4-5kw solar PV: advice please!

ahw23

Hello! I was hoping that one of you knowledgeable people might give us an extra opinion before we splash out on our PV. Sorry this is going to be a long post. We have just bought and moved into a semi in HP17 (Bucks), with 30 degree roofs facing 80 at the front (East and a tiny bit North) and 260 at the back (West with a touch of South). We have had three companies come for quotes, with the following being the best, and able to fit us in by the second week in December:
4kW SOLAR ARRAY

14 x Solar World 285W Mono all black (20 year product warranty - Only panel to give 90% output in year 25)
1 x SolarEdge Inverter
14 x SolarEdge Optimisers
1 x Clenergy mounting system
1 x AC / DC connections
1 x All access equipment
1 x Design / Supply / Install
1 x Technical & EPC Survey
1 x RECC 10 year (third party peace of mind) insurance
1 x Feed-In-Tariff form completed on your behalf

£6,295.00 inc VAT
There would be another £295 for iBoost, and a further £250 to remove a chimney which is causing a shading issue that would create an issue locating the panels on the back (which itself would push them slightly into the shade of the neighbouring house). Now we could either go with this (which adds up to 6 on the East, 8 on the West) or add another 2 plus a different Solaredge inverter for £500, which would apparently not break regs as they aren't facing in the same direction and the production would still be capped at 360. Any thoughts on whether it's worthwhile, or any other aspect of this plan? For what it's worth, they aren't really trying to sell us the extra two panels: the idea came from one of the other firms, but I was curious and asked them to check out the possibility. Thanks!

Martyn1981

Hiya ahw.

Straight of, have you had a read of the PV FAQs, you may find them useful.

The price is a bit too high. This is important to you as you have an E/W split (like me). Your generation will be about 20% less than a south facing system, so with the current very low FiT rate, you need a very good price.

You also need to consider leccy savings. An E/W split gives you a wider and flatter generation curve, which helps to maximise consumption (rather than one huge mass in the middle of the day), but you will pay a penalty in the winter ..... I'll explain ...

Like you I have 30d rooves (I also have 5 panels on a low 20d roof). Shallow panels don't work as well in the winter, especially off-south panels. Here's a comparison based on my location, 2kWp, 30d pitch, S v's E:-

South kWhs
1,940 pa
June 248 pm
Dec 57.4 pm

East kWhs
1,580 pa (-18.56%)
June 236 pm (-4.8%)
Dec 27.4 pm (-52.26%)

[Calculations from PVGIS (see section 5 of FAQs for a walkthrough))

What does this mean, well, in the summer when you export a lot of excess, you'll generate almost as much as a south facing system, but in the winter, when generation is much lower, and you consume far more of the generation, you'll have a lot less of it. The result is that you may see lower leccy savings.

So, all in you need a better price. It's not about haggling, it's about saying that due to costs and income, you simply need a better deal.


Onto the set up. Are you filling the rooves? The big win of an E/W install is the ability to fit twice as much PV as a single roof. Proportionately this is cheaper as so many PV costs are fixed (or mostly fixed) so going bigger will result in a proportionately lower cost, eg twice the size for 1.5x the cost.

A second benefit, something you've mentioned, is compliance with the local grid the DNO (District Network Operator), who have to give prior permission for any install that could export more than 3.68kW. A 5kWp system split E/W, running through a single 3.68kW capped inverter would see next to no capping. In fact 6kWp would probably be negligible.

So, can you go a bit bigger, and proportionately cheaper?

A recent 'newbie' got the price down to about £1k/kWp by going BIG.

Best of luck, ask me/us anything.

tunnel

I'm with Mart on this one, for a 4kWp system any price starting with a 6 is way too much, I'd be expecting a battery back-up thrown in for not much more money
If necessary knock on a few local doors(others with solar) and ask who installed and would they recommend them


The one thing I don't understand, why would you take a chimney down at a cost of £250 and then have solaredge fitted.
I'm guessing you don't fully understand what SE does? Each panel will work independent to each other so while one panel may go into shade and produce less energy the panel next to it that could still be in full sun will still produce to the maximum. It's custom made for shading from chimneys.
I don't actually believe that you'd recoup the £250 back in FiTs to justify taking the chimney down(unless its tower block size that'll shade the whole roof)


Back to the price, tell the installers it needs to at least start with a 5(4 would be better but I'm unsure now as to whether possible), you can see where I'm looking at here!


