Answers to questions on Solar

The following is a selection of commonly asked questions. Reading through here will answer most of your questions and some that you hadn't thought of yet!

What Size is the collector?
The 10 tube double-walled tube collector (47mm tubes) is 1760x 760 x130mm (LxWxH)
The 20 tube double-walled tube collector (47mm tubes) is 1760x1500x130mm (LxWxH)
The 30 tube double-walled tube collector (47mm tubes) is 1760x2170x130mm (LxWxH)
The 20 tube double-walled tube collector (58mm tubes) is 1900x1660x130mm (LxWxH)
The 30 tube double-walled tube collector (58mm tubes) is 1900x 2406 x130mm (LxWxH)

How do vacuum tube solar panels compare with flat plates?
On a hot, sunny day, flat plate panels will produce the same amount of heat, more or less, as for vacuum tube panels of the same area. Under ALL other conditions, the vacuum tube panel will outperform flat plate panels - usually by a very significant margin. Flat plate panels perform badly during windy weather, in cold conditions, in overcast conditions etc. Some of the very best flat plate collectors can compensate for this with more advanced design, but even then, they still do not perform as well as vacuum tube panels.

What weight are the collectors?
The 20tube 47mm panel is 48kg, the others are more or less proportional to this weight.
Are the tubes fragile? Are they tough enough to survive impact from hailstones?
The tubes are made from borosilicate glass, which is very tough (also known as pyrex). The tubes are designed to withstand hailstones up to 35mm - so they are unlikely to be broken, unless dropped onto a solid floor prior to installation.

What size solar cylinder should I fit?
We recommend that the 20tube panel is used with cylinders up to 175litres, and the 30tube panel is used with cylinders up to 260litres. Larger cylinders can be heated with 2 or more panels, and it is possible to add an extra panel to benefit from higher temperatures in the winter. In fact, if you fit a smaller cylinder, you will have hotter water, but of course less of it. We would recommend fitting a tank of 135litres if you prefer a smaller amount of hotter water.

What is the output of the panel in terms of kWh?
This varies according to the time of year - in summer we get almost 10times the amount of solar energy that we do in the winter. In the summer, you can expect to get 14kWh of heat per day from a single 20tube panel, whereas in December you can expect only 1.15kWh per day on average. Even in the winter, it is possible to preheat the water to 40C or more if the sun comes out. In fact, if you fit multiple panels, it is possible to heat your hot water to 100C in January (we have seen this in Cornwall).

What is the difference between the 47mm and 58mm tubes?
The standard tubes are 47mm, and are of twin wall construction. The 58mm tubes are also twin-walled, but longer (1.8m rather than 1.5m) and wider. This means that for a given number of tubes the 58mm tubes will produce 50% more heat than the same number of 47mm tubes (but the cost is 50% higher too!).

How hot will the water get?
This depends on the size of the cylinder you chose, and the amount of water you use. A smaller cylinder will be heated to higher temperatures, whereas a larger cylinder will heat more water, but not to the same extent. Systems are generally designed to heat water to 65C or so, although during the winter, it may be necessary to 'top-up' the heat on less sunny days. Large arrays, running high temperature solar antifreeze at high pressures can be designed to achieve temperatures of 170C or more!

Where do these need placing?
Panels should be sited on a south facing wall or roof. In fact, anywhere between South-West and South East will give good results. If you are limited to an East-West facing system, then you will need two panels to provide the same amount of hot water as a single south-facing roof slope. The most frequent solution to this problem is normally to mount one panel on the east slope and a second panel on the west slope. A special controller is available for East/West facing installations.

Does the roof need to be strengthened at all?
The solar panel in operation weighs around 50kg - this is really not much weight for a roof, when you consider the weight of the tiles or slates. Generally there is no requirement to strengthen a house roof prior to mounting the solar panel, except if you are fitting a panel to a very old roof, which has sagging and decaying timbers.

Are spares available?
Yes, spares are always available, should you need them. With no moving parts, it is very unlikely that you will need to replace anything, but occasionally customers break tubes during the installation process, in which case you can purchase a modestly-priced replacement.

Are the panels guaranteed?
Yes, there is a 12month guarantee, although, with no moving parts the panels are extremely long-lived, probably in excess of 25 years. In fact, the manufacturers offer a much longer guarantee, but in the UK we do not offer this extended period due to the legal requirements.

Can I fit this system DIY?
Yes you can! These systems are very easy to fit, and anyone with basic plumbing and electric skills can carry out a DIY installation. Mounting the panel on the roof is sometimes daunting, although it is actually quite simple.

Will the system need to be inspected by a plumber or be installed by a plumber?
No, you can do this yourself. However, you can call in a plumber to carry out the work if you feel you are not able to tackle to plumbing yourself. We normally recommend that you fit a pressurised system. This is not essential, but it allows you to place the solar panel on the roof without worrying about whether it is possible to place the header tank high enough to function correctly. With a pressurised system, the plumbing is simpler, and by running the system at 1-2bar, it is possible to increase the boiling point of the water to 120C or higher - allowing greater safety margins, and lower chance of fluid loss.

