This is a feature from Windpower Monthly's June 2021 issue. Click here to read the full edition
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Wind energy is poised to make a substantial contribution to the energy transition. But the rate of deployment depends on measures introduced by national governments to decarbonise their energy systems.
Two estimates, as shown in the chart below, suggest wind generation worldwide by 2030 will be around 3,000TWh — more than double the figure for 2020. Shell’s “Sky” scenario suggests there may then be a five-fold increase by 2050 (Shell Scenarios: Sky. Meeting the Goals of the Paris Agreement).
The World Energy Council (WEC) suggests a doubling of the 2030 figure by 2050 in its median scenario, somewhat oddly called the “Modern Jazz” scenario (World Energy Scenarios 2019, Exploring Innovation Pathways to 2040). It is defined as a “market-led, innovative and digitally-disrupted world, with faster-paced and more uneven economic growth”.
Differences are due to the underlying assumptions in the scenarios. Some assume modest changes to government policies, but “Sky” recognises that “a simple extension of current efforts is insufficient and is based on a complex combination of mutually reinforcing drivers being rapidly accelerated by society, markets and governments”.
The way forward for wind may not be entirely free of obstacles. Electricity system operators are becoming increasingly confident managing the hourly fluctuations in output, but as wind energy generation increases, there will be occasions when the amount of wind power produced may exceed the system demand.
In 2020 the year-round average wind generation on the UK’s mainland system (GB — excluding Northern Ireland) was 8,073MW; the minimum was 318MW and the maximum was 18,558MW. The latter was higher than the system’s minimum demand of 16,629MW. Peak wind generation in the UK — 50-100% above the average — is unlikely to coincide with minimum system demand, so there would not have been any need to curtail the wind output.
However, as the proportion of wind energy increases, it becomes more likely that its output may need to be curtailed. In practice, this is already happening due to local bottlenecks. It is not a new phenomenon and affects all generation sources. Once wind generation reaches around 40% of the energy demand, curtailments might be needed.
In western Denmark, with around 62% wind in 2020, peak wind output exceeded the maximum demand on the system. This is reflected in the chart below, which compares key data for the two systems. To facilitate the comparisons, the average system demand on the respective systems is used as a reference.
The chart shows peak demands were around 50% higher than the mean, and minimum demands were about 60% of the mean. Differences due to the high level of wind generation in Denmark are clearly shown.
There are several solutions to address this potential difficulty. The first is simply to ask wind-farm operators to constrain their outputs. Contracts in both Britain and Denmark allow operators to be compensated for “lost” output.
Alternatively, surpluses may be exported via interconnectors if possible — Britain and western Denmark have options for this. Sending wind power to storage is another possibility, whether in the form of pumped storage, batteries or heat stores — used in Denmark.
It is sometimes suggested that “surplus” wind be used for hydrogen production, but this is unlikely to be economic. However, surplus wind could possibly be diverted into dedicated wind-hydrogen systems, where it would improve the load factor of the electrolysis plant and make it more cost-effective.
There is considerable global interest in the prospects for hydrogen as an energy vector, and it has several applications. It may be a viable option for trains on lightly used lines, where the costs of electrification cannot be justified. German railway companies have ordered trains, and prototype vehicles are being tested in the UK and elewhere.
A prototype aeroplane has also been built and tested. The advantages of hydrogen over batteries for transport is the promise of a greater range and less weight. Further into the future, the feasibility of using hydrogen in gas networks is under consideration.
Blue versus green hydrogen
At present, most of the world’s hydrogen is produced by a chemical process (“reforming”) that uses natural gas and therefore it is not carbon-free. This is termed “blue” hydrogen, as opposed to “green” hydrogen, produced by electrolysis of water using renewable energy.
Green hydrogen is currently significantly more expensive to produce than blue hydrogen. This is mainly because the cost of the “fuel” — the electricity used for electrolysis – is much higher than the cost of natural gas.
The production cost of hydrogen needs to take into account the efficiency of electrolysis (around 70%) and capital repayments of the plant, currently at around $900/kW. The cost of water also needs to be factored in, although this is roughly balanced by sales of oxygen — which is also produced by the process of electrolysis.
As wind energy costs are expected to continue falling and the costs of electrolysers are also likely to go down as demand goes up, there is a reasonable expectation that the costs of green hydrogen may soon be able to compete with those of blue hydrogen. Rising gas prices and/or increased costs of carbon would also accelerate this process. The attractions of hydrogen as a carbon-free energy source would then increase.