Solar Panels – Which way do I face them? (And why?)
Which way should solar panels face? Ahh! That’s easy! Straight at the equator, right? (Due North in the southern hemisphere, South in the Northern.) Hmmm. Maybe, maybe not. Certainly not in the case of hot-climate areas.
The object of the exercise is to maximise conversion of incident solar energy into electricity, but will an equatorial orientation do the trick? No. For a couple of reasons (see addendum A). Hot solar panels give less power than cool solar panels.
When is it coolest?
In moderate latitudes, generally in the morning, then heating up gradually toward early mid afternoon, say, about 2:00pm. So conditions are usually cooler from sunrise to late morning and this would indicate due East as the preferred direction, but that doesn’t take into account the generally weaker light before about nine am, so to maximise solar gain, North-east in the Southern hemisphere (South-East in the Northern) will be a better bet. It gives you some ‘cool-time’ advantage and it also gets you the more intense sunlight around noon before it all gets too hot and by the time the hottest time of day has arrived, the sunlight is fairly oblique to the solar panel surfaces and therefore has less of a heating effect and doesn’t compromise output as much. Of course, the weaker solar gain at that oblique angle means less overall power production, but by and large, a North-eastern exposure will get you the most power for the day, but when your local climate is at greater latitudes, say, more than forty-five degrees, then the heating up of solar panels is much less of an issue due to lower air temperatures and then an equatorial orientation may well be the best option.
What about using solar trackers?
These mount your solar panels on a mobile frame that is caused to move so that the panels always directly face the direction of incoming sunlight throughout the day as the sun moves across the sky. Good idea in principle, but in practice, not so good due to reliability issues and solar panel heating issues. Because of their complexity, solar trackers add another level of failure modes to your system and they become a never-ending source of angst and frustration. Trackers are, first and foremost, mechanical and mechanical things that have to move wear out. All the more so when heavily loaded, as tracker structures are. Far better to spend the extra money a tracker costs (and they are not cheap!) on extra solar panels to make up any perceived solar gain deficit.
The photo demonstrates exactly what I mean….The shadow line on the ground indicates a sun elevation of around fifty degrees which means somewhere around ten am to eleven am and the shadow line is parallel to the line of the roof holding the solar panels, so the panels are facing either North-East or South-East, depending on the hemisphere.
Solar panels generate electricity by using sunlight to knock electrons around in the silicon of which they are made. This activity, not surprisingly, is somewhat stressful for the electrons and they tend to scatter all over the place like startled sheep, staying within the silicon but bumping into each other, forcing their way past others and generally acting like an undisciplined and panicked crowd such that even the ones going in the right direction have serious trouble trying to get out. This mechanical friction between electrons causes the silicon to get hot. In fact, much hotter than the ambient temperature and this heat has a deleterious effect on electricity production. Not so surprising when a lot of the electrons that should be streaming OUT of the solar panel to produce an electric current, are, instead, engrossed in playing a subatomic game of dodgem cars inside the solar panel structure. So, when solar panels get hot, their electricity output goes downhill and when they cool down, even a little bit, power production picks back up again. Of course, you could alleviate this problem by keeping the panels cooler by means of, say, circulating cool water around on the back of them, or you could arrange a fan to blow cooling air over them. However, this may set up physical stresses in the solar panel that might result in stress fracturing.