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Solar Thermal

Solar thermal is not to be confused with solar PV! Solar PV generates electricity directly from sunlight, solar thermal heats up water. It’s all in the name, thermal! A solar thermal system consists of a collector, a pump and a well-insulated hot water tank. The collector on the roof collects the energy from the sun with its absorbers and either transfers it directly into re-circulating water or more commonly into a heat transfer medium, a water glycol mixture, anti freeze to you and me, but let’s just assume it’s ‘water’ for simplicity. The heat is transferred through pipes into the hot water storage tank. The solar collector is best explained as like being a radiator working in reverse. In fact you can build a DIY unit FROM a radiator but the latest versions use evacuated glass tube collector. Glass lets light through but not heat so anything under a pane of glass can get very hot. If you eliminate any drafts it will stay hot and ideally if you remove the air (hence the evacuated tubes) there is even less heat loss. You then have a black tube running through the middle of the evacuated glass tube and pump the ‘water’ through it, slowly. The more tubes you have, the more surface area, the more heat you collect. They are normally located on the roof but they don’t have to be, ours is on a South-facing wall. The critical factor is to ensure they are not in shadow and are oriented to be heated by the sun throughout the day. The panel collects the Sun’s energy and transfers the heat to the ‘water’ hence to the storage tank via the tanks internal heat exchanger. Typically the water/glycol mixture is pumped around through a coil in your hot water tank just like your central heating system. Again the latest system use a pump powered by a small solar PV cell, the clever bit being it only comes on when the sun shines and, ergo, the solar collector is hot. Normally in the older system like ours the pump is switched on when the temperature sensors detects the water in the panels is 7oC or so hotter than the bottom temperature of your storage tank. A bonus is that a third sensor will tell you how hot the top of the tank is so you can decide when to have a bath or need to warm it up a bit with the central heating. The coil or heat exchanger is typically located in the bottom of your hot water tank and your normal central heating coil located above it in the middle of the tank. However you can have a completely separate storage tank acting as a pre-heat tank for the existing hot water tank. The storage tank allows the hot water to be stored until it is used at night or in the morning. A well-planned and well-designed solar system can give a maximum of 70% saving on water heating during a year. From about May to the end of October, it is possible for a solar system to cover 100% of all your hot water needs. For the remainder of the year, the cold water supply coming into the bottom of your tank will be preheated and the rest of the hot water will come from the existing method of water central heating system. Solar is simple, fully automatic, and completely reliable and requires no regular maintenance for 20-30 years. It is possible that you may need a service call over that time, but there is no need to change the fluid, clean the panels, or oil the pumps. Our 14-year-old system has a flat panel collector (radiator) located on a south facing wall and a pump that is powered by domestic electricity. It saves us over £300 a year and we only had to replace the pump last year. We have had a purely solar hot water bath in December on a bright, snowy winter’s day and during summer it's gets so hot you can do 'Whites Wash' with it. Your design can simple or complex as you want depending what you need and we can help you design and install it.

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