Spirit Solar
Installers of heat pumps, insulation, and domestic and commercial solar PV (electricity) and solar thermal (hot water) systems.

Our products - Solar Thermal

Collectors - general background

There are two types of collector: flat plate collectors and evacuated tubes.

Flat Plate Collectors

Flat panel collectors are composed of insulated flow tubes encased within an absorbing plate and surrounded by further insulation. This is all enclosed within a frame, usually aluminium or galvanised steel, and a transparent cover. The heat transfer fluid travels through the flow tubes and is heated, and then heats the domestic water.

Evacuated Tube Collectors

Evacuated or Vacuum Tubes are so called because the absorber sits in a vacuum, significantly reducing the heat loss, particularly in cold weather.

The tubes are made from glass - typically ultra-strong and heat resistant pyrex with a double wall construction. The glass on the inner tube is coated on its outer surface with an absorbant coating, and on its inner surface with a reflective coating. Inside each tube is a copper heat pipe containing a glycol / anti-freeze mixture.

There are two types of evacuated tube collector: "direct flow" and "heat pipe".

In direct flow technology, the fluid running through the copper tube is pumped all the way around the system, passing through the heat exchanger in the cylinder, and thus transferring its heat directly to the water in the cylinder.

In heat pipe technology, there is a second 'fluid circuit' running through the manifold (top) of the tubes. The fluid in the copper heat pipe in the tube is sealed off from the fluid in the manifold. As the tube gets hot, the liquid in the copper heat pipe is vapourised; the hot vapours rise to the top of the heat pipe where the copper tip connects with a header pipe through which the manifold fluid flows. The heat passes from the vapour to the manifold fluid. The manifold fluid is then pumped through the heat exchanger in the cylinder.

Heat pipe technology

The copper at the tip of the heat tube can reach well over 200 degrees easily heating water to 90 degrees celcius on hot days and to 60 degrees celcius even in the winter. This simple system is completely sealed and needs minimal maintenance over its 20+ years life.

See below to read about the benefits / features of heat pipe versus direct flow technology.

Flat Panel versus Evacuated Tube - Which one should I choose?

Flat plate collectors are generally cheaper per square metre than vacuum tubes, but less efficient. To achieve the same output you therefore require a larger area of flat plate (about 65% more), bringing the overall system cost up to the cost of a vacuum tube system.

Vacuum tube collectors are more efficient as they have a much lower level of heat loss due to the absorber plate being in a vacuum. In addition, the tube shape means that the sunlight is perpendicular for most of the day giving more consistent heating even in lower temperatures. Tubes are also smaller and lighter than flat plates making them easier to fit with less weight on the roof.

Tubes do not require an 'A' frame when installed on a horizontal surface i.e. a flat roof, thus avoiding wind-lift and making them less obtrusive. They can be installed horizontally directly onto a wall with the tubes twisted towards the sun at the optimum angle. They do not corrode. Tubes take less energy to make, less materials, there are no problems with condensation, snow slides off easily and they work in freezing conditions. They are 100% recyclable, hail proof and built to withstand substantial snow load.

Tubes are also modular, which means they can be customised for particular requirements.

Flat Plate collectors have been well proven over the last 100 years or so, typically lasting between 20 and 30 years. They work well when the water only needs to be heated by a small amount which makes them ideal for heating swimming pools and in extremely hot climates where the water needs to be heated by less than 20°C. They also look similar to Velux windows, and are more likely to get listed building consent, or planning consent in a conservation area.

In general for most domestic hot water requirements (apart from pools) we recommend tube collectors; however it is very important to choose a high quality tube collector, to ensure that the vacuum is not lost after a few years. See below for more information on our Thermomax tubes.

Our Evacuated Tube collectors - Thermomax from Kingspan

The original evacuated tubes were made by Thermomax, now part of Kingspan. With 25 years' experience in making tubes, Thermomax is firmly established as the world leader. Their panels were the first to receive the Solar Keymark certification of quality; in addition they have also received the International Forum Design award for excellence in product design.

Their collectors combine high efficiency with good reliability and unique safety features. Since Thermomax is a British company the collectors are also designed specifically for the North European market. The collectors are now manufactured and designed in Ireland. Quality is of paramount importance - the collectors are much better made from cheaper Far East imports, an important consideration given that the whole system will stop working if for example air gets in.

Thermomax solar thermal tubes maintain a superior vacuum over a longer period of time through:

• High quality glass - unique properties give good transmissibility with low reflection losses and increased durability.
• Superior vacuum - by creating a vacuum of 10-6 bar within the tube, thermal losses caused by conduction and convection are eliminated.
• Glass to metal seal - unique fusing process for durability.

Heat Pipe versus Direct Flow Technology

See above for an explanation of the difference between Heat Pipe and Direct Flow Technology.

Thermomax make four models: HP200 /HP100 (heat pipe), DF100 (direct flow) and the new Varisol model, which is a modular form of the DF direct flow tubes.

The HP-200 is the premium product. It is characterised by super fast heat transfer - the heat transfer fluid conducts heat much faster than the direct flow system. The HP-200 therefore functions better than other panels at lower levels of solar radiation.

The HP-200 has a slightly lower heat loss coefficient than the direct flow tubes and a lower stagnation temperature. It also has a unique safety cut out feature, incorporating a memotron valve which switches the tubes off at temperatures of 90°C / 135°C.

Another advantage of the heat pipe technology is that the system does not have to be 'drained down' if there is a problem with one tube. Individual tubes can easily be disconnected from the manifold and replaced or maintained.

The one limitation of Heat Pipe technology is that it relies on gravity (hot vapour rising) and it therefore needs to be mounted at an angle of between 20 and 70 degrees to the horizontal to work - so on a sloping roof, or on an A-frame on a flat roof.

The Varisol is a relatively new variation of the DF-100. It allows individual tubes to be 'clicked' together to create solar panels of varying sizes. This means collectors can be sized exactly to fit a space, or to meet the hot water requirements of the user more precisely.

Our flat plate panels

We use Kingspan flat plate collectors and EWF collectors. They are both highly efficient, cost effective and good looking.

Our controllers

We use DeltaSol controllers from Resol. They are easy to use, are very reliable and have been on the market for 30 years.

Our cylinders

We recommend a range of cylinders, including Newark (copper), Gledhill, Velux and Kingspan. Copper cylinders are generally used with vented systems and stainless steel cylinders are used with unvented systems.