Just over a year on from installation, I have now had a full years worth of gas bills with which to do a direct comparison with the previous year(s).
The solar system, commissioned at the end of March 2006, comprises a Navitron 20-tube 47mm panel, slightly south-east facing on a 25 degree roof slope with a 1200x450mm solar cylinder (of approx 172 litres), Resol BS/3 controller plus the usual extra bits. Total cost was £1,200 with all pipework, fittings, lagging etc.
Gas consumption saved over the year April 06 - April 07 is
5400kWh which equates to approximately 23% saving over the previous 05-06 period. The saving over previous years is a little higher but it must be considered that winters are getting warmer so the the use of less central heating in the winter quarters must be taken in consideration when lauding the savings.
Actual cost saving works out to around £120 year-on-year.
But, also consider that as part of the package I spent a further £300 to improve the exisiting CH/DHW controls to meet full Part-L specification so not alll the saving can be attributable to the solar installation. However this included dual cylinder stats on separately timed zones to maximise the solar gain vs boiler operation.
It must also be considered that this saving occured during the highest gas prices we have ever experienced but even compensating for this, it is still a very worthwhile return.
Putting this into context for anyone sceptical about spending even £1,500 to upgrade their entire system, £120 return on a £1,500 investment in 12 months equates to an interest rate of
8% tax free.
To get this sort of return you would either need to invest the same amount in an ISA at 8% or in a taxable account paying 10% gross - try doing
that in your High Street Building Society
For the first year, I ran Resol settings intended to transfer maximum heat into the cylinder (DTO=5.5, DTF=3.5). Total solar pump run time was 1200 hours and 6 hours on Heat Dump.
I have now set DTO to 7.5 and DTF to 4.5 to run a direct comparison over the next 12 months. This allows the manifold to heat up more and maintains a slightly higher differential temperature in the solar loop which should improve heat transfer to the cylinder I now also have the Heat Dump operating at 67.5 degrees rather than 65 to allow more input for days when little or no DHW is drawn off during the day.
Antman
