Transmission and storage key to renewable energy

Australian
Thursday 1/10/2009 Page: 2

AUSTRALIA'S renewable energy target is expected to drive $30 billion of' investment in wind, solar, geothermal and other energy sources in the next 10 years. But delivering this energy to consumers is not just a matter of building a windfarm or drilling down to source geothermal heat. It will require investment in transmission lines and, some say, a new way of thinking about how energy is transmitted across the continent.

Two key issues facing the transmission of renewabIes are the distance and variable load. Many of the best wind and geothermal resources are in remote locations, so new transmission lines need to be built. But energy sources such as wind also pose fresh challenges because they are intermittent and unpredictable. There is either no wind and no energy or strong winds that create huge loads of electricity and stress the system.

Networks built to handle a predictable energy source now need to deal with energy flows from a source that cannot be controlled. Meeting this challenge requires a greater amount of flexibility to be built into the grid as well as possible investment in new systems of energy storage and the development of smart grids. These will also help manage the two-way flow of energy that will arise from growth in home-based generation from small-scale solar, and the likely creation of an electric car network that can feed energy back into the grid at peak periods.

The Energy Supply Association of Australia estimates more than $31bn in capital expenditure on existing and new network assets will be needed in the next five years to facilitate the transition to lower emission generation and to ensure reliability of supply. In addition, there is a refinancing requirement of a further $30bn in network assets. Further detail is expected later this year when the Australian Energy Market Operator releases its national transmission statement, a study that will look at the needs of the transmission network: what needs to be upgraded and the expected demand for high voltage direct current lines.

The task facing Australia is no different from that of the rest of the world, where the move to a low carbon economy calls for fresh thinking on issues such as demand response and energy storage. One of the main challenges is the ability to cope with the expected increase in wind energy, which in Australia is predicted to account for up to 80% of the renewable energy target. Laurent Schmitt, the Paris-based vice-president for energy management at Alstom, says wind cannot be forecast more than several hours before it blows, creating a problem for dispatchers on the energy grid.

A standard grid such as Australia's would normally require 10% of its capacity to be flexible, but having a 20% RET largely satisfied by wind means that flexibility ratio would need to be increased by 20-30% of its capacity, leading to a large increase in demand for gas-tired peaking generators. And there is also the issue of the wind blowing at night, or on weekends, when the energy is barely needed. This happens now and on occasion has led to negative prices for wind retailers as they try to sell energy no one needs. Some of these issues may be solved with energy storage.

The traditional means of storage has been with hydro power, particularly in New Zealand, where excess energy is used to push water to a higher reservoir before it is released to drive turbines at a time of greater need. But Australia's capacity to expand its hydro-electric facilities is negligible. Schmitt says Alstom is conducting promising research into energy storage using compressed air. A gas-fired turbine uses excess energy to drive a compressor to pump air into a cavern, where it is stored until power demands call for it to be released and the expanded air is able to drive the turbine and generator.

Other options may include batteries that could store power at nights or weekends. Schmitt says greater flexibility may also need to be introduced into the present base-load generators. He believes Australia's coal-tired power stations can be modified to become more flexible and operate within a capacity range of 60-100%. Possibly the most important element in managing flexibility is the development of a smart grid, so that one end of the grid can communicate with the other and flows of energy can be controlled. This will be crucial in the development of the electric car network, and the expectation that large battery charging networks will be created to meet a spike in demand.

Schmitt says these battery networks could provide some of the flexibility the network will need. "We could replace peaking units if we could connect the car in a smart way. It comes back to the development of smart grids and the ability to charge and discharge when the system requires it," he says. "There will need to be a massive investment in the distribution network.., and in modernisation."