ISSUE
05
Information Tech-
November 2012
TekTalk this issue Solar water heating explained P.1 Capturing solar energy P.2 Solar fraction & system efficiency P.3 Evacuated tube collectors P.4 Contact us P.5
Solar water heating can make a big difference to energy bills. Learn how to invest in free energy from the Sun.
SOLAR WATER HEATING EXPLAINED
In short... Solar water heating systems gather energy radiated by the sun and convert it into useful heat in the form of hot water. Systems have been available in the UK since the 1970’s and the technology is now well developed with a large choice of equipment to suit many applications. Solar water heating systems work alongside your conventional water heater to ensure year round hot water.
Benefits... Typical solar water heating installed in a property.
Provide almost all of your hot water during the summer months and about 50% year round. Reduce your carbon dioxide emissions by 0.25-0.5 tonne per year, depending on the fuel replaced.
How much could you save from solar energy? READ ON TO SEE HOW IT WORKS...
What is Solar Energy? Solar Energy – Our Largest Energy Resource Solar radiation drives all natural cycles and processes on earth such as rain, wind, photosynthesis, ocean currents and several others that are important for life. From the very beginning of life, the overall world energy need has been based on solar energy. All fossil fuels (oil, gas, coal) are a result of solar energy. The energy from the sun acting on the earth’s surface, over a 15 minute period, is more then the earth’s total energy requirement for a year. The amount of yearly global radiation on a horizontal surface may reach over 2,200 kWh/m in sunny regions. In Northern Europe, the maximum values are 1,100 kWh/m2 and are 943kWh/m2 in London and 990 kWh/m2 in Rosslare, Ireland. The supply of solar radiation in UK and Ireland differs by a factor of 10 between summer and winter, e.g. Rosslare: 6.36 kWh/m2 day in June; 0.64 kWh/m2 day in December. Global radiation comprises direct and diffuse radiation. As sunlight passes through the atmosphere, some of it is absorbed, reflected and scattered by air molecules, clouds and dust particles, this is known as diffuse radiation. The portion of radiation that hits the earth’s surface without any change in direction is known as direct radiation.. In the UK and Ireland, diffused radiation makes up between 40% (May) to 80% (December) of the total solar energy available in a year.
CAPTURING SOLAR ENERGY
Solar Fraction When sizing a solar system for domestic hot water, we typically will size the system to achieve an annual solar fraction of between 55 – 60%. A correctly sized domestic system would see the following solar contribution over a year:
System Efficiency The system efficiency is strongly dependent on the solar fraction of the system. When there is a high solar fraction the system efficiency is lower. High solar fractions result in a higher return temperature to the solar collector, the effect of this is that less solar irradiation can be absorbed by the collector, hence reducing the system efficiency. In undersized systems with small collector areas, the solar fraction is low but the system efficiency is high. In oversized systems with large collector areas the solar fraction is high but the system efficiency is low. The counter effect of the 2 variables can be seen in the figure below:
SOLAR FRACTION VERSUS SYSTEM EFFICIENCY
FEATURED PRODUCT
Evacuated Tube Collectors Vacuum tube collectors perform extremely well particularly in Northern European countries. Solar vacuum collectors are the most efficient method of generating solar hot water even in cold, wet and windy conditions. This is due to the low thermal losses from the collector. By creating a vacuum of 10-6 bar within the tube, thermal losses caused by conduction and convection are minimised, this enables the collector to be very effective in utilising low amounts of diffused radiation. The tube is made from glass with p ro p e rt ie s th a t g iv e it g o o d transmissibility with low reflection losses and good durability. High absorption of solar energy is achieved by using an absorber. The main assembly parts of the absorber are the absorber plate and the heat transfer tube. The absorber plate is coated with a special high efficiency coating that ensures maximum radiation absorption and minimum thermal radiation losses.
EVACUATED TUBE COLLECTORS
CONTACT US...
Peak oil and insecurity of fossil fuel supplies are factors that exert ever upwards pressure on the price we pay for our energy. Registered address:
With energy costs representing an increasing proportion of property
Epsilon Consultants Ltd
overheads the imperative for building owners and managers to reduce the
7 Heather Lane
demand for energy has never been greater.
Douglas Isle of Man IM2 7EF
With a lifetime of experience in the design of building services systems Epsilon Consultants (IOM) Ltd are ideally placed to provide professional and independent advice on how best to reduce energy costs in buildings.
01624 677278 07624 346826
OUR SERVICES‌
info@epsiloniom.com
Low Carbon Building Services Design Consultants
mike@epsiloniom.com www.epsiloniom.com
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TekTalk Issue 05 November 2012