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How does solar energy work?

The Sun is a gigantic nuclear reactor in our solar system, at any one moment in time it produces 386 Septillion Watts of energy.

By, Ricky Goacher | Uploaded: 04/02/2020

The Sun is a gigantic nuclear reactor in our solar system, at any one moment in time it produces 386 Septillion Watts of energy - that's 24 zeros if you're wondering. The solar energy from the sun takes around 8 minutes and 20 to reach the Earth, if this energy was to be appropriately utilised and processed, it could easily satisfy mankind's appetite for energy. More importantly, it's a free and infinite energy source! The more perceptive of you will be thinking, but all energy produced by the Sun does not reach the Earth and of course you are right, but the Earth still intercepts a vast amount of solar energy, 173,000 terawatts actually - 10,000 times more than the planet uses. So how does solar energy work and how can we utilise it?

How does solar power work?

To answer this we must first look at how the Sun heats up our planet. The Sun releases energy in the form of photons. A photon is a bundle of electromagnetic energy. It is the basic unit that makes up all light and is sometimes referred to as a "quantum" of electromagnetic energy. Photons travel with the speed of light in a Vacuum of Space. They have no mass, they carry energy from the Sun, but they're electrically neutral - they don't carry any charge. However, when the photons encounter matter, they may be absorbed and transfer their energy to the atoms and molecules. So when the photons hit the surface of our planet, the energy turns into heat - the warmth you feel when you're sat outside on a sunny day.

About 40% of the solar radiation reaching our planet is reflected by the atmosphere, 20% is absorbed by it, and the other 40% of the energy reaches the Earth's surface. However, the sunlight is not evenly distributed across our planet. How much of it we actually get depends mostly on the positioning of the Earth in co-relation to the Sun, which determines the seasons and time of day. Latitude, so our location on the globe is also a crucial factor in this matter.

Though there's vast amounts of solar energy lost before it reaches the surface, there is a growing number of industries exploring the possibilities of harnessing solar energy from space. The Japanese company Mitsubishi Electric has planned a project called the Solarbird, which aims to launch 200m solar energy capturing satellites with reflective mirrors that will orbit 22,300 miles over the equator.

Solar panels

Solar energy is used in both industrial, commercial, and residential sectors by installing solar panels - devices that enable the light to be converted into energy that can be utilised by humans. There are two types of solar panels: photovoltaic panels, which turn the light into electricity, and photothermal panels that use light to heat water or other fluids that are stored in hot water cylinders. But just how exactly do these panels work? Solar panels are made of a collection of cells which work in unison to provide adequate amounts of energy. The more light hits the cells the more energy is produced, but it's worth keeping in mind that the panels have their capacity limits - they are not going to produce more energy than they were designed to, no matter how intense the sunlight is. However, on a cloudy day the amount of energy generated will be lower than it would be when the sky is clear. Let's take a closer look on the types of panels and what they actually do.

Photovoltaic panels

Photovoltaic cells that are located in PV panels consist of semiconductor components mostly made of silicon, rarely germanium or selenium. When exposed to sunlight, the cells produce a so-called p-n (positive-negative) junction, which is a boundary between two types of a semiconductor material, p-type and n-type, as the photons striking the cell cause a positive and negative layer of electrical voltage. This is the crucial part that makes it all work. The "p" side contains an excess of electron "holes", so when sunlight hits the silicon it knocks the extra electrons out of place, making them flow into the "n" section of the cell where the electrons are missing. This flow creates an electrical current that is then directed to an inverter that converts it into a usable form - acting as an electrical cell. This process is called a photovoltaic effect.

Typical silicon photovoltaic cells measuring approximately 6 inches long and 6 inches wide produces a current of between 3 and 4A and a voltage of approximately 0.5V, generating 1.5-2?Wp?of power in standard conditions. Of course, it all depends on various factors such as irradiation (how exposed the panels are to radiation). The solar cells are connected in a series circuit, forming batteries. When these cells are combined, they become a solar panel. Most solar panels for residential house's rooftop installation are made of 60 solar cells.

Photothermal panels

Solar thermal heating uses solar energy as a heating system. The solar panels called collectors are located on the roof. They vary in size from about 20-160 square feet. There are two main types of collectors: simple flat plate and a more advanced evacuated tube. Flat plate collectors capture the heat via special glass pipes that are filled with a heat transfer fluids (like water). Most systems also use antifreeze (e.g. propylene glycol) in these fluids as a freeze protection. These pipes are kept in an insulated container in order to prevent any heat loss. Heat collected by the panel heats up the heat transfer fluid that is being pumped using a small electric pump through a circuit of pipes into a copper coil in a hot water tank, located inside of the property, and that's where the heat's being stored. Then the cooled down fluid returns to the collector and picks up more heat. Note that the liquid entering the water tank does not stay there, but keeps circulating within the pipes between the collector and the tank. This system can be operated from a thermal controller that can be automated to best suit user's needs.

Evacuated collectors are less popular than flat plates. They consist of rows of glass pipes all aligned parallel to each other of 2-4 inches diameter. In each one of these pipes there is an another separate pipe made of copper, in which the liquid flows. This second pipe is connected to an absorber, which can be either flat or applied to the surface of the pipe. The void created inside of the glass pipe massively helps reducing the heat loss. This is due to the lack of convection - there is no external force involved causing any motion. The heat stays within the system, therefore the absorber heats up more efficiently and this is the reason why the evacuated collectors work better in cold climate and during winter months.

Advantages and disadvantages of solar energy

Solar energy technology has its advantages and disadvantages. In certain locations and markets it can be far too expensive. However as technology improves it is becoming far more cost competitive to fossil fuels.

Advantages of solar energy:

  • It is a renewable energy source.
  • here is a plentiful supply of solar energy.
  • The use of solar energy is sustainable. The Sun is not going to burn out any time soon and even if it did, we would have far bigger problems to worry about.
  • No emissions during operation. There are some emissions with the production and transportation of solar panels but this is minimal when compared to fossil fuel power station emissions.
  • Solar energy is available all over the globe.
  • Reduces cost of electricity bills when fitted to homes.
  • Solar energy has many uses and applications.
  • No noise pollution, some other renewable energy sources (such as wind turbines) can make some undesirable noises.
  • Lots of government or state subsidies available for businesses and homeowners. In some places the cost of photovoltaic solar panel systems can be halved.
  • Solar energy systems generally do not require much maintenance. Mainly just an occasional clean once every 6 months.

Disadvantages of solar energy:

  • Initial set-up cost of solar energy systems are quite high.
  • Solar energy output is not consistent, it depends on factors such as time of day and the weather.
  • Energy storage solutions such as batteries are expensive, so smoothing out the inconsistencies in the output is not as cost effective as some alternative energy sources.
  • Manufacturing solar panels is associated with nitrogen trifluoride and sulphur hexafluoride emissions.
  • Expensive and rare materials are needed for certain solar cells. Such as cadmium telluride (CdTe) or copper indium gallium selenide (CIGS).
  • Solar energy farms require vast amounts of space.

Bright future for solar energy?

  • The future of solar energy looks bright. In the age when people are struggling with conventional fossil fuels because they're either running low or cause a lot of environmental damage, the energy from the Sun makes a brilliant alternative. And more importantly, it is a renewable source. Solar panels become more and more popular across the globe, not only for industries but also for domestic use. Although it's not the cheapest investment, in the long term it significantly reduces the cost of energy bills. Technology is constantly improving, projects currently ongoing in the fields of nanotechnology and quantum physics have a potential to triple the output of solar panels. The potential for the future of solar energy is incredible and may light the way to securing mankind's future energy demands.