consumers, businesses and organisations that are seeking to generate greener energy as well as save on their energy bills. Indeed, most of us are familiar with the look of photovoltaic panels and rightly perceive solar energy as energy which is generated by the sun rays that reach photovoltaic panels. However, there is much more to solar energy both in terms of set-up as well as the types of solar energy. This article will shed some light on the different types of solar energy so that our readers can make better informed choices when choosing the kind of solar energy that they would like to see installed in their homes.
Solar energy technology is based on the ability to convert the sun’s light into usable energy. But it can do so in a variety of ways in order to provide heat, light, hot water, electricity, and even cooling to houses, buildings or even industrial complexes.
The most common types of solar energy
One of the most common ways to use solar power is to use photovoltaic systems or as they are also known solar cell systems, which produce electricity directly from sunlight. The basic principle behind this technology is similar to what we see in clock or calculators that are powered by the sun! The semiconductor materials used in these solar energy systems absorb sunlight which creates a reaction that generates electricity – to be exact, the solar energy knocks the electrons loose from their atoms which makes them flow through the semiconductor material and produce energy. Today, solar panel technology can absorb and convert into energy most of the visible light spectrum and about half of the ultraviolet and infrared light spectrum¹,².
Solar cells are typically combined into modules that hold about 40 cells and as a whole can measure up to several metres on the side. Because of their adjustable size and share, these flat-plate photovoltaic arrays can be mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day. Several of these photovoltaic arrays would be needed to provide enough power for a household; but for a large electric utility or industrial applications, hundreds of arrays would be required and these would be interconnected to form a single, large photovoltaic system².
What is more, this type of technology can also be run with thin film solar cells which use layers of semiconductor materials only a few micrometres thick. This has made it possible for solar cells to double as rooftop shingles, roof tiles, building facades, or the glazing for skylights or atria maximising use of the available space from where sunlight would be captured.
There have been major improvements in the efficiency of this technology particularly in terms of capturing and converting sunlight. For example, the first solar cells, built in the 1950s, had efficiencies of less than 4%. Today’s technology, on average, offers efficiencies of around 15% ².
A second type of solar energy is solar hot water which as the name suggests involves the heating up of water using the sun’s heat. The idea behind this comes straight from nature: the shallow water of a lake or the water on the shallow end of a beach is usually warmer compared to deeper water. This is because the sunlight can heat the bottom of the lake or seashore in the shallow areas, which in turn, heats the water. So, a system has been developed to imitate this: solar water heating systems for buildings are made up of two parts, the solar collector and a storage tank. The most common collector is called a flat-plate collector which is mounted on the roof and faces the sun. Small tubes run through the box and carry the fluid – either water or other fluid, such as an antifreeze solution – to be heated. As heat builds up in the collector, it heats the fluid passing through the tubes. The storage tank then holds the hot liquid. Similar technology is often used to heat swimming pools³.
A third way we can harness the sun’s power for energy is solar electricity; this is usually used in industrial applications. As most of us know, most power plants use non-renewable fossil fuels to boil water. The steam from the boiling water makes a large turbine rotate which in turn activates the generator to produce electricity⁴. This way of generating electricity is bad for both the environment and our health given the emission of greenhouse gases and air pollutants from the burning of fossil fuels. However, the good news is that a new generation of power plants is being introduced which rely on solar power! These plants use the sun as a heat source, and they can do so in three different ways:
- Parabolic-trough systems capture the sun’s energy through long rectangular, curved mirrors that are tilted toward the sun. In this way, they help focus sunlight on a pipe that contains oil. The oil is heated and used then used to boil water in a conventional steam generator to produce electricity.
- A dish/engine system uses a mirrored dish resembling in shape a very large satellite dish which collects and concentrates the sun’s heat onto a receiver. This receiver absorbs the heat and transfers it to the fluid within an engine. The heat causes the fluid to expand against a piston or turbine and produces mechanical power. This power is used to run a generator or alternator to produce electricity.
- A power tower system uses a large field of mirrors to concentrate sunlight onto the top of a tower, where a receiver containing molten salt sits. The salt’s heat is used to generate electricity through a conventional steam generator. Molten salt retains heat efficiently, so it can be stored for days before being converted into electricity. That means electricity can be produced on cloudy days or even several hours after sunset.
A further way that solar power can be harnessed is through the method of passive solar heating and daylighting. This is not a new concept – indeed, ancient civilisations such as the Anasazi Indians in Colorado had developed passive solar design in their dwelling ⁵. The impact of the sun is easy to understand: step outside on a warm sunny day and you can feel the sun. With proper design, buildings can also “feel” the sun’s energy. For example, south-facing windows will receive more sunlight while buildings can also incorporate materials such as sunlit floors and walls that absorb and store the sun’s heat. These materials heat up during the day and slowly release the heat at night when heat is most needed. Other design features such as a sunspace, which resemble greenhouses, concentrate a lot of warmth which with the right ventilation can be used to heat an entire building⁵. Such features maximise the direct gains from the sun’s heat but also sunlight itself. The even better news is that on particularly hot days, there are ways to ensure these features do not overheat buildings.
The sun is truly fascinating, no wonder our world evolves around it!