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The 'Achilles Heel' of Renewable Energy: Long Term Storage

Mr Bryan Leyland


Few people understand that a power system must always generate sufficient power to exactly match the load on a minute by minute basis. This is not easy to accomplish. Because they are intermittent and unpredictable wind power, solar power and other new energy technologies add to the difficulties in providing a reliable power supply.

This article provides an introduction to power systems and discusses the very real difficulties of providing a reliable, low cost, supply of electricity from wind, solar and other new renewable energy technologies. It shows that recent claims that the New Zealand system could be supplied entirely by wind power is wishful thinking. To do this, we would need to have a low cost, efficient method of storing large amounts of electricity for long periods. Such technology is not even on the horizon.

Overview of power systems and renewable energy

The capacity factor of a power system is the ratio of the average load to the peak demand in MW. Most power systems have a capacity factor of between 50% and 70%. In some countries the peak demand occurs in winter evenings (heating loads), and in others in the middle of summer (air-conditioning loads).

Three types of power generating plant are commonly recognised.

(a) Base load stations that operate ~90% of the time, thereby generating efficient low-cost electricity. Coal and nuclear plants are prime examples.

(b) Mid-range power plants that are often shut down in the early hours of morning, and that generate maximum power during the day and during peak demand periods. Hydropower and gas-fired stations are examples.

(c) Peak load stations that operate for between 1% and 20% of the time during peak demand periods. Open cycle gas turbines, hydropower stations and pumped storage hydropower are common examples.

Unlike wind, solar and marine power, all these plants can be relied upon to operate at full power when needed - unless they break down or fail to start - which occurs about 2% of the time...


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