| Our solar thermal system was installed in mid July 2010 by Solar Technologies, a British Gas company, which had already installed our solar PV system. The system consists of three flat panel collectors totalling 7.8 sq metres, heating a vented Gledhill thermal store of 450 litres capacity. |
| The system (panels plus store) cost £8,100 including installation of the panels and connection of the solar loop pipework, but excluding lifting the thermal store into the roof space. Connection to the mains water supply (via a feed and expansion tank), and conection to the domestic hot water system, the underfloor heating manifold and the log burner were also not included. The design, system integration and plumbing work for this was done by Mick and Sam Rennells of CMS Plumbing who did an excellent job, not just in doing very neat and professional pipework but also in understanding and solving problems. |
| Our system is designed to provide both domestic hot water and underfloor heating from the thermal store, fed by the solar panels and the log burner. Our experience so far has been that hot water is plentiful during sunny summer weather, but we have experienced some problems when there are two or three cloudy days in a row. Before the log burner was commissioned we resorted to the immersion heater, but this was not very effective - the 3kW heater struggled to heat the 450 litre store. However, once the log burner was working we found that a 2 hour burn at a high temperature would raise the store temperature by 10 degrees or so without heating the room significantly. |
| Another problem has been that the Gledhill thermal store was supplied with a 50mm insulation jacket - not sprayed insulation - which just isn't adequate. Overnight the temperature loss was initially around 7 deg, we have added a 200mm recycled glass layer (B&Q Space Blanket) which reduced the loss initially by about half. However, this was in the context of outside overnight temperatures around 10-12 degrees, but by late October we have had some nights when the outside temperature dropped well below zero. Losses from the store are back into double figures on these nights, which is just way too high. We are looking at further ways of improving the insulation, including building an insulated room within the loft space around the thermal store. It does seem inescapable that the Gledhill store insulation is seriously ineffective. |
| The log burner - a 12K Woodfire F12 with back boiler - can put around 10Kw into the thermal store, which raises the temperature at the top of the store quite quickly. This helps produce good water temperatures for showers, but it takes a lot longer to raise the temperature at the lower levels of the store. Since the underfloor heating coil is lower in the store. we weren't sure that running the underfloor heating in cold weather would be sufficiently offset by heat put back into the store by the log burner. By late October we have now had more experience of running the log burner and the underfloor heating, and it seems pretty certain that the log burner will comfortably put more heat into the store than the underfloor heating takes out, even in cold weather. There is an initial stage when the underfloor heating is switched on and the temperature in the lower part of the store drops quite quickly before the log burner starts to kick in. THis is exacerbated by the temperature losses from the store referred to above, if the underfloor heating is switched on when the lower store temperature is only 55 degrees, it will quickly drop to 40 or below at which point the heating is not effective. |
| One encouraging sign is that we have been monitoring temperatures inside the house upstairs (where there is no heating) and downstairs, and so far we have found that internal temperatures don't drop significantly overnight when there is no heating on at all. The lowest exterior overnight temperature we have had so far was minus 3 deg C, but the interior temperatures have remained at between 18 and 19.5 constantly. We hope this is an early indication that the combination of insulation (underfloor, cavity wall, exterior to the first floor, and lof insulation) with highly efficient triple glazing is working well. Not all the insulation is complete yet - some insulation particularly in the loft not yet in place and some odd draughts still to be dealt with - but we are hopeful that the heating requirement will prove to be very low. |
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