Considering solar PV installation

gm624

First time poster, but lurking for a while as usual. I'm looking at the possibility of solar PV panels, and any advice would be welcome. Located in Derbyshire; house has roofs pitched at approximately 30 degrees, facing east-ish (probably about 100 degrees from north) and west-ish (about 80 degrees from north). Plenty of space on the east-facing roof for panels (perhaps 15 or 20); more limited space on the west-facing roof (perhaps five or six). Not too much shade. Annual consumption of about 5000KWh, with plans to get an electric car in the new year, which should add quite a bit. I am thinking that a system of around 6-7KWp in total, distributed across the two roofs as much as possible, would be about right.

I've done a bit of research and am planning to get a few quotes; I'll share these when I get them, and any general advice would be most welcome. One thing I'm particularly interested in is what proportion, realistically, of annual production people manage to consume in practice. Is 50% realistic? More? Less? Clearly this makes a big difference to the financial case. Based on the following very crude assumptions:

• £1000/KWp
• 750KWh/KWp per annum
• 14p/KWh import
• 5p/KWh export

Then by my calculations, I'd reach the breakeven point in 10 years if I consumed all of it, but in 14 years if 50% was exported. And if I only used 20% of it, it would take nearly 20 years! Given that more of the generation is going to happen in the morning than the afternoon, I'd love to hear people's thoughts on the economics of this.

Solarchaser

Hi there, and welcome. 
I also lurked for a while before joining.

I have a similar ish system to what you propose.
I have a total of 6.6kw split evenly between East and west, however where your easterly aspect is more south facing, my westerly aspect is more south facing, at a guess id say my east array is maybe 60 degrees off north and so the west is 120 degrees off north.

I get roughly 35% from the east and so 65% from the west, I would imagine in terms of sun, yours will be closer as they are closer to 90deg from north.
But if you have a much larger array on east, then perhaps you will be 70/30 east to west, maybe even 80/20.

I generate a little over 4000kwh between the two, but with a fair amount of shading at the start and end of days in winter.
You are also further south than me, so with less shading and more sun, id say 4500kwh should be fairly easily achieved. 

My array generates more in the evening due to western bias,  which is good for the evening meals, yours will generate more in the morning which will be good for breakfast maybe??

How much you will use, its very hard to say.
Its very dependent on you, and your household. 
And how much of your usage you can offset to earlier or later times.

Thinking of things like running washing machine, dryer, dishwasher mid morning will be almost guaranteed to be free with your array.
Running a slow cooker through the day instead of cooking at night will be the same.

If there is someone at home during the day you will be able to self consume much more.

However if you are a household who can't (or won't cos of hassle) offset usage, then the likelihood is you will export the vast majority of your generation and self consume very little.

If you don't have mains gas, then diverting to a hot water cylinder will be a good way of saving, but if you have mains gas, this would be borderline, probably a cost rather than a saving owing to the cost of gas vs the export you are paid for.

Hope that helps

ASavvyBuyer

As Solarchaser says, a lot depends on your home circumstances. If you are retired or work from home, you have a lot more opportunities to use the power when it is being generated. But you do have to have the right mindset (for the whole family) to make the best use of what you generate.

We have managed to increase our own use to a yearly average of just over 85%, but we are retired, have a diverter for hot water, have two ASHP's & two EV's. Also, we are on deemed export; so no financial penalty for using what we generate.

JKenH

We also have an east/west PV arrangement - details in signature below. Our east roof is roughly ENE and the other roof is WSW. Any roof that faces even a bit north is at a disadvantage and our WSW is far more efficient than the ENE roof. Maximum steady generation (ignoring peaks on intermittently cloudy days) is about 0.85kw/kwp (inverter limited) on the WSW roof compared to about 0.7kw/kwp on the ENE roof. Although I have a 3.6kw inverter and 3.6kw panels on the ENE roof, the inverter is too big and not very efficient as most of the yearly is only running at a fraction of its capacity. A 2.5kw inverter would have been better - something to bear in mind for your west roof.

Overall I generate about 6MWh annually from my 7.8 kw panels. My December monthly generation is about a tenth of my May generation. E/W roofs are a waste of time from a solar PV point of view in winter but are great in summer. South facing roofs are better for generation figures but E/W roofs produce a more useable spread of power. On a good day in summer my panels will generate more than 2kw from 7am to 7pm peaking at about 4.5kw around midday.

This time of year a very good day will generate 8kw compared to 45kw in summer.

