I have read your web posting with interest - very detailed and scientific
Thank you.
1. As others have said 3kWh is very low for the heat absorption available - either you are starting with less than half a tank of hot water or a short immersion heater - as a typical 100 litres tank requires 9kWh to heat from 10 DegC;
Yes, I think we probably have a short immersion. I'll be checking that out when we get a warm day and the central heating stays off! I'm planning to check with an external heat sensor.
2. Your boiler efficiency may be 70% but this will be degraded by pipework losses and boiler cycling to a more typical 60% in the summer;
Agreed - and some folks believe even less. As it happens my old Camray is rated at 70%, but hopefully a newer condensing boiler at something like 93% efficient should come down to around 70% or better when taking pipes and other losses into account.
3. The orientation of your panels maybe a significant factor in output available so far as low winter sun will not be able to give much generation;
Yes, as I mention in the article, the panels are WSW which isn't terribly good. Also, it tends to be cloudy in the Vale of York. On the bright side, in the last month the panels offset 200kWh we would have pulled from the grid, but we did export 130kWh for our neighbours to use - if only there were some way to use that locally
4. Your base load of 800W seems very high, 300W seems more typical - as with all good energy management you should go round turning off things on standby, etc.
Indeed, it is high. Overnight it's down to about 350W but sadly during the day we're in the house. To be honest we get good value from the power we're using and tend to leave large loads until the sun is shining. With two young children who like muddy puddles, plus two adults doing computer-based work at home I sometimes think we are lucky to come in at 800W!
Interesting to see how your calculations develop over the next few months as I reckon that 1.5kW differential is break-even with gas and a 4kW system should give significant savings over the summer with a 3kW heater.
Yes, you could be right. Although my web page says "oil", you could insert
values for a gas based system into those text boxes and see what it says. I'm hoping to update it when I have more data - it could be enough to capture 'til the Summer solstice and then double everything up for a rough idea.
By the way, feel free to ask if there's some way of presenting the data that would help explain things you're interested in. Sadly the calculations included over 1million readings each for the house and solar over three months so even if I make my Javascript very fast, it'll stress your computer doing the detailed calculations.
If you have read all the posts on this thread you will be aware that I am marketing a simple SolarHeat controller which does not measure the differential but is cheap(ish) and can be configured to switch at 1.5kW or 2.5kW output. I recommend this type for summer use only.
Sounds like a good plan. Best of luck with your sales.
