RE: Renewables for Afirca12 Dec 2018 08:46
But, and this is where it gets really interesting - the grid is a distributed network and so balance also needs to be obtained at all lengthscales across the grid as well as all timescales. Not enough supply close a demand centre and the lights go off, too much power and nowhere to shunt it will end up blowing something up.
The naive assumption that it is ok to have a large excess of power generation at one point (A) balanced by a large demand at another point (B) is not true if the wires that connect A and B are not big enough to take the power flows. In small countries like the UK or the netherlands the grid connections are short and can be made high capacity relatively cheaply. In a very large country like South Africa (1000 miles from Capetown to Polokwane) providing high capacity grid connections from one end of the country to the other is prohibitively expensive, which is why it has not been done.
Even if you could provide high capacity power connections it becomes wasteful over those lengthscales - electtrical power wasted as heat goes up with the square of the power transmitted so you can lose 15% of the power when transmitting it from one end of SA to the other.
Distributed battery based energy storage can overcome many of the most extreme demands placed on the grid - you simply store the energy closer to where you are ultimately going to need it - the only trick is to have some idea of when you are going to need it. The peaks in power transmission, which are the most wasteful times, are reduced and overall system efficiency increases.
With real world grids you also benefit on system efficiency if you have more distributed power generating resources - smaller ones spread about more widely but close to population centres or industrial zones.
Thermal power plants (coal, oil, gas) not only generate CO2 and need to pay for fuel, but also need a source of cooling so are traditionally sited on rivers. In a country like SA where water is much scarcer than say the UK this is not always possible and even if you could locate such a plant on a river one might balk at the idea of using that water to simply make clouds instead of supplying to people or using in irrigation. Even nuclear has this problem as it too is a thermal plant.
Wind and Photovoltaic sources of course require no cooling, no fuel, generate no CO2 and generate electricity directly. They can be easily built at small and medium scale with fairly minimal infrastructure works. The only downside is that they are intermittent - which is why they too benefit from local energy storage - to shift power generated in windy periods or during the brightest part of the day to times when it is needed.
Thus we have two reasons - grid stabilisation and renewables smoothing/peak shifting that require the use of large scale energy storage. The wonderful, and unavoidable fact, is that Vanadium Flow Batteries, unlike short duration Lithium-ion, can do both of these jobs at the sam
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