Solar Panels

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How to buy solar panelsSolar panels
In a single hour the sun transmits more energy to the earth's surface than the world uses in a year. At present we don't make the most of this free and plentiful resource.

Passive solar power

Solar panels enable you to harness the sun's energy There are cheap and easy ways to capture the sun's energy. Passive solar power involves designing or redesigning your home to make the most of the sun. For example, you might add an extra south-facing window or more insulation to your roof so you can hold onto the sun’s heat longer (see our guide to choosing insulation). These ‘passive’ elements can be added when a house is built or undergoes major refurbishment. If you can't alter your home easily you should consider actively collecting the sun's energy and making use of it.

Active solar power
Active solar power involves installing a collector, usually a panel, to collect energy. No longer just the domain of specialist retailers, solar panels are now available from some larger high street DIY stores, such as B&Q. There are two mains types of active solar panel systems, solar water heating and photovoltaic (PV) solar panels. 50% How much you could save on annual water bills by using solar panels

Solar water heating
Solar panels fitted to your roof heat water for use around the home. An average household can save about 50% of the annual cost of hot water using solar panels and these are the solar panels you most commonly see on homes around the UK. There are two main types of solar water heating panels – flat plate and evacuated tubes (referring to the way in which water interacts with the panel). Evacuated tubes are more efficient than flat plate versions, so are often smaller but generate equal amounts of hot water. There are also drain back systems. These drain water from inside the solar panel when the pump is switched off to prevent water freezing or boiling inside the solar panel.

Choosing a solar water heating system
When choosing a solar water heating system, you’ll need to consider a number of factors including your average hot water usage, the area of south facing roof, the existing water heating system and your budget. You'll need roughly one square meter of collector area per person in the household. Each metre of panel area will need between 30 and 60 litres of water tank volume. If you use a less efficient collector (like flat plate solar water heating panels), you’ll need to cover a larger area than if you use a more efficient collector (like evacuated tubes). You'll also need to select system components (like a hot water cylinder, controls and pipe

work) and choose the location for your panels considering shade, pipe runs, roof pitch and future access.

Solar water heating can provide about a third of your hot water needs A competent installer will be able to assess your needs and property to work out the best system to suit you.

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Solar water heating can provide you with about a third of your hot water needs and about £40 a year off your hot water bills, depending on the fuel replaced. Solar energy is free, plentiful and clean.

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Provides hot water but not electricity. An unshaded, south-facing location is necessary to install solar panels. Initial costs are higher than conventional electric and gas-heater systems. Solar panels can be heavy, so your roof must be strong enough to take their weight, especially if the panel is to be installed on top of existing tiles. Solar panels are expensive compared to the amount of electricity they'll produce in their lifetime.

Photovoltaic (PV) solar panels
PV solar panels generate electricity from the sun's energy rather than just heating your water. You’re more likely to see these on offices or large developments than on homes. You can use PV systems for a building with a roof or wall that faces within 90 degrees of south, as long as no other buildings or large trees overshadow it. Less energy will be generated if the roof surface is in shadow for parts of the day. The are three basic types PV panels: monocrystalline, polycrystalline (or multicrystalline) and amorphous. All are made from silicon, but differ in the way the silicon is cut and treated to create collar cells. To install a system you need to decide how much electricity you want to generate. After submitting details of your property, a PV installer should help you to conduct a site survey and discuss your options with you.

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Only daylight is needed to create energy – not sunshine. Can be connected to the national grid and any excess electricity sold back to an electricity company. Can cut average household electricity bill by about 30%. Solar energy is free, plentiful and clean.

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A large roof area is needed to generate lots of energy. Significantly more expensive to buy and install than solar water systems.

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Solar panels are expensive compared to the amount of electricity they'll produce in their lifetime. The efficiency of solar panels depends on the number of solar light hours and climate. Initial costs are higher than conventional electric and gas-heater systems. An unshaded, south-facing location is needed for installation. Solar panels can be heavy, so your roof must be strong enough to take their weight, especially if the panel is to be installed on top of existing tiles.

How to buy solar panelsBuying solar panels

Solar panels should be mounted on a south-facing roof You'll need to put some time into investigating which system will be suitable for your needs and home. There are two main types of solar panel – those that heat water and those that generate electricity (photovoltaics). See 'Solar panels explained' to help you decide which is best for you.

