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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.

Scientists reckon that the surface of the Sun is a mind-boggling 4,000,000 °C!

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.

Solar radiation is the electromagnetic radiation emitted by the Sun in the form of heat and light.

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.

The semiconductor material is usually silicon.

When the sun hits a PV panel, it energises the cell and causes electrons to 'come loose' from atoms within the semiconductor. These loose electrons are set into motion by the electric field surrounding the semiconductor. The movement creates an electric current that can be used to power electrical appliances.

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.

CSP systems are primarily used in major power plants or as water heaters on roofs.

CSP systems make up less than 2% of solar energy generation worldwide. This is partly due to falling construction prices for PV panels.

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.

Photothermal solar power is commonly used on roofs to heat water for the home.

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%.

Solar Power blue polycrystalline photovoltaic solar cells StudySmarterFigure 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.

A p-n junction has two terminals, positive (p), which contains an excess of holes, and negative (n), which contains an excess of electrons.

This allows an electrical current to pass through only in one direction.

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.

Experiments using multi-junction photovoltaic cells have shown an efficiency of 46%, the highest for any kind of solar 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.

ARCs work by causing interference. Waves reflected from the coating are out of phase with the waves reflected from the semiconductor. These waves interfere with each other, preventing the reflection of energy.

Did you know that an example of wave interference is oil spills? Oil on water produces rainbow-like bands of colour as light reflection is disrupted.

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.

Many European countries, including Germany, Spain and Belgium, use solar cells to power parking meters.

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.

Solar power technology is most useful on a south-facing roof.

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.

Solar Power satellite photovoltaic cells solar energy StudySmarterFigure 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.

You might be asked to evaluate different renewable energy resources during your exams.

Advantages

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

Nuclear fusion is a reaction where two or more atomic nuclei fuse to form a heavier nucleus and release energy.

  • 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.

Solar Power house roof solar panel StudySmarterFigure 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.

Solar Power - Key takeaways

  • Solar power is the conversion of solar radiation into electrical or thermal energy.
  • Photovoltaic cells are used to convert solar radiation into electricity. They're made of silicon semiconductors. The more semiconductor materials in a solar cell, the more solar radiation it can absorb. Solar cells have anti-reflection coatings to maximise light absorption.
  • Concentrated solar power systems reflect and concentrate sunlight onto a receiver to generate heat. CSP technology is used in major power stations or as a domestic water heater on roofs.
  • Solar power is a portable and renewable source of energy, free from greenhouse gas emissions or pollutants.
  • However, it can be unreliable, as it relies heavily on the weather. As a result, it's most suitable for sunny regions.

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

Frequently Asked Questions about Solar Power

Solar radiation is harnessed and converted into either electrical energy or thermal energy.

Solar power is a zero-carbon renewable energy source. It doesn't emit any pollutants and has no fuel costs.

Photovoltaic solar cells absorb sunlight and convert the light energy into electricity. Alternatively, concentrated solar power systems use mirrors or lenses to concentrate sunlight onto a receiver, where it is converted into thermal energy.

Solar power is energy generated from solar radiation.

Solar power is a renewable energy resource.

Final Solar Power Quiz

Question

Define solar radiation.

Show answer

Answer

Solar radiation is the electromagnetic radiation emitted by the Sun in the form of heat and light.

Show question

Question

What is the semiconductor material in PV cells usually made from?

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Answer

The semiconductor in PV cells is usually made from silicon.

Show question

Question

How do photovoltaic cells generate electricity?

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Answer

Photovoltaic cells absorb sunlight and convert it into electricity.

Show question

Question

How do concentrated solar power systems work?

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Answer

Concentrated solar power systems use mirrors or lenses to reflect and concentrate sunlight onto a receiver.

Show question

Question

How are thermal losses minimised from solar collectors?

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Answer

Insulating material is applied to the back and sides of the solar collector.

Show question

Question

How do solar-assisted heat pumps heat water on a cloudy day?

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Answer

Solar-assisted heat pumps can extract heat from air.

Show question

Question

What is the conversion efficiency of monocrystalline cells?

Show answer

Answer

20%

Show question

Question

What kind of photovoltaic cells are manufactured by melting raw silicon?

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Answer

Polycrystalline cells

Show question

Question

What is the efficiency of multi-junction photovoltaic cells?

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Answer

46%

Show question

Question

How is the surface reflection of solar cells reduced?

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Answer

The surface reflection is reduced by texturing and adding anti-reflection coatings.

Show question

Question

Energy from solar power can be used off the grid.

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Answer

True

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Question

What direction should solar panels face?

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Answer

South

Show question

Question

Solar power generation emits pollutants.

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Answer

False

Show question

Question

How can you store excess electricity generated by solar panels?

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Answer

Excess electricity can be stored in a battery.

Show question

Question

Why is electricity from solar power unreliable?

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Answer

Electricity from solar power can only be generated during sunny daytime conditions.

Show question

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