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?

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.

 

[MattyS]

Assume you mean 18kWh?

yes probably!

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?

system 1 was quoted as a Alpha Smile ess 9.5kwh battery with a 3.86kw inverter, system 2 was quoted a Fox EVO 10.23kwh battery and a 5kw inverter

Can you clarify what you mean by that?

I've been led to understand by watching videos & reading etc that inverters can operate at 133% of their rated value, so 5kw = max 6.65kw.

According to Fox, the Evo has a stated max input of 15000 watts according to the spec sheet, which is 15kw or 300% of rated value. so, theoretically at least, the house could be using 10 and still charge the battery at 5 despite the 5kw rated value?

Am I understanding this right?

interesting idea about changing the settings to not charge the battery ! I'm sure most systems would be able to do the same. Thank you for the input.

 

[T1 Terry]

Do any of the systems offer V2X, where the DC from the solar can go straight to EV battery as well as the house battery, but can be drawn back out of the EV battery when needed.
Do you have an electricity trading market over there, where you can buy in power when there is excess and they actually pay to get power out of the grid, then sell back when it's peak demand and the wholesale price is high?

By going this route, if you don't use the car a lot for transport, you can use it to power your house and trade on the energy market to earn extra income .....

T1 Terry

 

[MattyS]

Do any of the systems offer V2X, where the DC from the solar can go straight to EV battery as well as the house battery, but can be drawn back out of the EV battery when needed.
Do you have an electricity trading market over there, where you can buy in power when there is excess and they actually pay to get power out of the grid, then sell back when it's peak demand and the wholesale price is high?

By going this route, if you don't use the car a lot for transport, you can use it to power your house and trade on the energy market to earn extra income .....

T1 Terry

Thank you for your input Terry.

My understanding is that my MG4 is not rated for v2h, so this isn't possible/ allowed? straight to mg4 from solar and battery is possible, drawing from the car, possibly not. It's an interesting point though so I'll question my potential installers! However, this sounds incredibly complex and I honestly want as simple as possible.

There is a startup called axle that will pay you upto £1 per kWh you send them at peak times, however it's very new and I'm unsure how this exactly works.

 

[T1 Terry]

Thank you for your input Terry.

My understanding is that my MG4 is not rated for v2h, so this isn't possible/ allowed? straight to mg4 from solar and battery is possible, drawing from the car, possibly not. It's an interesting point though so I'll question my potential installers! However, this sounds incredibly complex and I honestly want as simple as possible.

There is a startup called axle that will pay you upto £1 per kWh you send them at peak times, however it's very new and I'm unsure how this exactly works.

The V2X uses the DC connection in the MG4 CCS2 socket, so they can certainly do V2X.
@wattmatters posted quite a bit about his system over here MG4 in Australia and there are posts all through that thread about the V2X two way EVDC connection to the house system.
The system is really just plug and play modules as far as I can tell ....

T1 Terry

 

[Everest]

I've been led to understand by watching videos & reading etc that inverters can operate at 133% of their rated value, so 5kw = max 6.65kw.

According to Fox, the Evo has a stated max input of 15000 watts according to the spec sheet, which is 15kw or 300% of rated value. so, theoretically at least, the house could be using 10 and still charge the battery at 5 despite the 5kw rated value?

Am I understanding this right?

No.

The maximum input on the inverter's PV MPPT inputs does not relate to its maximum AC output. The 5kW rating of an inverter usually means its maximum continuous output on AC = the maximum your house load can be, without drawing any power from the grid supply. Some inverters will be able to supply very brief surge loads, but generally the rated value is the maximum they will provide.

So, with a 5kW inverter, if your house is using 10kW, then 5kW will be coming from the inverter and the remaining 5kW from the grid supply (which you will be charged for, obviously).

I suspect the confusing wrt the 133% value you mention, is that it is common to "overpannel" an inverter with more PV input than the inverter can deliver on its AC output. This is a good thing and will mean that your inverter is capable of delivering its max output more often, rather than that one sunny, clear & cold day in mid summer when the panels produce their peak.

 

[MattyS]

No.

The maximum input on the inverter's PV MPPT inputs does not relate to its maximum AC output. The 5kW rating of an inverter usually means its maximum continuous output on AC = the maximum your house load can be, without drawing any power from the grid supply. Some inverters will be able to supply very brief surge loads, but generally the rated value is the maximum they will provide.

So, with a 5kW inverter, if your house is using 10kW, then 5kW will be coming from the inverter and the remaining 5kW from the grid supply (which you will be charged for, obviously).

I suspect the confusing wrt the 133% value you mention, is that it is common to "overpannel" an inverter with more PV input than the inverter can deliver on its AC output. This is a good thing and will mean that your inverter is capable of delivering its max output more often, rather than that one sunny, clear & cold day in mid summer when the panels produce their peak.

Thank you!! I'm so glad I started this thread because obviously I've either misunderstood or been mislead about the 133% figure with inverters (probably the former).

