Ride the wind, but not too far

The possibility of relying on wind power to generate electricity seems to allow us to avoid some difficult future choices. What could be better than having electricity without needing to worry about the environment? While even the more optimistic official wind supporters — such as the Energy Efficiency Conservation Authority — expect it would provide no more than about 20% of total energy generated in New Zealand, the concept of a wind-based future is being used to promote the idea we are now free to abandon our reliance on sources such as coal. The imagery ranges from the Green Party posters contrasting wind and coal, to trivial stunts such as posing for photo opportunities in front of electric-powered trolley buses promoting the idea of ‘riding the wind’.

How real is the promise of wind for electricity generation? My view is we can use more, but it makes no sense to talk of a wind-based future. Using wind power doesn’t free us from making difficult choices between having a secure energy supply and the various impacts on the environment — no such luck.

While many technical issues associated with wind turbines are being solved, three fundamental problems won’t go away:
1. The variability of power produced, particularly in New Zealand conditions, where rapid switches in wind strength can lead to massive swings in the amounts of energy wind farms feed into the grid in a matter of minutes.
2. Relatively low power density. Large areas have to be covered in wind turbines to generate significant amounts of power. Land costs add to power costs, while availability of sites imposes a limit on development.
3. With few exceptions, useful sites for wind farms are likely to be located away from the main centres of electricity consumption, requiring additional investment in transmission.

A stable national grid has to be able to balance electricity supply and generation at all times. Every time generation from one source drops off, another source has to be brought online almost instantaneously to replace it. Variability of power supply from wind farms poses risks to the grid’s stability, and requires investment in backup generation that can be cranked up and down rapidly as wind generation varies.

To some extent, this role can be played by hydro generation. Hence, the idea that wind can, in fact, help improve the storage capacity of hydro lakes: when wind blows, hydro generators would slacken off and conserve water, and then would come back up when wind drops off or increases beyond wind turbine capacity. However, hydro is already used as much as possible to deal with plant outages, and reduce use of fossil fuels during the year. Using wind farms to meet load growth will still mean more peaking plants are required as backup.

Most likely, such backup would come from oil-powered plants. These are expensive to run and since such backup generation will emit greenhouse gases, wind power would not be emission free.

It is also unclear how dispatch processes will cope with the magnitude of swings in wind production as wind power becomes more significant in our overall portfolio. A recent study by Palmer and Samarasinghe of Manawatu wind farms found on three occasions in November and December of 2004, output increased by 100MW within five minutes.

For comparison, 100MW represents just under one year’s worth of New Zealand’s demand growth. Such rapid swings make it difficult to forecast wind output accurately a few hours ahead, and increase the risk of surprises in real time, which can unbalance demand and supply.

While variability of wind supply is already posing problems for the New Zealand system, we are obviously still able to cope. However, we can see from the example of other countries where the limits are likely to lie. Denmark, which has led the world in reliance on wind power (14% of its energy is generated using wind), recently cancelled three planned 150MW offshore wind farms due to their likely effect on grid stability. That’s despite Denmark being interconnected with the rest of the European grid, allowing it to draw on generation capacity across Europe to deal with supply variability. New Zealand has no such luxury.

To some extent, wind supply variability can be offset by building a diversified portfolio of wind generators nationwide. In that case, there is an increased chance that drop off in supply from one wind farm could be offset by an increase in wind somewhere else. But we don’t know yet whether such diversification is realistic, given New Zealand’s wind patterns and the change in patterns over time. However, even if it helps, it will need to be accompanied by significant new transmission investment. We would need to have a flexible and unconstrained grid across the length of New Zealand to shunt energy up and down the country in response to changing wind conditions.

The cost of building this additional transmission has to be considered as the cost of wind generation. More importantly, at the political level, if we want more wind power, we would need to accept the environmental and social impacts of transmission pylons. At present, the same voices who promise us a wind-based future tend to be the first to agitate against new transmission investment.

Greater reliance on wind in future will have to go hand in hand with an acceptance of more transmission and more backup thermal generation, as well as possibly less security of supply. Hard choices can not be avoided.