Community Solar 2020 – Roof Spotters Guide

This guide has been designed to help BWCE members and supporters identify and propose potential solar projects for us to develop. Having ‘spotters’ spread across our area will be very helpful, lending us lots of eyes out and about looking for sites to support the programme.

You can download a PDF version of the Roof Spotters Guide or read on…

Who would make good building owners for us to talk to?

  • Owners who are willing to engage in a long-term lease of their roof space and for the community to own the solar panels.
  • Strong proactive green activities and active participation in the community are ideal.

What sorts of buildings are we looking for?

  • Farms
  • Schools
  • Colleges
  • Universities
  • Private hotels
  • Private care homes
  • Hospitals
  • Police and Fire Stations
  • Local authority buildings
  • Libraries
  • Companies using refrigeration
  • Engineering firms with machinery use year-round
  • Food manufacturers
  • Office buildings

What attributes do these buildings need to have?

  • Southerly facing pitched roofs which are not shaded or are facing directly east/west.
  • Roofs which are in good condition and that can bear the weight of solar panels.
  • A minimum are of 280m2 for pitched roofs (slightly more than the size of a tennis court) and at least 650m2 for flat roofs (two tennis courts).
  • Buildings that are in good condition.
  • Buildings which use a significant amount of electricity all year round, particularly during the summer

We can consider listed buildings and flat roofs but for the first phase of development we will be focusing on roofs which do not need planning permission

To help you with this we have described these qualities and illustrated further in the rest of our guide.

What do I do if I find a potential solar roof?

  • Please find out the contact name, telephone number and email of an owner/manager/director amd the address, including postcode, of the building.
  • If possible please provide a photo of the building and the roof you are proposing.
  • If you have time you could try to identify the roof on Bing or Google Earth and even try measuring the roof.
  • Send the details to Alex Lockton at email [email protected] or call him on 07771 865115
  • If you are able to have a conversation with the owner of the site you can refer them to our webpages at where they will be able to read through some Frequently Asked Questions and complete an online survey to express interest.


More details on what we are looking for

Orientation of roof

Best if facing somewhere between south east and south west. The redder it gets in the table – the better it is.

(Source: Which Magazine).


Directly East-West could work and although the overall yield per kW installed will be lower, it will enable more panels to be installed and it will generate more electricity at either end of the day and outside of the summer months, which can be helpful in matching demand. See the graph at the end of this guide for an illustration.

Type of Roof

Preferably a pitched roof between 10 and 40 degrees. The example below is from from Ralph Allen School.

A flat roof could be possible but will take longer to organise due to the need for planning permission. Here is a flat roof showing an east-west solar array on Lewis House in Bath.


Size of Roof

Preferably 280m2 or larger. This is just a bit bigger than a tennis court. This is similar in size to this section of a stand at Bath Rec.

Or the roof of Magnet in Bath


Note that this image of Weston All Saints Primary School has good example of access for scaffold. It would be done in holidays to avoid work near children.


To give you an idea of the space we need this is Mead School which BWCE installed in 2012. It is a 50kw system, however in today’s panels we don’t need the space marked with the yellow Xs


The reason we don’t need as many panels is that panels have become more efficient since this this system was installed. We now get about a third more power from the same individual panel size.


Condition of Roof

The state of repair of the roof is important. Below are some poor roof examples to look out for.


We would not be able to consider an asbestos roof (see below). To avoid asbestos ask if the building was built post 2000.

Here are some good condition roofs:

Cement Fibre

Concrete Tile


Standing Seam


Avoid shading such as tall trees or other buildings over-shading the roof.


Listed Buildings

Many buildings in Bath are listed so if you can check this with the owner please do so. Listed buildings tend to be longer term projects with heritage planning considerations. Due to the timescales they may need to be considered in later rounds of the Community Solar 2020 project.


Electricity usage

We can only take on projects which enable us to:

  • Offer discounted solar power to the building owner
  • Pay interest to BWCE members
  • Contribute to the community fund

In order to make our figures work we need to make sure the site uses enough power.

If we are aiming for a 50kwp or 280m2 roof, this means we are aiming for sites which use more than 6,500 units of electricity in each of the summer months. This would cover the power of a system this size and ensure the site uses all the power.


This shows the seasonal power curve of a 50kw system.






This shows a 140kw secondary school system design. The yellow is solar generation, arguably this building could have more solar as it uses more even in August when it drops off in the holidays.



Below are some hypothetical examples:

The gap between the blue and the orange line in the summer corresponds to the amount of electricity which is unsold to the site owner. This won’t make the numbers work for us.





This shows a southerly facing roof which uses almost all the power that is generated. This is what we are looking for.






An East-West facing flat roof has an interesting generation profile that can be potentially attractive as there is a flatter generation curve throughout the day. There is still a peak in summer months and at midday/afternoon during a typical day.  What is slightly different is that at the beginning and the end of the day the generation will be slightly higher due to the panels facing sunrise and sunset. This profile is useful as it means we can match the power to buildings better and ensure more of the power is used as well as generating more in the morning and evening compared to south facing.

We have selected certain types of buildings in the list we gave at the beginning of this guide. This is because they are likely to have good power usage.

If you know the site owner and can ask them for 12 months of half hourly data from their electricity supplier this is ideal to help us work this out.

If you want more detail than this you can refer to our FAQs.

If you have any questions please email [email protected]

Good luck with your roof spotting!