How much maintenance do the systems require?
Very little maintenance is required for solar water heating systems. You should occasionally check the system pressure, to make sure there has been no water loss, and to check for any air in the system. The only other requirement is to ensure that there is an electricity supply connected at all times, otherwise without pump circulation, in strong sunshine, the panel could overheat, and start to boil off water.

What about freezing in Cold Weather?
The solar panel is very well insulated - the manifold is surrounded by 2"of rockwool insulation. This is better than your outdoor water pipes, so it is unlikely to freeze except in exceptionally cold weather. However, it is recommended that you take precautions to prevent the possibility of freezing, by either adding antifreeze to the system (use a non-toxic solar antifreeze) or you can use a DELTASOL B controller which has 'freeze protection' - this controller monitors the temperature of the collector - and if it falls below 4C, it will turn on the pump, allowing water to circulate and heat the manifold. You should turn this function off if you use antifreeze.

Can I use Solar Power with a Mains Pressure Hot Water Cylinder?
Yes. There are two ways to achieve this. You can either purchase a mains pressure unvented water cylinder (these can be expensive). Please note that you will have to have a pressure vessel certificate to install these. Alternatively, you can fit a 'solar store' cylinder (see below)

What is a Thermal Store?
A thermal store is a tank which has an additional large surface area high efficiency coil fitted. The mains cold water is fed into this coil, thus heating the water on its way through. The mains water exits the tank as hot as the hottest water in the tank, but without losing any pressure - thus providing mains pressure hot water to the household taps.

Can I get a grant for these systems?
The panels conform to BS EN 12975 standard and are eligible for a CLEARSKIES GRANT. This means (in theory) that grants are available for their fitting by approved installers.

How many panels/tubes do I require to meet my household needs?
This is a difficult question to answer as it depends on your water usage. First you should calculate how large a hot water cylinder you require to meet your needs. Remember that solar cylinders are normally designed to store water for use over 2 days, rather than one, thus allowing you hot water even if the following day is cloudy. Once you have calculated your cylinder size, you can estimate your panel size on the basis of One Solar Tube per 6.5 - 8.5litres of hot water cylinder (i.e. a 20tube panel can supply hot water for a 120-170litre cylinder, and a 30tube panel can supply 180 - 255litres). This assumes you have an unshaded south-facing roof slope to mount the panel.

What about overheating?
Many people worry about this, although on systems with long pipe runs the maximum temperature will be controlled by the insulation on the pipe-runs, as the pipes get hotter, heat losses will increase. If you correctly size a system, then overheating is not that likely, but if you oversize the cylinders - for example if you are a heavy water user and you want maximum gain, then you will need to consider cooling issues- particularly if you plan to go away on holiday during mid summer (ie no water drawn off for a week or two). There are various ways to do it, using the BS3 controller:

1. Overheating protection can be achieved by setting the controller to continue to circulate the water after the sun goes down (OREC) - this effectively utilises the pipework to cool the cylinder. When the cylinder drops below the set temperature, it ceases to circulate.

2. 'Aftercooling' function - when enabled, this function will divert the solar heated water through a separate loop to dump the excess heat - this could be

• A towel radiator in a bathroom
• A radiator installed simply for dumping heat - eg on the outside of the house (assuming it is weatherproof) or in the roofspace).
• If the existing boiler system connected to the top coil in the solar cylinder is pumped, you can use the BS3 solar controller relay to drive the existing central heating pump directly, which will effectively extract heat from the coil inside the cylinder by pumping water around the boiler and house radiators. You should ensure that the boiler is turned off or use a relay between the pump and the boiler controller, to prevent the boiler switching on (normally if the pump is powered-up, as it is connected to the 'call' function of the boiler controller, it will also fire up the boiler). This method involves NO PLUMBING so it can be more attractive for that reason.
  

Even if you have not implemented any of the above, when the panel gets too hot, and steam is produced, the extra volume of the system will be absorbed by the expansion vessel. When the system recools, the steam will condense again and the system will start to work again, without the need to refill or top-up. You should not rely on this method routinely, but it will protect the system without causing damage.

Do I need planning permission for solar panels?
You should refer this question to your local planning department for a definitive answer, but the answer is normally 'No, you do not require planning permission'. This is because solar panels satisfy the 'permitted development' requirements that they 'do not significantly project above the roof plane'. If you live in a listed building, an AONB, Conservation Area etc, then you may be subject to different planning rules. In these circumstances, it is usually possible to site solar panels without the need for planning permission but it varies from case to case. It is also usually possible to mount the panels at ground level to avoid the need for planning permission, if necessary!

