Monday, October 27, 2014

Storing renewable energy

Once you are producing renewable energy, there is a strong financial incentive to use as much of it as possible rather than drawing power from the grid. This is for the simple reason that (in Australia) the compensation for exporting power to the grid is as low as 8 c/kWh, whereas it can cost more than 35 c/kWh to draw power from the grid.

The optimal way to use your renewable energy is: use as much of it as possible, and draw as little from the grid as possible.

That's all very well, but the sun only shines in the daytime -- how do you use your home-generated "free" energy at nighttime? The obvious idea is to use batteries: charge them when the sun shines, and use the power later. The problem is that they're too expensive for this to make economic sense (though their price is rapidly decreasing). Is there any way around this? Here are some ideas:

Use a delay timer so that appliances run in the day time, when you are producing energy.

  • Many appliances these days have timers (for example, my washing machine has a "delay" function that let's me delay a cycle's completion by up to 12 hours. I try to always run the machine in the middle of the day.
  • If it's a hot day, and you think you'll be using air-conditioning, then run it during the day to pre-cool the house (this will only work well if your house is well-insulated).
  • It is possible to cook during the day too, even if you're not at home, using a slow cooker, or something similar. Cooking when not there can be a fire hazard, so be careful.

Design your systems so that power consumption occurs during the day, when you are producing

  • There are fridges and freezers that will create and store "coldness" when power is available (eg. these -- I have not used them though). I think it would be similar to do something similar with a conventional fridge/freezer -- this is something I plan to experiment with.
  • If you run pumps, etc, then run them during the day. If you need pressurised water at night, it may be possible to use a header-tank.
  • If you need electricity to heat your hot water, time it to occur during the day.

On weekends, try to perform energy-intensive activities during the day

  • vacuuming the house
  • cooking, especially the oven
Doing some of these will help you to use more of the power that you produce, and will increase the benefit of your renewable energy system. Note that, if you want to go off-grid, tricks like these can allow you to use a smaller off-grid system (which is cheaper!)

this article was written by Angus Wallace, and first appeared at

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