Solar energy is an alternative to traditional ways of generating electricity by burning and processing fossil fuels. Solar panels make it possible for us to harness a clean and renewable energy source, the sun. By installing solar panels, we are able to provide electricity for ourselves and potentially add to the amount of national renewable energy available to others.
The international solar industry is growing exponentially with large amounts of progress being seen in solar technology, making solar energy more and more affordable and accessible.
But how can electricity be generated by the sun and some strange looking panels perched on your roof? This article will explain all you need to know. But first, you need to know a few terms:
Photovoltaic: the ability to produce voltage from radiant energy, particularly light. This usually happens through photoemission (the release of electrons from a surface when it is hit by light).
Direct current electricity (DC): In DC, electricity electrons move in one direction around a circuit or route. Electrons move from the negative side of a battery towards the positive side.
Alternating current electricity (AC): In AC, electricity electrons are both pushed and pulled while changing direction from time to time.
The Different Parts of Solar Energy Systems
Now that we know what these things mean, let’s move on to what you can find inside a solar system and it’s solar panels.
Photovoltaic (PV) solar panels generate direct current (DC) electricity. Many electricity grids use AC electricity as it is cheaper to transmit over long distances. In order to convert DC electricity to AC, an inverter is used.
There are two different kinds of inverters: central inverters and micro-inverters. Central inverters have been most prominently used in solar systems. They convert electricity for the entire system as a whole. Micro-inverters adjust for each individual solar panel. This means that they are able to draw the maximum amount of electricity from the solar array even if one panel in the system is not functioning optimally.
What are Solar Panels Made of?
PV panels consist of a collection of solar PV cells. Each cell is octagonally shaped, bluish-black (for maximum absorption), and roughly the size of an adult’s palm. PV cells have two layers of semiconducting material. This is a material that is neither a conductor, such as copper, nor an insulator, like wood. The important bit of a semiconductor (especially for solar energy production) is that it can conduct electricity under the correct circumstances. In PV cells, this material is usually silicon (not to be confused with silicone – that’s the stuff you put around your bath!).
These cells are combined to make a solar panel. Panels can be linked and fitted to a frame to make a module, and a few modules can be linked together to make a solar array. Users can customize the system to meet their electricity needs by adding more panels for larger quantities of solar electricity, or using less if a lower amount of solar electricity is needed. Usually, a rooftop solar system comprises a few hundred individual solar cells.
How Does Solar Energy Work?
The short answer is that sunlight hits a solar panel. This panel converts the energy to DC electricity, which then passes through an inverter where it converts to AC electricity. The AC current can then be connected and used in your home. About 70% of solar radiation (or energy) that reaches the earth gets reflected back. The remaining 30% is more than enough to meet our energy needs.
What Exactly Happens in the Panel?
Electricity always flows from a negative to a positive charge, and it is this flow that generates a current. Thus, there need to be oppositely charged areas. These areas are created by charging the two pieces of silicon in a photovoltaic cell. They do this through something called doping.
In the doping process, the top layer of silicone is seeded with phosphorus, antimony, or arsenic, adding extra negatively charged electrons to that layer. This is referred to as n-type silicon. Boron, with fewer electrons and as a result has a positive charge, gets added to the bottom layer. This is known as p-type silicon.
When the two layers are placed on top of each other, a sort of barrier is created at the junction of the two layers. Electrons cannot cross this barrier, and at this stage, the cells are essentially useless in terms of energy generation. The magic happens when light is shined onto the cells containing these two layers.
Electrons are knocked free from atoms in the silicone layers when light particles, called photons, hit the panel. These electrons then move into the circuit. They are constantly moving, like a river, and this creates a flow of electricity or current. How I hear you ask?
There are metal conductive plates on the sides of the cell. These plates collect the electrons and transmit them to wires from where the electrons can flow in an electric current. But this is a direct current. This DC then passes through a solar inverter, which converts the DC to AC and works as ground fault protection for the solar panel array. From here, the electrical current goes to an electrical box (also known as a breaker box) from where it can be used in your home or business or sent into the grid.
The electrical field runs in a closed loop. The electrons will move from the solar cells through the inverter, into the building, and back to the cells.
How Much Electricity Can a Solar System Produce?
Energy cannot be created or destroyed; it only converts from one form to another – this is a fundamental law of physics. So, your solar system cannot make more electrical energy than the amount of light energy (or photons) it receives and converts.
Theoretically, a single-junction silicon solar cell can transform about 30% of the energy it received into electricity. This is known as the Shockley Queisser limit. In reality, only about 10-20 % is converted. This is because the photons (or light particles) that makeup sunlight all have different energies and wavelengths, while a solar cell can only tune in to one frequency band. The rest of the energy goes to waste.
Having said that, a single solar cell can generate between 3 and 4.5 watts. One solar module of 40 cells can make about 100 to 300 watts, which means a solar array of 3 – 4 modules can generate only a few kilowatts of power.
Several different factors can affect how efficiently your solar power system generates electricity. This includes how they were constructed, as well as their angle and position where they are installed, and if they are being kept clean. It is also affected by how much sun they get (or if they are in shadow at times), how hot they get, and whether they are properly ventilated.
