SOLAR THERMAL WATER HEATING – THE BASICS
OVERVIEW
Domestic water heating is considered to be one of the most appropriate applications for utilising solar energy in the UK when you consider that water heating accounts for approximately 6% of the total national delivered energy use.
Domestic water heating demand continues throughout the year and still needs to be satisfied in the summer when there is plenty of solar energy available. Incoming mains water is usually at a temperature of around 10oC in the UK and has to be heated to a storage temperature of in excess of 60oC.
For water heating a typical UK house uses 5kWh per day of useful energy (that is the energy content of the water leaving the taps). This figure can vary considerably from house to house, dependent on household size and water usage. The actual amount of delivered energy (the energy registered on a gas or electricity meter) can be considerably higher, particularly in summer.
Running a boiler with a continuously burning pilot light, and un-insulated hot water pipe runs, for small quantities of hot water reduces efficiency considerably. Even electric immersion heaters may only manage 50% efficiency in terms of useful energy at the tap, boilers considerably less.
Solar water heating systems use heat from the sun to work alongside your conventional water heater. The technology is very well developed with a wide choice of systems to suit many applications.
How a Solar Thermal System works
The solar collector mounted on the roof converts the light that penetrates its glass panes into heat. The heat is created by the absorption of the sun’s rays through the absorber plate. This is the most important part of the collector.
In the absorber is a system of pipes filled with a heat transfer medium (antifreeze mixture) for flat plate systems, or evacuated tubes with copper collectors that connect to a manifold with a heat transfer fluid flowing through it (for vacuum tube systems).
The general heat then flows to the hot water cylinder and the heat is transferred to the domestic hot water circuit by means of a second coil in the hot water cylinder. The first coil remains connected to the boiler for back up hot water heating when there is insufficient solar energy.
The cooled heat transfer medium then flows via a second pipeline back to the collector while the heated domestic water rises upwards in the hot water cylinder. The solar heating coil is always the lower coil in the cylinder which makes it the dominant coil. This means that if there is sufficient solar energy available your boiler will not flash up to heat the water.
Does my roof have to face in a certain direction?
Yes, ideally the collector should be on a roof within 45o of south and with a pitch of between 30o and 60o. If you only have an east/west facing roof a collector can be fitted to both elevations but there is obviously a cost implication.
Collectors can also be mounted on purpose made frames either at ground level, on a flat roof, or attached to a wall.
Average costs of a typical installation
The installed cost for a professionally designed complete domestic flat plate system without grant (including a solar cylinder, piping, insulation, controller and commissioning) which can be bolted onto the roof or roof integrated is around £4,000 inclusive of VAT. *
The installed cost of an evacuated tube system will be around £4,500 inclusive of VAT. * Once the survey has been carried out, all prices will be given as fixed prices. The price we quote will be the price you pay.
Prices are about £500-£700 higher if your house is fitted with an un-vented hot water system or they will be higher if we have to do extensive plumbing works or if we have to make building alterations to your airing cupboard.
* Prices based on an average sized 3 bedroom semi detached house.
A Government grant will reduce these costs by £400 in England and more in Scotland and Northern Ireland. We will help you with the grant application.
Is maintenance required on my Solar Thermal System?
Yes, but only minimal maintenance is required. We recommend an annual visual inspection of the system and a more detailed five yearly system inspection.
The benefits of Solar Thermal System Installation:-
- Can provide almost all of your hot water during the summer months and about 70% year round.
- Reduces your impact on the environment – the average domestic system reduces carbon dioxide emissions by around 400kg per year.
- Reduces your energy bills, as you do not use as much alternative energy to meet your hot water requirements.
- Reduced use of your “heating generator” means less use, less wear and tear – potentially extending the lifespan of your “boiler” – although this cannot be guaranteed.
Calculating your system ………….. and system components
There are basically four different methods that can be used for designing dimensioning system components. These are:-
- Rough determination
- Detailed calculation
- Graphical design
- Computer aided design with simulation programmes
We use a combination of all four methods, matched against the individual circumstances. This allows for accurate dimensioning of collector surface areas and store volumes.
Type of systems available
We are able to supply and install a variety of collectors and each system has its advantages and disadvantages. We will always give you well considered advice on what is the most suitable collector for your project and for your budget.
The types of collector that we supply and install are:-
- Flat plate – roof integrated or bolted onto the roof
- Evacuated tubes – on roof only
- Unglazed and un-insulated collectors for swimming pools
Do I need a large roof Area?
Ideally you will need 4m2 for a flat plate collector of 3m2 for an evacuated tube collector for the average four bedroom house, or slightly less for a smaller two or three bedroom house.
For detailed sizes of panels please contact us as there are more options available than it is practicable for us to list in this fact sheet. There are very few projects where we are not able to come up with a satisfactory solution!
Solar Thermal Solutions for Swimming Pools
The heating of swimming pools is one of the best established applications of solar water heating and also one of the most appropriate because of the high system efficiencies that can be obtained. Average collector efficiencies of approximately 75% can be achieved.
Which option is best for you?
The system that best suits your needs depends on a number of factors, not least of which is the area of south facing roof available, your existing water heating system, individual water consumption and of course budget available.
To find out more please call, email or send us a set of drawings of your specific project.
How we design a highly efficient and cost effective Solar Thermal system matched to your requirements/specifications
We try to design a solar water heating system to give as close as possible to 100% of the daily requirements in winter. This would be at an unacceptable cost relative to the financial returns and would give too much hot water in summer. Our solar water heating systems for domestic hot water are designed to achieve almost all summer requirements, and will use your existing heat source to provide the shortfall over the rest of the year.
A designed system will typically provide up to 90% of a family’s hot water requirements during the months of April to September and make a very useful contribution during the rest of the year. In an average year the system will provide up to 70% of a family’s annual domestic water heating needs. This percentage is sometimes referred to as the “solar fraction”.
Solar water heating systems are designed to absorb solar energy efficiently and transmit that energy to the storage cylinder with minimum loss. It should also be designed to have a life of at least twenty years or more.
We can provide a competent professional installation, after assessing your span requirements, designing the most suitable cost effective system configuration to meet your needs.
Solar Hot Water Cylinders
There are various design features that have a significant impact on the suitability of a solar hot water cylinder. We ensure that all the following relevant features are designed into our systems and that only cylinders designed for solar are used:-
- Narrow cylinder – to ensure stratification
- Baffle plate at cold water input – to prevent mixing between hot and cold water
- Hot water extraction – to prevent destruction of the stratification effect
- Heat exchangers – correct positioning for solar
- Insulation of the cylinder – good heat insulation, including floor of store
- Cylinder temperature sensor (Solar) – correctly fitted in middle of solar heat exchanger
- Cylinder temperature sensor (Auxiliary) – same height as auxiliary heat exchanger or higher
Pipeline Insulation
In conventional heat installations, and some cheaper solar thermal installations, insufficient attention is often given to the insulation. What is the use of the best heating technology if a large and unnecessary amount of heat is lost on the transport routes and in the cylinder?
It is important to insulate all the piping without gaps, and without open spots. In the solar circuit a temperature resistant insulation material must be used. External pipelines must be UV and weather resistant, as well as being waterproof, and should offer protection from animal damage.
It is for this reason that we use high quality super insulated pipeline units, consisting of copper pipe, insulation and sensor cable all as one unit. They are more expensive, however, they ensure that your system will be trouble free for many years.