Feature

Catching Water and Power

Imagine a glass-covered catchment which provides electricity as well as water. The idea has its merits.

By Earl Bardsley

Technological advances mean that we could see glass-covered water catchments providing not just water, but also electricity in the future. Instead of having to embark on major water supply or power projects to meet the demand of a growing city, planners would be able to answer that demand by small-scale incremental expansion.

It is now possible to manufacture glass panels which can generate electricity directly from solar radiation, at a cost some 90% less than the equivalent power output from conventional photovoltaic cells.

Glass is also probably the best water-yielding surface available with respect to both water quality and reducing interception loss from rainfall, so the electricity and water generation units can now become one and the same. A square-metre panel of glass in an Auckland water-supply catchment would yield about 0.5 m³ of additional water each year -- a 50% increase in output relative to the present forested land use. At the same time, an "energy glass" panel the same size would yield about 10 watts of electricity averaged over day and night.

The glass panel units can be incremented as demand requires, up to the point where the existing water-supply catchments have been fully transformed. Such an approach would see the Auckland area meet its electricity and water needs well into the future. There is room in the present supply catchments to expand up to an area of 200 km², which would have an enhanced water yield of 3.0 m³/s, and a time-averaged power output of about 2,000 megawatts, using current technology.

In keeping with the multiple-use concept, there is no need to slowly convert the Auckland supply catchments into a glass wasteland. Much of the incoming solar radiation passes directly through the glass panels, allowing for the possibility of setting up extensive all-weather desert gardens by raising the panels off the ground. The excess solar radiation could be used in other situations to evaporate industrial wastewater.

Constructing even small glass catchments will be expensive, but there are mitigating factors such as the absence of on-going fuel costs. Probably the single most important economic factor for New Zealand is that the panels are not particularly high-tech, so they could be mass-produced here by a revitalised local glass industry. This contrasts with the need to use overseas funds to purchase generating units for traditional power stations. There is also the more intangible export-related economic advantage associated with the "clean, green" image of a country generating water and power from glass catchments.

If they are shown to be viable, large-scale glass catchments are likely to be considered for those localities where major projects for water and energy supply are under active investigation. For example, a 600-megawatt coal-fired power station is being planned to augment the Perth electricity supply, for an estimated cost of $2 billion dollars. At the same time, there has been talk of constructing a long pipeline to transport water to that city from the north of Australia.

What could be done right now is to set up a "notional" glass catchment at a selected locality, with a small number of isolated panels distributed over a wide area. This would form the input data for a model of a complete system. Decisions could be made later as to whether the first "increment" should go ahead, taking into account the economics of panel production at that time.

It may turn out that the hydrological cycle is the missing link in establishing the economic viability of alternative energy sources. Despite high capital costs, a sustainable zero-pollution system for supplying both water and power has a lot going for it in the modern world.

Dr Earl Bardsley is senior lecturer in hydrology at Waikato University.