I've looked around and the Fox EVO is my best option that will physically fit in the space I have available, discounting powerwall because reasons.

I've just got the final quotes through and honestly, the company who suggest less panels and lower size inverter are also the most expensive AND it looks like they filled out open solar with 0% electrical losses taken into account which is both surprising and obviously completely inaccurate. Payback period is 4 years longer etc etc.

Long story short, they've ruled themselves out.

Thank you everyone! Looking forward to starting my solar journey now.

 

[Bam Bam]

Thank you!! I'm so glad I started this thread because obviously I've either misunderstood or been mislead about the 133% figure with inverters (probably the former).

With the 133% comment I wonder if this could have referred to a few other things ....

In sun vs. darkness?
I believe that our inverter can output 5kw (up to 4kw from the battery to make up the difference) while it is sunny but only 4kw when there is no solar. So that is a potential 133% difference.

Battery mop-up
The other thing is that where there is battery capacity available the inverter could put any surplus generation above the output level in there. So if you oversize the solar (which you should do) then it might still be possible to make use of that surplus until the battery is completely full.

Rolfe and I had long discussions about this on a previous thread.

It wouldn't mean that you could have 10kw for the house if the maximum output is 5kW, but it would mean that you could provide 5kW to the house and still put a few kW into the battery if there was capacity available.

So their 133% comment could be legitimate, depending what they meant by it.

 

[Bam Bam]

Do any of the systems offer V2X, where the DC from the solar can go straight to EV battery as well as the house battery, but can be drawn back out of the EV battery when needed.

I think Sigenergy are offering DC charging.

They are a premium brand and so there would be a noticeable cost difference but it isn't completely out of reach.

Do you have an electricity trading market over there, where you can buy in power when there is excess and they actually pay to get power out of the grid, then sell back when it's peak demand and the wholesale price is high?

Yes, there are 'agile' tariffs that track wholesale prices for import and export.

By going this route, if you don't use the car a lot for transport, you can use it to power your house and trade on the energy market to earn extra income .....

Yes, not clear if it would be worth the extra cost of the install, but could be worth doing.

 

[MattyS]

With the 133% comment I wonder if this could have referred to a few other things ....

In sun vs. darkness?
I believe that our inverter can output 5kw (up to 4kw from the battery to make up the difference) while it is sunny but only 4kw when there is no solar. So that is a potential 133% difference.

Battery mop-up
The other thing is that where there is battery capacity available the inverter could put any surplus generation above the output level in there. So if you oversize the solar (which you should do) then it might still be possible to make use of that surplus until the battery is completely full.

Rolfe and I had long discussions about this on a previous thread.

It wouldn't mean that you could have 10kw for the house if the maximum output is 5kW, but it would mean that you could provide 5kW to the house and still put a few kW into the battery if there was capacity available.

So their 133% comment could be legitimate, depending what they meant by it.

I got the idea from a different source, but this explains the idea. As I said, I'm probably misreading it. Inverter Oversizing

 

[MattyS]

With the 133% comment I wonder if this could have referred to a few other things ....

In sun vs. darkness?
I believe that our inverter can output 5kw (up to 4kw from the battery to make up the difference) while it is sunny but only 4kw when there is no solar. So that is a potential 133% difference.

Battery mop-up
The other thing is that where there is battery capacity available the inverter could put any surplus generation above the output level in there. So if you oversize the solar (which you should do) then it might still be possible to make use of that surplus until the battery is completely full.

Rolfe and I had long discussions about this on a previous thread.

It wouldn't mean that you could have 10kw for the house if the maximum output is 5kW, but it would mean that you could provide 5kW to the house and still put a few kW into the battery if there was capacity available.

So their 133% comment could be legitimate, depending what they meant by it.

For example :

"Why should we oversize solar inverters?​

Those who have been installing inverters for a long time know that they your can actually handle a lot more energy than you would think – around 133% or more. So to get more energy early on and throughout the day, your solar array should add up to much more than 5kW."


Using the example of the 5kW inverter, instead of matching it up with 5kW worth of solar panels, you can go all the way up to 6.6kW of solar panels

 

[Bam Bam]

For example :

"Why should we oversize solar inverters?​

Those who have been installing inverters for a long time know that they your can actually handle a lot more energy than you would think – around 133% or more. So to get more energy early on and throughout the day, your solar array should add up to much more than 5kW."


Using the example of the 5kW inverter, instead of matching it up with 5kW worth of solar panels, you can go all the way up to 6.6kW of solar panels

Oh it is just about oversizing the array, as Everest correctly guessed.

That is perfectly good advice.

In the morning and evening you've got more panels producing at, sat 50% capacity. 50% of a larger number is more energy so for those hours you are generating more.

During the peak of the day the output will be clipped, but that is fine.

The inverter is still limited, though.

Adding in the potential battery storage would even enable some of that otherwise clipped excess to be captured as well.