How hot will the water get?
This depends on the size of the cylinder you chose, and the amount of water you use. A smaller cylinder will be heated to higher temperatures, whereas a larger cylinder will heat more water, but not to the same extent. Systems are generally designed to heat water to 65C or so, although during the winter, it may be necessary to 'top-up' the heat on less sunny days. Large arrays, running high temperature solar antifreeze at high pressures can be designed to achieve temperatures of 170C or more!

Where do these need placing?
Panels should be sited on a south facing wall or roof. In fact, anywhere between South-West and South East will give good results. If you are limited to an East-West facing system, then you will need two panels to provide the same amount of hot water as a single south-facing roof slope. The most frequent solution to this problem is normally to mount one panel on the east slope and a second panel on the west slope. A special controller is available for East/West facing installations.

Does the roof need to be strengthened at all?
The solar panel in operation weighs around 50kg - this is really not much weight for a roof, when you consider the weight of the tiles or slates. Generally there is no requirement to strengthen a house roof prior to mounting the solar panel, except if you are fitting a panel to a very old roof, which has sagging and decaying timbers.

Are spares available?
Yes, spares are always available, should you need them. With no moving parts, it is very unlikely that you will need to replace anything, but occasionally customers break tubes during the installation process, in which case you can purchase a modestly-priced replacement.

Are the panels guaranteed?
Yes, there is a 12month guarantee, although, with no moving parts the panels are extremely long-lived, probably in excess of 25 years. In fact, the manufacturers offer a much longer guarantee, but in the UK we do not offer this extended period due to the legal requirements.

Can I fit this system DIY?
Yes you can! These systems are very easy to fit, and anyone with basic plumbing and electric skills can carry out a DIY installation. Mounting the panel on the roof is sometimes daunting, although it is actually quite simple.

Will the system need to be inspected by a plumber or be installed by a plumber?
No, you can do this yourself. However, you can call in a plumber to carry out the work if you feel you are not able to tackle to plumbing yourself. We normally recommend that you fit a pressurised system. This is not essential, but it allows you to place the solar panel on the roof without worrying about whether it is possible to place the header tank high enough to function correctly. With a pressurised system, the plumbing is simpler, and by running the system at 1-2bar, it is possible to increase the boiling point of the water to 120C or higher - allowing greater safety margins, and lower chance of fluid loss.

How much maintenance do the systems require?
Very little maintenance is required for solar water heating systems. You should occasionally check the system pressure, to make sure there has been no water loss, and to check for any air in the system. The only other requirement is to ensure that there is an electricity supply connected at all times, otherwise without pump circulation, in strong sunshine, the panel could overheat, and start to boil off water.

What about freezing in Cold Weather?
The solar panel is very well insulated - the manifold is surrounded by 2"of rockwool insulation. This is better than your outdoor water pipes, so it is unlikely to freeze except in exceptionally cold weather. However, it is recommended that you take precautions to prevent the possibility of freezing, by either adding antifreeze to the system (use a non-toxic solar antifreeze) or you can use a DELTASOL B controller which has 'freeze protection' - this controller monitors the temperature of the collector - and if it falls below 4C, it will turn on the pump, allowing water to circulate and heat the manifold. You should turn this function off if you use antifreeze.

Can I use Solar Power with a Mains Pressure Hot Water Cylinder?
Yes. There are two ways to achieve this. You can either purchase a mains pressure unvented water cylinder (these can be expensive). Please note that you will have to have a pressure vessel certificate to install these. Alternatively, you can fit a 'solar store' cylinder (see below)

What is a Thermal Store?
A thermal store is a tank which has an additional large surface area high efficiency coil fitted. The mains cold water is fed into this coil, thus heating the water on its way through. The mains water exits the tank as hot as the hottest water in the tank, but without losing any pressure - thus providing mains pressure hot water to the household taps.

Can I get a grant for these systems?
The panels conform to BS EN 12975 standard and are eligible for a CLEARSKIES GRANT. This means (in theory) that grants are available for their fitting by approved installers.

How many panels/tubes do I require to meet my household needs?
This is a difficult question to answer as it depends on your water usage. First you should calculate how large a hot water cylinder you require to meet your needs. Remember that solar cylinders are normally designed to store water for use over 2 days, rather than one, thus allowing you hot water even if the following day is cloudy. Once you have calculated your cylinder size, you can estimate your panel size on the basis of One Solar Tube per 6.5 - 8.5litres of hot water cylinder (i.e. a 20tube panel can supply hot water for a 120-170litre cylinder, and a 30tube panel can supply 180 - 255litres). This assumes you have an unshaded south-facing roof slope to mount the panel.

Do I need planning permission for solar panels?
You should refer this question to your local planning department for a definitive answer, but the answer is normally 'No, you do not require planning permission'. This is because solar panels satisfy the 'permitted development' requirements that they 'do not significantly project above the roof plane'. If you live in a listed building, an AONB, Conservation Area etc, then you may be subject to different planning rules. In these circumstances, it is usually possible to site solar panels without the need for planning permission but it varies from case to case. It is also usually possible to mount the panels at ground level to avoid the need for planning permission, if necessary!