Solar panels are an ideal method of reducing fuel bills and making a home more energy efficient and environmentally friendly.

 

What are solar panels?

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Solar panel electricity systems, also known as photovoltaics (PV), capture the energy from the sun using photovoltaic cells. These cells are able to generate electricity on an overcast day, not relying on direct sunlight to function.

The cells convert sunlight into electricity which a household can utilise.

What does photovoltaic (PV) mean?

Photovoltaic (PV) describes the process by which a material converts sunlight into electricity. Derived from the words ‘photo’, which is Greek for light, and ‘voltaic’, meaning voltage, photovoltaic basically means electricity from the energy of the sun.

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The benefits of solar PV

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There are several benefits of switching to solar PV:

• Solar is a renewable energy source which can be harnessed everywhere in the world, every day;

• Using solar energy means you will be reducing your electricity bills. The more solar energy you generate, the less you’ll be paying for electricity;

• Solar energy systems typically don’t require much maintenance, cleaning twice a year should suffice.

 

The cost and savings of solar panels

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Most domestic solar PV systems are 4kWp and cost between £5,000 and £8,000. These systems are capable of generating approximately 3,400 to 4,200 kilowatt hours of power a year, depending on whereabouts in the UK you are based and how they have been installed at your property.

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How many solar panels do you need?

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The number of panels you will need will depend upon mainly the size of the space where the panels will be situated and how much electricity you currently consume. Generally, for a 4kWp solar PV system you will need space for 12 to 16 panels as different panels have different wattage capabilities.

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Finance availability & considerations

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If you are looking to purchase a 4kWp solar PV system then it could cost you between £5,000 and £8,000. This is a considerable investment and you may need to look at different finance options available to you. Your options could include:

• Obtain finance from a lender via the installer (if the installer has a finance facility);

• Taking out a personal loan;

• Re-mortgaging your property.

Government grants 

Following the closure of the Feed-in tariff and the export tariff on 31st March 2019, the Government have introduced a proposed replacement in the form of the Smart Export Guarantee (SEG), which, if implemented would see energy providers pay homeowners for energy they generate. 

 

Solar panel efficiency

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Solar panel efficiency is determined by testing panels at Standard Test Conditions (STC), using a temperature of 25°C and an irradiance of 1,000 W/m2 – the equivalent of a sunny day with incident light hitting a sun-facing surface tilted to 37°. A solar panel efficiency of 15% with a 1m2 surface area would produce 150 Watts under these test conditions.

How to calculate the performance

If you would like an estimation of how you can expect your solar system to perform over the years, your installer will be able to calculate this using the following method:

• Take into account the direction of the solar panels facing the sun;

• Take into account the angle of the solar panels;

• Take into account any obstacles surrounding the solar panels which are obstructing the line of sight towards the sun;

• Take into account degradation of the solar panels (i.e. panels performance reduce overtime).

 

The house direction

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In the UK, solar panels are most effective when south facing, as this means they will be facing the sun for the majority of the day. Panels facing north will be far less efficient as they will be facing away from the sun.

Slope of roof

The optimal angle of tilt to position solar panels isn’t straightforward. In the UK, the sun is higher in the sky in the summer and lower in winter, meaning that if your panels are pointing at the position of the sun at midday in midsummer, they’ll maximise efficiency over summer but lose out in winter.

In the UK panels that are tilted at 15° or more have the benefit of being cleaned by rainfall to ensure optimal performance.

 

Shading

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Shade is the nemesis of solar panels, capable of having a really adverse influence on their efficiency. It’s important to assess the area that you have earmarked for your panels in order to establish any nearby buildings or vegetation that could cause an issue. Also, due to changes in the angle of the sun, shadows will be in different positions at different times of the day and year. It would be prudent to gauge this over a six month period. 

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Will solar panels work during the night?

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This simple answer to this is no, as solar panels need sunlight in order to produce energy. However, homes can still be powered at night with the solar energy that has been captured during daylight hours, if the system is linked to a solar storage battery.

 

Performance during the cold winter

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A common misconception is that winter weather will mean lower efficiency. The opposite is often true. Though solar panels are designed to withstand average temperatures, they’re more inclined to function better when they’re cooler. This is true with most electronic equipment. And since solar panels need light (not heat) from the sun, bright winter days can be highly productive. However, as the days are shorter in the winter months, production would be less than in the summer.

 

How well do solar panels work when dirty?

