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See also: EVworld.au – heaps more EV-specific info.
Since installing solar panels we have become used to timing our use of electricity, where possible, to coincide with the availability of sunshine – utilising our solar-generated electricity to run our pool filter and solar heating pumps (our main power culprits), and also the dishwasher, washing machine, etc, along with battery charging for all our gardening and power tools, phones and tablet devices.
We have now added one more device to our list of devices to charge – an electric vehicle (EV).
Can we utilize electricity generated from our solar panels to run/charge all these appliances and devices? Plus an electric vehicle?
Well, yes – up to a point….
Managing the electricity balance
Our first consideration is our solar generating capacity – we have a relatively small 4.2kW solar system on our roof. This energy is produced from 17 panels – which is all we can fit on our roof!
It is also worth remembering that our panels are a few years old now, and their output isn’t as high as more recent panels. (Our panels produce around 250W each, while more recent panels are outputting closer to 450W.) Our panels face east and west – a 50-50 split – so we only get close to maximum output during the middle of the day.
Once our consumption exceeds the output of our solar panels, we begin drawing electricity from the grid. So we need to balance our use of appliances and battery charging so as not to exceed this output.
And we like to use as much of our solar-generated electricity as possible, rather than send it back to the grid for a paltry 5c/kWh.
Initially we set about measuring how much electricity our various devices consume, just to get it all in perspective….
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- Pool filter pump – 0.9 kW
- Pool solar pump – 0.7 kW
- Washing machine – 0.03 – 0.2 kW (depending on washing cycle)
- Dishwasher – 0.9 kW
- Fridge – 0.04 kW
- TV & Sound – 0.08 kW
- Lawn mower, edger – 0.25 kWh (battery)
- iPhone – 0.012 kWh (battery)
- iPad – 0.03 kWh (battery)
- Electric car – 2.0 kW (Granny) 7.0 kW (Wall)
The above appliance consumption should be considered in light of the (maximum) 4.2kW that is available from our solar panels during a sunny day. In reality, given the east-west orientation of our panels, we work on 3kW output, especially outside of summer. A battery-powered car drawing 7kW is in another league, compared to our regular devices – it well and truly blows the solar panel limit. (If we choose to charge the car on a sunny day we can use the 2kW ‘granny’ charger to utilise maximum solar energy.)
But all is not lost….
Stop Press!
Even using all the output from our solar panels on a sunny day, I estimate we would still be paying about 20c/kWh to charge our EV – if the EV is charging at 7kW and the solar panels are only outputting 3kW. So, we will be charging the car between 12am and 6am for 8c/kWh. At this rate the cost of travelling 100kms will be under $1.50! |
Forget all the solar balancing calculations – we have just signed up to the The EV factor
It may seem odd that we are embracing a device that consumes a rather large amount of electricity, when we are trying to ‘escape the grid’.
A more accurate assessment of our goals is that we are trying to minimise our use of energy, particularly from non-renewable energy sources, and minimise the cost of our energy consumption.
Our most easily-accessible renewable energy source are the solar panels on our roof. It is also our cheapest supply of energy, so focusing our energy consumption through our use of our solar-generated electricity is a high priority.
However, our 4kW solar system isn’t able to supply enough energy to charge our EV via a 7kW wall connector. (A 2kW granny charger is an option, but it would take days to re-charge during sunlight hours!). So, the grid becomes an option again, when we consider the off-peak rates detailed above.
Our previous car with an Internal Combustion Engine (ICE) used petrol as its energy source. At the time of writing this post, the cost of 98 octane fuel (recommend for our VW Tiguan) was $2.25 a litre, and we were consuming around 8 litres per 100km.
The cost of travelling 100 kms in our VW Tiguan was $18, plus the ‘cost’ to the environment of pumping out our exhaust.
Our new MG EV is propelled only by electricity, which at the time of writing is costing us $0.08 per kWh (see panel above). The MG consumes around 17 kWh of stored battery energy per 100km.
The cost of travelling 100 kms in our MG EV is under $1.50, using ‘off peak’ domestic electricity, and the car expels no exhaust at all and is much cheaper to service.
So the EV is a winner all around. Even moreso if utilising solar-generated electricity.
The EV impact on our electricity bills
Prior to purchasing an EV we were consuming around 7 kWh per day from the grid in Summer. In Winter this could jump up to 20 kWh per day, with shorter days (less sun on the solar panels) and the use of heating appliances at night.
The 72 kWh battery in our EV is classified as ‘long range’, which gives us a range of around 450 kms. So if we travel 200 kms (which is an average weekly commute for us) consuming stored battery energy at the rate of around 17 kWh / 100km, we have consumed around 34 kWh of our battery capacity or around 50% of its capacity.
To recharge this capacity at the general daytime rate of 34c/kWh costs $11.90. At the off-peak rate of 8c/kWh it will cost us $2.80. (At commercial fast chargers this can be anywhere from 60 c/kWh to 85 c/kWh.)
The overnight off-peak rate is cheaper than we can manage from our solar panels on a sunny day. The 4.2kW of solar output (at its maximum rate) isn’t able to provide enough energy for the 7kW car charger, so we will be drawing the deficit from the grid – and during the day this will be at 34c/kWh.
So, we are better off going with overnight off-peak charging at 8c/kWh – $2.80 for 200kms looks to be pretty cheap motoring. And even though our solar feed-in tariff has recently been reduced to 5c/kWh – our excess solar energy feeding into the grid still covers a decent percentage of these charging costs.
Of course, an alternative option to make better use of our solar energy, is to charge during a sunny day using the 2kW ‘granny’ charger – but this is a very slow option.
2023 – Changing our electricity provider >>>