Renewable Energy
Background image is the Eden Project, Cornwall
JWD Ltd undertakes research into renewable energy products. In April 2007, a solar hot water
heating system was installed, consisting of 3 sq.m of Thermomax heat pipe
evacuated tubes, Deltasol controller and a 210 litre cylinder:
3 sq.m Thermomax solar collector, 2.1 MWh per year
There are three sensors in the system, one at the base of the tank, one at the top of the tank (the store),
and one on the manifold on the roof.
The Resol controller is set to run the pump when the manifold temperature
is 4 degrees C higher than the tank base temperature. The plot below shows the
three temperatures during a typical day:
Looking at the collector temperature, (red), we note a gradual increase until about 15.00hrs when
the system prevents the tank contents exceeding 70 degrees C (black line).
The cold water from the mains enters the cylinder base (blue). At about 08.00 hrs, the base temperature drops
rapidly as hot water is used for showers etc. The store temperature drops slightly, showing
that the cold mains is not mixing with the hot stored water - the tank is well stratified.
When the sun is not illuminating the collector, from about 17.00 hrs, the collector and tank base
temperatures are seen to drop, but the store temperature drops very little, showing good tank
insulation and little mixing.
It is vital to consider many other energy saving measures before installation of such a system.
Of greater environmental impact (and far less cost) than any solar system is the replacement of light bulbs,
updating loft insulation and persuading the family to turn off lights, boil the minimum
volume of water in the kettle etc. However, the heating system is quite efficient at capturing
the 1000W/sq.m in the UK (98%) compared to solar PV at 16%. The solar system described here cost in the
region of £4000 and generates about £220 of energy per year based on 10p per kWh.
Other areas of research include the use of LED lighting, high efficiency switched mode
white LED drivers and solar PV arrays:
Power output of a small solar cell
In this case, the maximum output power is obtained at full sun when the load
on the cell is about 60 Ohms. However, when there is less sun
it will be better to increase the resistance to maximise the available power.
The optimum charging system might include a
switched mode supply charging a supercapacitor pile (to maximise the current when it is available)
then constant-voltage charge a lead acid battery bank from the supercapacitor.
A Cree 3 Watt warm white LED
The "cool white" Cree and Luxeon high power LEDs are very blue and produce
a cold light that is unsuitable for domestic use. The warm white varieties are better in terms of appearance,
but far less bright. The Cree varieties are much easier to use because of their isolated heatsink.
Setting up a Steca controller with a Kyocera KC65T multicrystal 65 Watt solar PV array,
17.4V at 3.5 Amps
The optimum extraction of energy from the panel is at the knee of the response.
The output drops with increasing temperature, so the panels must be well ventilated. Note that
the smallest shadow reduces the output to virtually zero.
Contact details:
JWD Ltd
Telephone/Fax: +44 (0)1403 261251, Mob: 07973 173808
email:
julian @ jwdltd.demon.co.uk