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The White Hat Guide to Photovoltaic Solar Panels

Solar panel orientation

As most of our readers will remember from when they were escaping from prison, the light from the spotlight spreading its way at a low angle over the marshes may produce a low enough illumination for you to get away unobserved. However when the spotlight was coming straight at you there was nowhere to hide. It’s the same with solar panels. There is the most usable light when the sun is shining directly at them rather than glancing off at an angle.

Most standard solar panels in Australia sit on a roof fixed in one orientation. Most of us don’t have roofs pointing in the optimal direction or at the optimal angle and as a result when they reach the end of their life they have only created a portion of the energy of which they were capable.

So what is the ‘optimal’ orientation’? The conventional advice in Australia is facing due north and tilted at an angle equal to your latitude. This means for two fleeting instants a year (midday at the equinox) your solar panels will be pointing directly at the sun and at other times they are producing the ‘best compromise’ for a fixed panel. Sometimes, particularly when mounted on a flat roof they may have a rack which allows the owner to adjust to summer and winter positions and provided they remember to do so this eliminates some of the inefficiencies of fixed positioning.

However this is only part of the story. Your weather patterns may be such that you generally have cloudy mornings and clear afternoons. In which case you may get the best efficiency by orienting in favour of the afternoon sun. If on the other hand, you live in a warm clear climate you may get better performance by favouring the morning sun because most standard solar panels are silicon based (like computers) and usually work more efficiently in cooler temperatures. So you may get improved efficiency by favouring the morning sun. Then your own energy usage may peak at a particular time during the day and by using the energy directly rather than suffering the losses involved by pumping it into the grid may influence your favoured orientation (I hasten to add that your ‘favoured orientation does not refer to your sexual preferences but to the direction you choose to point your assets).

We know that all our readers are Intelligent, Informed, Independent and concerned about having those valuable non-renewable products used in your solar panels to maximum effect over their lifetime. Fortunately there is a wide range of government agencies, installers, NGOs and lobby groups who should be able to advise you on the optimal orientation for your area. However not all are equally well informed or have a grasp of the simple maths and science involved, so you may find you need to do a bit of research yourself.

Tracking The Sun

One way to significantly increase the efficiency of solar panels is to have them always facing directly towards the sun as it travels across the sky.

So why don’t we all fix solar tracking devices (sometimes called heliostats) to the solar panels on our roofs? Well, once you introduce moving parts, particularly in a city environment, you raise a number of maintenance and reliability issues. The standard fixed array on a suburban roof is practically ‘install and forget’. However research originating at RMIT in Melbourne is hoping to have domestic solar tracking devices on the market at an affordable price within a year or two which has a large potential to increase  the efficiency of photovoltaic domestic solar power.

Larger arrays with more space are better suited to operating more efficiently by tracking the sun. There are several ways of doing this. One is to have a light sensor detecting the major light source feeding to a servo controller which adjusts the direction of the panels continuously. Another way is to pre-program a circuit to point the panels in the known direction of the sun at any time of year. Both methods use energy from the panels to drive their mechanisms, but obviously less than increased amount of additional energy that is being harvested otherwise there would be no point doing it.

The controlling mechanism may be such as to allow the panels to move on:

• One Axis - to follow the east west movement across the sky – good.
• Two axes – to follow the sun across the sky and allow for its angle in the sky throughout the seasons – better.
• Three axes - Sometimes, when the sun goes behind a bank of clouds you will see a light tracking group of panels (often referred to as a ‘forest’) turn to face a hole in the clouds which is producing the most usable light. – best. You can see such a tracking solar forest here.

So why don’t all systems use three axes? The more movement possibilities the more current drawn, the more wear on the motors and the more complex the mechanism. As with all things to do with solar energy it is a trade-off between power generated, price, production and maintenance issues.

Currently a third mechanism for following the sun is being trialled which tracks heat rather than light. A cunningly designed set of hydraulic pistons (using compressed canola oil) use the hydraulic pressure created by heat to orient the panels in the direction of the greatest heat. It is ‘passive’ in that it uses no electrical energy and is just driven by the heat of the sun. You can see examples such a system here.