Wednesday, October 1, 2014

Imagine 100% renewables -- what happens when there's no sun or wind?

Imagine an Australia running on 100% renewable energy:
  1. Each house has 2 - 5 kW of solar PV
  2. Each house has 1 - 2 days' energy stored (eg. in batteries, or similar)
  3. Ditto for commercial and industrial buildings
  4. There are also scattered wind farms and singleton wind turbines where feasible
  5. There is scattered storage that is owned by the utility
What is the issue? Intermittency.


This is the problem that is always raised when renewable power is promoted: renewable power is intermittent:
  • solar PV only produces electricity when the sun is shining
  • wind turbines only produce electricity when the wind is blowing
Neither of these conditions are met all the time, so does that imply rolling blackouts?


Imagine an interval between sunny, windy periods in NSW during which the local renewable generation produces very little, if any power. Imagine that there is somewhere else in Australia that at that time is producing plenty of power. Let's say it is in SA. From where will people in NSW get electricity?


Luckily, our scenario includes some distributed electricity storage. There is not very much (a typical off-grid house would have 5 days' electricity storage or more), so it is much cheaper. It does mean, however, that after a few days of cloud and no wind people's batteries would be running down.

The solution is to use the existing grid. While Australia's current grid cannot send enough power around in real-time (ie. if it's sunny in SA and cloudy in NSW, SA can't in real-time supply Sydney's power demands), what is rarely considered is that this is unnecessary. Remember that the existing grid is vastly underutilised -- it is built with peak demand in mind (which occurs a couple of times per year). Most of the time, the grid is running well below capacity.

In this scenario, power can be sent from SA to NSW overnight, when demand is low, to keep batteries in NSW topped up. It does not need to power customers in real-time -- all it needs to do is stop the batteries going flat.

To restate it another way -- the transfer of power from SA to NSW would not need to match the maximum instantaneous rate of consumption in NSW -- it would only need to match the average rate over the period covered by the batteries. In fact, even this is not required since the batteries can be assumed to begin this period relatively full and end it relatively empty.

By doing this, we would obtain maximum benefit from the existing grid infrastructure, and also be able to install a much smaller storage system, while retaining the benefits of distributed generation.

In other words, I question whether the oft-repeated statement that high renewable penetration requires a much more extensive grid is true. We can use electricity storage to greatly mitigate this (though by exactly how much, I am not sure. Some time, I will try to get the data together and run the numbers).

The post "Imagine 100% renewables -- what happens when there's no sun or wind?" was written by Angus Wallace and first appeared at


  1. I see that you're aware of the idea of "consuming electricity during the night, when it's cheap" (not necessarily in this article). But it's cheap overnight because coal and nuclear boilers are most efficient when run at a constant power level, day and night. If we bought electricity on a dynamic "spot market", electricity would be cheap when the sun shines, when the wind blows, and when there's plenty of water behind the dam.

    The complication is that the consumer cost of electricity is (in the US, at least) tightly regulated, and industrial users make massive long-term investments based on the expected cost of electricity. Some industrial users can adjust their demand to track current supply. Some do that now, like steel-making furnaces that melt during the night and pour during the day. But how can they plan their production without knowing from one week to the next whether power will be cheap or expensive? How does the average consumer decide when power is "cheap enough" to store?
    Suppose the grid allowed the voltage to fluctuate a little more than it does now. +5% is a signal that power is cheap; -5% is a signal that power is expensive. Then a simple sensor could adjust some kinds of consumption automatically. (We already know that a voltage sag means that the grid is stressed, that power is getting scarce. Now connect that to the price.)

  2. Hi latheChuck,

    I agree with you. I try and avoid using power at night, precisely because I feel it supports coal power (in Australia we have no nuclear). However, in this article I'm talking about 100% renewables, and the transfer of that renewable energy around the country -- much of which can happen during periods of low demand.

    Right now, demand is low at night (relative to the day) and this is despite incentives to use more power at night -- if we remove the night-discount, and create a day-discount (when PV is plentiful) then we'd see an even larger shift to day-use of electricity.

    "How will they know when power will be cheap.."
    I think it would be down to the amount of electricity held in storage, and weather forecasts. To be honest, I don't know -- there's a lot to work out here!

    I like your idea of fluctuating the voltage to signal price. The only problem then is billing -- we'd all effectively be paying a rapidly-fluctuating "spot price" for electricity which would be hard for customers to understand, and would also require that everyone had a smart meter. This might be what we have to do.

    Cheers, Angus


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