Solar panel location; East & North facing pitched roof Vs South facing Flat roof

purpledino

Hi, 
I live in an extended dormer bungalow with unusual shaped roof- limited pitched roof, lots of south facing flat roof. 
I have been given a quote by GSL for 9 panels on the pitched roof (4 East facing, 5 North facing). They don't recommend  panels on the south facing flat roof due to difficulties of mounting them on flat roof, and risk of them coming loose in high winds. 

I have 3 questions I hope the group can help with-
1) What do you think of using east/north facing roof?
2) is the quote reasonable?
3) any experience of solar panels on flat roofs? Mountings, efficiency, etc.

Thank you. 

Information that might inform the above:

Annual electricity use: 2318kwh. At home most of the day. Cheshire.

Solar Panels £4924
LONGi 3.87 kW Total Solar Power
(2,071 kWh per year)

Inverter 

Growatt, 3.68 kW Total Inverter Rating

Battery £3466

Growatt New Energy Technology Co. Ltd.

6.6 kWh Total Battery Storage 

Module-level PV Optimizer (TIGO) £450
Bird Netting £600
Additional scaffolding £500

Screwdriva

Sorry to say, that’s a poor quote on several levels:

1) Longhi and Growatt are extremely low end brands with poor support, app, device integration and reputations.

2) Your annual consumption is very low. You would be wise to skip the battery entirely and export your excess Solar generation to the grid via Octopus Flux instead. Said another way, the battery will never pay for itself within warranty. 

3) Flat roof installs using Van Der Valk mounting kits are not complicated for experienced installers and are quoted at similar price points as on-roof systems. (see image from a friends roof I helped with)

4) I’d skip a pure North facing roof as the generation ranges between 40-60% lower than other aspects.

5) Assuming your South/ West/ East aspects are maximized in the above 10 panel quote, here’s one I’ve seen recently that is superior in every way:

10 X Sharp 420W black panels (30 year warranty)
10 X SolarEdge optimizers 
  1 X SolarEdge inverter (20 year warranty)

£5500 installed. Bird netting + G98 + Hies included. 

purpledino

Thank you, this is exactly the kind of information I was looking for. 
I joined my Council's scheme for solar panels in the hope it would mean reliable prices & up to date information, but your reply has confirmed what my limited research has shown. 
2) I did wonder whether a battery would be worth it, especially as I work from home. 
4) Agree- it was this suggestion that made me worry they weren't the best company to go with
5) no West facing roof (semi-detached). Could get 2 (maybe 3) panels on south facing pitched roof. 

Would it be worth just having 7/8 panels on South/East roof with no battery, or would you look at installing more on very sunny flat roofs?
Is there a way to upload images as it might help discussion?  (I'm not allowed yet as newbie!)

Screwdriva

purpledino said:

Would it be worth just having 7/8 panels on South/East roof with no battery, or would you look at installing more on very sunny flat roofs?

I would maximize coverage on the flat roofs and the South East roofs as well as skip the battery. Council schemes are rarely good value and are plagued with low end brands at premium prices. 

94JDH

Agree with the Van Der Valk system - I've 26 mounted with this system and it's very easy to install.

Exiled_Tyke

Agree with what's been said. I really wouldn't trust any installer who suggests using a North facing roof in the UK.  

Netexporter

I really wouldn't trust any installer who suggests using a North facing roof in the UK.

I wouldn't want only a northish facing array, as the annual output is only about 60% of a southish array. However, in the summer months, where I live, the sun comes up over the mountains at about 5.30am, the sky is often clear, and the temperature is relatively low, which helps panel efficiency, and shines on the back of the house until about 9am. That coincides with the morning peak price period, so on Agile export you could make a nice bit of income for a good part of the year.

Exiled_Tyke

Netexporter said:

I really wouldn't trust any installer who suggests using a North facing roof in the UK.

I wouldn't want only a northish facing array, as the annual output is only about 60% of a southish array. However, in the summer months, where I live, the sun comes up over the mountains at about 5.30am, the sky is often clear, and the temperature is relatively low, which helps panel efficiency, and shines on the back of the house until about 9am. That coincides with the morning peak price period, so on Agile export you could make a nice bit of income for a good part of the year.

Interesting thoughts. I like your thinking.  I would want to run the numbers very carefully though to make sure that it's a worthwhile investment.  

Netexporter

As the two faces will be peaking at different times you shouldn't need a bigger inverter, it will just be working at a higher rate for a larger part of the day. So, essentially, it is just panels, which are getting cheaper all the time, and a bit of additional scaffolding.

I just run 10kWp on both sides of my house, in PVGIS, and it comes out about 8200kWh 20 degree azimuth and 5600kWh -160 degree azimuth. (my roof is a rubbish slope of 25 degrees) I think it could be economic done as a complete new system. Possibly/probably a bit flaky as an addition, depending on how many panels your north roof can take.