Off-river pumped hydro (ORPH) would be used in conjunction with batteries, efficient long-distance transmission and demand management, but would do the heavy lifting, literally, of energy storage.

ORPH comprises the third leg of the clean energy tripod, along with electricity generation by photovoltaics and wind turbines. Together they can provide a complete solution to the need for reliable, dispatchable zero-carbon electricity. It can support the strategy to ‘electrify everything’, including in space heating, transport and many industrial uses. Renewable energy would still be cheaper than alternatives.

ORPH can be built relatively quickly. There are many suitable sites and judicious selection of sites can substantially reduce costs, both of construction and grid connection. As well as some large systems being constructed or contemplated, small- and medium-scale systems are feasible, and many storage sites would enhance the resilience of the electricity system.

With all these advantages, there would be no need for gas-fired peaking plants, nor for the speculative technologies of carbon capture and storage and small modular nuclear reactors. So-called offsets could be quickly replaced by real and reliable reductions in carbon emissions. Conventional nuclear reactors would not be available for at least fifteen years, with cost estimates of two to five times wind and solar, or more. Nuclear power would create intractable toxic waste problems and is compromised by being a path to nuclear weapons.

The concept

Off-river pumped hydro comprises two water-storage ponds at different elevations, connected by a pipe or tunnel, with a pump/generator at the lower pond. The lower pond can be replaced by a river or the sea, though sea water is a more challenging medium.

The ponds are much smaller than big on-river irrigation reservoirs, though they might still be quite large. The opening image is of an ORPH pond and the Eucumbene irrigation dam is shown below.

For example, a pair of 100 hectare reservoirs with a head of 600 metres, an average depth of 20 metres, a usable fraction of water of 90% and a round trip efficiency of 80% can store 18 Gigalitres of water with energy potential of 24 Gigawatt-hours (GWh), which means that it could operate at a power of one Gigawatt (GW) for 24 hours.

This far exceeds the power and energy of any battery.

Cost

A 2021 paper by Bin Lu and others in Blakers’ group at ANU uses detailed modelling to conclude that a 100% renewable energy system, replacing 80% of Australia’s carbon emissions, would cost $70-$100 per MWh (megawatt-hour). This system features off-river pumped hydro storage, batteries for smaller and short-term needs, some demand management and efficient high-voltage direct current transmission over long distances.

This cost is significantly lower than estimates that do not take full account of ORPH. Recently CSIRO said ‘firmed’ solar and wind would cost $100-$150 per MWh (see graph below). Either way the triad of solar, wind and storage is cheaper than all alternatives. 

Estimates of the costs of nuclear power very widely. CSIRO estimated conventional nuclear to cost $150-$250 per MWh, though that does not fully account for likely cost and time overruns. Bernard Keane of Crikey estimates conservatively that cost overruns could be around 30% more based on other large projects, but notes that nuclear power plants are notorious for even greater delays and cost blowouts. Thus costs of $200-$400 per MWh are not implausible, and even higher costs possible. Thus conventional nuclear would be in the range of 2-5 times more expensive than firmed wind and solar, or possibly even more.

The presence of carbon capture and storage in the CSIRO estimates is problematical, as the technology is still in early stages of development and has not come close to capturing 100% of carbon emissions from coal and gas burning. It is vulnerable to highly local subsurface geological conditions and would encounter strong challenges at scale, requiring both large water supplies and geological sites for burial whose safety and capacity would be hard to establish in advance. It seems still to be a speculative option.

To summarise, a system of wind and solar with off-river pumped hydro storage, transmission balancing, demand management and some batteries is substantially cheaper than other options. It would be capable of displacing 75-80% of Australia’s greenhouse gas emissions using exisiting technologies.