I am retired and therefore able to make use of practically all my daytime generation for the  dullest 6 months of the year, using ASHPS, IBoost hot water diverter and a Zappi charger for my EV. In summer a lot goes to the grid. As others have said, how much you use will depend on your lifestyle. The first year I had my solar panels I cut my grid consumption by half to around 3500kwh but since then I have installed ASHPs and bought an EV so although I now use a higher proportion of what I generate my overall consumption has increased.

gm624

Thank you everyone - this is really helpful. I will be sharing quotes when I get them and any comments would be great. Of course this isn't a purely financial decision, but it would be good to know that I'm not pouring money away.

A question re. SolarEdge - given the size of the system and the fact that it will be distributed across two aspects, is it likely to be worth extra expense? There's a little bit of shading (one tree likely to obscure some of the east-facing panels in the morning) but not much.

ASavvyBuyer

gm624 said:

Thank you everyone - this is really helpful. I will be sharing quotes when I get them and any comments would be great. Of course this isn't a purely financial decision, but it would be good to know that I'm not pouring money away.

A question re. SolarEdge - given the size of the system and the fact that it will be distributed across two aspects, is it likely to be worth extra expense? There's a little bit of shading (one tree likely to obscure some of the east-facing panels in the morning) but not much.

We are glad we have Solaredge, with optimers, as they help make the most output from all the panels. We have some shading, but also like the fact that each panel produces its max, rather than being restricted by the panel with the lowest output/efficiency.

Coastalwatch

ASavvyBuyer said:

We are glad we have Solaredge, with optimers, as they help make the most output from all the panels. We have some shading, but also like the fact that each panel produces its max, rather than being restricted by the panel with the lowest output/efficiency.

I'll echo that!

Petriix

We currently use around 40% of what we generate but anticipate that being closer to 66% when we have an EV in the new year. We work from home and try to use the appliances when it's sunny. But the simple truth is that we generate far more than we could ever use in the summer and use far more than we can generate in the winter.

I'm going to go against the grain (as usual) and advise against wasting money on optimisers and solaredge unless you genuinely need them as they will greatly add to the break-even period. A simple dual string inverter should suffice.

Post FIT, all the calculations I've done point to around 12-14 years to break even. Unless you don't have mains gas, where the sums are a bit different, then you're better off avoiding any kind of diverter.

At 7kWp you should look to pay closer to £6k ideally.

gm624

OK, I've now had three quotes. All from local companies with good reputations - knowledgeable and helpful surveyors, and I'd have no qualms about going with any of them. Thoughts welcome!

• Company 1: 6.46KWp (4.76KWp east-facing; 1.7KWp west-facing). 340W panels. Inverter model not specified. £7200 with SolarEdge; £6000 without SolarEdge.
• Company 2: 8.13KWp (5.2KWp east-facing; 2.93KWp west-facing). 325W panels. Inverter model not specified. £8500 with SolarEdge; £7300 without SolarEdge.
• Company 3: 8.28KWp (6.21KWp east-facing; 2.07KWp west-facing). 345W panels. SolarEdge 6000H inverter. £8000 with SolarEdge.
  

(There was a fourth company, but they only provided a quote based on a map and a questionnaire - it didn't look competitive, and they charge £150 for a site visit, so I ruled them out).

Each company had a slighlty different estimate of annual KWh/KWp, presumably because they were using different software? Using the same estimates for east- and west-facing panels across all three, the third company has a clear advantage. Under £1000/KWp with SolarEdge seems like a competitive price. I guess this would produce well over 6000KWh per annum - I'm not sure I'd consume all this, but I've modelled various assumptions about proportion used and proportion exported, and I think I'd be looking at recovering the cost of the system within perhaps 13-15 years - which is good enough for me.

Any thoughts from you knowledgeable people? One thing I do want to check, particularly with the higher-output quotes, is whether I would need any extra equipment to limit export if the DNO requires it. Other than that, any other questions I shoudl be asking?

Coastalwatch

Number 3 seems a good choice to me, don't know if they might throw in iboost as well for DHW! Looking good otherwise, I'd have been delighted with that figure two years ago. Just wondered if you've checked likely output in the darker months against pvgis so there'll be no unexpected surprises!

Solarchaser

I'd agree with Coastalwatch,  3 seems the clear "winner".
A few days ago, there was a similar discussion about solaredge, my understanding is that their inverters can export limit to the dno's satisfaction,  so you should be good there.

I have to say though, at £1200 less, id be tempted to ditch the solaredge,  on a 12 year payback it has to earn you £100 per year more, so at say 15ppkwh you are talking an extra 600kwh+ a year.... I dunno.
I dont have it, but I think I'd personally doubt that its "that" good. 

Happy to be shot down by those that have it (might even convince me to fit it to mine if so)