Questions and Answers about Solar Thermal Hot Water Systems

What is a Solar Hot Water system?
A Solar Hot Water System or Solar Thermal System put simply is a solar system that heats water. Usually you will have solar panels installed on the roof or on a frame at ground level and a hot water cylinder installed near to the panels. The solar panels heat up when day light (the Sun's radiation) falls onto them. This radiation heats up a liquid inside the panel, usually anti-freeze. This heat is then transferred by the heat transfer medium (the anti-freeze) to your cylinder or pool heat exchanger. You can then use this heated water in your cylinder to wash, heat your home or pool.

Is Solar Water Heating suitable for use in the United Kingdom?
Our solar systems are designed to work in northern Europe; a well sized solar thermal system can supply 70% of your hot water per annum. It is possible with a combined pool and water system to get over 90% of you domestic hot water per annum. Solar Thermal systems work very well in the UK.

Can a Solar Hot Water (Thermal) system power the lights or T.V?
No. Solar Thermal System only heats water, another type of solar system produces electricity to power your electrical appliances, and it’s called a Photovoltaic System or P.V System.

Doesn't a Solar Thermal system need bright sunshine to work?
A Solar Thermal system needs daylight to work, not direct sunlight. Any solar collector works on how much of the Sun's radiation or light is getting through to the Earth. You will collect energy on a clear summer’s day but you will also collect energy on a cloudy winter’s day. The Max-Tec Evacuated tube solar thermal system are a highly efficient solar collector system converting over 85% of the available Sun’s energy into heat energy

What is the heat output from a solar thermal system?
The maximum output from a domestic solar hot water system (on a clear summer day) with evacuated tubes is approximately 800W per m2 aperture area. So a system with a gross collector area of 5m2 but an aperture area of 4.4m2, would equal to 4.4m2 x 800Wm2 = 3.5kW. So a system of this size would have the same output as a 3.5kW immersion heater typically found in hot water cylinders. At maximum output of 3.5kW it would take approx 5 hours to heat 250 litres of water from 5 to 55 degrees C, but the hot water in your tank would very rarely be at that low temperature, so the average heat up time for your hot water is much quicker than that.

What is the annual energy yield from a solar thermal system?
Every installation is different and every collector brand is made slightly differently so this will affect the annual energy output. In the UK, the Max-Tec series collectors produce around 519kWh per m2. This figure is heat to the heat exchanger allowing for pipe and pump heat losses on the way. This figure is also in relation to the aperture of the collector which is the opening that collects the Suns radiation, not the gross surface area of the solar collector. All quotations come with their own system design and calculations so you will know exactly what you will be getting.

How do Solar Thermal systems for domestic hot water work?
The collector (solar panel) is usually installed onto the roof of the house or on ground mounted frames. The hot water cylinder can be placed anywhere in the building, only the solar panels need to be on the roof to collect day light. An electronic controller constantly compares the temperature of the solar collectors with the temperature of the water in the bottom of the cylinder. Whenever the collectors are hotter than the temperature in the bottom of the cylinder, the controller switches on the solar systems circulating pump. A solar grade anti-freeze is then circulated through the collectors and the cylinder's heat exchanger, heating the cylinder in just the same way as a central heating boiler. With both systems the anti-freeze never directly mixes with the water in the cylinder. They are called in-direct systems, it is essential to use an in-direct system as this eliminates any problems with frost and ice splitting the solar panels or hard water damage.

How do Solar Thermal systems for domestic hot water work?
The collector (solar panel) is usually installed onto the roof of the house or on ground mounted frames. The hot water cylinder can be placed anywhere in the building, only the solar panels need to be on the roof to collect day light. An electronic controller constantly compares the temperature of the solar collectors with the temperature of the water in the bottom of the cylinder. Whenever the collectors are hotter than the temperature in the bottom of the cylinder, the controller switches on the solar systems circulating pump. A solar grade anti-freeze is then circulated through the collectors and the cylinder's heat exchanger, heating the cylinder in just the same way as a central heating boiler. With both systems the anti-freeze never directly mixes with the water in the cylinder. They are called in-direct systems, it is essential to use an in-direct system as this eliminates any problems with frost and ice splitting the solar panels or hard water damage.

What is a Pressurised Solar Thermal system?
A pressurised solar thermal system is a very efficient type of solar thermal system. They are designed in a similar way to a pressurised central heating system with an expansion vessel, pressure relief valve and pressure gauge. The liquid inside the solar system can operate safely at temperatures in excess of 100*C without boiling or vaporising because the liquid is under pressure so the boiling point is raised. Pressurised solar thermal systems should always be filled with a solar grade antifreeze and because of this will still work at -28*C. Our pressurised solar thermal systems collect the most energy.

What is a Drain Back system?
The Drain Back is a system that empties the collector when it is not in use. All the heat transfer medium drains away from the collector leaving it dry, this prevents the collector from boiling or freezing. There is less that can go wrong with a drain back system because there are less moving parts but there's also a drop in efficiency compared to our pressurised systems.

