The shop obviously has a need for electricity to power fridges and freezers, but the amount we are able to contribute to our own electricity consumption via the Solar Voltaic Roof is helping the community and the environment and keeping our electricity bill down.
The building is heated by a system known as a heat pump.
A heat pump works by virtue of the fact that the temperature a metre or two underground is at a fairly constant temperature, while the air temperature varies considerably during the day.
The Solar Voltaic Roof
The solar electric tiles are made in groups of 333. These are known as shingles.
A group of shingles connected together are referred to as a string.
There are two inverters, which turn the direct current (dc) supplied by the solar electric roof into alternating current (ac) at 230V 50 cycles per second (50Hz), which is connected to the mains supply.
The one inverter is fed from 4 strings composed of 35 shingles. The other inverter is fed from 4 strings composed of 40 shingles.
This makes a total of 300 shingles. Each shingle has a maximum output in clear sun normal to the tiles of approximately 17 watts, the maximum theoretical output being 5100 Watts.
Since it started operating in 2005 the solar roof has generated in total about 29,500 kWh (as of March 2011
A graph showing the electricity generated by the roof for 2009 and 2010 can be seen here.
The Heat Pump
Water leaves the heat pump at a low temperature and after circulating through the pipes below the field adjacent to the shop, arrives back at the heat pump about 5 degrees Celsius warmer.
As there is about 230 litres of water in the pipes this represents a considerable amount of energy.
Heat from this water is transferred to the heat pump. The heat pump raises the temperature to a useable value.
The heat is now transferred to water, this being circulated in the heating pipes within the building.
A full explanation of the technology can be found at Wikipedia here
Since the shop opened, the average annual consumption has been 7236 kWh.
Compare this with an average house using economy 7 heating:
Low user 3,300 kWh
Medium user 6,600 kWh
High user 9,900 kWh
And the average house user, unlike the shop, is not opening the front door many times throughout the day.
Even during long cold spells, the ground source heat pump keeps the shop very warm. To do that using oil or electricity (there is no piped gas supply in Brockweir) would be considerably more expensive.
Environmental Aspects of the Shop
The shop is of green oak construction insulated with 10 inches of fibreglass, an infrared reflective layer and plasterboard.
The internal floor area is approximately 160 square metres and has a ground floor volume of 420 cubic metres and a first floor volume of 470 cubic metres.
The Ground Floor has a thermally insulated concrete base in which heating pipes are embedded.
The first floor has heating pipes between the joists.
An 8.5 kilowatt heat pump supplies heat to the building.
Most of the heat energy is obtained from a field adjacent to the shop by means of three pipes about 1.2 metres below the field surface through which water circulates.
We also use and sell ecologically friendly cleaning products, recycle all our waste and sell shop cotton bags to reduce the use of carrier bags.