Our Sun produces two forms of energy, photovoltaic energy produced by the Sun’s light and solar thermal energy, produced by the Sun’s warmth. We use both forms; photovoltaic energy can produce electricity and thermal produces warmth.
According to Emily Kerr of Harvard University “The Sun emits enough power onto Earth
each second to satisfy the entire human energy demand for over two hours”. In one Earth hour, our Sun baths our small blue planet in enough energy to power the Earth for an entire year.
The use of solar energy is not new. The ancient Egyptians used mirrors to redirect light into dark rooms and they designed their houses to store up the Sun’s heat during the day to keep their homes warm at night and cool during the day. The Romans used similar technology in their own homes. It is said that in the 3rd century in Syracuse, Archimedes, the Greek mathematician, and inventor, used highly polished shields to amplify and reflect rays of the Sun on to attacking Roman ships thereby setting them on fire.
On the 4th of April 1931, the headline “Use of solar energy is near a solution” appeared in the New York Times. Although the timeline was a little off, the prediction has come true with millions of humans using solar energy to power their homes and businesses.
Over the past 20 years, the costs associated with solar cells, the structures capable of converting light energy into electricity, have
been steadily decreasing. The National Renewable Energy Laboratory, a US government lab that studies solar cell technology, estimates contributors to the increasing affordability of solar. According to Fu, Feldman and Margolis, “The cost of solar cells is now more than half of what they were in the year 2000”, mostly due to decreasing material costs and an increased ability of cells to capture light. Engineering more cost-effective and efficient solar cells has required careful consideration of the physics involved in solar capture in addition to innovative design.
Because solar cells are used to convert light into electricity, they need to be composed of some material that’s good at capturing energy from light and be inexpensive enough for people to afford. Historically, silicon has been the most popular material for solar cells. Not only is silicon good for converting light to electricity, it is also inexpensive and is one of the most abundant elements on earth. The cost of refining silicon has decreased dramatically since 1980. New “bulk” purification techniques have driven down the cost and these cost reductions have in turn driven consumer demand.
Engineering breakthroughs have also contributed to the efficiency and cost-effectiveness of solar panels. For photons to be converted to energy, they must collide with an electron. To improve the odds of this happening, engineers have formed microscopic pyramids with the silicon. When light is absorbed by this pyramid, it is forced to travel further increasing the likelihood of light colliding with an electron before escaping the cell thereby producing more electricity. Anti-reflective coatings on the glass of the solar panels have improved efficiency by ensuring that there is a higher probability of light hitting an electron before it escapes the cell. Similarly, putting a reflective surface on the back of the solar cells increase the probability of light hitting an electron.
Other technological advances are used in many of the top-quality panels such as Winaico, SunPower, LG, REC, Hyundai and Q-Cells. PERC or passive cell architecture is used in solar panels to allow the absorption of more light photons while PERT
technology is used to improve the diffusion of light.
Another recent innovation is using half-cut or half size cells rather than full size square cells and moving the junction box to the center of the module. This effectively splits the solar panel into 2 smaller panels of 50% capacity each which work in parallel. This has multiple benefits including increased performance due to lower resistive losses through the bus bars (current collectors). Since each cell is half size it produces half the current at the same voltage which means the width of the busbar can be reduced by half in turn reducing cell shading and losses. The lower current also translates to lower cell temperatures which in turn reduces the potential formation and severity of hot spots due to localised shading, dirt or cell damage.
Bifacial cells absorb light from both sides of the panel and in the right location and conditions can produce up to 27% more energy than traditional mono-facial panels. These can be seen used in solar farms or in commercial settings. Bifacial solar panels typically use a glass front and clear rear polymer backsheet to encapsulate the cells which allows reflected light to enter from the rear side of the panel. Bifacial modules can also use a glass rear side which lasts longer and can significantly reduce the risk of failure, with some manufacturers now offering 30-year performance warranties on bifacial panel models.
A technology Symons Energy has found very useful are Power Optimisers. These are small power conversion units attached directly to individual solar panels. Optimisers are designed to supply the optimum voltage for maximum power generation. If a panel is shaded, dirty or underperforming resulting in low voltage or current, optimisers can bypass or compensate for the poor performing panel to provide the optimum voltage to the inverter. Power optimisers from companies such as Tigo and SolarEdge have been available as an add-on component for many years but now both SolarEdge and Tigo are have panels with inbuilt optimisers within the junction box on the back of the panel. SolarEdge differs to Tigo in that the SolarEdge optimisers must be used together with the SolarEdge inverters, while the Tigo optimisers can be attached to any existing panels as an add-on optimiser.
In theory, it is possible for a silicon cell to convert 32% of the Sun’s light energy into electric energy. Solar panels in today’s market convert between 14% and 22% of light energy into electric energy. So, you can see, there is room for potential improvement in efficiency. Around the world, research is moving at an incredible pace to improve the efficiency of solar panels.
Work is being done to add hardware to solar cells to capture more light. For example, a group of engineering students in Switzerland designed an “optical micro-tracker” that is under the glass of a solar panel which funnels concentrated beams of light to the solar cells. This micro tracker tracks the movement of the sun inside the panel using small mirrors. (remember the Egyptians). The panel does not move. They claim a 36% efficiency with this system. It has not come to market yet, but the potential is huge.
Others are working to improve the performance so that they are better at converting sunlight to energy. For example, solar cells with more than one layer of material can capture more photons than cells with a single layer. A recent lab test using solar cells with four layers can capture 46% of incoming light energy. Unfortunately, these cells are too expensive to make them commercially
viable. Research is continuing in the hope that these super-efficient cells will one day reach the market.
Still, other researches are working on ways to reduce the cost of solar panels and the cost of installing them. Some of the research is in “thin-film solar panel” while others such as a team at RMIT, the Royal Melbourne Institute of Technology (RMIT) has developed a paint that can be used to generate clean energy. While Elon Musk’s Tesla has developed roofing tiles that double as solar panels. A research team from the University of Newcastle made headlines last year when they installed a 200-square-metre array of working solar panels on a factory roof in Newcastle. These solar panels were printed on a reel to reel printer. Before you get too excited, although very inexpensive, about $10 per square meter, they are not very efficient and only have a three-year life expectancy.
Currently, the cost of silicon-based solar cells continues to decrease, and, despite predictions to the contrary, the cost of silicon itself continues to decrease. Silicon solar cells are likely to remain popular for the next few years. Alternatives to silicon solar cells have been developed but aren’t far enough along to be commercially viable. But the research continues and breakthroughs will happen