Do your Vacuum Tube systems have the external reflective back plate?
No, we choose systems that don't have this design feature. The reflective back plate is open to the elements so it degrades over time and reduces the output of the system. Under test conditions, shortly after installation the output from systems like this dropped by 15% because of this outdated feature.

Can a Solar Thermal system heat my radiators or underfloor heating?
No not on it’s own but combined with an Air Source Heat Pump with a COP (coefficient of performance) of 3.9, you will get all your hot water demands and heating loads for 12 months of the year from Sustainable Energy, the Sun and the ambient air

Do I still need a boiler?
Solar heating on a normal domestic scale in the UK will provide around 60-70% of the average annual household hot water requirements. However due to hours of light becoming shorter in the winter months there is less energy produced and the system will then need to use some power from a secondary heating source, this could be from an Air Source Heat Pump or conventional gas or electric boiler.

Can a MAX-TEC Solar system heat my Pool?
Solar is well suited to heating swimming pools. With the advanced Max-Tec solar collectors, they will provide you with a highly efficient system for heating your pool, unlike the traditional ugly black poly swimming pool collectors that you might have seen before. We need a smaller area of collector because they are more efficient and the system is better at heating the pool water in the colder months because the collectors have a selective coating that absorbs light and are insulated so loose much less heat.

How do solar swimming pool heating systems work?
An electronic controller constantly compares the temperature of the solar collectors, usually located on the roof of a building or frames in the garden with the temperature of the pool water. The temperature of the pool water is measured in the pool pipe work in the plant room. Whenever the collectors are hotter than the temperature of the pool water, the controller switches on the solar systems circulating pump. A solar grade anti-freeze is then circulated through the collectors to the new Bowman solar swimming pool heat exchanger. The heat exchanger is fitted to the pool pipe work in the plant room or near to the filtration pumps, heating the pool in the same way as a boiler. It would also be an advantage to design the pool with passive solar heating in mind. A dark coloured tile would draw more heat in and a transparent pool cover would also let light heat up the water when the pool isn't in use. Designed like this the pool would act as a solar collector in its own right.

How do I look after a solar thermal system?
Once installed the system looks after itself. But like any other automatic system a regular check should be made to see that it is operating as it should be. A solar system is an intrinsically safe system but it should be treated like your existing gas or oil heating system. A check every other year is recommended from a suitably experienced engineer.

How long will a system last?
The average lifetime of a well designed and built solar thermal collector is over 30 years. At Sustainable Energy Technologies, we source only the highest quality, award winning solar systems that are recognized for their excellence throughout Europe and the World.

Why install a Solar Thermal system?
There are many reasons to install a Thermal system:

• Free hot water for over 30 years.
• It will save tonnes of CO2 being released into the atmosphere.
• Solar Thermal can be integrated into the fabric of a building.
• There is very little maintenance required for a Solar Thermal system.
• After the initial installation costs, there are no further fuel costs.

What is sustainable / Renewable energy?
Sustainable / renewable energy is best thought of as energy which can be replenished within a human lifetime and which causes no long-term damages to the environment. Solar energy, wind energy, and geothermal energy, amongst others, are all self-sustaining. They all have sources that cannot be depleted. Extended use of these energy sources aids the conservation of other non-renewable energy sources such as fossil fuels.

How does solar technology work?
The idea behind technologies which use solar energy is to harness the freely available rays from the sun in a useful form. The technology used for solar water heating is simple and effective. The basic principle uses an absorber plate which is heated by the sun's rays. This heat is collected in a transfer liquid which is in turn used in a heat exchanger to heat water.

Do I still need a boiler?
Solar heating on a normal domestic scale in the UK will provide around 70% of the average annual household hot water requirements. However due to hours of light becoming shorter in November and December there is less energy produced and the system will then need to use some power from the boiler. Although we could design a system that would not need to use the boiler we recommend that the conventional system is kept in parrellel to the solar system to ensure the highest level of service.

Do I need to have a particular type of roof for solar installation?
A. In the UK the best orientation for solar panels is facing due south and tilted at around 35 degrees from the horizontal. However a variety of brackets and frames are available for solar systems to suit both different types of roofs eg Flat and Pitched, and all types of roof tiles.

What does this mean?

AAV
Automatic Air Vent. This is an air valve that automatically releases air from the system without any manual intervention.

Absorber
The blackened surface in a collector that absorbs the solar radiation and converts it to heat energy.

Aperture
When comparing collectors a reference area is important - that is, the surface area from whish the collectors characteristic values are drawn. In the collector test methods according to EN 12975 the reference area is equal to either the aperture area or the absorber area.

Active System
A solar heating or cooling system that requires external mechanical power to move the collected heat.

Ambient Temperature
The temperature of the surrounding air.

Auxiliary Heat
The extra heat provided by a conventional heating system for periods of
cloudiness or intense cold when a solar heating system cannot provide enough.

Azimuth
The angular distance between true south and the point on the horizon directly below the sun.

British Thermal Unit - BTU
The quantity of heat needed to raise the temperature of one pound of water one degree Fahrenheit.

