Solar Heating
Solar energy has been harnessed for heating use for thousands of years
Over 2000 years ago the Greeks used solar architecture in order to use the sun to heat their homes during the winter.
The Romans put glass into window spaces, allowing sunlight and heat energy to still enter the building, but now the heat energy was trapped inside. The Romans also built glass greenhouses which enabled them to use solar energy to grow fruit and vegetables throughout the year, and to also grow some exotic fruits from seeds that they had brought home from their travels to faraway lands. Solar heating was so important to the Romans that they made it an offence to obscure another persons' access to sunlight. In 1700 it was discovered that very hot temperatures could be achieved by placing a box covered with a panel of glass into direct sunlight. By placing a black container filled with water inside the box, the water could be made to boil. This is an example of an early solar water heater. Then in 1909 William Bailey from California separated the solar collector from the water tank in order to minimise the loss of water temperature during the night. This is the principle used by solar collectors today.
Solar Collectors – Solar Panels for Hot Water
'Solar heating' or 'solar thermal' are terms used for heating water by using energy harnessed from the sun through the use of solar collectors.
The sun can be used to heat water by the use of solar panels that convert sunlight to heat. These panels are commonly known as solar collectors. Solar collectors are usually installed on the roof of your home. The inside of the collectors contain dark coloured materials that are excellent at absorbing heat energy from the sun, whilst the sides are well insulated to minimise heat loss from the collector into the outside atmosphere. As the sun shines heat energy is absorbed by the collector, causing the collection areas within the unit to become hot. Running through the inside of the collector are thin tubes that have a heat exchange fluid flowing through them. The heat exchange fluid is usually a mixture of water and antifreeze. The heat exchange fluid absorbs heat energy from the collection areas before being pumped to the hot water storage cylinder. At the hot water storage cylinder the heat exchange liquid is pumped through a heat exchange coil inside the tank. The temperature of the water in the tank rises as heat energy is absorbed from the heat exchange liquid. At night or when it is cloudy, the temperature of the heat exchange liquid leaving the solar panels will be insufficient to heat the water in the hot water storage tank. To prevent heat energy being absorbed from the hot water tank, thermostats are used to control the flow of the heat exchange fluid by simply switching the pump on or off. This ensures that the heat exchange liquid is only pumped to the hot water cylinder when it is hot enough to provide heating for the water in the cylinder.
Heat energy from solar collectors can provide hot water in a variety of ways
Two Cylinders To include solar water heating into your heating system can be quite straightforward. If there is sufficient space available a simple and highly effective way is to use an additional hot water storage cylinder. The additional cylinder will be included into your existing system where instead of cold water being fed into your existing hot water cylinder, it is first fed into the new solar hot water cylinder. The water from this cylinder will feed your existing cylinder, but whilst the water is in the solar cylinder it will be heated by solar energy. Cold water is fed into the bottom of the solar cylinder and as it heats it will rise. Hot water is taken from the top of this cylinder to feed your existing cylinder. On sunny days, also known as good solar days, the water being fed into your existing hot water tank will already be at the desired temperature and will not require any further heating from your boiler or immersion heater. On cloudy days the water may be below the required temperature and will therefore require some additional heating from your boiler. Any water heating provided by solar energy is free from carbon emissions and also a financial saving. Twin Coil Cylinders Due to space being a common restriction a twin coil cylinder is not only popular but also a very cost-effective option. This method uses one hot water cylinder which has two separate heating coils. The coils are arranged one above the other, the lower coil is heated by solar energy and the other is heated by your boiler. Hot water will float on top of cold water, a phenomenon known as stratification. Therefore as water is heated the water with the highest temperature will float at the top of the cylinder and cold water will sit at the bottom. This means that any cold water entering the cylinder to replace hot water as it is used will sit at the bottom of the cylinder where it will wait until it is heated by solar energy. The water higher up in the cylinder can be further heated and kept at the required hot water temperature by the boiler fed heating coil that is higher up in the cylinder. On hot sunny days the solar fed coil will be able to provide all the water heating required without assistance from the boiler fed heating coil.
Solar heating to provide home heating
In the UK solar water heating is usually only used to provide the domestic hot water, but it can also provide hot water for heating the property. Solar energy can be used to heat a home by using a solar heating storage cylinder which is connected to the plumbing for move domestic heating system.
However, it is rarely used for home heating in the UK because it works best on sunny days when there is little demand for home heating. Furthermore, on cold cloudy days when home heating is required the system will struggle to provide hot water.
