KW,

Assume you mean 18kWh?

we have a combi boiler, and we are very limited on space, with a max width of 700mm and height of 1380mm with which to work. This unfortunately means we are a bit stuck by what will fit . I was looking at the fox EVO system , but that's only gota choice of 5kw or 8kw inverter. The alpha smile will fit just about. I was considering a powerwall but it's too expensive unfortunately.

Have heard good reports about Fox 8kW system - the only downside, IMHO, is it's HV proprietary battery system. What inverter is proposed for the 5kW system you first mentioned?

I've just realised actually that I mistyped and the company have suggested 15 not 14 460w panels.

Having done so calculating, the 5kw inverter would have a potential max 6.6kw output

Can you clarify what you mean by that?

so id only lose around 350w or so even on the sunniest of days ( PV quoted at 6.9kwp)

Most hybrid inverters can be overpanneled so that they can take more PV input that their rated AC output; the 'remainder' being used to charge batteries. Our 6kW, for example, will take 9kW from panels, and output up to 6kW of that to power the house, and still put 3kW into the batteries.

You won't 'lose' much power compared to peak kWp rating of panels (which you'll only achieve in high summer on clear cold day) but you will gain by the inverter being able to supplement PV power with battery discharge to power house loads.