Questions & Answers On Solar Thermal
Questions and Answers about Solar Hot Water Heating Panel 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 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, sometimes up to 80%. 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.
Does a solar thermal system work in the winter?
On average solar thermal system will provide about 25% to 35% of your hot water energy heating in the depths of winter. It will not work when it's foggy, snowing, raining or heavily overcast.
Solar assisted underfloor heating systems produce the most useful energy for space heating in the Spring and Autumn seasons.
Do I need planning permission for the solar panels?
From April 6th 2008, all homeowners will be able to install microgeneration equipment, like solar panels, without needing to get planning permission if the property is not a listed building or in a conservation area.
A solar panel is just a radiator painted black in a box on the roof, isn’t it?
No. A Solar Panel or Solar Collector isn’t a radiator painted black. This is where solar collectors today differ greatly from solar panels in the past. A solar collector is very efficient at turning light into heat, there is a special coating called an Absorber Surface Coating that is spluttered or fused at a very high temperature with the metal sheet inside the solar collector, it’s this surface that makes the collector so efficient and so effective.
How and where are your solar panels made?
The solar panels are made in Germany and Austria. All good panels are made from a strong aluminium body that will not corrode. A toughened solar glass screen or tube that does not break under hail conditions and/or heavy snow loads and a highly efficient absorber surface coating spluttered (fused) onto the absorber itself. The panels are also insulated with kiln dried glass fibre.
Are your systems Flat Plates or Vacuum Tube?
We install flat plates and vacuum tube collectors but each installation is looked at individually and usually the flat plates have more merit. It's all about the 'aperture area or absorber surface' which is the part of the collector that collects light and turns it into heat. Shockingly flat plate collectors also work on cloudy days, in fact all solar collectors work on cloudy days. If you compare flat plates and evacuated tubes by m2 for m2 of aperture area some, yes only some vacuum tubes are more efficient than flat plates. But if you look at costs per solar panel, collector or system you typically have a much larger absorber surface area on a flat plate system so for a similar cost you would normally expect more output from the flat plates, just because the installed area is larger.
Orientation of flat plate collectors isn’t a problem and vacuum tubes have no benefit over flat plates except on an east facing or west facing elevation where vacuum tubes would be more desirable, especially for winter use. Vacuum Tubes are also more suitable for assisted space heating systems where high temperature and winter output is more important.
As a rule of thumb you would expect a good vacuum tube system with 3m2 aperture area to have a similar output to good 4.5m2 aperture flat plate system.
PLEASE NOTE: A good flat plate has a higher out put per m2 of aperture area than a poor vacuum tube panel.
Other solar company's that aren’t so honest or with less experience might tell you that vacuum tubes are brand new, very exciting and are 'super' powerful and are more powerful than all flat plates. Unfortunately they are falling victim to their suppliers marketing blurb or wishing that you fall victim to their marketing ploy...Beware!
How much does a solar hot water heating system cost?
A solar water heating system for a small bungalow will cost in the region of £3,500, for a family home £4,500 and for the larger home £5,000+. Price varies depending on scaffolding, cylinder type, grant, amount of people to be supplied and vacuum tube or flat plate systems etc.
What grants are available?
£400 from the Low Carbon Building Programme.
Does a solar panel work at night?
Unsurprisingly, even with a full moon, a solar panel does not work at night!? (Yes, we have been asked this before!)
What's the difference between in-roof and on-roof panels?
In-roof or roof integrated panels are fitted in with the tiles and come with a flashing kit. Roof integration is ideal for new builds because the panels can be fitted onto the roof as the roof is being built. If the client wishes to have roof integration on an existing building a scaffolding will be erected and part of the roof area will be stripped of tiles. The solar panels will then be mounted onto the roof batons and flashed. The tiles will then be re-laid on the roof and cut to fit if need be. When a system is installed like this the pipework is hidden within the flashing kit and the finished panel installation looks very neat.
On-roof or Roof mounted panels don't come with a flashing kit because the solar panels sit above the tiles on a sturdy aluminium frame. The frame is bolted to the rafters that support the weight of the roof and the frame stands proud of the tiles creating an air gap. The panels are then fixed to this frame. The flow and return pipework is then connected to the sides of the panels and installed through a tile-slate and into the loft space. When the installation is finished you will be able to see a small amount of pipework and insulation to the left and right side of the panel. You will also see the frame and roof fixings that are aluminium/stainless steel in colour. Please see the pictures of solar panels installations to see the difference for yourself.
I haven't got a south facing roof, can I still have solar?
Not having a south east to south west facing roof is no problem. You have a few choices depending on your project. The first is an east/west split where collectors are installed on the east/west elevations of the roof to collect the Suns energy as it moves through the sky. In the morning the east collector will work, midday both collectors will work and in the afternoon the west collector will work. Systems like this work very well, a solar collector installed on an east or west elevation will only loose 20% efficiency. Another option is flat roof mounting where a vacuum tube solar panel can be installed flat on a flat roof or you could install at 90* on a gable end wall. You also have the option of installing on 'A' frames in the garden. There is always a solution.
Can a Solar Hot Water (Thermal) system power the lights or T.V?
No. A Solar Thermal System only heats water, another type of solar system produces electricity to power your electrical appliances, it’s called a Photovoltaic System or P.V System.
How do you work out what % gets supplied by solar per annum?
