The Basics of Solar Energy – How Does Solar PV Work?
Given the large push society and governments are putting towards renewable energy as a whole and more specifically solar electric energy.
Solar electric energy (often referred to as Solar PV or Solar Photovoltaic) is not a new technology. In fact in Europe and Asia the use of this technology is widespread. However in North America the technology is just beginning to catch on. But how does the sun get converted to electricity?
Simply put, the energy from the sun’s rays strikes the surface of a silicon wafer (mono), crystal (poly) or thin film surface and part of that energy is converted to direct current electricity. The majority of the energy, however is converted to heat rather than to power (which is why solar electric – or photovoltaic – panels have such a low efficiency compared to solar thermal heating).
The electricity generated travels through an inverter (converting the DC power to something that is ‘consumable’ by the power grid) and then is altered to AC current. This then flows through a load centre (circuit breakers) an AC disconnect, and then to the revenue meter.
Understanding the basics, the next question that arises is typically the alignment of the panels.
The ideal direction for panels to face in our hemisphere is south (true solar south, or zero degrees). Often it is not possible for your panels to face true south. However don’t despair; it is still quite possible for your location to provide quite a bit of power. In actual fact, the only direction that does not produce significant power for us in Ontario is facing to the North. This measurement is referred to as the ‘azimuth’ of the array.
The other factor is called the ‘inclination’ of the array. This refers to the angle (or pitch) that the panels are mounted at. In situations where a tracker is being used, the inclination isn’t as important. However for a roof mounted system, your inclination will be the pitch of your roof. Depending upon your longitude and latitude, you will have a different ‘ideal’ azimuth and inclimation. One of the things you should look for from a company assessing your location for solar is whether they have identified the ideal azimuth and inclimation and compared the ideal to your actual situation. Why is this important? Because the azimuth and incination have quite an effect on the power produced by your array.
Where I’m located in Ontario, Canada, zero degrees (true south) and a thirty degree inclination will capture 100% of the potential power (assuming a clear, sunny day). Changes in this ideal will still produce power, however it will not provide maximum output. In fact a roof at thirty degrees off true south, on a fifteen degree slope will only capture 96% of the available power. Even an array at due East or West, at a 90 degree inclination (straight up and down) will still produce 51% of the ideal power.
Another question that arises when someone is looking at having solar PV installed at their home or business is the type of panel (technology, not brand) that should be used. With so many people becoming more interested in the different solar panels on the market, it’s important to note that the different panel types do have different strengths.
Monocrystalline (Mono) panels have silicon ‘wafers’ inside them. These wafers are made of the same material as computer chips and their structure results in the highest efficiency panels (14-17%). These panels depend on direct sunlight and do not do as well in indirect light conditions (cloudy days). You can recognize a mono panel by the ‘honeycomb’ design that you can see.
Polycrystalline panels (Poly) are made from ‘flakes’ of silicon. These are the most common types of panels and are less expensive to manufacture than mono panels. The cell efficiency in a poly panel typically ranges from 13% to 15% efficiency. These panels are less sensitive to temperature and also capture more energy on cloudy days than mono panels.
In later articles we’ll examine inverters and ways to connect to the electrical grid.