Sustainable energy has powerful future

energy

OPPONENTS of renewable energy from the coal and nuclear industries, and their political supporters, are disseminating the fallacy that renewable energy cannot provide base-load power to substitute for coal-fired electricity.
If this becomes widely accepted, renewable energy will remain a niche market rather than achieve its potential of being part of mainstream energy supply technologies.
Electricity grids are designed to handle variability in demand and supply and have different types of power stations — base-load, intermediate-load, peak-load and reserve.
A base-load station is, in theory, available 24 hours a day, seven days a week, and operates most of the time at full power. In mainland Australia, base-load power stations are mostly coal-fired while a few are gas-fired. Coal-fired stations are by far the most polluting of all power stations, in terms of greenhouse gas emissions and local air pollution. Overseas, some base-load power stations are nuclear-powered.
An electricity supply system cannot be built out of base-load power stations alone. These stations take all day to start up and, in general, their output cannot be changed quickly enough to handle peaks and other variations in demand. They also break down from time to time.
A faster, cheaper, more flexible power station is used to complement base-load, handle the peaks and handle quickly unpredictable fluctuations in supply and demand.
These peak-load stations are designed to be run for short periods each day. They can be started rapidly from cold and their output can be changed rapidly. Some peak-load stations are gas turbines (like jet engines) fuelled by natural gas. Hydro-electricity with dams is also used to provide peak-load power.
Some renewable electricity sources have identical variability to coal-fired power stations and so they are base-load. They can be integrated into the electricity supply system without any additional back-up. Examples include:
■ Bio-energy, based on the combustion of crops and crop residues, or their gasification followed by combustion of the gas.
■ Hot rock geothermal power, which is being developed in South Australia and Queensland.
■ Solar thermal electricity, with overnight heat storage in water or rocks, or a thermochemical store.
■ Large-scale, distributed wind power, with a small amount of occasional back-up from a peak-load plant.
Moreover, energy efficiency and conservation measures can reliably reduce demand for base-load and peak-load electricity.

The inclusion of large-scale wind power in the list may be a surprise to some people, because wind power is often described as an "intermittent" source, that is, one that switches on and off frequently. While a single wind turbine is certainly intermittent, a system of several geographically separated wind farms is not. Total wind power output of the system generally varies smoothly and rarely falls to zero. Nevertheless, it may require some back-up, for example, from gas turbines.
When wind power supplies up to 20 per cent of electricity generation, the additional costs of reserve plant are relatively small. For widely dispersed wind farms, the back-up capacity only has to be one-fifth to one-third of the wind capacity. Since it has low capital cost and is operated infrequently, it plays the role of reliability insurance with a low premium.
Of course, if a national electricity grid is connected by transmission line to another country (for example, as western Denmark is connected to Norway), it does not need to install any back-up for wind, because it buys supplementary power from its neighbours when required.
By 2040, renewable energy could supply more than half Australia's electricity, reducing greenhouse emissions from electricity generation by nearly 80 per cent. In the longer term, when solar electricity is less expensive, there is no technical reason to stop renewable energy from supplying 100 per cent of grid electricity. The system could be just as reliable as the dirty, fossil-fuelled system that it replaces.
The barriers to a sustainable energy future are neither technological nor economic, but the immense political power of the big greenhouse gas polluting industries — coal, aluminium, iron and steel, cement, motor vehicles and part of the oil industry.
Dr Mark Diesendorf is the director of Sustainability Centre, senior lecturer in environmental studies at the University of NSW, and a member of the EnergyScience Coalition. His new book, Greenhouse Solutions with Sustainable Energy, will be published by UNSW Press next month.
Page 1 2
Next page
Email
Print
Normal font
Large font
When you