24/7 Renewables: Bye-bye Base Load
Posted: 15 Feb 2015
Tagged: Residential | Solar PV |
It’s one of the most common objections rolled out against renewable energy: What do you do when the sun doesn’t shine and the wind doesn’t blow?
And it’s not an entirely bad question, but it’s also one that the fast growing renewables sector has been addressing for some time.
To answer those who are skeptical about clean energy, there are a number of things worth bearing in mind. Here are three important things to start with:
- High level of renewables won’t crash the gridThere are frequently expressed concerns that high levels of renewable energy penetration will “crash the grid.” And given that today’s electricity grid is designed with a centralized system of power plants in mind it is also not a bad question.The electricity grid in Australia and elsewhere around the world has been designed to transport electricity from — generally fossil fueled — power plants via poles and wires out to homes and business where the electricity is needed.So how does it cope with “intermittent” electricity supplies from wind and solar arrays built at various points along the grid? Essentially, how does the electricity system go from a system where the power is on all the time, and can ramp up when needed, to one where supply is variable?
From the examples we have in areas where there is a high penetration of solar and wind we can confidently answer that the grids have been standing up very well.
It is certainly true that electricity supply from a wind farm in particular can vary, as gusts of wind send the rotors spinning. To a lesser extent, production from solar PV panels can fluctuate as clouds pass overhead. But forecasting tools, based on good weather predictions and monitoring equipment installed on site can provide grid operators with reliable predictions as to how much electricity will be fed into the grid and when.
Grid operators can then deploy fast-reacting power generation sources, like modern gas-fired plants, to make up the gap when the wind drops, or ramp down when renewable generation is strong.
Real life examples in parts of Germany with extremely high levels of wind penetration – such as the states of Schleswig-Holstein and Mecklenburg-Vorpommern – show that excess wind electricity can be transported to other parts of the grid where there is simply less wind. Respectively, these two states have around 100% and 120% of their electricity needs supplied by wind.
In Australia, where the interconnections between electricity grids may not be as well established as populous Germany, high-renewable grids have also performed well. By 2014, wind supplied well over a quarter of South Australia’s electricity needs, and Hugh Saddler (from consultants Pitt & Sherry) noted that there were several occasions in September last year where wind and solar exceeded the total electricity demand in the state, with much of the excess being exported to Victoria.
Saddler notes that during the periods in which wind and solar were doing most of the heavy lifting, fossil fuel generation was wound back down and wholesale electricity prices went through the floor.
- Renewable production sources form a good match:With its large amounts of solar and wind, Germany also provides good data as to how the two major renewable electricity sources provide a match.Data compiled by the Fraunhofer ISE institute shows that in the first ten months of 2014, electricity output from both solar and wind had an inverse relationship: In short, that when the wind was blowing and turning turbines, there tended to be little sun, and vise versa.
This demonstrates that while solar and wind may not always produce electricity “on demand,” they tend to compensate for each other, providing a relatively complementary supply of electricity.
- Modeling shows a 100% renewable energy system is possible:German commercial research body – the Fraunhofer ISE – has also performed electricity supply modeling that maps out how Germany’s electricity system could function without fossil fuel or nuclear power.In the system, vast amounts of solar, offshore and onshore wind can be coupled with batteries, for short-term storage, and power-to-gas conversion to create methane gas, for seasonal storage – from summer through to Germany’s long and dark winter.Key components of the Fraunhofer system include:
- The continued roll out of energy efficient technology, like home insulation to reduce the need of heating;
- The increased interconnectivity between power grids, including on the high voltage network to cope with levels of either high or low wind or solar production;
- The installation of communication technology onto electricity grids, to allow for better and faster information exchange and control;
- Short and long-term energy storage technologies.
Australia’s 100% renewable system: Researchers at the University of New South Wales (UNSW) have carried out similar modeling, this time on the National Electricity Market that connects all the eastern states, the National Electricity Grid. They too found that a 100% renewables system could be realized in Australia by 2030.
The renewable mix that the UNSW team envisage would be dominated by wind and solar PV, with the two supplying two-thirds of the electricity the country needs, for all but a handful of hours, on a handful of days. These shortfalls in wind and PV supply come during times of large amounts of cloud cover and little wind.
To provide supply during these periods, the UNSW analysis envisages relying on gas turbines powered by biofuels, hydropower and concentrating solar power (CSP) – which can store energy in thermal storage.
One of the storage solutions developed for CSP – which uses mirrors to focus the sun’s rays onto a central tower – is through heating salt stored to such an extent that it becomes a liquid. The heat can then be used to power steam-driven turbines when electricity is required. The German models don’t use CSP because it’s just not sunny enough in Germany.
The UNSW model envisages a 2030 100% renewables electricity system that would cost the country, and consumers, $7 to $10 billion per year more than business-as-usual. But this is using very conservative cost projections for the renewable technology. It also doesn’t factor in the health and climate damage being done by the unchecked carbon emissions.
All of this data and research indicates that the superficial objection of what to do when the sun doesn’t shine and wind doesn’t blow can and is being solved.
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