Solar Water Heating
Questions and Answers

The greater the hot water demand the bigger the saving

Will water heat on a cloudy day?
Yes, although the heat output of the solar collector is reduced on overcast days it will still be able to provide heating. If it is a heavily clouded day or raining, then electric or gas backup may be needed to maintain water at the required temperature. This system will be automatic so you don’t have to worry about running out of hot water on a rainy day.

Can the solar collector heat water to a high enough temperature?
Yes. In good weather our solar collectors can bring water to boiling point. Generally this is not necessary and so the system should be designed to provide a peak temperature of around 70-80 degrees c in the summer. If you consider that when having a shower the water temperature is usually around 42-45 degrees C and scalding can occur at 54 degrees C (130 degrees F) this temperature output is more than sufficient.

How does solar water heating work?
A typical solar water heating system uses a roof mounted collector, angled towards the south to capture heat from the sun. About 1m2 of collector area is needed for each person in the household, with a minimum size of around 2.5m2. The collector may be a flat panel, or a series of vacuum tubes: in both cases it contains a heating fluid which is warmed by the sun's rays, and then pumped through a heat exchange coil in the hot water tank. As this coil warms up, it transfers the heat to the water in the tank. An expansion vessel built into the system allows for any expansion or contraction of the heating fluid as it warms and cools.

Any solar-based system will still need a conventional water heater - powered by gas or electricity - to provide back up. However, in hot weather solar energy should be sufficient to provide all the hot water needed, and even on a cool day it will help to raise the temperature of the water a little, meaning the conventional system doesn't have to work as hard.

In some cases the conventional water heater is used to heat a main water tank, with the solar heating system warming water in a second tank which feeds into the main supply via a diverter valve. It is simpler and more efficient, however, to have two heating coils in a single tank. One is heated by solar energy, and the other by the conventional heating source. The conventional heater takes over when a thermostat in the tank warns that the water temperature has fallen.

Is the UK sunny enough?
While we love to complain about our weather, in fact the UK has quite enough sunshine to make solar water heating practical. It is estimated that we receive over a thousand kilowatt hours of solar energy per square metre every year. Even if sunshine is diffused through clouds, the energy can still be collected and used by a solar water heating system.

Over a year, such a system will supply about 60% of the hot water requirements of an average house. During the summer a solar heating system can supply virtually all the hot water needed, with water temperatures of 70-85 degrees C not uncommon. Even in winter, the system can reduce water heating costs by around 20%.

What about fitting solar water heating?
While commercial contractors will quote to fit solar water heating, the costs can be high. A householder with some DIY plumbing skills may want to consider fitting their own system. However, they will not qualify for grants if they do their own installation.

The most difficult task is fixing the panel to the roof of the house. Flat plate panels are bulky and can be heavy, and some assistance will probably be needed. A scaffolding tower is recommended.

Some householders take the opportunity to replace their old hot water cylinder with a more efficient, better insulated one (and this will almost certainly be necessary if opting for a two coil version).

Is Solar Hot Water a good investment for me?
The potential savings on water heating bills are affected the most by the type of fuel you are using to heat that water and the number of people in the home. If you are heating hot water for two or more people and you heat water with electricity, LP gas or oil, then you should take a look at solar water heating, it could be a great investment.

What is the "payback" on a solar hot water system?
The term "payback" is a misconception. Electric and gas water heaters do not have a payback! When you purchase a more efficient refrigerator, the decision to buy comes not from how long the savings generated will pay you back for your initial investment, but from getting better service for a lower operating cost with a better rate of return on your expenditure. Solar water heating systems provide quality hot water at a lower cost than heating with electricity or LP gas and add equity value to your home when you come to sell it.

Solar collectors are typically designed to last as long as your home with little or no maintenance. These systems give a yearly non-taxable return on your money - even for a two person household. It is important to remember that hot water is a constant daily expense; other large household appliances, like boilers, are seasonal expenses.

Hot water is typically 20% to 30% of the annual utility bill. If you are spending £800 per year on energy then hot water usage for showers, dishwashing, and laundry is likely to be costing £160-£240 annually.

Payback calculation

In this calculation assume that gas prices, maintenance charges and fossil fuel savings grow by 7% per year.

1. Write down an estimate of how much you pay for water heating this year. This is usually around 25% of you total energy utility costs. With an £800 annual bill this figure will be at least £200 a year. Add your annual maintenance charge to get total annual fuel costs.

2. Increase fuel costs, maintenance charges and fossil fuel savings at 7% / year.

3. Show cumulative savings from Year 1 to Year 10. Your total outlay for a solar water heating will usually have been recovered in 10 years or less. Note : a 7% increase in fuel costs is probably going to be a large under-estimate if recent energy price increases are any indication of what may happen in the future.

4. You will obviously save a proportion of your energy costs every year and this will grow as energy prices increase. Beyond the payback period (which will probably be shorter than you think) your solar water heating system will be providing around 60% of annual water heating FREE. If you use underfloor heating there will also be up to 30% recovery of your space heating costs as well.

We can guarantee no increases in the cost of solar energy!

Put savings another way, the extra mortgage loan on a typical £2500 solar heating system will be only £125.00 per year (assuming interest rate at 5%). A new solar heating system can save money, reduce pollution and add to the value of your home. Remember : you buy appliances to do a job at the least cost. No-one expects a payback from a refrigerator, washing machine or central heating boiler.

Don't forget that all solar savings are essentially non-taxable income, so £1.00 saved on your water heating cost is equivalent to £1.30 or more of your taxable income.

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What about freezes and cloudy weather?
Both active and passive solar water heating systems come with a 100% lifetime guarantee against freeze damage. Solar water heating systems are approved by the UK authorities. Active solar systems often have a conventional immersion heater element to heat water on the few days in the year when it might be needed. All solar water heating systems deliver both higher temperature water and more water volume than conventional water heaters.

What about the appearance of a Solar Collector on your roof?
Today solar collectors are typically integrated into the slope of the roof. This method of installation gives the solar collector the appearance of a quality, opaque, glass skylight. In most cases, since the piping is not seen, it actually improves the appearance of the home because it looks like an elegant, expensive skylight. Installers offer a free solar site survey to determine the location of the solar collector, and to verify that you will not have any collector shading problems.

What about the environmental benefits of going solar?
Any time you use solar energy to offset the amount of fossil fuels that are burned, you contribute to everyone's health and welfare. Operating a solar water heater instead of an electric water heater saves burning fossil fuels and reduces carbon dioxide emissions (a greenhouse gas) and sulphur dioxide (contributes to acid rain) emissions. Multiply those emissions per household by all the homes in the UK and the benefits -- and the air and water -- become even more clear. Environmental Consciousness is a state that induces action through your belief in leaving a better world for yourself and future generations.

Are there easy payment deals to let me fit a solar water heating system?
All banks and lending institutions will loan you money to put in a solar system. The good news is that even for two people the equity value and savings will result in a net positive income for the length of the loan and that equity value has been proven to last over 30 to 40 years. Then the system will generate non-taxable income each year. Solar hot water systems usually cost £2,000 to £4000 depending on the size and type of system you install. The money you save on your monthly utilities is actually being used to purchase your own water heating system.
There may also be various local council or city-wide subsidy schemes; eg. Solar for London.

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For information, pricing and all other requirements contact office@energyenv.co.uk