Energy from rail

David Tranter suggests that storing energy from a local rail line could help ensure cheap, reliable, renewable power.

David Tranter at the wheel of a Tesla Model 'S'

CANWin Life Member Dr David Tranter looking startled in a Tesla electric car at The Goulburn Group electric vehicle expo, November 2014

Coal-fired power stations are either on or off. When they run, they run at peak capacity to ensure that consumers get all the energy they want all the time, including those few heat wave days each year when the more affluent rely on air conditioning to keep cool. When the grid was privatised in the name of “energy security”, it was “gold-plated” at the expense of the consumer: the needy subsidising the greedy.

Australian coal-fired power stations have access to cheap coal, are heavily subsidised, and do not cover the environmental costs of their production. As a consequence, their production costs are very low by international standards (3-5c/k). They could easily sell electricity on the cheap. In practice, however, they sell their energy at up 10 times its production cost, making a killing at the expense of households and businesses.

To be fair, most energy suppliers offer discount rates of about 15c/kWh for off-peak (night-time) use. But that doesn’t suit most consumers, who continue to pay the peak-hour rate of 20-40c/kWh. Clearly, there is scope in the Australian Energy Market for a more efficient system, one that could guarantee consumers the electricity they need without overheating the atmosphere and de-stabilising the climate.

Renewable energy plays a useful role in stabilising the grid by ironing out its peaks and troughs, since much renewable energy is harvested by day. In practice, however, the grids and conventional energy providers depend more on each other than on potential renewable energy suppliers, which they see as unwanted competition. They deny renewables access to the grid — because they can. It is time, perhaps long past time, for a “smart grid” to provide people and industry with the energy they need, rather than the energy they want.

One way to smooth out peaks and troughs in demand is to store surplus night-time electricity for daytime use. Battery technologies are now evolving fast and costs are tumbling as fast as photovoltaic panels have done over the past 10 years. Lithium ion storage systems are already available on the Australian market for both household and business use, but it will probably be some time before they have the potential, on a grid-wide scale, to meet daytime demand by storing night-time excess.

That being so, NSW could follow the Californian lead and look to gravity storage options, which use off-peak electricity as a resource that can be bought on the cheap and sold at twice the price. Eraring Energy already does this on a small scale. By night they use cheap electricity to pump water from downhill Lake Yarranga into uphill Fitzroy Reservoir. By day they can release the water to generate hydro electricity, which they can sell to the grid for up to twice the price of pumping.

The generation efficiency of this option, however, is limited by the friction between water and pipe. A more efficient alternative to move heavy materials uphill is to use a railroad train, which loses much less energy in friction, an initiative of the Californian company ARES (Advanced Rail Energy Storage).

A variant of that principle is the “regenerative braking” that is being introduced on the new generation of NSW suburban trains which, by their nature, stop and start to pick up passengers. Regenerative braking recovers energy otherwise lost as heat and feeds it back to the source through their overhead power lines. Its limitation as a storage option is that such trains run mainly on gentle gradients by day, rather than by night, a limitation that does not apply to the ARES option.

ARES plans to use a purpose-built railroad up a mountain in Nevada to generate 50mWh of off-peak storage energy to meet peak energy demand. The dimensions of the Nevada railway track (distance 9.2km, grade 7.2%) are remarkably similar to that of the existing Illawarra Mountain Railway that is currently used on a daily basis by coal, limestone and (in season) grain trains that lose their braking energy in heat.

Perhaps there is a case for electrifying the Illawarra Mountain Railway to stabilise the grid by recovering the braking energy that is currently being wasted as heat until such time as NSW can afford to build the proposed electric railway line between Dombarton and Maldon?

David Tranter, D.Sc., OAM

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