A copy of the commissioner's report, Evaluating solar water heating: sun, renewable energy and climate change, can be found at www.pce.parliament.nz

Harnessing the sun has inspired people across cultures for thousands of years. From gods to practical applications, solar energy has been entwined with human history. But how we seek to use the sun has changed.

The oil price shocks of the 1970s led to fears that the world was running out of fossil fuels, pushing countries to investigate renewable energy sources such as solar and wind power.

The promotion of renewable energy continues. The Government has set a target of 90 per cent of the country's electricity to be generated from renewable sources by 2025. Most electricity is already renewable - 77 per cent of electricity came from renewable sources last year.


Using the sun to heat water feels instinctively right. Nearly 12 per cent of all the electricity generated is used to heat water in our homes, and replacing much of this electricity with sunlight has great appeal.

Governments have been involved in promoting solar water heating since the 1970s. Subsidies for solar water heaters continued right through until last month. There is now, however, increasing interest from local government and 30 local authorities have become involved in promoting solar water heating or are considering doing so.

This includes Auckland where a solar pilot scheme was launched this year - one of Mayor Len Brown's "100 projects in 100 days" initiatives.

Reason tells us that solar water heaters perform at their best in summer when days are long and sunshine is often bright. But electricity use rises in the winter, driven by chilly temperatures and early darkness.

At these times, virtually every power plant in the country will be generating electricity and carbon dioxide emissions will be at their highest. And as these winter peaks rise, more power plants must be built.

From the climate change perspective this is entirely the wrong result. We want fewer of these fossil fuel power stations to be used, and even more importantly, not have to build them in the first place.

Every new fossil fuel plant "locks in" carbon dioxide emissions for decades. Unfortunately, solar water heaters do little to prevent the need to build these. So what does?

Flattening the high peaks in electricity demand that occur in winter has great environmental value. Most forms of renewable energy cannot be stored - geothermal, wind, and run-of-river hydro are all "use it or lose it". Supplying peak demand in winter must be done through using stored energy - either in fossil fuels or water in large hydro dams. And the higher the peaks, the harder it will be to meet the 90 per cent renewable target.


Controlling the electricity used for water heating in order to flatten peaks in demand has a long history. About 60 years ago Kiwi ingenuity developed ripple control - the ability to turn water heaters on and off remotely by sending a "ripple" (a high frequency signal) down the power lines.

Ripple control can turn off water heaters during the day so that all water heating is done at night when demand for electricity is low. Householders who opt for night-only water heating are being very "green".

They are reducing the need to build new fossil fuel power plants and lock in carbon dioxide emissions into the future.

Night-only water heating will not work for everyone, but in Christchurch at least 30 per cent of households have opted for night-only water heating at half the cost of "anytime" water heating.

Other options for managing demand include smart meters that support the development of a smart grid.

These too have the potential to change the way we use electricity and help the environment.


In my report I have made three recommendations to the Minister of Energy and Resources. One is to ensure that we don't just strive for renewability when carbon and climate change are the real concern.

I have also asked that good information be available so consumers can compare the environmental benefits and cost-effectiveness of different energy efficiency and renewable options.

And I would like to see some work done to identify whether present electricity regulations work against the environment and the economy.

Using sunlight to heat water holds great appeal. But making electricity use more consistent over time is the key to achieving the 90 per cent renewable electricity target.