With rising energy costs and an erratic grid supply, I started investigating various options to save energy and reduce my energy bill. My plan was to adopt a phased approach to first reduce consumption, then produce energy via renewable resources and finally to provide backup energy when the grid fails.
I first started with looking at my current energy consumption. This entailed looking at my utility accounts for the past two years to determine my average monthly and daily consumption. What I learned from this is that our household was consuming on 30kWh of energy per day. I suppose that’s not too bad for a household of two adults, two kids and a live-in domestic worker.
We have had LED and CFL lamps installed for quite a while now, so the energy use for lighting is as low as can be – around 350W for all the internal and external lighting. Realistically, the consumption is around 200W in total as not all the lights are on at the same time.
In order to further reduce consumption, I would need to identify the big loads and find alternatives to power these. First thing I did was to install an Efergy energy monitor on the main incomer to monitor our load profile. I got mine from one of my new favourite websites: Sustainable.co.za.
This consists of a transmitter with a clamp-on CT unit and a small wireless receiver that connects to your Wi-Fi network. The transmitter measures energy consumption and transmits to the hub every 6 seconds. The measurements are then accessed via the online portal to create a load profile that can show energy use as kW consumed or kWh units consumed. It also allows you to enter the unit costs so you can get an idea of what your electric bill will be at the end of the month.
What I learned from this was that we had some serious spikes in our consumption at certain times of the day: morning, midday to early afternoon, early evening and late evening.
Looking at the graph I realised that my geyser was coming on at some some really strange times: from 1am to 2.30am, again at midday, once again at around 6pm and and then at 9pm. (The 9pm time show in the graph because that particular night we had a bout of load-shedding from 8.30pm to 10pm!
First thing I did was to re-programme my geyser controller. I have had a Geyserwise controller ever since we bought the house, but never set it properly. I can’t comment on the effectiveness in terms of energy saving as it’s always been there for me, but it does help with shifting the peak load around.
The graph above shows the usage after the geyser controller was reprogrammed. Now it switches on at 5am to make sure we have hot water for the morning shower then again at 5pm to make sure the kids have hot water for their shower at 6pm and finally at 9pm for the adult showers. So far we haven’t had an issue with running out of hot water.
Another thing that I noticed, was a big spike in consumption at around 6pm every night. This was due to the stove being used for dinner. At the same time our live-in housekeeper was preparing her dinner on her 2-plate electric stove. Some nights the peak went up to close on 10kW!
With the ultimate goal being to install a solar power system to reduce our grid dependance, the first thing to do would be to reduce the peak demand during the day in order to reduce the size of the solar PV array and the inverter required.
To do this, I decided to go about my energy saving mission in the following order:
- Install solar water heating: either evacuated solar tubes retrofitted to my existing geyser or a dual element powered via PV.
- Replace electric hob and oven in the house as well as the 2-plate stove for the housekeeper with gas stoves.
- Install a grid-tied PV system to supplement the utility supply during the day.
- Install battery back-up that gets charged by the PV system during the day to provide back-up power during load-shedding or grid-failure.
This is not a cheap exercise, so a bit of research is going to be necessary for this. My initial guess at costs was as follows:
- Solar water heating: R 15,000
- Gas stoves: R 12,000
- Solar PV system: R 50,000
- Battery back-up: R 15,000
- Total cost: R 92,000!
Assuming I can reduce my utility bill by R 1,000/month, this would give me a payback period of 92-months or 7,5-years. That’s based on current energy charges, so the actual payback would probably be around 6-years with energy charges set to increase by at least 15% a year if Eskom get their way.
My plan is to do most of the installation work myself to reduce costs as much as possible and also to have the satisfaction of making the system work the way I want it to.
Time now to do some homework and get the plan in motion!