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Are You Specifying Your Solar Thermal Cylinders Correctly?
The rising cost of gas and electricity, together with the global movement towards more sustainable energy sources, is seeing a growing demand for renewable energy installations.
Solar thermal systems are a simple and well-proven technology producing low-carbon energy. A small amount of electrical energy is consumed to run a pump circulating a fluid, which is heated in the solar collector by free energy from the sun.
The lure of ‘free’ hot water, the potential to cut energy bills and the potential to earn money via the government’s Renewable Heat Incentive (RHI), is making solar thermal installations an increasingly attractive proposition.
Renewable Heat Incentive
The UK’s RHI was the first scheme in the world to provide financial incentives for people installing renewable heat technologies, as the government aimed to reach its target of having 12% of heating coming from renewable sources.
In September 2012, the government published their consultation on domestic RHI where they proposed that householders with solar thermal heating installations may be able to receive payments for heat generated.
The government has now set a launch date of spring 2014 to extend the RHI scheme to include technologies such as heat pumps, biomass and of course solar thermal.
Getting the Right Cylinder
Whilst the actual savings of a household’s hot water requirement provided via the solar installation will dependent on a number of factors, including geographic location, type of panel and panel orientation. The specification of the hot water cylinder is absolutely critical to the overall success.
Solar cylinders are made from various different materials, including copper and stainless steel. Solar coils manufactured in Copper transfer the heat more effectively, though Stainless Steel offers a cost effective alternative.
To maximise the heat transfer process, it is vital to maximise the specification of the coil and most manufacturers of solar hot water cylinders, use high efficiency finned or ribbed coils and attempt to maximise the length of solar coil in the cylinder, with a best practice ratio of 0.3 Metres Square of coil, for every metres square of solar panel.
The solar thermal circuit is linked to a high efficiency coil located in the bottom of the cylinder. Heat rises, and the draw-off point for the water to the taps is at the top. This means your solar system is capable of heating the whole volume of water stored in the cylinder. So on a sunny day, when solar works at it's very best, this entire volume of water will get hot.
On gloomier days, when there is little solar gain, your boiler or immersions will need to 'top up' the heat - although you'll be very surprised at just how much heat a solar system will capture even on an overcast day! You may find that the temperature of the stored water may well reach 30-40 degrees, so a very much reduced top up for your second heat source. This ensures having a solar thermal system, helps cut a household’s energy bill all year round.
The cylinder sizing will vary due to a number of factors depending on property type, number of panels etc. As a general rule of thumb, the typical consumption of hot water is approximately 50 litres per person per day. However, with solar cylinders, we also need to allow a minimum of 25 litres of designated solar volume per square metre of solar collector. Cylinder manufacturers have a wide range of options and can advise the installer of exact requirements and options available.
Solar Thermal Flexibility
Solar Thermal is extremely flexible and can be used in Vented, Unvented and Thermal Storage systems. It can be used with a wide range of secondary heat inputs - Gas/Oil/Electric Boilers, Electric Immersion, Heat Pump and Solid Fuel.
Solar Thermal Installations for Existing Properties
Low maintenance as well as ease of installation is often what a client is after, so when it comes to installing Solar Thermal cylinders into properties with existing hot water storage cylinders, there are two options available. The existing cylinder can be completely replaced with a new purpose built solar cylinder. However if size constraints do not allow for a larger cylinder in the desired location, a pre-feed/pre-heat system is often favoured. This dedicated solar cylinder feeds the preheated water into the hot water storage cylinder, which then tops it up if and as required.
A typical solar thermal system will meet 50-60% of a households hot water requirements and with the RHI proposals, Solar Thermal is a very viable renewable. Systems tend to be low maintenance and will generally last up to 25 years. Panels and system design are improving constantly and carried out by a qualified and approved installer, solar thermal is often the easiest and cheapest renewable option to fit. With its ability to link with so many other heat sources, serious consideration must be given to Solar Thermal as a renewable option.