Solar Panels on Flat Roof (south) or sloped roof (north)?

Hedwig2023

I had solar panels in my previous house & am keen to get them on new house.
I would appreciate some thoughts on which set up would be better for a dormer bungalow with several extensions! 

1) 6-10 panels on a south-facing flat roof 
2) 7 panels on east-facing sloped roof and 5 panels on north-facing sloped roof
3) another solution e.g. invest in solar farm co-op as your roof isn't really worth it!

Thank you. 

Image shows approx roof [🟩= flat roof; 🟦= sloped roof]

pramsay13

Probably panels on south facing flat roof but mounted at an angle. 
Best to get a few companies out to talk through options once they've seen your roof. 

Martyn1981

I would definitely go for south facing roof, and as @pramsay13 suggests, mount on an angle. Previously we needed PP for a flat roof if you didn't match the pitch, but now it's PD so long as you don't exceed 1m (I think) in height off the roof.

The E roof is worth doing too, E/W roofs are extra poor in the winter, but a shallow pitch will be a benefit in the summer.

Does the E roof get any shading when the sun moves across S and into W? Just wondering what is to the south of main building, is that a garden, driveway etc? I'm pondering whether a carport or pergola, same thing really, could add some significant capacity, assuming you want one? [I'm guessing the south is the back / garden?]

sheenas

The south side makes sense with a slight angle, its almost a DIY job. There are plenty of planning tools on various websites you can use. Further capacity on the east if needed.

Screwdriva

Lots of enthusiastic advice! Here's mine:

1) I would definitely panel the flat roof with 10 or more 500W bifacial panels. I've attached an image of what a Van der Valk flat roof installation with these panels can look like (note the surface of the roof has been painted with Solar reflective paint to maximize albedo gains). The installer will need to carefully measure all viable aspects via an in person survey. 

2) Definitely not a DIY type job.

3) I'd skip the North facing aspect.

What's your annual consumption? If it's substantially higher than 3500 kWh per year, a 18 X 500W bifacial panel system paired to a Tesla PW3 will cost ~£13K and is limited to three aspects (flat roof counts as one). If consumption is lower, skip the battery and go with a SolarEdge based PV only system which should cost ~ £7.5K. 

Hope this helps! 

Hedwig2023

Thank you, this is very helpful. 

I didn't want to influence the outcome, but I've had quotes from several companies. I sent them the above image showing the flat/sloped roof, and specifically asked if flat roof panels would be better. Two companies visited the house. The proposals I received suggested £7,000-12,000 for panels on the east/north sloping roof and ALL ignored the flat roof. One included a battery.

Further questions- 

1. Will solar panels affect house insurance?
2. How long does installation take? (flat roof is single storey)
3. Battery or not (considering budget below)?
4. Any recommendations for companies who cover the NW of England

Potentially useful information

• Electricity usage 3738.531kWh/12 months
• The south-facing sloped roof could potentially fit 2 panels
• No shading on S roof through the day
• There is garden to the south of the house
• I work from home
• Owner of 2 soon be teenages (I assume electricity usage increases exponentially around this age??)
• GCH & double glazed
• Petrol car but would like an EV in the future (unlikely in the next 1-2 years if I get panels)

Hedwig2023

I've just seen some of these questions might be answered on the PV thread; thank you @Martyn1981 for including the link in your signature!

MyRealNameToo

1. No one is asking about them but need to include them in the rebuild valuation if you arent buying a bedroom rated policy. 

Screwdriva

Hedwig2023 said:

Thank you, this is very helpful. 

I didn't want to influence the outcome, but I've had quotes from several companies. I sent them the above image showing the flat/sloped roof, and specifically asked if flat roof panels would be better. Two companies visited the house. The proposals I received suggested £7,000-12,000 for panels on the east/north sloping roof and ALL ignored the flat roof. One included a battery.

Further questions- 

1. Will solar panels affect house insurance?
2. How long does installation take? (flat roof is single storey)
3. Battery or not (considering budget below)?
4. Any recommendations for companies who cover the NW of England

The reason lesser installers ignore flat roofs is the amount of extra work it takes to create and send a design to VDV for approval (only way VDV will warrant their flat roof installations) before installing. Good installers typically include this as part of their survey/ quote. Just know that these types of installers are rare today (vs. the fit low end kit,  sub-optimally,  and then forget the customer variety)

1. Not typically. I always inform my providers that I have a PV system installed.

2. One full day

3. If you can afford it, the PW3 is the most future proof solution sold in the UK. 

NedS

@Hedwig2023 Have a look at the PVGIS website (free to use) where you can model different solar arrays based on your location, slope (assume around 8-10 degrees for the flat roof system) and azimuth (0 deg is due south):

https://re.jrc.ec.europa.eu/pvg_tools/en/

This should give you a very accurate prediction of what each option is capable of producing, but does not account for any local shading issues you may have. Just use the same installed peak PV power (array size) for each roof aspect to get a like for like comparison.