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…
[email protected]
Low Carbon Building Services Design Consultants
[email protected]
www.epsiloniom.com
BSS listed energy efficiency consultants
Energy benchmarking & auditing
Renewable energy investigations
Cogeneration studies
Digital thermography
Air tightness testing
TekTalk Issue 05 November 2012