So now I have a solar PV system how do I make the most of it???

EricMears

Our installer applied for & got DNO approval for our 4.0kWhP system. It didn't take very long to get and I don't think it cost anything (at least he didn't charge me for doing it, so if there was a fee it must have been small enough to absorb).

Helen18

Hi all,

Thankyou so much for all your comments. I'm learning so much. Don't worry Mart, I'm just about keeping up and really welcome all the suggestions. I'd much rather understand all the options and know the final solution is chosen for good reasons.

I'm a little lost with the bit about inverters needing to be 3.68kwp but am very interested in the idea of going over 4kwp. Will explore that. I guess though there must come a point on bright days when, even if the aga is using its max 2kw the whole time, when we'd generate more than we could use? Or not? Would say a 5kwp system actually be of more benefit in poorer weather?

We need to explore the shading and make a guesstimate about where it will reach and how often. It would certainly effect the area the nearest two panels would be in. Not sure if it would stretch across any others. If not then I don't think there should be any other shading issues. I suppose you can't put micro inverters or power optimiser just on the panels effected by shade?
I'm worried about having lots of gadgets with potential to go wrong sitting on the roof. Fine if there are no problems but could end up costly. However, might end up a risk worth taking.

Perhaps a larger number of panels with slightly less efficiency might be a good option? Just might get too expensive.

If some panels on the south roof do get shade I wonder if it's better to stick them on the east? Does orientation trump shading?

Not sure if it was a good plan, but I inadvertently registered on an ecoexpert website (something like that at about 2am!) consequently have had several calls today from local installers wanting to quote/survey so will bend their ears with all my new knowledge and complicated questions!!

Hx

tunnel

Helen18 wrote: »

Hi all,


Not sure if it was a good plan, but I inadvertently registered on an ecoexpert website (something like that at about 2am!) consequently have had several calls today from local installers wanting to quote/survey so will bend their ears with all my new knowledge and complicated questions!!

Hx

Bet your glad you posted on here then.....forewarned is definitely forearmed. I have to go to my elderly parents later today to keep an eye on someone who has cold called them concerning PV. Wouldn't want them signing up to something they could get £000's cheaper elsewhere.;)

Martyn1981

Helen18 wrote: »

Hi all,

I'm a little lost with the bit about inverters needing to be 3.68kwp but am very interested in the idea of going over 4kwp. Will explore that. I guess though there must come a point on bright days when, even if the aga is using its max 2kw the whole time, when we'd generate more than we could use? Or not? Would say a 5kwp system actually be of more benefit in poorer weather?

Hx

Morning Helen, Doesn't sound like you're confused as you're asking all the right questions.

Quick lesson on the rules. When you install a SSEG (small scale electricity generation) yo have to inform the local DNO (District Network Operator), so they are aware of all sources. As long as it's done properly (the paperwork is correct) they have to accept it. However, for anything with the potential, or theoretical potential of exceeding 16amps (at a deemed 230V, our supposed grid voltage) you need prior approval from them, otherwise they may tell you to disconnect whilst they consider, and they may decide you can't connect if there are too many SSEG's nearby, or the local network just isn't robust enough.

16A * 230V = 3,680W (3.68kW). So many inverters are capped at 3.68kW even if they are actually a bit bigger.

Size wise (within reason and likelihood of permission and budget) you want to go as big as possible. The natural point to normally stop is a 4kWp system as the FiT rate drops 10% for 4-10kWp systems, and a 4kWp system is perfectly matched to a 3.68kW capped inverter for DNO compliance..... so everyone is happy!

A system produces it's max when lined up with the sun, and in cold weather (panel output drops as temp rises). When everything is 'just right' expect about 90% or less as a general rule, dropping off as weather gets worse. During very grey days (or worse) generation could drop off completely, so sizing a system to demand doesn't really work (again, within reason).

It's a numbers game, but don't be too scared of the 10% FiT drop at 4kWp, export and leccy savings aren't effected. So perhaps, find out how much a 2.7SSW + 1.3ESE or 2.5SSW + 1.5ESE will cost, then compare the cost of going bigger on the ESE, perhaps to 2 or 2.5 and see how the income/cost figures compare (I'm happy to help number crunch if you'd like). My theory is that once 'they' are on the ESE roof, with the scaffolding in place, the extra cost won't be that much proportionately.

