What is the best angle for solar panels on your roof? And how does the energy you get change as your roof angle changes? We take a look.
Roof Angle, Orientation and Where You Live
The second-most asked question we get about solar is: “Is my roof suitable – I think it might be too steep / not completely south-facing”. (For the inquisitive, the top question is: “How does the subsidy / tariff thing work?”).
There are three main factors that go in to the calculation of how much sun a roof receives. Roof angle or pitch, roof orientation (how south-facing your roof is) and your location. We’ll focus this article on roof angle; the next articles will look at roof orientation and location.
Solar Energy and Roof Angle
We’re sure you know that there is an optimum angle for solar panels on your roof. This is the angle where, over the course of the whole year, the panels get the most amount of direct sunlight which produces the greatest electricity.
The question is: what is the perfect angle, and if my roof is not at exactly this angle how much energy will I miss out on? We’ve picked a location in London and a south-facing roof for this example.
The chart below shows how the solar energy varies as the roof angle varies.
So for this roof the optimum angle is 35° and at this angle the roof generates 1,265kWh/m2/day. You can see how the energy reduces as we move away from this optimum angle. At 30° the energy drops to 1,260kWh/m2/year – a reduction of just 0.4%. At 20° (15° away from the optimum angle) the energy drops to 1,229kWh/m2/day – a reduction of 2.6%. It’s only when you look at very steep roofs – say over 60° – when the solar energy really drops off.
If you want to see how this works for your roof you can create a free SolStats report – take a look at the bottom of the report and you’ll see a version of the chart above for your location.
It is obviously preferable to have a roof at the perfect angle. But with the very generous government subsidies we believe it absolutely makes sense to install on roofs that are not at the perfect angle. You’ll lose a few percent of solar energy but it should still make financial sense.