Solar Power

Nuclear fusion takes place inside the Sun's core. The protons in hydrogen atoms violently collide and fuse to form helium. This process emits a gigantic amount of energy in the form of electromagnetic radiation, providing the Sun with continuous power and heat.

After eight and a half minutes, this electromagnetic radiation reaches the Earth, providing more energy than humans could ever need. Enough sunlight hits the Earth's surface every ninety minutes to power humanity for an entire year! Solar power technologies utilise this energy, converting it into heat and electricity.

Solar Power Generation

Solar radiation is the scientific term for sunlight.

So, solar power generation is the conversion of solar radiation into energy. Solar radiation is used to produce electrical energy and thermal energy (i.e. heat).

Types of Solar Energy

Solar radiation is used to produce electricity or thermal energy. Each product uses a different type of solar energy technology. Photovoltaic panels convert solar radiation into electricity, while concentrated solar power converts the radiation into thermal energy.

Photovoltaic (PV) Panels

PV panels are comprised of lots of tiny solar cells. These cells are made from thin layers of semiconductor material between layers of glass.

Concentrated Solar Power (CSP)

CSP systems use mirrors or lenses to reflect and concentrate sunlight onto a receiver. Concentrated solar energy is converted into heat, which is used to produce electricity or stored for later use.

Solar Power Systems and Technologies

Solar power systems and technologies are constantly advancing. In the future, solar power will be an affordable, efficient source of zero-carbon power.

Concentrated Solar Power

Photothermal Solar Power

This form of CSP technology converts solar radiation into thermal energy. Radiation is directed at a solar collector. These devices require a solar-absorbing surface in thermal contact with the medium being heated (usually fluid or gas). Thermal losses are minimised by insulating material at the back and sides of the collector.

Heat Pumps

Heat pumps are combined with a solar connector to provide hot water in the home. These solar-assisted heat pumps can extract heat directly from sunlight and even air! This allows the system to produce hot water on a cloudy day. Solar-assisted heat pumps can even meet heating requirements for small or thermally efficient houses.

Photovoltaic Solar Power

Types of PV Cells

There are three types of PV solar cells, categorised by their semiconductors.

• Monocrystalline: these dark-coloured PV cells are made of thin slices of silicon cut from a single crystal. The high silicon purity enables over 20% conversion efficiency.

• Polycrystalline: these blue PV cells are made of thin slices of silicon cut from a block of crystals. They're manufactured by melting raw silicon, which is a faster and cheaper process than manufacturing monocrystalline cells. However, polycrystalline cells have a lower conversion efficiency of 15%.

Figure 1: This solar farm is made using polycrystalline cells, unsplash.com.

• Thin-film: films of photovoltaic material are placed onto a base made of glass, plastic, or metal. The photovoltaic material itself can be silicon, cadmium or copper. These cells are the easiest and cheapest to make because they require fewer production materials.

  However, they are less efficient than crystalline photovoltaic cells.

Multi-junction Photovoltaic Cells

These solar cells contain multiple semiconductor materials. The boundary between two different semiconductor materials is known as a p-n junction.

Each junction produces an electric current in response to varying wavelengths of light. The more semiconductor materials that are used, the broader the range of wavelengths that can be absorbed, thus the higher the electrical conversion efficiency of the cell.

Anti-reflective Surfaces

Bare silicon has a high surface reflection of over 30%. This reflection is reduced by texturing and applying anti-reflection coatings (ARCs) to the surface.

Energy from Solar Power

Energy from solar power can be used to generate heat and electricity at a variety of scales. Tiny solar cells can be used to power simple devices, like calculators, phone chargers, or camping torches.

At a household scale, it's not uncommon to see solar power technology on roofs. CSP systems utilise the sun's energy to heat and store hot water, whilst PV cells generate free electricity.

At an industrial scale, hundreds of panels are combined to make a solar farm. Alternatively, major power stations use CSP technology to heat water to produce steam. The steam drives turbines that power generators, producing electricity.

Energy from solar power is incredibly useful in remote areas. It can produce electricity off the grid in areas with limited supplies of clean water. This is important because most forms of energy generation require water (for fuel extraction, processing, or water power). In these areas, clean water can be prioritised for irrigation.

Figure 2: Photovoltaic cells are used to power satellites in space, pixabay.com.

Storing Solar Energy

Energy from solar power can be stored to respond to fluctuations in demand.

The most common method of storing solar energy is a battery. Made of either lithium-ion or lead-acid, these batteries store the energy as chemical energy. When the demand for energy is high, the battery can be switched on and produce electricity. Alternatively, solar energy can be stored as heat. The hot fluid is stored in rooftop CSP systems or underground pipes.

Solar energy can also be stored mechanically as an alternative to battery storage. Technology includes:

• Flywheels: accelerate a rotor at a very high speed and maintain the energy as rotational energy.

• Pumped water: pumping water uphill where it is stored as gravitational potential energy. When the energy demand becomes high, the water is forced through turbines which generate electricity.

• Compressed air: energy is stored in the form of heated compressed air and released into a turbine when the demand for energy increases.

Solar Power: Advantages and Disadvantages

No energy resource is perfect! It's important to understand the benefits and drawbacks of solar power.

Advantages

• Renewable: as long as the sun releases radiation from nuclear fusion, we'll have an unlimited supply of solar power.

• Clean: solar power is a green, zero-carbon source of energy. It doesn't release any Pollutants or greenhouse gases.

• Free: sunlight has no fuel costs.

• Saves Money: solar technology can be used to power homes, saving on electricity and energy bills.

Figure 3: This neighbourhood is making the most of the good weather - and lowering their electricity bills, unsplash.com.

• Storage: excess electricity can be stored in a battery until it's needed.

• Low Maintenance: solar technology is long-lasting and requires little maintenance.

• Off-grid Capabilities: unlike many other Energy Resources, solar energy can be used anywhere in the world (or even in space).

Disadvantages

• Unreliability: electricity can only be generated during sunny daytime conditions. During the night or overcast conditions, households must rely on the National Grid for power. Solar power alone cannot respond to demand surges, such as on weekday evenings.

• Weather-dependent: solar farms are most effective in sunny countries. Furthermore, CPS technology may only produce very hot water in warm, sunny climates. Temperate regions like the UK may need to be supplemented with a boiler.

• Expensive: installing solar power technology has a high initial cost. Furthermore, storing electricity to use later requires a costly battery.

• Space: solar power systems and storage batteries take up a large area.

The energy from the Sun can be converted into electricity using photovoltaic solar cells or converted into thermal energy using concentrated solar power technologies. Solar power is a clean and renewable source of energy, albeit weather-dependent.

^{1. Christiana Honsberg, Anti-Reflection Coatings, PV Education, 2022}

^{2. Energy.Gov, Solar Energy Technologies Office, 2022}

^{3. Frank Dimroth, Four-Junction Wafer-Bonded Concentrator Solar Cells, IEEE Journal of Photovoltaics, 2015}

^{4. Hossein Karami Lakeh, Photovoltaics: Everything You Need in One Guide, Green Match, 2021}

^{5. Professor Johan Lilliestam, After the Desertec hype: is concentrating solar power still alive?, ETH Zurich, 2017}