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Significant amounts of dirt and dust can also reduce efficiency. For the most part, solar panels are self-cleaning. A rain shower can clear dirt and dust away, thereby helping your panel regain its efficiency in just a few minutes.

 

Choosing a solar system – which is right for me?

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There are three types of system set-ups for solar panels: Grid-tied, Off-grid and Hybrid. The systems typically require different inverters to manage the set-ups.

1. Grid-tied

Grid-tied solar PV systems are linked with the National Grid so unused electricity can be exported from the home into the grid. With the FITs coming to an end on 1st April 2019 the export tariff is being replaced by the Smart Export Guarantee. Consumers who are currently receiving export payments will not be affected. 

2. Off-grid

Off-grid solar system are not attached to the grid and any electricity not used to power appliances can be stored either by heating water in a tank for domestic use or in batteries.

This system is usually used in remote locations to supplement other off-grid energy sources.

3. Hybrid

A hybrid solar PV system combines grid-tied and off-grid systems. Excess electricity generated can either be exported to the National Grid or stored locally.

As flexible energy develops, hybrid solar systems will enable homeowners to take advantage of emerging smart electricity tariffs. For example, storing renewable solar power in solar storage batteries and selling back to the grid when they will be paid the most for each kWh.

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Type of solar inverters for solar panels

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Solar inverters play a vital role in any solar installation. Their main function is to convert the captured energy from DC to required AC, but they are also used for monitoring and enabling installers and homeowners to keep an eye on how the system is performing. Inverters are also able to provide diagnostic information to make it easier to identify and fix any issues. There are several different kinds of solar inverters and your installer will be able to advise you which one would best be suited to your project.

• String inverters : Each row of solar panels is installed on a string, with multiple strings connected to one string inverter. Each one of these strings transports the DC power from the solar panel to be converted to AC power by the string inverter.

• Central inverters: While similar in function to string inverters, central inverters are much larger and are capable of a greater number of strings of panels. However, these strings are linked to a combiner box, rather than directly to the inverter. Central inverters are best suited for larger installations.

• Microinverters: These are installed on each individual solar panel and convert DC power to AC at the panel, removing the requirement for a string inverter. This allows each panel to be monitored for performance, and if some panels are in shade then it won’t affect the others.

• Power optimisers: These offer many of the same benefits as microinverters, but tend to be slightly less expensive. Power optimisers are often considered a compromise between more expensive microinverters and the standard string inverter.

• Battery based inverter/chargers: Requiring a battery to operate, these can be off-grid, standalone grid-tied or grid-interactive. Battery based inverter/chargers are capable of providing for continuous operation of critical loads, whatever the condition or presence of the grid.

 

Solar panel installation process

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The process of installing solar panels on a roof consists of the following steps:

• Scaffolding: Most properties will require scaffolding if the solar panels are to be installed on the roof. It’s erected to provide a safe work platform for installers to access the roof safely.

• Roof anchors: These are screwed to the rafters of the roof.

• Frame: Aluminium bars are locked into the roof anchors to create a frame, with care taken to ensure that the solar panels will be straight.

• Panel installation: The solar panels are then clamped into the frame, again making certain that they look straight.

• Wiring the panels: This step is quite straightforward as solar panels are already wired by the manufacturer. The connecting wires are attached to the rails of the panels to lift them from the roof tiles.

• Connecting to the inverter: The DC wiring is then connected from the panels into the home, taking care to hide as much of it as possible.

• Internal: A qualified electrician will connect a solar inverter to the property’s electricity supply, as well as a small consumer unit and generation meter next to the existing fuse box.

• Powering up: Once the wiring is complete, the installer will switch on the inverter and power up the system, ensuring that everything is functioning correctly.

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Maintaining your solar energy panels

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Once fitted, your installer should leave written details of any maintenance checks that you should carry out from time to time to ensure everything is working properly. This will include details of the main inverter fault signals and key troubleshooting guidance. Ideally, your installer should demonstrate this to you at the point of handover.

Consult with your installer for exact maintenance requirements before you commit to installing a solar PV system.

How to keep them clean

Solar panels which are mounted at a sloped angle are typically cleaned by rainwater, but certain conditions can require measures to ensure the amount of electricity they generate isn’t reduced, such as dust or bird droppings.

You will need to shut down your system before undertaking any additional cleaning – your manual will instruct you how to do this.

If possible, it’s safest to clean panels from ground level with the recommended materials – these should also be detailed in your manual, or you can ask your installer.