We use solar thermal simulation software to do this for us. We enter the location of your house, number of occupants, brand of solar collector, position on the roof, direction, hot water consumption, distance from solar panels to cylinder, insulation used etc, etc, all site specific information to build a picture of your project. We then run a few simulations and select the best system for you. The report we issue with the quotation gives a % supplied by solar as well as kWh saved, units in gas or litres in oil saved and CO2 saved. Each simulation is different but usually the solar coverage is around 55% to 70% per annum. Sometimes it's as high as 80%! We supply and install excellent systems.
Can the solar thermal system be powered by solar electricity?
We can design a solar thermal system to be powered by PV. It is ideal for remote applications or for people who wish to have a zero carbon solar thermal 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 summers day but you will also collect energy on a cloudy winters day. Thermal systems now are much more efficient than they were years ago.
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) is approximately 700W per m2 aperture area. Our flat plate systems for 3 to 5 people have a gross collector area of 5m2 but an aperture area of 4.4m2. So 4.4m2 x 700Wm2 = 3.08kW. So a system of this size would have the same output as a 3kW immersion heater typically found in hot water cylinders. At maximum output of 3kW it would take just over 5 hours to heat 250 litres of water from 5 to 55 degrees C.
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 effect the annual energy output. In the South of England 'Green Systems' flat plate collectors give around 377kWh per m2 and our vacuum tube collectors produce around 519kWh per m2. This figure is heat to the heat exchanger allowing for pipe and pump heat losses on the way in an average home. 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.
Suppose there’s not enough Sun to heat the domestic hot water?
The most user friendly way of operating your boiler with the solar system is to have the boiler timed to come on and heat your domestic hot water at dusk. The easiest option for the user to have this set all year round. This way the solar is free to work all day without hindrance from the boiler. If the solar has heated your hot water to 65 degrees C or above your boiler will not come on, or will just heat your radiators if this function is selected on your central heating controller. If the solar has heated your cylinder to 35 degrees C the boiler will come on, top up the domestic hot water by 30 degrees to 65 degrees C and then turn off. Or if you have your central heating on it will then just work on your central heating.
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.
Am I at risk from Legionella?
As with conventional domestic water heating systems, it is always a good idea to heat your hot water to 65 degrees C before use. This eliminates the very small risk from Legionella bacteria that can infect any hot water system and may cause Legionnaire’s disease in susceptible people (less than 5% of the population). This simply requires the setting of the water heating thermostat on your cylinder to 65 degrees C so that all water is brought up to this temperature and kills the bacteria before use. It is advisable to have your system set to carry out this task on a daily basis.
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 oporate safely at temperatures in excess of 100*C without boiling or vapourising 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.
What is a freeze tolerant system?
A freeze tolarant system is a system that will tolerate being frozen. These systems are vulgar, cheap DIY systems that won't be accredited for any grants, because the panels won't pass the safety tests. This type of panel will freeze in the winter. We don't install this type of system because you can't get heat from a lollipop now can you?
If solar's so good why isn't it included on all new builds?
Part L of the Building Regulations deals with the conservation of fuel and power for buildings in England and Wales. Part L was revised in April 2006 to raise overall energy efficiency standards. The improved standards mean that developers need to consider using low or zero carbon systems (LZC), such as solar panels, to demonstrate compliance.
However, because the regulations set functional requirements, which the individual aspects of a building design and construction must set out to achieve, particular technologies are not demanded in new homes. This performance based approach offers designers the flexibility to choose solutions that best meet their needs, and that are both cost-effective, practical and allow for innovation.
On 23 July 2007 the Government confirmed its timetable for the move towards zero carbon homes, via a planned major progressive tightening of the energy efficiency standards in the Building Regulations, up to the zero carbon target in 2016. There are indications are that LZC technology will increasingly be needed to achieve compliance.
Can Solar Thermal system heat my radiators?
No, but it can heat underfloor heating. It is possible to heat all your home with solar but it is unlikely that you would install the system because of cost. It is easier and more cost effective to assist your boiler with solar.
How does a Solar Thermal system that heats underfloor heating (UFH) work?
An electronic controller constantly compares the temperature of the solar collectors that are usually located on the roof of the building with the temperature of the water in the bottom of the thermal store water 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 to the cylinder's heat exchanger, heating the cylinder in just the same way as a central heating boiler.
The water in the cylinder is then diverted to the underfloor heating system by the use of a valve that monitors the temperature of the return water to the boiler. If the temperature of the return water to the boiler is cooler than the temperature of the water in the thermal store then the valve will divert solar heated water through to your space heating system assisting your boiler.
With a solar assisted domestic UFH system you will need a thermal store cylinder of at least 550 and a 10m2+ solar collector area. A store 1000 litres would be better or larger and a large collector area at a steeper inclination angle than a domestic hot water system. A 60 to 90 degree incline is essential for better performance in the winter months. Any solar heating system designed to a smaller specification than this will have very little effect IE <10% assistance to the heating system.
Can a Solar system heat my Pool?
Solar is well suited to heating swimming pools. We install the new advanced glazed collectors and vacuum tubes, they are much more efficient at heating swimming pools than the traditional ugly black poly swimming pool collectors that you might of 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 pipework 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 pipework 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 it's 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 Green Systems UK we source only the highest quality, award winning solar systems that are recognized for their excellence throughout Europe and the World.
What are the guarantees with the solar thermal system?
Five years on collectors
Two years on parts
One year on labour
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