Calorie
The quantity of heat needed to raise the temperature of one gram of water one degree Celsius.

Collector
The collector or panel usually is positioned on the roof of you house. When solar radiation falls on the collector it is absorbed by the selective coating on the absorber plate. This turns solar radiation or light into heat.

Collector Efficiency
The ratio of usable heat energy extracted from a collector to the solar energy striking the cover.

Concentrating Collector
A device which concentrates the sun's rays on an absorber surface which is significantly smaller than the overall collector area.

Controller
This is the brain of the system. The controller monitors the temperature in the collectors and in the bottom and top of the storage cylinder. When it is warmer in the collectors than the bottom of the storage cylinder the controller turns on the solar pump and pumps the heat round from the collectors to your storage cylinder, where it is stored ready for you to use.

Diffuse Radiation
Indirect sunlight that is scattered from air molecules, dust and water vapour.

Direct Radiation
Solar radiation that comes straight from the sun, casting shadows on a clear day.

Evacuated Tube
See Vacuum Tube.

Expansion Vessel
A large steel drum with a rubber balloon inside. This rubber balloon inflates and deflates with Tyfocor GLS as the solar system warms up and cools down. The expansion vessel is designed to take and thermal expansion and contraction that happen in the solar circuit.

Flat Plate Collector
A solar collection device in which sunlight is converted into heat on a plane surface without the aid of reflecting surfaces to concentrate the rays.

Heat Exchanger
A device, such as a coiled copper tube immersed in a tank of water that is used to transfer heat from one fluid to another through a separating wall.

Indirect System
The solar circuit is called an indirect system and refers to the heat exchanger inside your storage cylinder. It is the most common form of solar water heating system. The storage cylinder is manufactured with two heat exchangers inside. The highest one is what the hot water from the boiler flows through (the boiler will heat 70% of the cylinder) and the lower heat exchanger is what the solar systems Tyfocor flows through (the solar system will heat 100% of the cylinder). The heat exchanger allows water from the boiler and Tyfocor from the solar circuit to pass through, but not mix with the water in the storage cylinder itself. Thus, in effect, it really consists of three systems that appear to join at the storage cylinder.

Insolation
The total amount of solar radiation direct, diffused and reflected-striking a surface exposed to the sky.

Night Time Cooling
The cooling of a building or heat storage device by the radiation of excess heat into the night sky.

Pressure Gauge
Informs the user about the current pressure in ‘bar’ in the solar circuit. The black hand will point to the systems pressure. This gauge will normally read 1-1.5 bar. It can read as high as 6 bar. It should never read 0. If it does turn off the solar system and call Sustainable Energy technologies.

PRV
Pressure Relief Valve. This is a safety valve that will only open up and release liquid if the pressure in the system becomes too great and reaches 6 bar.

Pump
The solar pump is usually located in your airing cupboard or in the loft space. It is a different pump to your central heating pump. The solar pump will only work when there is heat to be transferred from the collectors to the cylinder.

Radiation
The flow of energy through open space via electromagnetic waves, such as visible light.

Reflected Radiation
Sunlight that is reflected from surrounding trees, terrain or buildings onto a surface exposed to the sky.

Retrofitting
The application of a solar heating or cooling system to an existing building.

Scale Inhibitor
Fitted inline to the storage cylinder. This inhibits scale formation in the cylinder increasing life expectancy and efficiency of the product.

Selective Coating or Surface
This is where the science is in new solar collectors and makes them much more efficient than solar collectors of years gone by. The selective coating is a special paint that absorbs solar radiation and doesn’t let much reflect out again. It absorbs radiation of one wavelength (for example, sunlight) but emits little radiation of another wavelength (for example, infrared). This way most of the radiation that falls onto the collector is turned into heat.

Solar Radiation (Solar Energy)
Electromagnetic radiation emitted by the sun.

Standby Heat Loss
Heat lost though storage tank and piping walls.

Storage Cylinder
This is where all the heat collected during the day is kept. The storage cylinder is usually sited where your old cylinder was. Warm water is stored here for you to use when washing or bathing.

Tilt Angle
The angle that a flat plate collector surface forms with the horizontal plane.

TMV
Thermostatic Mixing Valve. This valve located in you airing cupboard near the storage cylinder will mix cold water with the hot water coming out of the cylinder. This will reduce the risk of scalding and allow the solar to store temperatures of 85 degrees C in the cylinder. You can change the temperature of the hot water coming out of you cylinder by rotating the knob on top of the TMV.

Tyfocor GLS
Tyfocor GLS is a solar anti-freeze that flows through the pipes on the solar circuit. It is designed to protect down to –28 degrees C. It can also withstand very high temperatures that occur in solar thermal systems without degrading. Tyfocor GLS is not a harmful product.

Vacuum Tube
Vacuum tubes are solar collectors with the absorber surface coating sealed inside a vacuum. Collectors that are produced like this have better insulation and produce more energy per m2 of aperture area compared to flat plate collectors.