Science Centres: Energy

Getting the most out of solar panels

NIWA has developed a new method for analysing the best position for solar panels at any location in the country.

The placement and tilt of solar panels is crucial to the amount of solar radiation they can capture. Conventional wisdom advises that in this part of the world the panels should face north, and that the tilt should match the latitude of the site. So, for instance, at latitude 45 °S, a panel should be tilted by 45°, whereas at the equator, panels should be laid flat because the sun is directly overhead.

The solar tracker and instrument array for measuring direct and diffuse solar radiation at Lauder, Central Otago.

Previously, we have studied the optimal angle of solar panels assuming clear skies. That work suggests the traditional rule of thumb significantly underestimates the best tilt.

But the situation changes if conditions are cloudy. This is because clouds obscure some or all direct solar radiation, which largely determines the optimal angle for solar panels. That means it’s important to distinguish between direct and diffuse radiation to get a realistic idea of what solar energy can be captured from a particular site, and how the panels should be placed for best effect.

We have developed a new technique to determine the direct and diffuse components of the total amount of solar radiation measured by our National Climate Network. We then take these measurements and combine them with an analysis of cloud data for that location. The presence of cloud reduces the optimal angle for the solar panels. It gets closer to the conventional wisdom, depending on how cloudy the site is, but our results still recommend a higher angle than might be supposed using latitude as a guide.

There are, of course, other considerations which constrain the placement of solar panels, such as roof angles for solar water heating or threshold energies below which a photovoltaic cell may not operate. We hope to work with individuals and organisations already operating solar panels to test our predictions further in practice.