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This is a terrace house in a city about 120 km north of London.
It has a small front
garden so scaffolding could be put up. The main roofs face roughly NW
and SE. This is not ideal but was allowed for in the generation
estimates. None of the roofs are shaded at any time of the day by other
buildings or trees. The house had just been reroofed.
The owners wanted to install enough solar panels to meet their average daily needs at all times of the year. This is currently 11.9 kWh but they intend to reduce to nearer the average of 7.4. They accepted that there might be some gloomy, short days in the winter months when there wasn't enough light to meet that need. Therefore they did not want to risk going 'off-grid', and had to continue to pay the absurd standing charges, though there might soon be an option not to, for a higher kWh charge.
There is no parking allowed outside the house so they would not need to charge an electric car from the system. They also wanted a battery for overnight use. They were fortunate that while the installers were fitting the system, the rules changed and now required that, for safety, the battery should be outside the house. They fitted the battery into a box that they made at no extra cost.
The installers provided excellent specification documents running to
23 pages that included itemised costings, electrical schematic diagrams,
weight and wind loadings on the roof, and payback times based on a 25
year estimated useful life and 2% average inflation. It was encouraging
to see all metric units used, even including newtons (N) for weights
and forces.
These are the design data:
Front roof: 8 x 400 W panels 72° east of south, inclined 35 degrees from horizontal
Rear roof: 8 x 400 W panels 107° west of south, inclined 35 degrees from horizontal
That is a total of 6400 kW peak, which is larger than the average installation due to the house orientation.
The estimated yearly energy generated is 2669 +2269 kWh (4938 total)
based on 'standard procedures'. This gives an average of 411 per month.
Now the results based on one year of use
As expected in a high summer month they generated 750 kWh and used
370. In February 2025 it was 144 kWh and use of 449. February was an
unusually gloomy month, and though you don't need sunlight, you do need
light. In the strong sunlight in April and May 2025 they achieved 32
kWh/day and, as they only used 7 kWh a day, they exported a lot to the
grid.
The installers proved excellent, carrying out a clean job, and they stuck to their estimated time. So
overall an excellent result. They deserve a mention. They are
Projects4renewables, though of course there are many other installers.
However a genuine account of a successful project is always useful.
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(C) Peter Scott 2024
Last edit 15 May 2025