The Sun is an incredibly large source of energy. To put it in perspective, consider this… 18 days’ worth of sunshine has an equivalent amount of energy as what is contained in practically all the natural resources (including natural gas, coal, oil etc.) on Earth.
As of now, there are two methods by which we harness the power of the Sun, i.e. solar energy: Photovoltaic technology and thermal technology. Let’s look at how each of these work.
You have likely seen flat, glass-like structures installed in an angled fashion over rooftops of buildings and solar power plants. These are called solar panels, and they are solely responsible for taking light from sun-rays and running our electric appliances with that energy. The question is… how do they go about doing that?
Photovoltaic (PV) cells
Solar panels consist of the aptly named ‘photovoltaic cells’, which convert sunlight (photo) to electricity (volt). An array of photovoltaic cells make up a solar panel. These cells consist of silicon atoms that lose an electron when sunlight strikes their surface.
It works this way: sunlight consists of extremely small particles called ‘photons’ that are capable of knocking electrons off of the silicon atoms present on photovoltaic cells. These electrons make up direct current (DC), but as most of our household appliances function on alternating current (AC), it becomes important to convert electric current from DC to AC. This is done by another component called an ‘inverter’, which is yet another important element of the system.
The inverter takes the DC formed by the excited electrons and converts it into AC, which is then routed to the main power supply of your house.
From there, that AC reaches different appliances through wires (note that the presence of the inverter in a solar energy system depends entirely on the type of current required by the system). As a result, the moment you flip the switch on, the electric circuit is completed and the bulb lights up!
Since you can only harness solar energy when there’s sunlight (e.g., when it’s not cloudy or rainy), batteries also form a noteworthy part of the system. Power generated throughout the day is stored in the battery to be used when required.
The efficiency range of the PV system typically lies around 20-22%, which means that it converts 20-22% of the sunlight falling on it into electric current. However, in the more common systems found on rooftops, the efficiency is a bit less.
The other method of harnessing the energy from sunlight is through the use of solar thermal technology. This consists of ‘solar collectors’ – devices that capture solar radiation. ‘Flat plate’ and ‘evacuated tube’ are two types of collectors.
The flat plate variant, as its name indicates, consists of a dark flat plate absorber, containing a heat-transport liquid. Evacuated tube collectors, on the other hand, contain multiple evacuated glass tubes containing an absorber plate, along with a transfer fluid (e.g., water).
How does the thermal technology work?
Both of these thermal variants have different components, but the basic functionality remains pretty much the same in both.
In the presence of sunlight, solar collectors heat up and transfer the heat to the heat-transport liquid (typically water, or a mixture of glycol and water in cold regions to prevent the mixture from freezing). This liquid is then transported to a heat-exchanger liquid housed inside the water tank. After transferring its heat to the water in the tank, the heat-transport liquid flows back to the collectors to be heated again. This process is repeated until the desired temperature is achieved.
Note that no electricity is produced in this thermal energy case; instead, heat from the Sun’s rays falling on the system is transferred to another medium, such as water, food, etc.
Therefore, water heaters and solar cookers are some of the most popular examples of systems that utilize solar energy to boil water and cook food, respectively. Solar thermal collectors typically have an efficiency in the range of 60-80%, which is much higher than the efficiency of a PV system.
Solar energy is undeniably a tremendous source of energy that can power houses and offices for extended periods of time. There are some countries that readily promote the use of solar and other renewable energy sources in order to ease the pressure on the limited natural resources on planet Earth and promote good conservation practices. With continuous improvements to the technology of harnessing solar energy, we’re getting closer to a world that is powered and heated purely by the power of the Sun… even at night!