New PV system (dormer windows) 11 September 2021 at 10:56AM in Green & ethical MoneySaving 8 replies 163 views

M0ney

Hi all, 

I recently moved house and whilst my roof faces more or less directly south, I wanted to ask about anyone's experience with dormer windows, how much is lost because of the shade that they cast over the roof....my last house had 16 panels which were 1.65m x 1m and I'm thinking at best I could get would be maybe 12 onto this roof because I have a velux window and 2 dormer windows. The panels that I had before were rated to 285w (I think, since the whole system was rated to 4.56Kw) so the other thing that I wondered is whether there are panels available now which can generate significantly more power for a similar surface area?

TIA 

QrizB

Answering your last question first, yes. 1650x1000 is a standard-ish size and panels that size currently generate 330 watts or so. Having said that, panels are also available in larger and smaller sizes woth correspondingly larger and smaller outputs. There's a selection of examples on this comparison webpage (only a fraction of those on the market but gives an idea).

Shaded panels are a problem. If you have a string of panels daisy-chained together, shade on one panel will drag them all down. For example I have four 240W panels as a standalone string in my garden; putting my hand over one cell on one panel reduces the output to less than half. You would probably benefit from optimisers or microinverters. There's a decent explanation of the two technologies (better than I could write in this thread) here.

arty688

Panels are a bit better and as well as more powerful they are more efficient. There is no standard size for example on my roofs the most powerful system would use 340w panels not say the 500w panels you can get as they are a lot but bigger. Also it may be worth looking at premium panels if space is short.

M0ney

Thanks very much for the responses so far, this is the roof and yes, I'd definitely be wanting to include microinverters. It's a pity the dormers were put on the north facing side. 😂 
Anyway, I see that from that table there are panels which are just over 1m x 1.75m ish it's hard to judge how many panels of that size I could be able to fit but I would think at least 12 which would get me over 4Kw....

QrizB

The biggest challenge that people on the forum have had recently is finding an installer who:

• isn't booked up for the next 12-18 months, and
• is willing to have a proper conversation with the buyer about what their options are.

Either people can't get quoted, or the installer gives an desk-based quote based on a quick squint at Google Maps and then doesn't respond well to questions. If you can find an installer who is happy to discuss your installation and quote on that basis you shouldn't have a problem getting a well-suited installation.

M0ney

Thanks very much for the responses, I have AES solar coming to see me on Monday at 11:30am, they didn't say anything about being booked up months ahead but he did say the lead time could be quite long for a battery, I don't mind waiting a few months because the winter is coming up soon.
I'm hoping AES can give me a competitive quote as they are a local company only about 20 miles from me. 

arty688

Interested to hear what they say.

M0ney

OK so a wee update, he said that the lead time on some batteries has been quite long although he wasn't specific I guess it would  have been difficult to say off the top of his head. He was very thorough and was will to consider all possibilities with regards to the space available on my roof and was happy for me to go back and forth with the different sized panels with his engineers. He also said that the install date would be March/April so they are clearly busy also and he said that he would come back to me with some quotes in around 2 weeks. I think I'll probably get around 4Kwp at best, although he didn't say that I was with him when he was doing all the measurements.

Meatballs

That is some lead time!