The 2 main types of thermal panel
Flat plate solar panels
Flat plate solar panels are also known as flat plate solar collectors or flat plate solar heating panels The basic flat plate solar panel is made up of a transparent cover, which is usually a layer of glass or plastic. Beneath this cover is a small gap and then there is a dark, usually black, heat absorbing surface. The sun shines through the transparent cover and heat energy is absorbed by the dark surface, which then heats up. This black layer has pipes running through it. The pipes have a heat transfer fluid flowing through them. The heat transfer fluid absorbs heat from the dark surface as it flows through the pipes. The transfer fluid therefore heats up and is ready to be used. A good flat plate solar panel absorbs as much of the sun's rays as possible converts the sun's rays into as much heat as possible restricts heat loss from the collector unit before this heat energy can be absorbed by the transfer fluid.
Advantages of a flat plate panel
1. Flat plate solar panels are usually cheaper to buy than vacuum solar collectors. 2. They can be fitted flush to or integrated into roofs so that they are less noticeable. 3. They are stronger and more robust than evacuated tubes.
Evacuated-tube collectors
Evacuated-tube collectors also known as evacuated tubes or evacuated solar panels Vacuum solar heating panels are made up of a number of round glass tubes that can capture sunlight from various angles. The inside of the glass tubes have been 'evacuated', and within this vacuum are more tubes made of glass or metal which have a special aluminium nitrate coating. This special coating is an excellent light absorber that can absorb light over a wide spectrum. The absorbed light converts into heat energy raising the temperature of the internal tubes. The internal tubes have a heat transfer liquid (usually a mix of water and anti-freeze) running through them. The heat transfer liquid absorbs heat energy from the tubes and heats up. A well insulated manifold controls the flow of heat transfer liquid to the tubes and also to the hot water storage tank in the home. The outside tubes have been 'evacuated', hence their name, to leave a vacuum. A vacuum is an excellent thermal insulator and prevents the heat energy that has been absorbed inside the tubes from being lost to the outside tube. Any heat energy in the outside tube can be absorbed by the outside atmosphere before it can be used by the transfer liquid. Highly reflective weather proof mirrors are positioned behind the evacuated tubes. These mirrors are shaped so that they reflect as much sunlight as possible back towards the evacuated tubes. A good evacuated-tube absorbs as much of the sun's rays as possible converts the sun's rays into as much heat as possible restricts heat loss from the collector unit before this heat energy can be absorbed by the transfer liquid.
Advantages of an evacuated-tube
1. Tubes can be added or removed from the solar collection system 2. Individual tubes can be quickly and easily replaced if they are damaged or should they develop a fault 3. Evacuated-tube systems can be moved around corners 4. They can be built in sections to pass around obstructions or other obstacles 5. Although more expensive than flat plate panels, evacuated tubes require a smaller surface area. 6. It is widely accepted that during the winter months in the UK evacuated tubes perform slightly better than flat panel collectors.
Combi boilers and solar heating panels
Combination boilers, often referred to as combi boilers, heat water only when hot water is demanded and therefore do not require a hot water storage tank. Solar heating panels can be used with combi boilers but a hot water storage tank will be required. When solar heating is used with combi boilers the boiler still heats the water when it is demanded. However, the combi boiler is no longer fed with cold water, instead it is fed with water from the hot water storage tank that has been preheated using energy harnessed from the sun. The combi boiler will raise the temperature of the water fed to it, to the desired hot water temperature. Therefore free energy from the sun is used to partially heat the water and the combi boiler only has to cover the shortfall. When the temperature of the water in the hot water storage tank is already at the desired temperature, the boiler is either bypassed or it will not fire up depending on the type of system. Before installing a solar heating system you will need to find out if your combi boiler can accept pre-heated hot water. Considerations for installing a solar thermal system
Planning permission
Most solar thermal panels are considered permitted development in England and Wales. Therefore they don't require planning permission provided that the solar panels are not installed above the ridgeline of the roof on your home. However it is always best to consult your local planning office, especially if you live in any of the following, because restrictions may apply:
a listed building a conservation area a world heritage site Scotland or Northern Ireland
Direction that the solar panels should face
Solar panels are best positioned facing due south. However, they are still very effective facing anywhere between south east through south to south west. If it is not possible to position solar panels anywhere between south east through to south west, the installation can be split into 2 sets of panels positioned to face east and west. This option will however require more panel area to provide the hot water required which will obviously mean a greater cost.
Where to position solar panels
Solar panels are most usually mounted on the roof of a home or garage and you will need about 5 square metres of roof space that receives direct sunlight. They can also be mounted at ground level, but it is important that they collect direct sunlight and are not positioned where their performance may be reduced by shadows from trees, buildings, telegraph poles, etc.
Weight of the solar panels
The solar panels are not lightweight so make sure that your roof or any other structure that you intending to mount your panels on are strong enough.