Choosing a location for your solar panel
For maximum efficiency, solar panels should be mounted on a south-facing roof at 30 degree angle to the horizontal (up to 65 degrees will still work in the UK) and away from the shadows of trees, buildings or chimneys. Some panels require regular checks of the unit and connections, or a wipe of the panel glass with mild detergent. Bear in mind how difficult this will be when panels are up on your roof. You'll need to consider both the type of system and how to install it carefully to get the best solar panel system for your home.

Planning permission
You won’t need planning permission for most domestic solar panels, as long as they respect certain size criteria. Exceptions apply for listed buildings, buildings in conservation areas and world heritage sites, so it’s best to inform you local authority of your intentions.

Installing solar panel systems
A solar water heating system includes pipe work, a thermostat and hot water cylinder, while a photovoltaic system includes inverters, switchgears, cables and more.

Solar water heating panels can be added to most hot water systems You can add solar water heating panels to most existing hot water systems, though you’ll usually need to add an additional cylinder for pre-heated water, or change your existing cylinder for one with a twin coil. It’s difficult to use a solar water heating system with a combi boiler because these are designed to take cold mains pressure water and solar water heating systems supply low pressure warm water. Some new combi boilers accept pre-heated water so check with the manufacturer. The type boiler you have is not an issue if you choose a photovoltaic system.

Professional installation
You’ll have to use an accredited installer if you want a government grant towards the costs of your solar power system. In this case start your search for an installer on the Low Carbon Buildings website. There are lots of solar panel installers out there, so it's worth collecting a range of quotes to compare.

Costs and savings
Solar power is clean energy but comes at a price. Payback periods are long, especially for photovolatics which can take up to 50 years to pay for themselves.

Solar water heating systems
The Low Carbon Buildings Project, the government's grant programme for renewable energy systems, offers grants of up to £400 towards solar water heating systems, which typically cost £3000 – £5000. These prices are approximate for a whole solar system including installation, and vary depending on how many panels you need and other elements of the system you choose.

Photovoltaic systems
Prices for photovoltaic systems vary depending on the size and type of the system as well as the structure of the building where the panel will be installed. You can get a grant for up to 50% (with a maximum of £2500) for a photovoltaic system which typically costs around £6000 to £9000 installed. A photovoltaic system using PV panels can cost anything from £6,000 upwards. A photovoltaic system using solar tiles will cost more than typical PV panels, from £7,500. To be eligible for a grant you'll need to buy a system approved by the government and use an accredited installer. You'll also need to undertake a number of energy efficiency measures at your home first – find details at the Low Carbon Buildings website. Find other retailers near you using the Solar Trade Association website.

How to buy solar panelsSolar panel jargon

'Active' solar power involves using a panel to capture the sun's energy

A type of PV solar cell. Unlike multicrystalline and monocrystalline cells (see below), amorphous panels are not made from interconnected solar cells made from expensive crystalline silicon. Instead, a very thin layer of silicon is spayed onto a backing material to make solar roof tiles. As the silicon is much thinner than the silicon wafers in a typical crystalline solar cell, material costs are greatly reduced.

Active solar
Using a collector, eg a solar panel, to capture the sun's energy and use it to heat water or convert it to electricity.

Drain back system
A solar water heating system where the water inside the solar panel drains into a small back bottle when the pump switches off. This protects the system against damage due to boiling and freezing, without the use of antifreeze.

Evacuated tubes
A type of solar water heating panel. Evacuated glass tubes collect the sun's energy and heat water running through a container at the top of the tubes.

Passive solar
Capturing the sun's energy without a panel or collector, eg through large south-facing windows, and minimising heat loss through insulation.

Photovoltaics, PV
PV cells are thin layers of semi-conducting material (usually silicon). Electrical charges are generated when the silicon is exposed to light which can be conducted away as direct current. Multiple cells are connected together (usually behind glass) to form a panel.

Pressurised system
Water is pumped through the solar panel and heated. This heated water flows through a heat exchanger warming the water stored in your hot water cylinder ready for use. These systems typically use antifreeze.

Solar tiles
Use the same technology as photovoltaic cells, but are smaller and narrower than large PV panels and look like roof tiles.

Solar water heating
Water is pumped through a solar panel and heated by solar energy. The heated water then flows through a heat exchanger, warming the water in your hot water cylinder.

Monocrystalline silicon cells
The most efficient and expensive PV cell. Cut from single crystals of silicon, this system can harness around 15% of the sun's energy that falls on it.

Multicrystalline silicon cells
PV system made from silicon cut into wafers. It’s slightly less efficient than monocrystalline cells but also slightly cheaper.

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