new heating and hot water system

[benluke]

Hi,

We're just about to replace the heating system in our house. We have a (soon to be) four bed semi-detached house, currently 3 bed. We are replacing the boiler and all radiators and are considering the most efficient way to heat our home and provision of hot water.


We have been monitoring how we generally heat the house and where we need the heat to be during the winter months. We rarely turn on the heaters up stairs. Down stairs we have a large lounge which houses a large wood burner. We run the wood-burner as much as possible during the winter. This heats the lounge more than adequately. We then have two reception rooms and a large kitchen - these are the rooms that really need heating during the winter.

Our gas bill rockets as soon as we start using the heating in the winter. I'm very aware of the cost so we don't just have the heating on all the time. Our gas bill goes from between £15 to £45 a month from April to October then jumps to between £70 and £100 during November to March.

A thought we have had is to install solar panels and run "smart" electric heaters in all rooms. As we really only need to heat the 3 previously mentioned rooms we have been considering whether this would be a more efficient (cheaper to run) solution than a standard gas central heating system? We would install electric heaters in all rooms of course for the odd occasion that we would need to heat the other rooms.

Would the panels supply enough electricity in the winter to run such a heating system?

Long term would have it have a negative effect when selling the property? I suppose not if it were more efficient than standard gas combi boiler set up.

If we went for panels + electric heating we would still need hot water so what would we need to install to supply this? Combi?

I know electricity is approx 2.5 times more expensive than gas but will having the solar panels result in a more efficient solution? At the moment we are getting stung with the gas bill every winter.

If we need to install a combi anyway for hot water would it be best to go for standard central heating system.

If anyone has any advice or guidance it would be greatly greatly appreciated.

Thanks
Ben

 

[stem]

Most domestic solar installations generate a maximum of about 4kW in bright light and dependent upon the orientation of the panels. If you are spending £100 per month on gas I reckon that means you are using approx 2,000 kW / hours of gas per month during the worst winter months. I've assumed for the purpose of calculation, that 75% of the gas consumed (1,500 kWh) is actually used to heat the radiators. The rest would be for cooking, hot water and what is lost via the boiler's flue. There are variables to my assumptions, so you may want to tweak the figures to reflect reality, but at least this will give you an idea.

If I've done my sums right, then based on you having your heating on for an average of 8 hours a day* that would equate to a average demand of 6.25 Kw, [1,500 kWh / 30 days / 8 hours = 6.25 kW] In reality though, the heating load would be higher when it first comes on, say 10 kW, but would drop as the house warms and the thermostats start lowering the load to give an overall average of 6.25 kW.

From the above, you can see that there is already a shortfall from the 4 kW available if the panels were working at maximum capacity, but it gets worse when you consider that in the winter that there may only be 6 hours of daylight, so no energy would be produced by solar panels first thing in the morning or during the evening when you most likely would require heat. So in reality, the solar panels may only provide a usable 10% of the electricity required for heating, or even less, depending upon when you use it.

Then, when you consider any electricity you use from the grid (when it's dark, or to supplement the 4 kW during daylight) would cost 250% (2.5 times) more than gas, a 10% saving in usage isn't looking good.

This figure is based on the worst case months and would improve slightly as the days get longer and the weather improves.

So Currently with the estimated 1,500 kWh of gas used for room heating at £0.05 per kWh = £75 per month.

With electricity 1,500 kWh, less the 10% saving from the solar = 1,350 kWh still required from the grid. Using 1,350 kWh of electricity at 2.5 times £0.05 = £169 per month.

Don't forget too, that a solar installation will cost in the region of £7,000 but you would get that back eventually over about 15 years assuming that you use all of the energy generated during the daylight and receive the current government incentives.

[*If you have your heating on for less than 8 hours per day then the kW increases to get to the monthly 1,500 kW / hours, if you have it on for longer the kW decreases to get to the 1,500 kW / hours]