The Pros and Cons of Solar Trackers for Australia

The gain from having a solar tracker is dependant largely upon the latitude and upon the climate at that location. The maximum gain that you may expect is in summer and at the greatest latitude. You would get more than 100% gain from a tracker on the north or south pole in mid summer as opposed to a fixed solar array at that location. In mainland Australia the greatest gain would be in Tasmania. In Launceston you may expect up to 36% gain in January compared against a fixed array tilted at the best angle for January whilst in Hobart you may expect 34% gain in January compared against a fixed array tilted at the best angle for January. I expect that Launceston gives a better result than Hobart because it has less cloud cover. You lose most of the advantage of a tracker as a result of significant cloud cover.

Solar modules still work under cloud cover, but at a reduced rate because the module is operating mostly from diffused sunlight instead direct sunlight. When it is heavily overcast, the solar module ceases to function completely, but that occurs surprisingly rarely. The reverse happens with gain from a solar tracker in winter when you may expect no power generation at all on the north and south pole and the gain is significantly reduced at other latitudes.

The sun rises south of east and sets south of west in the summer months in the southern hemisphere. Therefore if you have a fixed solar array pointing due north it shines on the back of the array in the early morning and again in the evening. These are also the times when the sun is least intense. You may expect 1% or 2% of your daily solar energy for each half hour at these times whereas you may expect 7% to 8% of your daily solar energy for each half hour around midday. This is assuming cloudless skies. Conversely the sun rises north of east and sets north of west in the winter months which means that the sun will be shining on the front of a fixed solar module all day. You may expect a 15% gain of a tracker over a fixed array set at the best angle for the month of June in Hobart, and a 10.5% gain in Launceston. Therefore you would probably consider buying an extra solar module instead of buying a tracker, depending on gain compared to cost.

In Sydney you may expect a 30% gain in summer and a 10.9% gain in winter. In Rockhampton you may expect a 30% gain in summer and a 6% gain in winter. North of Rockhampton we add an extra variable that makes things more confusing because in summer the sun is to the south all day long whereas in winter the sun is still to the north.

From these figures it would appear that climate, especially overcast days is as important a consideration as latitude. If a fixed solar array is set at the best yearly average tilt angle all the gain figures cited above are increased, in some cases quite significantly.

In the tropics, the sunlight hours remain much the same regardless of the season whereas in Hobart the daytime goes for slightly more than 15 hours in December but less than 9 hours in June. And so in Hobart you may have greater need for the extra solar energy in winter when you get the least gain from a solar tracker.

A very important consideration for the advantage of solar trackers is the type of loads that you wish to operate. Refrigeration, space cooling and to some extent water pumping may be considered as summer type loads as you would expect these devices to use more power over the summer months. Lighting, assuming you don't use electric lights in the daytime and possibly entertainment may be considered as winter type loads as you would be more likely to use artificial lighting and spend less time outdoors.

Another consideration for solar trackers is how reliable they are. According to Murphy's Law, wherever you have moving parts you are inviting something to go wrong. Unless the solar tracker stops in the midday position you are likely to be worse off than with a fixed solar array. Solar trackers are also more prone to storm damage than fixed arrays. A large solar array up on a roof or on a pole structure is like a sail ready to fly off when the wind gets underneath it. The most likely time for severe storms is late afternoon when a solar tracked array may be in its worst position giving it the least amount of strength as a result of the lack of triangulation. You certainly don't want an expensive solar array to be destroyed because it is more prone to storm damage.

Lastly you need to consider how reliable the solar tracking process is. For instance, if it is dependant upon "seeing" where the sun is, what happens when it is overcast for the first half of the day? Can the reflection of the sun off a cloud falsely trigger the tracker?

If you are considering buying a solar tracker and the increased likelihood of storm damage does not concern you, then you should do your sums first or employ a professional solar system designer to do the sums for you. What is the cost and the seasonal gain of a solar tracker as opposed to the cost and seasonal gain of buying extra solar modules?