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BRYAN LEYLAND: Storage: the Achilles heel of wind and solar power

The Government’s “Net Zero New Zealand by 2050” ambition foresees 12,000 MW of new wind and solar power – 1.5 times the entire existing installed generating capacity – to meet the 50% increase in energy and peak demand expected from electrifying transport and heating. The disproportionate increase in installed capacity results from the low average output of wind and solar farms. Installing this much new capacity is a major challenge in terms of technology, cost and resources. According to Professor Kelly, an eminent New Zealand engineer now residing in the UK, it will cost more than $500 billion.

At times, this 12000 MW of wind and solar power will be producing virtually nothing because the wind is not blowing and the sun isn’t shining. Our existing hydro and geothermal power can’t fill the resultant 4000 MW shortfall because there is not enough spare power available. As coal and gas are being killed off, the only option is to store the large amount of surplus energy available whenever the sun is shining and the wind is blowing. This can be as much as 4000 MW – something like 50% more than current demand.

We need a technology that can store all this energy when it is available and use it as necessary to cover the hourly, daily, weekly and seasonal fluctuations. Although many people believe that the 1200 MW Onslow pumped storage scheme could provide this backup, it cannot do so because it is too small, in the wrong place and it would need to have a very large lower storage lake.

In the words of Apollo 13, "Houston, we have a problem"!

To back up wind and solar, we need a large scale low-cost technology that can store and deliver up to half the existing power demand with time scales varying from a few hours to several weeks or even months. There is no suitable technology available or on the horizon. Without low cost storage, large scale wind and solar power cannot provide an economic and reliable supply.

4000 MW of hydro pumped storage in the North Island might work. But there is no chance of finding even one site with two large storage lakes close together with something like 500 metres difference in level that is capable of storing and providing more than 1000 MW for days on end.

The Government’s dreams of developing wind and solar power to eliminate the need for fossil fuels while providing a low cost and reliable supply are doomed.

A separate problem is the need for extra generation during dry years when hydropower generation drops substantially. Traditionally, this has been achieved by storing as much water as possible in our relatively small storage lakes, supplemented by gas and the coal stockpile at Huntly.

In 2019 the interim Committee on Climate Change produced an excellent report that told the government that it was a waste of money to aim for a “carbon zero” power system. The Government shelved this report and, in 2020, the Government set up the "NZ Battery Project” to look at ways of eliminating CO2 from power generation.

The prime objective of the NZ Battery Project is to investigate the 1200 MW Onslow hydro pumped storage scheme that has a large lake in a valley north of the Clutha river forming an upper basin that can provide all the extra energy needed in a dry year. According to the latest estimate from the Battery Project, it would take at least 11 years to build and cost $15 billion – about $12,000/kW, twice the cost of a geothermal station that generates day and night.

The scheme has many serious problems.

25% of the pumping energy would be absorbed by losses. Extra pumping would be needed to make up for evaporation losses from the lake. Pumping power would cost at least 5¢/kWh and maybe much more because, unless the electricity market is reformed, generators that have surplus power available for pumping would jack up their price the moment pumping starts.

The scheme’s major source of income would be from generating during a shortage. During the four months duration of a shortage, it would have to earn enough money to cover the capital charges and operating costs of $5 billion accumulated over the previous five years or so. This means that it would need to charge $1.6/kWh while generating. 10 times the current spot price!

But it gets worse: the way the market works, all generators would get $1.6/kWh so the extra cost of as much as $20 billion over the four month period would eventually be passed on to consumers. Every tonne of CO2 saved would cost about $7000. The current CO2 market price is only $85/tonne!

The common-sense alternative to Onslow is 1 million tons of coal on the stockpile at Huntly. Say $200 million to buy the coal plus about $40 million a year for capital charges and the like. Every time there is a dry year, the coal stockpile would need to be replaced and there would be a CO2 cost of $25 million. It should be easy to choose between $400 million or $20 billion every five years?

There are far better and cheaper options for reducing emissions of CO2 from power generation. More hydropower, more geothermal, substituting gas for coal and the most effective of all – clean, safe and reliable nuclear power.

Other options like hydrogen storage, batteries, compressed air storage, etc are all substantially more expensive than pumped storage hydropower. For instance, sufficient batteries to solve the dry year problem would cost $5 trillion.

The sooner the Government realises that a system dominated by wind and solar power cannot provide a reliable and economic supply and starts looking at cheaper and better options, the better.

Bryan Leyland is an electrical and mechanical engineer with 60 years experience in the power industry in New Zealand and overseas.

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