T

ahw23

Thank you! In particular, I really appreciate the point about barely getting any capping, as we really didn't feel we had the information to decide whether going larger was a good idea or not. In that case, we might go up to 18 panels (slightly over 5kw).

As for price, I'm hopeless at haggling, and had thought that was about as good as we would get, as we're in a hurry and live in an expensive area (red-trousered London commuter area). To be honest, I didn't believe a thing the salesmen told me about when it would pay off, anyway: I've been wanting to get solar since before there even was an FIT but didn't have the right roof (i.e. one not on the brink of collapsing) at the right time. However, I'm happy to call one or two more people so long as it doesn't make us miss the deadline. Thanks for the suggestion.

We realise the chimney wouldn't make a massive difference with the solar edge, but it might make a little more than you would guess if you hadn't see the house. I'm going to try to draw a plan of the original suggested configuration and hope the formatting comes out right:
E
.....................
. PPP .
. PPP . S......................
.....................
. PP PP . .Neighbour's house
. PP PP . ..........................
..........X......... .
.
........................
W

"P" is a panel, "X" is the chimney in question (although it actually projects away from the wall of the house rather than sticking up just through the roof), and houses/ridgelines are in dots. The installer proposed locating the West facing panels in two blocks, located away from the chimney to minimise shading. Unfortunately, this pushes four of them into the area potentially shaded by the neighbours to the south, as their house is set further back than ours. It seemed better to spend £250 to get rid of it now when the scaffold was there, rather than regret not doing it and spend more later.

If we did go up to 18 panels, where would you allocate them? Both of the installers who actually talked (as opposed to the one who cut his thumb on the loft ladder, asked for a bandage, ran away and never submitted his quote) seemed keener on the front, despite the orientation, presumably to avoid shading issues.

ahw23

Sorry! The picture failed entirely, and I haven't got a photo on the computer. If the description makes no sense I'll try to load a picture tomorrow.

Martyn1981

ahw23 wrote: »

Thank you! In particular, I really appreciate the point about barely getting any capping, as we really didn't feel we had the information to decide whether going larger was a good idea or not. In that case, we might go up to 18 panels (slightly over 5kw).

Hiya. Regarding capping, I'm in a tricky situation here, but I'm going to risk saying, 'you can take my word for it'.

Over the past 5 years I've read lots of comments on other forums, and estimates, some even of placing 8kWp on a 4kW inverter, and the capping is surprisingly low. My faith that the information is correct has steadily grown, but recently on here and elsewhere, folk have been posting actual results that seem to defy logic, because capping is so low.

Why is capping so low?

Firstly having an undersized inverter helps boost efficiency when generation is low (poor weather, morning, evening etc) so it works well for the UK, but not sensible for sun rich countries.

Secondly, capping only effects generation over and above the cap (obviously), but you might initially think that having a system twice the size of the inverter will cap half the generation, but it will cap nothing till the 3.68kW limit is reached, so all of that generation is 'safe'.

Thirdly, not only does the UK not have perfect sunshine for a significant amount of the time, but PV efficiency is affected by the panel temps. So in the summer, especially if there is little wind, the panels will rapidly drop to 80% or less of rating, so 5kWp becomes 4kW output.

Fourthly, for you and I, and just to repeat, the E/W panels will peak at different times, and both be a bit off-peak when the sun is midway. My 5.58kWp system can sustain about 4.2kW if the sun is high enough, and the weather good. This occurs from around 11am to 3pm, in the best 3 months ....... on the best days.

Lastly, you can ask the DNO for permission to go bigger, I have permission for 5.9kW of export (the sum of my inverters). But it might not be worth bothering for approx 5kWp E/W as that's probably the sweet spot for 3.68kW.

Martyn1981

ahw23 wrote: »

As for price, I'm hopeless at haggling, and had thought that was about as good as we would get, as we're in a hurry and live in an expensive area (red-trousered London commuter area). To be honest, I didn't believe a thing the salesmen told me about when it would pay off, anyway: I've been wanting to get solar since before there even was an FIT but didn't have the right roof (i.e. one not on the brink of collapsing) at the right time. However, I'm happy to call one or two more people so long as it doesn't make us miss the deadline. Thanks for the suggestion.

Sorry, thought I'd split this up, to address the different issues.

