Which Solar set up to go with?

Snowy44

EDIT: I would like to thank everyone who responded. My preferred option was No2. My partner was very focused on No1 due to the higher number of panels. I just needed to hear comments on the size of inverter without being prompted.

We went back to supplier No2 and asked for a reconfiguration. We ended up with 10 panels on the main roof and 5 on the other. Having the panels span over the two roofs had a much better output on the performance summary considering we only increased the number of panels by 1 overall. 

We had the system installed last week and we're very happy with it: 15 panels over two roofs, 5Kw inverter and 10Kw battery. I'm surprised at how much is generated on a cloudy day.

I knew to take 'saving costs estimates' with a pinch of salt, it was the other point my partner was focused on when making their decisions.

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We have two solar setup quotes, and we can't seem to agree which is best? Can anyone shed any light without getting 'too' technical please?

We have an air source heat pump, so our energy requirements are all electric. We have also just got an electric car, day time car charging is a possibility as the user occasionally works from home.

1. 7kW solar array, with 12panels on one roof and 5panels on another, with 3.6kW inverter, and 10kWh battery. =£16,000. The solar performance summary states this could cover us for 50% of our costs, assuming 10,000kW per year usage.

Main roof is -62 degrees south with 20degrees inclination, smaller roof 25 degrees south with increased shade factor at the end of the day

Sunsynk inverter (life 3.5) and battery

2. 6kW solar array, with 14 panels on one roof, with 5kW inverter, and 10kWh battery =£12,500. The solar performance summary states this could cover us for 40% of our costs, assuming 10,000kW per year usage.

Main roof is -62 degrees south with 20degrees inclination

G3 GivEnergy inverter and Gen2 GivEnergy battery

Thanks!

matt_drummer

We would need far more information to work out whether the figures you quote are reasonable.

The first thing that jumps out though is why is there such a small inverter for the first quote?

You would probably lose a lot of the generation at the sunniest times of the year as the inverter will not be able to handle the peak generation.

I think you need to give a lot more information such as the orientation of the panels and the make and models of the inverters and batteries.

Reed_Richards

So for an extra £3.5k you get an extra 1 kW of peak solar power, possibly power for longer if the two roofs have different orientations (you don't say) but your ability to export power is more limited so you'll earn less from export.  On the basis of your limited information I would have thought that option 2 is a clear winner.    

markin

5kw on 1 roof on the 3.6 inverter seems a little small, But it's good to have 2 angles facing difrent directions so you get less peak and more in the morning or evening, so what way are they facing?

Can you daytime car charge? You won't ever charge the car from the 10kw battary alone after sun set, you will need to workout if you do enough miles to need an EV tarrif that usually comes with a higher day rate.

Snowy44

I have added some more info to the original post, thanks

DougMLancs

Personally I would agree that option 1 specifying such a small inverter is a red flag. The installer has not got your interests at heart- they’re just saving themselves the paperwork required for a larger inverter. 

QrizB

A 10kWh battery is something like £6k, installed.

Taking that out of the equation, you've been quoted £10k for 7kWp on two roofs or £6500 for 6kWp on one roof.

The 6kWp system seems like better value.

I also have deep reservations whether either of the estimated energy bill savings is realistic.

10,000kWh is currently about £3000-worth of electricity. With a heat pump , your biggest demand is in the winter when there's not much sunlight.

For system 1 your installer is suggesting that you'd get £1500 of value from maybe 6000kWh of electricity. That's an average of 25p/kWh.

For system 2, it's £1200 of value from perhaps 5400kWh of electricity. 22p/kWh.

Both of those sound quite optimistic, even allowing for an exotic tariff like Octopus Flux.

How exactly did they estimate these savings?

markin

Get more quotes for a split system, With a bigger inverter and cheaper price, Even with extra scaffolding 3K seems a bit much of a premium unless the inverter and battery really is far more than than the GivEnergy, probably not but it has to be duel input for the 2 arrays.

Reed_Richards

QrizB said:

I also have deep reservations whether either of the estimated energy bill savings is realistic.

Yes, sorry, I took it as read that estimated energy bill savings are almost always wildly over-optimistic but I should have mentioned this in my earlier reply.  I have both a heat pump and solar panels and they really don't mesh together.  You only have to think a bit about why winter is cold to see why that is.

[Deleted User]

Surely what matters is the predicted annual solar output. In these days of smart time-of-use tariffs, actual savings are difficult to calculate. Yes, I have generated £600 of SEG income so far this year and saved 3500kWh of import. Given that I could be on a tariff that allows me to charge my battery at 7.5p/kWh is my saving on grid import £ 3500x0.075 or £3500x0.3 ( the flexible rate) - or for that matter any other import tariff that I can find?

Will Octopus Flux and Cosy continue, or will we see Intelligent Flux and Intelligent Cosy or some other unknown innovative tariff? In sum, basing any purchase decision on today’s tariffs and the likely return is fraught with difficulty.