Solar Thermal

ST Panel

Solar HFC








Heat water for your home using energy from the sun.

Solar water heating systems use free heat from the sun to warm domestic hot water. A conventional boiler or immersion heater can be used to make the water hotter, or to provide hot water when solar energy is unavailable. 

Greenacre Renewable Energy can supply and install systems to meet your all your hot water requirements. We work with Navitron, who are one of the leading UK suppliers.

Please contact us for a free no obligation survey.

What Size Is The Collector?

10 tube double-walled tube collector (47mm tubes) is 1760x 760 x130mm (LxWxH)
20 tube double-walled tube collector (47mm tubes) is 1760x1500x130mm (LxWxH)
30 tube double-walled tube collector (47mm tubes) is 1760x2170x130mm (LxWxH)
20 tube double-walled tube collector (58mm tubes) is 1900x1660x130mm (LxWxH)
30 tube double-walled tube collector (58mm tubes) is 1900x 2406 x130mm (LxWxH)
10 tube single-walled tube collector (70mm tubes) is 1760x1000x130mm (LxWxH)
20 tube single-walled tube collector (70mm tubes) is 1760x 1950 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. Even the best flat plates may underperform by 20% compared to a similar area vacuum tube panel in the UK.

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 falling 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 25mm - so they are unlikely to be broken, unless dropped onto a solid floor prior to installation.

What Size Cylinder Should I Fit?

We recommend that the Navitron 20tube panel is used with cylinders up to 175litres, and the Navitron 30tube panel is used with cylinders from175 - 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 difference between the 47mm, 58mm and 70mm tubes?

The standard tubes are 47mm diameter,1.5m long, and are of twin wall construction. The 58mm tubes are also twin-walled, but longer (1.8m) 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!). The 47mm tubes are easier to transport, and are less fragile in handling due to their shorter length. The 70mm solar tubes are single-walled construction. This is more expensive to manufacture, but provides better performance in extremely cold conditions. A 10tube 70mm panel should produce around 90% of the output of a 20tube 47mm panel.

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 and at what angle?

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. The panels should be mounted at the angle of your latitude. For example, at our location in the UK, this is 53º. This is AVERAGE optimum angle. In fact, in winter the optimum angle is around 10º steeper, whereas in the summer it is 10º shallower. The panels will function anywhere between 15º and 90º angle of inclination. This is actually academic, a variation of 10º will make very little difference to the output, so most people simply settle for whatever angle their roof slope is. The extra cost of trying to stand panels off the roof to achieve better efficiency would probably be better spent on purchasing a second panel, or energy-saving measures such as extra loft insulation!

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. However, it is not possible to post a replacement tube, so you will need to collect it. The tubes are made of borosilicate glass (aka 'Pyrex') so they are actually very tough - and have been independently tested to withstand the impact of a 1" hailstone without damage!

Are The Panels Guaranteed?

Yes, we offer a 24month guarantee on the panels, although, with no moving parts the panels are extremely long-lived, probably in excess of 25years. We can provide a 10year+ warranty if required on the complete installation, for an additional fee.

Can I Fit The 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. We also run training courses, for those who wish to cover the subject in detail. Mounting the panel on the roof is sometimes daunting, although it is actually quite simple - but we can offer this service, if required.

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.

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.

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 pipes freezing, by either adding antifreeze to the system (use our non-toxic solar antifreeze) or you can use a controller which has 'freeze protection' - these controllers monitor the temperature of the collector - and if it falls below 4C, it will automatically 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 an Unvented 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?

Grants were only available for professionally installed systems (NOT DIY). Navitron panels are approved under the Clearskies grant scheme, also for the Republic of Ireland and Scottish Grant schemes. Since the Coalition government took over, grants have been removed for all renewable energy systems. However, Navitron systems will qualify for the RHI incentive when it is eventually introduced).

The RHI will provide owners of Navitron-installed solar thermal systems with an attractive annual cash bonus for the next 25years. However we are still waiting for the RHI to be introduced.

Do I need planning permission?

No you do not need planning permission, unless you are installing on a listed building.

Can I power the pump with solar energy?

Yes, this is possible. We feel that a mains-powered system is the best option, but if you wish to have a PV-powered system, then we can supply the appropriate components.

