You’ve heard about the solar revolution and the dreams to one day have a world powered entirely by solar energy. So what exactly is solar power and how does it work?
Solar is derived from the word ‘Sol’ which is Latin for Sun. Therefore solar power or solar energy is simply a system of collecting the sun’s energy and then transforming it into another form of useable energy.
A form of renewable energy, it reduces the world’s dependence on fuels, improves air quality, and offsets greenhouse gas emissions. Solar power can be used as a heat source or an energy source, leading to a promising solar industry that can stimulate the economy through the creation of work opportunities in its manufacturing and installation sectors. However as ideal as that sounds, the solar energy system is not yet perfected and it still has its cons.
Moving on, how does solar energy work? What does it take to convert the rays of the sun into thermal and electric energy?
Briefly, you can convert the energy via the 2 methods of Photovoltaic (solar energy technology) and solar thermal technology.
Photovoltaic
Photovoltaic technology literality would translate as light-electricity technology; as its name is derived from the words photo and volt.
Photovoltaic devices therefore work the simple physics of changing sunlight directly into electricity. Though also known interchangeably as PV devices or photoelectric cells, photovoltaic devices are much more commonly known as ‘solar cells’.
Solar cells are made from semiconductor materials -commonly thin wafers of monocrystalline, polycrystalline or amorphous silicone that produce electricity by absorbing enough photons.
They come in a variety of sizes that range from anything small to large. A group of these individual solar cells make a solar module and a link of solar modules would result in a solar array.
A photovoltaic system commonly includes solar panels, an inverter and a metering system or charge controller, battery bank and a backup generator, all depending on if the on grid or off grid method is used.
The solar panel serves to gather the energy from sunlight and create direct current (DC) from it, while the inverter serves to convert that direct current into alternating current.
With the on grid solar system, a metering system exists to connect the photovoltaic system to the main electricity network (utility network), stabilizing the power and allowing for the use of traditional electricity when there isn’t enough solar energy and the selling of any access power back to the power grid when there is too much. With the on grid system, you are linked to the utility company and need not worry about energy storage or energy shortage.
Alternatively, if the off grid system is used, the solar power generated is kept regulated by the charge controller and stored in the battery bank. A backup generator set is present to provide power when there isn’t sufficient solar energy left in the battery bank. In the off grid system, you are not linked to the utility company. Your energy system is a standalone unit, independent from the utility power grid.
Solar Thermal Technology
Solar thermal technology is essentially the use of solar thermal collectors to generate heat that will produce enough steam to power a generator, thereby creating electricity. The science is identical to that of the conventional steam power, only in solar thermal technology; photons from the sun are used instead of fuel to generate the heat.
There are solar power plants and solar power towers. Both apply the technology of solar thermal power amidst some differences in the appliances used.
Solar Power Plant
The main elements employed in a solar power plant are:
- Parabolic trough collectors,
- Evacuated absorber tube receivers;
- Heat transfer fluids,
- Heat exchanger,
- Turbine generator, and
- Condenser/cooling tower
These elements work together in a fairly straightforward manner. Troughs will focus the sun’s energy into the receiver tubes, heating the thermo oil within with solar radiation, thus allowing it to generate steam in the heat exchanger.
After which the steam is then directed into the turbine generator where is it pressurised to produce electricity. The cooling tower then serves to transfer the waste heat back into the atmosphere.
Solar Power Towers
Also known as the Heliostat Power Plant, the main elements engaged in this system are:
- Heliostats which are large sun tracking mirrors
- Collector tower
- Heat transfer fluid/material such as molten nitrate salt
- Thermal storage tank
- Steam generator
- Turbine generator
- Condenser
Just as with solar power plants, solar power towers also employ solar radiation to generate electricity via steam. The main difference is the use of heliostats, which work to focus the sun’s rays at the receiver on top of the collector tower.
The heated heat transfer material within the receiver is then directed into a thermal storage tank and pumped as required into the steam generator. The steam generated then powers the turbine to generate electricity and the condenser completes the Rankine cycle.
The use of solar power is time old and the idea behind it is simple. It is the mechanisms it involves that makes it take more complex as cost and environmental factors leaves us with much more to consider.
Image source: NASA