Best angle for solar panels
To obtain the best performance from solar panels they should be positioned at an angle of between 20° and 50°. Most pitched roofs usually provide a suitable pitch angle, but brackets should be used in order to achieve the best operational angle when being installed on flat roofs.
Amount of solar panels required
Generally you will require up to 1 to 2 square metres of solar collector panels for each person living in the house.
Suitable hot water storage cylinder
If your existing hot water cylinder is not compatible with a solar heating system you may need to have an additional hot water storage cylinder or change your cylinder. Quite often you will require a larger cylinder to store enough hot water for 2 days, especially in the UK where cloudy days can be common. Hot water storage cylinders used with solar heating systems are usually tall and thin. Most of these hot water storage options will probably take up more space than your current hot water cylinder uses.
Will solar water heating be of benefit
Make a note of how much hot water you use in your home and what the hot water is used for. Then check to see if solar water heating will be of benefit! For example, if you use hot water for showers, washing clothes and dishes, solar water heating won't be of benefit if you have an electric shower and a cold water fed washing machine and dishwasher! Solar water heating is most beneficial for homes that use a lot of hot water that is heated by a boiler and/or immersion heater.
Adapting to make the most of your solar heating system
A good solar system can provide between 50 to 70% of your annual hot water requirements. However, to achieve this you will need to learn to adapt to make the most of what your system can offer. For example and depending on your system, it may be better to bath or shower in the evening after your hot water has had the chance to heat up during the day using solar energy, rather than showering in the morning when the hot water will need to be heated by your boiler or immersion heater.
Programming your boiler or immersion heater
If a boiler or immersion heater heats water to the desired temperature in the morning, there maybe no requirement for solar water heating during the rest of day. To ensure that a solar water heater takes advantage of the free energy that is available from the sun during the day, boilers and immersion heaters should be programmed to heat the water during the evening. This will ensure that on cloudy days any shortfall in the water temperature will be made up before it is required in the evening. To obtain the best efficiencies from a solar heating system you should only 'boost' the hot water heating after the sun has gone down.
Heating control panel with seperate control of heating and hot water
Some control panels and boilers are unable to provide heating and hot water separately. Being unable to control your heating and hot water separately will prevent you from receiving the maximum benefit from your solar heating system. For example if you turn your heating on during the day you will also be paying to heat your hot water and not receive benefit from your solar system.
SavingsIn the UKHeating water accounts for 17% of domestic energy use and 20% of domestic carbon emissions. The average home uses 3000 kWh of energy each year to heat water. 3000 kWh requires 75 gallons of heating oil. 3000 kWh heated by a gas boiler could produce 1.3 tons of carbon 3000 kWh heated by electric from a coal fired power station would produce 3 tons of carbon and 20 kilograms of carbon if generated by a nuclear power station or by wind turbines. 3000 kWh of solar heat energy can be generated by just 3 square meters of thermal solar panels. Choosing and purchasing a thermal solar systemPrices for a solar thermal system vary tremendously.Prices will depend on The type and specification of the system that you require Whether or not your existing hot water cylinder is suitable or if you require a replacement or additional cylinder How much work is required to install your solar panels and whether or not scaffolding required The amount of work required to integrate the system into your existing hot water system Also be aware that Prices will vary from one supplier to another. Profit margins vary considerably between manufacturers and suppliers and higher prices do not guarantee better systems! Extensive tests have shown that the best solar collectors can be twice as efficient as the worst. The best flat plate collectors tend to be made in Austria and Germany, whereas the best evacuated tubes tend to be made in Switzerland and Northern Ireland. Benefits and Advantages of Solar Heating
Reduce your energy bills
any water heated using the energy of the sun is free from heating fuel costs. Solar thermal panels should provide most of your hot water from April to September and make a worthwhile contribution during the months either side of this period.
Cut your carbon footprint
the sun is a completely renewable energy, therefore any water heated using solar energy is free from carbon emissions.
Solar energy maybe the only renewable option available
The most suitable renewable energy for the vast majority of homes in the UK is solar power. To make use of hydropower a property needs to have access to a suitable stream or river. Wind power requires access to an exposed area that is at least 300 metres from the nearest neighbour. Solar panels can be installed on the roof of most houses in the UK.
Low maintenance
Solar heating panels require very little maintenance. It is advisable for you to visually inspect your panels once a year for cracks, breaks or any leaks and have them checked every 3 to 5 years, or as specified by the system's instruction manual, by a professional solar panel installer. Most solar heating systems have a 5 to 10 year warranty.
Long Lifetime
Solar panels have an expected lifetime of 30 years or more.
Increase the value of your house
Due to their desirability installing solar panels can increase the value of your property.
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