SOLAR ENERGY FAQ

What are the benefits of solar energy?

So how does it work?

Water is circulated between the solar collector on the roof to heat your hot water cylinder (usually in the airing cupboard). Once installed, it's fully automatic and its performance can be monitored with the controller display.

The vacuum tube solar collector concentrates sun's energy to the manifold at the top of the collector.  The controller continuously compares the temperature in the manifold against that in the hot water cylinder.  When the water temperature in the manifold is hotter than the water in the cylinder, a pump circulates water through the manifold, down well insulated pipe-work and through a second heat-exchange coil in your hot water cylinder (referred to as a solar cylinder or twin-coil cylinder). The water+antifreeze flowing around the solar system is used to heat the water in the cylinder indirectly. This means that no water in the Solar Heating system will come into contact with water in your hot water cylinder. The heat is transferred, not the water.

The slightly cooled water then returns back to the solar panel.  As long as the water in the hot water cylinder is at the required temperature, your existing boiler will not switch on.

Will I need planning permission?

From April 6 2008, homeowners have been able to install solar panels, without needing to get planning permission, as long as there is no impact on others. Size limitations have been set to reduce impact on neighbours.  Solar panels attached to the building must not protrude more than 200 millimetres from the roof slope.  The only exception is if your property is a listed building or is in a conservation area, in which case you will need to consult with your council planning department.

Will I still need my fossil fuel boiler?

A solar system will provide typically between 50-70% of your hot water annually. This ranges from 95% in summer to 10-20% in winter.  Your existing boiler will provide the rest.  Solar systems can be used effectively with gas or oil boilers, Agas, Rayburns, solid fuel boilers, and many combi-boilers.

Do I need to replace my existing hot water cylinder?

Replacing your existing cylinder with an efficient purpose-built, twin-coil solar cylinder will result in the most efficient system, so this is recommended.  However a lower-cost option is to use a "retro-fit" solar coil, which can be fitted in place of the immersion heater in your existing cylinder.  This will reduce the initial outlay, and if required the system can be upgraded by replacing the cylinder some time later.   Another option is the use of an external heat exchanger (Willis Solasyphon).  This can be used with pressurized and unpressurized tanks.

Do I need a larger cylinder?

In many cases, it is recommended to increase the size of the hot water cylinder by ~25% due to the higher position of the boiler coil in a solar cylinder.  Since in winter, when the solar contribution is less, some water below the boiler coil will not always be heated.

How can I connect solar panels to my existing combi-boiler ?

Any solar hot water system requires a tank somewhere in the system to store the large quantities of heat generated.  When connecting to a combi boiler, a tank (referred to as a "Thermal Store") is situated upstream of the combi-boiler, so that the water going into the combi is pre-heated.  For all but the most recent "solar-ready" combis, it is necessary to install a mixer valve to limit the temperature of the water on the inlet to the combi to about 40-45 degrees.  This prevents the combi from cycling.  For most of the summer the combi can be switched off completely and the mixer valve temperature can be increased to ~60 degrees.

Does the solar water heating system contribute to the central heating?

In most installations the system is designed for water heating. This reduces the load on the central heating boiler and the improved insulation of the new cylinder makes the conventional water heating system more efficient. Towel rails can be added to system, however winter space heating is not a recommended application.  If a company tells you otherwise, seek a second opinion.  (The reason for this is that when the energy demand is at its peak (e.g. cold long winter evenings) the supply of solar energy is at a minimum.) 

Can I install this myself?

Yes, but you will not be eligible for the Government Grants available. For a successful installation, a solar hot water system requires plumbing, roofing and to a lesser degree, electrical skills. Some solar training is recommended, but many competent DIYers have successfully installed their own systems. What is most important is an appreciation of the high temperatures that these solar collectors can achieve.

We offer training, and advice on installation, and can provide assisted on-the-job training (one of our experienced installers will guide you through your first installation). 

Where will I place the solar collector?

On a roof or wall, ideally facing South, or anywhere between South-East and South-West for best performance. If your roof ridge is oriented north-south, you can install two smaller panels, one on each side of the roof (a dual-aspect installation).  This works well since the east facing panel will take advantage of the morning sun and the west facing panel the afternoon sun.  The controller can be programmed to take account of dual panel installations such as this. 

What is the ideal angle to mount the panel?

Usually when mounting on a roof just use the roof angle.  Angles between 25-90 degrees (i.e. wall mounted) are fine.  If you are not constrained by a roof angle (such as with a flat-roof installation) then the simple answer, is to use the latitude.  Using a south facing panel in Southern England as the example (latitude 51 degrees North). At the spring/autumn equinox the ideal angle for the panel is 51 degrees to the horizontal.  The earth's axis is tilted 23 degrees, so at the height of summer the ideal angle would be (51-23)=28 degrees, and in mid winter (51+23)=74 degrees.  Some people prefer to set the optimum angle for winter (~60 degrees) since there is a surplus of energy in the summer.  If you specify larger panel size but use a winter-optimized panel angle, this is one way of flattening the supply/demand curve, and giving more contribution out of season. 

How does a thermosyphon system work?

As water is heated, it expands and becomes less dense, so hot water rises.  If the solar panel is positioned below the hot water tank, this natural convection effect will automatically circulate the working fluid around the system.  The top of the panel should be at least one metre below the hot water tank, and it is best if it is positioned close, but 2-3 metres below.  A thermosyphon is simple and elegant since it does not require a pump, or electronic controller.

I have a swimming pool, will I benefit from this system?

Swimming pools are a very good application for solar heating. Our collectors can be roof-mounted or pool-side. Its possible to design a system that will provide hot water for your home as well as your pool. Heating a pool using conventional fuels is an expensive business. Solar will make significant energy savings and enable you to maximize the season.

How do we know the solar system is working properly?

The electronic control unit provides information on the performance of the system via its LCD display.  Many people find that in the summer they can switch off their fossil fuel boiler and leave it off for several months.

Is there enough sunshine for it to work?

Our modern hi-tech panels work brilliantly in the UK climate.  They work best in direct sunlight, but still work effectively on diffused solar radiation, and hence contribute well to water heating even on cloudy days. They are more efficient than conventional flat panel solar systems, and hence can provide more of a contribution to water heating outside of the peak summer season.  For the level of solar insolation in your locality check our solar map.

What does the expansion vessel do?

The expansion vessel / kit allows the fluid in the system to expand as it heats. This makes the system 'sealed' and virtually maintenance-free.  It also keeps the working fluid under pressure, which raises the boiling point so the water/antifreeze can circulate at temperatures in excess of 100degC.

I have a large house / several bathrooms 

We can supply collectors and cylinders suitable for your hot water needs.  We have experience of supplying large residences with large scale systems.