September 2022 update:

Thank you to those who helped with the September walk around.

If you missed our walk around then there will be a STEM practical activity for children and parents at St Mary’s Church on Saturday 15th October from 9am until midday.

The church has a South-facing roof and a larger North-facing roof. There is a smaller West-facing roof by the entrance and a very small porch. The church is principally shaded by a large deciduous tree in the South West corner. There are two vents/flues of interest and they are indicated with rectangular keep out zones on the roof.

The South-facing roof is around 8° West of South and is partially shaded by the tree in the South West corner. Maximum number of panels would be 56. It has a shallow roof pitch of 12.5°.

The West-facing entrance might be possible to cover in solar panels. It is 8° North of West and has a pitch of 14.5°. It is heavily shaded by the church and the tree making so it is doubtful that this would give a good investment return. It is analysed with 18 panels for completeness. The South-facing side of the porch could accommodate a single panel but this is ignored for aesthetic and cost reasons.

The large North-facing roof has a shallow pitch of 12.5° and would not normally be considered suitable for solar panels as it faces away from the Sun.

Roof	Number of Panels	kWp (assume 300W panels)	kWh/year (unshaded)*
South-facing roof	56	16.8	14575
West-facing entrance	18	5.4	3626
(North-facing roof)	(93)	(27.9)	(19197)
Total	74	22.2	18201

* Estimate from europa.eu, The West entrance has had a modified horizon applied to account for church but shading from the tree is not included.

Note: unshaded annual energy per panel roughly shows which roof has the best investment return (260kWh/panel/year for South-facing roof; 201kWh/panel/year for West-facing roof; 206kWh/panel/year for North-facing roof). Somewhat surprisingly, the North roof is actually a better location than the West roof and this is because the West roof has to wait until the Sun passes the main roof section before it can get direct sunlight and also that the roof pitch angle is actually quite shallow.

Example House

How does the solar power potential compare to a domestic property? Many domestic arrays are rated at 4kWp, but some people opt to maximise their solar generation, especially if they have electric heating systems or electric vehicles.

Here by way of comparison, a previously calculated example house in Allestree has length 9m by width 6.5m and 35° roof pitch and is oriented at 30° from North (so that it has an 30° South of West facing roof and a 30° North of East facing roof). It is a gable end roof design with no unusual features but with a central chimney that could give some minor shading.

Normally the installation would be for the South-West facing side. Here we look at both sides for interest.

Roof	Number of Panels	kWp (assume 300W panels)	kWh/year (unshaded)*
South-West facing	16	4.8	4142
North-East facing	16	4.8	3158
Total	32	9.6	7300

* Estimate from europa.eu, No shading is assumed.

Note: unshaded annual energy per panel roughly shows which roof has the best investment return (259kWh/panel/year for South-West-facing roof; 197kWh/panel/year for North-East-facing roof). A perfectly aligned South-facing roof on this house design would give 291kWh/panel/year: 60° off South is equivalent to a 32kWh/panel/year loss (11% down) whereas a 120° off South is equivalent to a 94kWh/panel/year loss (32% down).

Project Background:

We are looking into the feasibility of solar panels at Holy Family. As part of this we will start with a practical walk around at 11:00 on Saturday 3rd September. This is a STEM (Science, Technology, Engineering and Mathematics) activity which may be of interest to children and parents as well as parishioners keen to help with this exciting project! We will try and measure building dimensions, roof angles and orientation (if you happen to have a long tape measure or large protractor or a North locating compass then please bring them along – if not then don’t worry as we will have some we can share). We will talk about the solar angles from the position of the sun in the sky, consider what happens in different seasons and look at shading. This event is a local event during the Season of Creation. Look at some of the global events too here.

Can’t make the day? Get in contact using our contact form with your availability and we will try and organize a repeat in September or early October.

Keep an eye on this page for project updates!

If you are keen you are very welcome to start preparing…

Look at Google Maps to understand the position of the church buildings

Make a sketch of the buildings noting North and ready to write down the measurements on the day:

Many thanks.