An introduction to renewable energy and solar domestic hot water heating

The current vogue within the media regarding renewable energy has come about through necessity. There is a definite need for change regarding existing types of energy used. Fossil fuels are increasingly in short supply. Issues regarding sustainability, increased energy efficiency and renewable energy are beginning to occupy the minds of everyone. Consumer interest has been aroused and now continues to increase at a rapid rate.

In an era when energy efficiency and resulting financial savings are key considerations to everyone, the demand for solar hot water heating and related products is rapidly increasing. Household energy bills have doubled in three years to record levels and utilities have warned of further increases.

The amount of energy required to heat a modern home is actually decreasing due to higher levels of insulation in walls and ceilings and better glazing, but the amount of energy required for a homes’ hot water needs has increased due to high performance showers, larger baths, dishwashers etc. Unlike heating, the demand for hot water is constant - 365 days per year.

A well designed solar hot water system can provide around 70 per cent of this annual energy need. The remaining energy requirement provided by conventional means i.e. gas boiler or immersion heater. There is a widely held misconception that the UK does not have enough sun to make solar systems worthwhile. In fact, parts of the UK have annual solar radiation levels equal to 60 per cent of those experienced at the equator.Our solar collectors can provide up to 500kw/hr of heat energy for each square metre per year.

The advantage of solar hot water heating over other renewable energies is it is relatively inexpensive and very reliable. A well designed solar hot water heating system installed in a family house which previously used an electric immersion heater to heat water can save in excess of half a tonne of carbon dioxide emissions per annum. Solar hot water heating is the most practical and effective way in which you can use and enjoy renewable energy in your own home.

Concerns regarding cost and return on investment are at the forefront of peoples minds. Solar water systems do, unlike many home improvements, give a financial return upon investment. With the introduction of the government’s ‘Energy Performance Certificate-EPC’, every property for sale will have to provide information on its likely energy consumption and fuel bills. Each property will be given an energy rating from A to G, similar to the ratings seen on refrigerators and washing machines. The EPC will outline the financial costs and carbon emissions of heating, hot water and lighting. It is therefore safe to assume that houses with renewable energy sources will be given a higher rating, thus increasing value and saleability.

Technical information

A solar hot water heating system consists of:

a solar collector or series of collectors
a hot water cylinder
a control panel
a pump unit.

Our ‘evacuated tube’ solar collectors are highly efficient due to the fact that they work on diffused light. Their shape and selective surface harness indirect solar radiation as well as direct sunlight, maximizing efficiency even on cloudy days.

Each evacuated tube is made up of two strong glass tubes, similar to large test tubes; one tube within the other. The tops of the tubes are fused together and the gap between them ‘evacuated’ creating a vacuum, just like a thermos flask. The outer tube is made of clear glass that allows the sun’s rays to pass through it with minimal reflection. The inner glass tube is coated with a special selective coating that absorbs the sun’s rays whilst preventing any heat losses from radiating. Once the heat has been captured it cannot escape because the vacuum is an excellent insulator. Temperatures inside the tube can reach over 180 degrees Celsius, while the outer tube remains cool to the touch. This is the reason why evacuated tubes work well in all climates and can easily out perform flat plate collectors in cold weather.

Down the centre of the inner evacuated tube a heat pipe is threaded. This narrow copper pipe is partially filled with a fluid that boils at approximately 30 degrees Celsius. As the fluid boils it turns to steam and rises to the bulbous tip of the heat pipe where it dissipates its heat via the manifold. After dissipating its heat the fluid condenses and returns to the bottom of the heat pipe ready to start the process again. The manifold is the rectangular box visible at the top of the collector, which links all the tubes together. Inside the stainless steel casing of the manifold is a copper tube with a series of ports that accept the heat pipes. These ports use dry joints, with the heat pipe tips requiring no more than a gentle push to locate them. This system means the water in the manifold never mixes with the fluid in the heat pipe and because the water in the manifold never enters the evacuated tube, the whole system can work even when a tube is broken. Broken tubes are easily replaced without the need to drain down any part of the system.