When shouldn’t you be using the energy from your solar panels?

When isn’t it a good idea to be using the energy produced from your solar panels? In a normal household, you should be using the energy as much as you can. However one of our customers, Jay, has an interesting situation where she could save a lot of money by not using the power from her solar panels on her roof.

To find out why we need to first understand how feeding solar power back into the grid actually works in Australia on Tarrif 11 – continuous power. Solar panel will obviously be generating electricity in the daylight hours. To keep things simple, this electricity can go to two places. First it can go to your house and be used up (by your fridges, air conditioner, heat pumps etc.). The second place it can go is the grid where electricity companies will pay you for the extra juice.

Where it gets a little bit complicated is that the energy being fed back into the grid will usually only get you 6c/kWh, but if you buying electricity from the grid, you’d pay 23c/kWh. This is a sizeable difference. That’s why in most cases, it’s actually better to use as much of that electricity being generated by the solar panels during the day, otherwise you’d be spending a lot more buying it back from the grid at night.

However in Jay’s case, she signed a deal with electricity companies to sell her energy from her solar panels at a fixed rate. When she signed the deal she locked in a rate of 50c/kwh for her energy being generated from solar. So unlike a great many solar panels owners out there, it’s actually better for Jay to not be using the electricity from her solar and rather sell it back to the energy companies at an incredible rate. Let’s do a bit of an example to see just how that would work in real life:

Scenario 1: Run the Hydrotherm during daylight hours where the Solar panels were producing 3kWh of energy per day.

If you ran the system on Scenario 1 (knowing that you could have sold this energy back):

3kWh x $0.50           = $1.50 per day
= $548 per year

Scenario 2: Run it before and after your solar panels start producing energy (Tarrif 11).

3kWh x $0.23           = $0.70 per day
= $253 per year

So while this doesn’t take into account the changes in efficiencies of the system during different times of the day (i.e. heat pumps are more efficient in warmer temperature than colder temperatures), it wouldn’t make up for the large difference from selling it back to the grid. Per year, Jay can save almost double the amount. The last time we spoke, she had over $1,000 credit on her electricity bill!

We almost always recommend that our heat pumps be put on timers during daylight hours, however it made more sense for Jay to be running her system during the early morning and late afternoon. The best part is, she’s locked in for another 10 plus years!

2 thoughts on “When shouldn’t you be using the energy from your solar panels?”

  1. Jays situation may not as unusual as implied above. Those of us who obtained the 44c feed-in tariff on the Qld. Govt. Solar Bonus Scheme (before July 2012) are in a similar position. Our Solar was installed in early 2012, and it seemed best to shift any discretionary load to non-sunlight hours.
    While the Solar Inverter is connected solely to Tariff 11, and the HWS (HydroTherm) is on Tariff 33, it seems logical that any HWS load during major solar-charging hours would still reduce the feed-in return. Do you agree?
    My HydroTherm timers are currently set for 4-8am and 6-10pm.

    1. Hi Frank,

      If your system is connected to Tariff 33, the system will only ever draw power from the grid. Therefore even if a HWS on tariff 33 heats up during the day, the feed-in return will not be affected.

      Just on a note to make, even if you have Solar PV producing power and at the same time appliances are running, technically they are still being powered by the grid. The reason being is that your Solar PV always only feeds directly into the grid and not into your house. Your power bills are then calculated from the net amount of power input from your solar PV and then the amount used by your household only netted against Tariff 11.

      Finally your timers set on your system will work nicely if your Hydrotherm is on Tariff 11 but if it’s using Tariff 33 then we would recommend setting the timers during the hottest time of the day from 10-6pm to run the system the most efficiently.

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