BIG question, what deadline, there isn't really any deadline. There are quarterly reductions in the FiT, but they are now tiny

4.18p/kWh (qtr 4 2016) down to 3.55p/kWh (qtr 1 2019)

So let's say (made up numbers) that you generate 4,000kWh pa, then the FiT drop over the next 2+ years will cost you £25pa. that's £500 over 20yrs, so well worth spending some time trying to save £500+ on the install cost.

Obviously, I appreciate that local prices may be higher, and I'm also useless at haggling, but when I got the 2kWp WNW extension done, I simply told the guy how poor the economics were and said the price I needed (I was totally genuine) and he found a way. For you, perhaps ask them to offer a price when the have no work on.


I have to jump onto your statement about wanting PV regardless. Personally, I'm a big fan of renewables, and believe in the Green & Ethical side of this board, but I tend to moderate my position on PV to the over-riding economic position of MSE in general.

However, if you see a non-financial benefit to PV, then, for you, that's added value, and should be included in your decision. Totally justified.

Martyn1981

ahw23 wrote: »

"P" is a panel, "X" is the chimney in question (although it actually projects away from the wall of the house rather than sticking up just through the roof), and houses/ridgelines are in dots. The installer proposed locating the West facing panels in two blocks, located away from the chimney to minimise shading. Unfortunately, this pushes four of them into the area potentially shaded by the neighbours to the south, as their house is set further back than ours. It seemed better to spend £250 to get rid of it now when the scaffold was there, rather than regret not doing it and spend more later.

If we did go up to 18 panels, where would you allocate them? Both of the installers who actually talked (as opposed to the one who cut his thumb on the loft ladder, asked for a bandage, ran away and never submitted his quote) seemed keener on the front, despite the orientation, presumably to avoid shading issues.

Guessing at this point, but if you want the chimney gone anyway, then take advantage of the scaffolding and get it done.

For panel placement, you're probably best simply covering as much area as possible. Some panels will lose efficiency, but hopefully the economics of the larger system will make up for that.

So long as you go for the SolarEdge (SE) kit, then most concerns will be solved. I was hopeful at first about my SE system on the WNW roof, but over the past 4 years have been shocked at the results. Using PVGIS and pretending there is no shading, I should get 1,430kWh*. So I crossed my fingers and hoped for 80%.

Actual results (and 2016 prediction):
2013 1,464
2014 1,491
2015 1,513
2016 1,438

Now check out the shading, noting that my massive chimney is to the south of my panels!

[Edit: *At the time of install, PVGIS suggested 1,359kWhs, but their estimates have increased about 5% over the years. M.]

django01

I recently got PV installed on my property in London. I found that I could not get the kind of prices that other MSE folks have managed to get. I mean the sort where you pay max £5 k for a 4 kwh system.. In fact I was chasing prospective installers down and asking them for quotations and they were not in the least bit interested. Some not bothering to return calls or email enquiries and others promising a quote and not turning this around. I found (thanks to a fellow forum mate) a supplier on fleabay..highly recommended. but they don't work as far south as London ..Anyway this experience influenced my choice of technology..I went with a simple string inverter.

tunnel

Martyn1981 wrote: »

For panel placement, you're probably best simply covering as much area as possible. Some panels will lose efficiency, but hopefully the economics of the larger system will make up for that.

So long as you go for the SolarEdge (SE) kit, then most concerns will be solved.

Have to agree with his Martyness....go large if you can. It's the same FiT rate up to 10kWp so it'd be rude not to.

ahw23

Well, you've sold me on getting more panels. 18 x 285kw would give 5130kw. Thanks also for pulling me up on the "money saving" aspect of this: as you can see, I'm not entirely objective, and a clear-eyed view is exactly what I came here for. Whilst I believe strongly in renewables, every pound saved on solar is one more to spend on other ways to improve our carbon footprint.

I can see it's not the end of the world if we don't have it all sorted by New Year. At the moment, however, looking at what's going on in the wider world, think I'd feel a lot more comfortable if we had major purchases out of the way, especially imported ones, before these inflation rumours come to pass. It's also the least intrusive of the improvements we'd like to make, hence putting ourselves through this less than a month after moving in.

So what I'm going to do is chase the contractor who ran away without quoting and contact the one recommended by Tunnel, but first of all email the one with the best quotation, explaining that now my OH has crunched the numbers over the weekend, we think we can't justify that price per kw, and in any case would benefit from a larger system. That puts the ball in his court and the worst he can do is say no.