A guide to solar power and solar panels

In spite of our often questionable weather, solar panels are becoming an increasingly ubiquitous sight across the UK. But how exactly do they work, and can you really save money on energy bills by installing them?

Read on to find out.

What is solar power?

Energy created by the heat and light from the sun is called photons, or solar energy. Certain technologies capture these photons to create electric or thermal energy.

How does solar power work?

There are two main types of solar power technology:- solar photovoltaics (PV) and concentrating solar-thermal power (CSP).

Solar photovoltaics (PV)

Solar PV materials and devices convert sunlight directly into electrical energy. A single photovoltaic device is known as a PV cell, or solar cell.

A PV cell is made of semiconductor material. When photons from the sun hit a PV cell, they can either be reflected, passed through, or absorbed by the semiconductor material. The photons that are absorbed provide the energy to generate electricity, and when enough of this solar energy is absorbed, electrons - each carrying a negative charge - dislodge and migrate to the surface of the cell. This migration causes an imbalance of the cell's front and back surfaces and results in a voltage potential similar to the negative and positive terminals of a battery.

If electrical conductors are attached to the positive and negative sides of a solar cell, it absorbs these electrons to create an electrical circuit, generating electricity.

The most common form of solar PV cell is usually covered in glass and surrounded by an aluminium frame to form a solar panel. These panels can be installed on the roof of a house for residential use, or even used to create a large-scale solar farm.

Solar PV panels are the most common type of solar PV technology.

Concentrating solar-thermal power (CSP)

Concentrated solar thermal uses the heat from the sun to create large-scale power generation. Using a field of mirrors, it reflects sunlight onto a device called a receiver, which transfers the heat to then be used as electricity or stored for later use in a thermal energy storage system. Energy can then be released from this storage system as and when needed.

CSP is most commonly used in large power plants.

Solar PV panels: how do they work?

The sun releases tiny packets of energy called photons, which travel nearly 150 million kilometres to Earth. It is estimated that the amount of photons that strike the Earth's surface in 90 minutes is sufficient to handle the entire world's energy consumption for a full year.

With solar PV panels, when photons strike a solar cell, they loosen electrons from their atoms. If conductors are attached to the positive and negative sides of a solar cell, it forms an electrical circuit. When electrons flow through this type of circuit, they generate electricity.

There are multiple cells in a solar panel, and the more panels you have, the more energy you can generate.

How do solar panels generate electricity?

PV solar panels generate direct current (DC) electricity. You now have solar panels working efficiently to transform sunlight into electricity, but the electricity generated is called direct current (or DC) electricity, which is not the type of electricity that powers most homes, which is alternating current (or AC) electricity. Fortunately, DC electricity can easily be changed into AC electricity by a gadget called an inverter. In modern solar systems, these inverters can be configured as one inverter for the entire system or as individual microinverters attached behind the panels

Solar panels transform sunlight into electricity, but this electricity is called direct current (DC) electricity. The type of electricity that powers most homes is alternating current (AC) electricity. To convert DC electricity into AC, a device called an inverter is used. An inverter is installed with your solar panels.

Once converted from DC into AC electricity, it runs through your electrical panel and is distributed throughout your home to power your appliances. Because it works the same way electric power generated by the grid from your energy supplier, nothing within the home needs to change. And because you'll remain connected to your traditional power company, you can draw additional electricity from the grid to supplement any shortage of energy from your solar panels.

Types of solar panels

In the UK, there are three main types of residential solar panels available: monocrystalline, polycrystalline, and thin film.

Monocrystalline solar panels

Monocrystalline solar panels are so called because they are made of one piece of silicon. Although generally regarded as the most expensive type of solar panel on the market, they are also the most efficient and can be identified by their black colour and octogonal-shaped cells.

Polycrystalline solar panels

Unlike monocrystalline panels, polycrystalline solar panels are produced by melting a number of pieces of silicon together into square moulds, forming the solar cells. Polycrystalline panels are cheaper and easier to produce than monocrystalline. However, because there are numerous crystals in each of these cells, there is less space for electrons to move, meaning a lower efficiency rating compared to monocrystalline cells.

Polycrystalline panels are cheaper and easier to produce than monocrystalline ones and look blue in appearance.

Thin-film solar panels

Because they require less material than monocrystalline and polycrystalline to be produced, thin-film solar panels are the cheapest type of solar panel on the market. Thin-film solar panels are created by placing several thin layers of photovoltaic (PV) material on top of each other. There are various types of thin-film cells, including silicon, cadmium, and copper.

Compared to monocrystalline and polycrystalline, thin-film panels are the least efficient. However, because they can be wrapped around objects, thin-film solar panels are a great choice for homes with limited roof-space.

Solar panel cost

With advancements in solar energy technology, the cost of solar panels has fallen dramatically over the last few years.

An average 4kW solar panel system covering 29 square meters of your roof currently costs around £6,400. And, although it is estimated that the inverter will need to be replaced every 10 - 15 years (£500 - £1,000), the solar panels themselves once installed, require very little maintenance and can last for more than 30 years.

How much could I save on energy bills with solar panels?

How much energy your solar panels will generate, and therefore how much you can save on your energy bills, depends largely whereabouts in the UK you live.

For example, a home situated in the South of England will likely generate much more solar energy than a household in Scotland.

Other factors such as the direction of your roof, and how much time you spend at home is important to consider, too.

Using these metrics and more, the Energy Saving Trust has an energy calculator that can help you work out how much you're likely to save.

Pros and cons of solar power

Pros

• Because at least some of your energy needs will be met using the electricity generated by your solar system, your energy bills will drop.
• Can take advantage of the Smart Export Guarantee (SEG).
• Solar panels are incredibly low maintenance. Depending on the type of solar panels you opt for, they can last up to 30 years. 

Cons

• The amount of solar energy you'll generate is largely dependent on the weather.
• The Feed-In-Tariff (FIT) scheme, - where you would be paid for solar energy fed into the grid - has now closed.
• The up-front costs involved for installing solar panels can be expensive.

What is the Smart Export Guarantee (SEG)?

The Smart Export Guarantee (SEG) is a government-backed scheme that compels energy suppliers to pay you for any solar energy you "send back" to the grid. This is electricity you have generated but don't use yourself.

The Smart Export Guarantee was introduced in January 2020 as a replacement to the now-defunct Feed-in-Tariff (FIT) scheme.

All energy suppliers with more than 150,000 customers must offer an SEG tariff, but smaller suppliers can opt in, too.

A fixed-rate SEG tariff pays out a fixed amount per kWh of electricity you export to the National Grid.

A flexible-rate tariff pays a different rate per kWh depending on how valuable the electricity is to the grid at different times. In this case, you may get more money than a fixed-rate if there is a high demand.

Finally, a multi-rate tariff offers a fixed amount paid depending on the time of day e.g., day and night rates.

Solar panel installation

Installing solar panels is very much a professional’s job. If fitted to your roof, you’ll need the services of a surveyor to check if your home is suitable for solar panels and scaffolding to allow the workmen to gain access and install the panels safely.  

Your installer and system should meet the standards of the Microgeneration Certification Scheme (MCS). This certificate ensures your panels have been adequately tested and fits the criteria of the Renewable Heat Incentive. The actual installation involves fixing brackets to the roof and clamping the solar panels to these brackets. 

Installing solar panels at home should only take a day or two and will require little to no maintenance over a 25-30 year period. And, unless your property is a listed building or in a conservation area, you won’t usually need planning permission to install solar panels.