Electricity

Apropos of yesterday's post on electric tanks, during the electricity price crisis, and as I've written before, we've had our underfloor heating switched off and are using our 12.3kW log burner to heat the house (a wise investment).

However, to heat the domestic hot water we've had to keep part of the system on, and that relies on the air-source heat pump to operate.

Now, while the cost of using the air-source to heat domestic hot water is a negligible extra when the underfloor heating is on (and free when the solar panels are generating lots of electricity during the day when sunny, but not at night), it's a relatively high cost when everything else is switched off - around 16kWh per day, just for 24x7 hot water, which we don't use 24x7.

What's needed is more of an on-demand system for the domestic hot water - some form of geyser system. This will become more important once we lose the feed-in tariff in 16 or so years time. Electric showers may also be more economic to run when there's no underfloor heating operating.

The electricity crisis has really focussed our minds on how to run the house more cost-effectively. Having oodles of free, solar energy has made us rather complacent.

Below is an analysis of the cost of running the house on electricity over the last year (click to enlarge).

You can see the huge down-spike (down is greater cost) over this Christmas when we put the underfloor heating on and had No.2 Son staying. There are other spikes, but that's due to one of our rented cabins, which is connected to our system and only has electric heating. It's inhabited by a business for around 2 or 3 days a week and puts a huge drain on our supply.

You can also see, in the last week, where I have switched the air-source heat pump off, resulting in no domestic hot water (it's far more efficient to use either a kettle for a bowl of hot water, or leave a pan of hot water on top of the log fire). This has returned us to summer consumption levels, obviously, but we are spending a couple of hundred quid a month on logs. That said, the feed-in rebate pays for those.

It demonstrates the inefficiency of an air-source heat pump when used solely for domestic hot water, it being far more efficient to use an on-demand system for the few times during the day that hot water is actually needed. Use it in combination with a standard home heating system and it's not too bad.

We should have installed a back boiler to the log burner when we built the house, but we never envisaged the electricity price crisis. At least we can heat the vast majority of the house (except one room) with the one log burner - and very effectively too.

Our annualised electricity consumption continues to nosedive spectacularly, specifically due to our efforts this winter, as you can see from the chart below (again, click to enlarge).

We're down to 7,000 kWh per annum from an average of 14,500 kWh and a very profligate peak of 17,500 kWh.

I've been invited to sign up for the Peak Usage scheme by British Gas (our electricity supplier), whereby if you use less electricity between 5 and 6pm than you used just before that time, you get a payment. You're emailed on the days the scheme applies. However, given we're using only 6kWh a day at present, due to having all forms of electrical heating off, it's doubtful we'll actually receive any payment.

Given the hour the Peak Usage scheme operates, it's doubtful if anyone can get a payment, as few people are home before 6pm anyway. That hour, nevertheless is when peak demand happens, possibly because 5pm is precisely when timed heating systems are timed to crank up into operation in preparation for when people get home at 6 - although the majority of those heating systems will be gas and not electric. I guess you could time it to come on at 4, go off again at 5 (when the house will at least be partially heated) and then come on again at 6, which achieves the overall aim of flattening the 5-6pm peak. 

Flatten the curve is a mantra we should be well acquainted with now.