Your installer should have a rough idea how your DNO will react.

Phew, and that's just the first paragraph!

Helen18 wrote: »

We need to explore the shading and make a guesstimate about where it will reach and how often. It would certainly effect the area the nearest two panels would be in. Not sure if it would stretch across any others. If not then I don't think there should be any other shading issues. I suppose you can't put micro inverters or power optimiser just on the panels effected by shade?
I'm worried about having lots of gadgets with potential to go wrong sitting on the roof. Fine if there are no problems but could end up costly. However, might end up a risk worth taking.

Now's the time to assess shading. The sun's getting lower, but generation at the ends of the day is still decent, so having a good stare at your roofs in October will tell you a lot. You might be pleasantly surprised, but on the other hand, shocked at just how far shading can stretch at these times.

Not sure if you can mix and match PO's or MI's. There is probably something you can do, but then you'll have extra costs, complication, more kit to go wrong and the worst of both worlds (as well as the best). Hope I'm not making this up, but I seem to remember somebody saying that they have their MI's inside the roof, with the cables for each one going through the roof fabric. That'll solve any access issues, but sounds slightly scary.

Helen18 wrote: »

Perhaps a larger number of panels with slightly less efficiency might be a good option? Just might get too expensive.

If some panels on the south roof do get shade I wonder if it's better to stick them on the east? Does orientation trump shading?

Again, all a numbers game, you'll need to get prices and compare to estimated annual generation, then work out the different incomes. The slightly lower performance of ESE v's SSW will probably still be better than the extra cost of higher efficiency (proportionately smaller) panels ..... but, don't forget the added benefit of widening your generation curve, think 'don't put all your eggs in one basket'. A slightly lower but longer generation is easier to make use of, maximise consumption, and minimise export.

Shading v's orientation, guess what 'numbers game' again. Depends on the orientation and the shading. I'd guess that the comparative generation of the SSW's (Wp v's Wp) will be about 10% better than the ESE.

Helen18 wrote: »

Not sure if it was a good plan, but I inadvertently registered on an ecoexpert website (something like that at about 2am!) consequently have had several calls today from local installers wanting to quote/survey so will bend their ears with all my new knowledge and complicated questions!!

If it doesn't stress you, or bore you, then the more people you speak to, the more you'll learn, and fast. So probably a very, very good plan.

I'd suspect, you are much closer to the end now, than the start. Just need to start ruling ideas in or out, then it'll all come down to the price - such is life.

Mart.

Helen18

Ah thanks again Mart. I'm armed and ready now. Bring on the salesmen! Could do with a bit of sun to look at this shading too!
Hx

Estwing

Helen18 wrote: »

Could do with a bit of sun to look at this shading too!
Hx

Now you're just taking liberties lass.........

Helen18

Hi all,
Well a sunny day arrived and it's all rather depressing....
Next door on both sides have some large trees which have more impact than we'd thought and so does the back of the house next door and our own gables!

It seems our east ish roof gets shade froms trees and buildings until sometime after 10am. It was clearing by 9.45 but I had to go out. This roof was in shade again by 3.45 but was prob much earlier, around 2.30 we think.

The south ish roofs seem to have a diagonal line of shade across them from our gables which clears on one side by 10am ish from the 40 deg section. Later on the lower. At the other side it was later still, but then that stays in the sun a bit later.

In the afternoon one side gets shade from a large conifer esp on the 22deg roof.

We're also concerned from measuring our plans, that we won't fit as many panels on as is being suggested.

I suppose the reality is that our generating days will be shorter than hoped because of the time it takes for the shade to move away, esp through the autumn/winter. Maybe we'll only generate about 10% of our useage (3-400 units per week). Beginning to wonder if it's worth it? I suppose every little helps. All a bit disappointing though.

Hubby is trying to do some more shade calculating using sketch up but it takes ages!

We've had two more quotes with diff suggestions.

