Post 18 – We Use So Much Electricity

While we were away on our recent holiday, I decided to take the opportunity to see how much electricity the house uses, even if it is not lived in. I was shocked by the result. Actually, shocked is not the best word to describe how I felt, I think frustrated, bordering on angry, better describes my feelings. I like to think we are low users of electricity, especially given how much effort I have put in, and continue to put in, to minimizing our consumption of the commodity, but for what result? It took me a day or so to remember that at least we are buying certified Green Electricity so we are not contributing green house gas emissions to the atmosphere but we are still using far more electricity than I expected. So why do I care how much electricity we use when we are paying a premium to buy renewable electricity? I care for a number of reasons. First, I care because of the cost. Second, I care because it seems like I have wasted a lot of effort for little return and third, I care because I think that in the future we will still have to minimize our use of electricity. I am not of the school of thought that says we will be able to achieve a wholesale exchange of fossil fueled electricity for equivalent volumes of renewable electricity. Another question that I asked myself is why I didn’t realize some time ago how much ‘background’ electricity our house consumes. I have blogged about how little our electricity costs us in summer but not how much it costs in winter. The answer to the ‘why didn’t I understand this before question’ is that the little 1.5 kW solar array on our roof contributes more than I realized to minimizing our draw from the grid. What I see on our electricity invoice is the amount we export, not the amount generated. I checked with our electricity retailer and they confirmed that it is only the exported amount that shows up not the amount generated. They called it ‘net metering’. I would need to get a separate device if I want to know how much we generate, how much we export and how much we use from our own supply.

So now to the details of my holiday experiment. If you are not an electricity consumption nerd, stop reading here!

While we were on holidays, I left the following things running:

Heat pump for hot water
Refrigerator (but I turned off the freezer)
Hot water recirculator
Water pump for the house
Sump pump for the septic system
Solar air heaters to keep the air in the house fresh
Beside lamp
NBN modem/router

Our average daily use was 10 kWh! I was shocked because, if the truth be told, I had this unstated aim that I expected our daily use to be 3 kWh or less, even when we were not on holidays so we are way, way, way off that figure. Now I stop to think about that aim, it is probably very unrealistic during winter, on days when the sun isn’t shining, given we both work from home, and given we need electricity to power our water, sewerage system and heating.

So, back to the analysis of our disappointingly high usage. Of these items that I left on, not all were on 24/7 and each drew differing amounts of electricity. To calculate how much electricity each used in a 24 hour period, I used the manual method published by the South Australian government that is towards the bottom of the page accessed by the green hyperlink. The results were as follows:

Heat pump 0.700 kW on for, say 5 hours/day = 3.5 kW.
Refrigerator – manufacturer says is uses 270 kWh per year so in daily terms = 0.740 kW.
Hot water recirculator 0.025 kW on for 15 hours/day = 0.375 kW.
Water pump for the house – assume it only comes on once a day for 5 minutes to account for evaporation from stock water bowls (that are plumbed into the supply) so 1.500 kW by 12 = 0.125 kW.
Sump pump for the septic system – this shouldn’t have come on at all so = 0 kW.
Solar air heaters to keep the air in the house fresh – these each have 80w fans and we have two of them so 160w fans become 0.160 kW by 24 hours/day = 3.84 kW.
Beside lamp – on for 2 hours/day with an 11w compact fluorescent globe is 0.011 by 2 = 0.022 kW.
NBN modem/router which shows 9v = 0.6 amps and using a calculator translates to 5.4 watts or 0.005 kW by 24 hours = 0.120 kW.

Based on these calculations, I can account for 8.77 kWh per day. I have most likely underestimated the hours per day the heat pump was on. If it was actually on 6.5 hours a day instead of 5, then I would have completely accounted for the 10 kWh. Wow! A useful, if somewhat depressing, exercise.

Now, what have a learnt from this? If I consider the two items using the most power, then my focus shifts to the solar air heaters and the solar heat pump. The first thing I have learnt is that the solar air heaters shouldn’t have been left on as they actually use quite a lot of electricity. When we purchased them six years ago, they were touted as having a fan that uses very little power. Maybe that was considered low usage six years ago, but it isn’t now. I have blogged about solar air heaters before but this is yet another reason not to install solar air heaters in places that have cloudy winters (us).

The second learning that arises out of this exercise, is that the hot water heat pump, which I think is great, and is also touted as being a very efficient appliance (they even get purchase rebates as a solar appliance) still uses a lot of electricity. There is no doubt that they are more efficient in warmer climates and at warmer times of the year. So what can I do to reduce its consumption of electricity without effecting our hot water supply?

A few days ago I put the hot water heat pump onto a timer switch so it now runs from 10 am to 10 pm each day when the ambient air temperature is higher than it is overnight. I checked the booklet that came with the pump to see if there was any commentary about not running the pump the 24/7 and it was silent on the matter. I then did the requisite Google search to see what was said on the web. I was reassured to find out that others had asked the same question. There didn’t seem to be a definitive answer one way or the other. The only issue that spiked my interest was the issue of Legionella contaminating the water and it seems that this isn’t an issue if the water is heated to 60°C once a day, which ours now is. After the first night of the pump being off, the water next morning was plenty hot enough for the little we use to clean up after breakfast. It was also nice and not on mornings two and three (I was concerned that there would a cumulative lowering of the water temperature but it seems not to be so).

Having established that the water was hot enough it then became a question of what happened to our overnight use of electricity. Over the first night most half hour periods seem to be using nearly 300 watts less than the previous night. Yeah! When I have few more nights of data available, I will work out the old average usage between 10 pm and 6 am and the new average usage. I am really hoping for a good result. It looks like this approach could save us the best part of 2.5 kWh a day which would be great.

The other thing I did was change the timer on the water recirculator which was on for about 16 hours a day. Now it is only on from 6 am to 9 am, 11.30 am to 12.30 pm and from 4 pm to 10 pm so a total of 10 hours a day. These times coincide with washing hand, cleaning and showering. All being well, this initiative will save us another 0.15 kWh a day. Well, enough of this nerdy post and so bye for now, Jane.