How much seasonal energy storage will we really need?

We are moving towards an electrified future relying heavily on variable renewable sources, and with added complications such as charging Electric Vehicles, changing lifestyles and changing climate.

This raises many questions, including how cost-effective, reliable, zero emission electricity can be provided, and how a transition from fossil gas heating, hot water and cooking can be managed. Concerns about potential winter gas shortages in southern states are also emerging.

Most studies assume both peak electricity demand events and overall winter electricity demand will grow significantly as we replace gas heating. Electricity availability will become increasingly variable and winter solar generation, when we need it most, is lower than in the rest of the year. The usual recipes are more renewables, short and long-term storage and demand response. But are these the only possibilities?

Winter electricity and gas demand are already high, as shown in Figures 1 and 2. We already have a problem.

The future could look quite different if we reframe the challenge and apply more strategies. The underlying drivers of winter electricity multi-day peak issues are cold, cloudy weather and shorter days. This article looks at some ways of addressing these issues.

If we assume that future short term electricity demand will be managed by batteries (including EVs), demand management and targeted energy efficiency, high spikes in electricity demand can be smeared over at least a few days on a rolling basis. As long as the total amount of electricity required over periods of a few cold, cloudy days is available, the batteries and smarts could vary short term supply to match demand spikes.

Before discussing demand side options, let’s consider the problem of producing enough total electricity to get through winter cold spells and the winter season. The obvious answer is long-term energy storage using pumped hydro, hydrogen and bioenergy. But maybe we there are other options if we ‘think outside the square’.

We have large existing hydro storage and generation capacity. For example, Victoria has over 500 MW of hydro locally, and access to almost 2000 MW from Basslink and its share of Snowy. So measures that hoard stored water for winter hydro operation may help. What might this involve?

Actions that cut demand for hydroelectricity outside the winter season, such as solar electricity combined with short term storage and energy efficiency could leave more water in dams to supply winter electricity. This would not suffer the round-trip losses of pumped hydro. Many of our hydro dams also provide water for irrigation, so it would require balancing the timing and amounts of water for irrigation and winter electricity: this may be politically challenging. But it is worth exploring.

Bioenergy can be stored for winter use as solid, liquid or gas, and can be used in those forms to provide heat and gas to reduce winter electricity consumption, as well as for electricity generation.

On the demand side, thermally efficient buildings, efficient space heating appliances and lighting can reduce winter consumption and associated demand peaks. On a cold day, a 6-star home requires about a third as much peak day heat as a 2-star one.

Even in warm climates, peak day use of resistive electric heating can be high, as building thermal performance is often poor and many homes rely on plug-in electric heaters. Yet many have reverse cycle air conditioners but don’t realise that they could provide efficient, low cost heating. Many existing heating systems are very inefficient: programs targeting high winter gas and electricity consumers could help.

Further, improvements in efficiency of other appliances and equipment, particularly water heaters, don’t just save electricity, but are almost as useful as cutting peak demand when you have distributed batteries and smart demand management to shift timing of supply and use. They can cut year-round consumption and demand peaks too.

For example, NEM weekly winter electricity consumption for water heating is around 180 GWh (about 5% of total consumption), of which around three-quarters could be saved through adoption of heat pump HWS and water efficiency. Heat pump water heaters use less boosting energy in winter than most solar thermal units, especially in cold, cloudy conditions when electricity demand can be high, though they use more electricity in summer: but we have plenty of solar electricity then.

Indeed, Saul Griffiths’ exciting ‘electrify everything’ vision could be described as ‘smart, efficient, equitable electrification of everything – fast’. We know what to do – we just have to implement much more effectively, especially in winter.