One really doesn't have any alternatives but to use micro inverters (after looking at the shading we're inclined to agree). This comes in at £7-£7.5k depending on choice of panels. He suggests 10 panels on east ish roof (this is a squeeze and means putting them up towards the house end where shading is worse from next door) and 6 split across the two southish roofs.
This makes sense but I'm somewhat put off by their quote as it is accompanied by a whole load of figures and predictions of our return over 20 years amounting to £47k! This is all rubbish. There's no allowance for shading and they assume 90% usage. Well with a diverter gadget maybe just we might use 90% but it's still ambitious. He visited the house, stood in the garden and never mentioned shading from building or trees next door. We're annoyed with ourselves for underestimating this but for someone who does this for a living not to be able to tell (well I guess he could but chose not to mention it!) is just wrong. He kept saying about the micro inverters improving the generation to help with the shade. I appreciate this but some of the panels need to be in the sun! I'm worried that the amount of shade might start to make it not really viable.

So, a reasonably sensible solution but not impressed by the lack of consideration of shading.

Second quote comes in at £6.1 but no micro inverters. Neither quote includes diverter. Both recommend immersun at £475/£500 which seems steep.

This quote done over phone only so far but hoping to get surveyor out this week. Quite impressed with the company. Very quick returning calls/emails and very thorough. Have had some probs working out measurements from plans over phone hence surveyor coming.
First suggestion was to put 8 panels on east ish roof on one string of inverter. Then put other 8 all on 40 deg sections of southish roof keeping number of strings needed to 2. Nice idea except we'd got measurements wrong and we think we'd get max of 6, maybe only 4 on 40deg sections. Absolute max we can fit on east we think would be 10, maybe 9 so might have a prob with that.
I've then gone back with photos of shading probs and they are now suggesting micro inverters or solar edge optimisers might be a better solution. New quote with micro inverters adds £600 but they want surveyor to come out as it is so complicated so guess quotes could all change again. They are also offering 20 year guarantee on standard inverter (may not be relevant) and guarantee 1st year's predicted income. Not a major factor as want it right for 20 years, but does suggest better consideration of shading issues. Had originally taken off 20% for shading on south roofs but none on east, but over phone can't see property and google is from 2007 before our extension and trees way smaller!

Ho hum!
Found myself looking out when it was cloudy yesterday and thinking 'oh well, at least the shading wouldn't matter today, wouldn't be generating anything anyway!' Must be bad!
Hx

tunnel

Hi Helen,

Don't give up, I'm currently looking at an 8kWp for my parents and you wouldn't believe the difference in price range for what they require. Thanks to the good folk on these forums for the information and input they give I blew one salesman out of the water and made him look a right nunce, he wouldn't budge on his extortionate price and was adamant he knew best(he really should do more reading on the products he's selling:D). It took nearly 3 hours of my life to get rid of him(flippin window salesmen).

Good luck with your quest and don't forget you still have the west'ish roof if it helps(good for evening consumption when we all need it most)

Please continue to post too cos it may help many more people make the right decision and not get ripped off.

tunnel

Helen18

Ah thanks tunnel. I'm glad you think my drivel might help others! I agree that the difference between what one person says and another is tremendous! It's so hard getting past the sales pitch.

Interesting about the west roof. We'd more or less ruled that out as it's a bit north west really so didn't think it would be so useful. Will check out any shading there though in case. If we go with micro inverters I guess we could dot panels about anywhere really? So maybe a few on west would help. With the aga being on all the time, extending the length of the generation day is always going to be a benefit for us.

How is the 4kwp worked out? Is it a max of 16 panels? Or if you know that there'll be shading can you put more and still come in at 4kwp? I'm guessing not.

I wish we had room for 8kwp....mind you don't think we'd have the cash in the first place!
If we hadn't built our extension we'd have a lovely big southish roof. Ah well, then we wouldn't have a lovely extension! Can't have my cake and eat it unfortunately.
Hx

EricMears

16 panels is only a limit if you're using 250W panels. You could have more smaller ones (or fewer larger ones) for a total output of 4kWP. And of course the 'limit' is only the limit for getting the top rate of FIT payment; nothing to stop you having acres of panels if you have the room.

If the house roof is shaded, you might consider some panels elsewhere - e.g. on a garden shed roof or even a steerable array on the lawn. It all depends on how big your garden is and if there's an unshaded area available.