Small portable electricity generators – inefficient, polluting and noisy

Fires and floods around Australia have raised interest in small generators to provide basic energy services when grids fail. Many campers use them.

They are widely used in developing countries by businesses and fragile household grids where lengthy blackouts occur. As more Australians shift off-grid, they will become even more common here.

But there are some big issues. After the fires in Mallacoota, fuel had to be helicoptered in, and the helicopters would not carry petrol for safety reasons. Small generators use a lot of fuel.

I was puzzled when told that some bushfire-affected households were consuming up to 20 litres of fuel per day just running basic services like fridges, lights and mobile phones.

To put this into context, a 25 per cent efficient generator using 20 litres per day would produce around 50 kilowatt-hours of electricity. These households would have been using more like 5kWh per day, at under 3 per cent efficiency!

This situation has global implications. Large numbers of small generators are being used throughout the developing world, seemingly at appallingly low efficiencies and extremely high fuel costs while creating air pollution, noise and safety risks.

When fuel is transported long distances in small quantities, these impacts are amplified, as is the risk of spills and fires.

Yet I could not find much discussion of this issue in international literature. We really need to sort out this issue.

After internet-searching the efficiencies of small generators over their operating range, I found data is scarce. At full load, small generators are typically 15 to 20 per cent efficient. At 25 per cent load, they are more like 5 to 10 per cent efficient.

Efficiency would undoubtedly fall even lower at lower loads. This seems to explain the real- world experience I had been told about.

This means that people in crisis and in developing countries are paying extremely high prices for small amounts of electricity while polluting our environment.

At 5 per cent efficiency, each kilowatt-hour requires two litres of petrol – that’s $3 or more per kilowatt-hour, over 10 times what most Australians pay.

The logistics and costs of keeping them functioning in remote areas or after crises are much trickier than they should be: they should need much less fuel.

I suspect that small generators should incorporate or be connected to a battery, so the generator runs at optimum efficiency to charge the battery, which then efficiently provides the energy people need. Generator manufacturers could then optimise overall real-world efficiency.

Alan Pears. This column was first published in Renew magazine. Reproduced with permission of the author.