I’m due a proper contemplative look back at the past few years. A thoughtful assessment of the whole process of building a house. But given the speed life is moving at the moment, I’m finding it hard to sort the velux blinds (that I ordered the wrong size) let alone sit down in a quiet place for a few hours of contemplation.
So in lieu of that, I’ve been doing some meter readings and calculating things. It’s been a trying time for Adrian the heating engineer as I have been trying to get my head around the system, and calling him with puzzled questions, but I think I’ve now worked out which of the four metres is which and the various false alarms about energy use have been put to bed.
It’s worth noting that these figures are perhaps not that indicative of the house in normal use because
1. It covers just the winter months Oct-end April
2. Much of the measurements have been during the build when the heating was on quite warm to dry the house out but not much hot water was being used.
The space heating and hot water is delivered by a heat pump (and solar gain is providing a really good level of heating when the sun is out). In this allegedly temperate coastal climate (though you wouldn’t know it judging by the outside temperatures today, the first day of May, and the snow on the hills) an air source heat pump is supposed to be quite effective as the air temperature doesn’t drop too low very often.
We also have solar panels on the SW and SE facing roofs and large Southwest facing windows for solar gain.
So here’s all the boring ol’ figures….
Since October, when the heat pump went on, we have used
3406 units of electricity (EM1) to run the heat pump (it has its own electricity meter). Which cost us 14p a unit, making a total cost £476.84 for the electricity to power the heat pump
With this energy we generated 8870KWh of heat (HM1).
The equation used to calculate how much we should be paid for the Renewable Heat Incentive is, for some reason,
which means, with a RHI of 7.51p/KWh this gives us a payment of £369 for the total period.
Our solar electricity meter tells me we have produced 817.6KWh since it was commissioned in November.
Which at 12.8p/KWh (which I think is our payment rate but I’d have to wait for the payment to come through to double check) I think will have brought in £104.65
The electricity company also assume that I export half of what I use and pay a fee of 4.88p/KWh for that.
This means I should receive £124.60 payment for the electricity I have produced over the winter since November.
So the total calculation is
476.84-369-124.60 = negative 16.76 (i.e. A profit of £16.76)
So, if I’m not counting other use of electrical energy in the house, I’m managing to get my heating for free/make a small profit.
However, to complicate matters, some of the electricity made by the solar panels will have been used to power my heat pump (or other electrical appliances in the house like MVHR that are on when the sun is shining), as electricity generated while electricity is in use in the house is used rather than exported, but still receives the payments.
It’s hard to know how much of the energy I produced has been used but I can calculate a maximum and minimum. As a minimum this is zero and the maximum is that all of the energy I produced was used which means I would have saved buying in 817.6 KWh of electricity saving another £114.5 (at a cost of 14p per unit).
This means that the cost balance was between £16.76 and £131.26 in my favour. Which strikes me as good, given that it was taken over the winter when heat demand will be at its highest and solar energy will be at its lowest.
I’m looking forward to looking again at my meters after the summer to see how things stack up then.
However, the point of building this house was to be all green and smug and eco and, although compromises needed to be made over the process, it’s really the carbon emissions from space and water heating I think I ought to be minimizing. So how do we do in this regard?
The total electricity use minus that generated by solar is 2588 KWh. The estimate of carbon emissions from electricity is 0.496kg CO2/KWh *
Therefore my space and water heating between start October and end April (seven months) has produced 1.3 tonnes of CO2. I’ve been trying to find the datasets to compare this against and I ought to have access to them from all my previous carbon counting efforts. It won’t come as a surprise to you but it seems all my posts but one on travel have been lost, which isn’t very helpful. However from recollection the average house emits 6 tonnes CO2 per year so this seems ok. I’ll update the calculations after the summer.
Apologies if that was stupendously boring, but my guess is that if you have actually made it to the end of this post, you have an unnatural interest in things related to energy and carbon emissions, so I am hoping you enjoyed it.
You may also want to point out schoolboy errors I have made in my calculations. Please feel free to use the comments box!
* ref: Energy Saving Trust http://www.energysavingtrust.org.uk/corporate/our-calculations
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