The amount of electricity generated can be done in large volumes on solar farms. These farms often supply electricity to numerous properties. If the farm is large enough to achieve utility-scale solar farm status, it would be able to sell the energy that it generates to utility companies, who then sell it to the public. While this is one way to increase the national renewable energy resources, these farms need large amounts of solar panels, which tend to take up a lot of space – often space that could be used for food farming.
What About Cloudy Days?
Solar panels can still work, perhaps at a lower efficacy, on cloudy days as sufficient sunlight still reaches the earth’s surface. Contrary to what you might think, cold weather is ideal for solar power generation; in fact, they do much better in cooler conditions with lots of sunshine, than in warmer climates.
Excess Energy
Solar systems might produce too much electricity for a particular household or business. This surplus of energy can be fed to the grid. When this happens, the surplus energy producers are compensated through a system called net metering (recorded by a net meter). Net metering is a way for the energy producers to receive credit for the surplus energy that they supply to the grid. These credits can then be used in instances when they are not able to produce enough electricity for their own demands, like at night. One way to avoid this and cut energy costs completely is to create an off-grid solar panel system where the electricity is stored in a battery via a charger controller.
In net metering, the electricity meter in the producer’s home runs backward while excess electricity is being fed into the grid – providing energy credit to the producer. When the producer needs electricity from the grid, the meter will then start to run forward.
Another form of compensation that is available in some areas is feed-in tariffs. Here, the nearest utility company has to purchase excess electricity from producers at a set rate with the agreement that this will continue for 10 to 15 years. This option gives a return on investment of cash in hand, instead of savings on electric expenses as the net metering system does.
Take Your Electricity With You Wherever You Go.
Portable PV arrays generate an electric current in the same way that their larger counterparts do, but in a much smaller quantity. While mounted PV arrays typically generate around 30 kWh of electricity each day, portable PV systems only generate between 5 to 10% of that.
Solar radiation or energy is used by plants for photosynthesis and absorbed by the ocean where the heat creates wind and currents. The heat can also be used for heating up homes and water systems.
Solar thermal systems (also referred to as solar collectors) use the heat of the sun, or thermal energy (instead of the light), to generate electricity and heat water. For these systems to produce electricity, the heat is added to water to create steam. This steam is then used to turn turbines, which generate electrical current.
Solar thermal systems are dark glass panels or pipes (usually painted black for maximum heat absorption) through which water is circulated. As the water passes through these pipes, it absorbs the heat from the sunlight. The panels of a solar thermal system are positioned to absorb the maximum amount of heat throughout the day. By using this system, users can see massive savings on their electricity bills as no electricity is required for these kinds of solar water heaters.
Solar Power in Everyday Products
While solar power is a relatively new technology, it is already becoming an integral part of our everyday lives. Products like quartz watches and calculators are powered by small solar cells, as are solar-powered garden lights.
They Come in Generations
Most of the world’s solar cells are first-generation solar cells, made from slices of crystalline silicon cut from blocks of lab-grown silicon blocks. These slices can have either single silicon crystal (known as monocrystalline) or multiple crystals (polycrystalline or multicrystalline). Two slices form separate silicon blocks are doped and placed on top of each other, creating a photovoltaic cell with a junction, as explained above.
Solar cells made from monocrystalline cells are often darker (black or dark grey), while polycrystalline cells tend to be dark blue in sunlight. Monocrystalline cells have a higher panel efficiency but are also more expensive. Some solar panel manufacturers combine mono and polycrystalline cells into their modules, giving them the ability to absorb light with different frequencies or wavelengths and making them more efficient.
Monocrystalline cells are better for solar installations where there is limited space available, but polycrystalline panels are cheaper.
The cells are then coated with an anti-reflective coating (for maximum absorption), a plastic backing and glass front and metal connections to wire a cell into a circuit.
Second-generation cells are made up of amorphous silicon. Here the silicon (cadmium-telluride or copper indium gallium diselenide) atoms are not arranged in order like their crystalline counterparts. Instead, the atoms are arranged randomly, enabling the wafers to be extremely thin. While first-generation silicon wafers are around 200 micrometers thin, second-generation wafers are about 100 times thinner than that.
Second-generation solar cells are thin, light, and flexible enough that they can be bonded to windows, skylights, roof tiles, and other backing materials. While these thin-film solar panels are a convenient way to integrate solar generation systems into multiple areas of a home or business, it comes at a cost. While first-generation cells can convert between 15 to 20% of the energy available to them, second-generation cells can convert only between 7 to 11%.
Third-generation solar cells are the baby of the family. Work is being done on combining the best features of first- and second-generation cells. These cells could use amorphous silicon (amongst other materials) to create thinner cells with multiple junctions. The hope is that this would make them cheaper, more efficient, and more practical than their predecessors.
As the need for renewable energy grows, more and more people are choosing to install solar panels not only to provide electricity for themselves but also to build larger capacities of national renewable electricity resources. Solar panel technology is constantly improving and evolving, leading to more efficient and cost-effective solar panels being produced. The way solar energy works is seen by some as having the potential to start an energy revolution. Are you part of it?