What is the difference between the single-walled and double-walled solar panels?

The difference relates to the design of the solar tubes. The standard tubes are double-walled, with a vacuum between the two walls of the glass. The centre is filled with air and the heat pipe runs up through the centre. The single walled tube is entirely filled with vacuum, and the vacuum is sealed by a glass-metal weld sealing the heat pipe to the glass. This is technically much more difficult to do, hence the cost is much higher. The single walled tube has a marginal advantage over the double-walled tube in that it reacts much quicker to sunlight (e.g. in winter it starts to heat water within 5-10minutes rather than 10-15minutes, and in summer the single walled tubes will start heating in just 30-45seconds whereas the double-walled tubes will take 2-3minutes) - so it is slightly more efficient in marginal conditions. However, it also cools down quicker, whereas the standard tube will continue to heat for 10-15minutes after the sun goes in. A 10tube single walled panel (70mm diameter tubes) produces about 10% less heat than a standard 20tube double-walled panel (47mm diameter tubes).

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. For example, one person that contacted us lives in a motorhome, and uses only 70litres of hot water over a two week period. A young couple we spoke to estimated that their hot water consumption to be at least 400litres per day! Give us a call and we can talk you through your installation and calculate the appropriate hot water storage volume and suitable panels.

Can I heat my house with evacuated solar tubes?

There is 10 times more sun energy in the summer than in the winter. (This is the reason for the different seasons, after all). Therefore you immediately have the problem that the bulk of the energy is at the wrong time of year. The other problem with using solar to heat your house is that it is not present at the times when it is really cold - at night, on very overcast days, in winter evenings etc. In practice you can provide a significant amount of supplementary heat in the spring and autumn (and some people have implemented such systems), but the contribution in the winter will be minimal, restricted to sunny days, but you will need to fit many more panels, as heating a house is a lot larger task than heating an insulated cylinder of water. Solar water heating on the other hand, can be effective even in the winter, as the amount of heat required is considerably less than that required to heat a house. How much heat energy can I store in my cylinder? Let's use this example - a 260litre cylinder of water, heated to 65C. Assuming that room temperature in the house is 18C, then the difference between the cylinder water and ambient air temperature (dT) is 47C. The heat energy stored can be calculated by multiplying together the volume of water in the tank (in litres) by the dT by the specific heat capacity of water (4200kJ/kg K) - i.e. 260 x 47 x 4200 = 51.3MJ. (if we are really fussy, we can add the heat capacity of the copper cylinder itself - i.e. 0.2MJ). If we divide this by 3.6M, we arrive at the number of kWh storage i.e. you can see we'll need a big storage tank. However, the RHI will provide a very real financial incentive for designing systems able to store heat from the end of summer to heat your house through winter.

What about over-heating?

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 (i.e. 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. 'After cooling' function - when enabled, this function will divert the solar heated water through a separate loop to dump the excess heat - this could be a.) A towel radiator in a bathroom. b) A radiator installed simply for dumping heat - e.g. on the outside of the house (assuming it is weatherproof) or in the roof space). c.) 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. 3. 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 re-cools, 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.

Are The Navitron Panels Certified?

Yes, the Navitron Solar Collectors are certified. Most are certified to the Solar Keymark standard (required for MCS and FITs), and the others are certified to EN BS12975.

How many panels do I need to heat my pool?

It depends what area of pool you need to heat, how well insulated it is, whether it has a pool cover, if it is above/below ground, how many weeks of the year you need to use it etc. However, as a rule of thumb we recommend that you start with solar panels equivalent to 25% of the pool area, but you can increase this up to 35% if more heat is required. As the panels are modular, it is easy to upgrade the panels at a later date if required. We strongly recommend the use of a pool cover when the pool is not in use, as it dramatically reduces heat loss through evaporation.

Can I use a Navitron vacuum tube solar panel with a drain-down system?

Drain down systems are a fairly primitive method for frost-protection. The components are large, expensive, and can easily be avoided using Navitron solar antifreeze or the frost-protection feature of the Navitron controllers. However, if you already have a drain-down system, it may be possible to replace your existing panel with a Navitron panel, although it could cause air locks.

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Greenacre Place, Bristol Road, Highbridge, Somerset TA9 4HA
T: 01278 781821
M: 07881 912845
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