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A pumped hydro primer

Nearly all electrical storage to date has been pumped hydro storage (PHS), which makes up 97% or 142 GW of global power capacity for electrical storage. The three leading PHS countries are Japan with 26 GW, China at 24 GW and the US at 22 GW. The Eurelectric region comprising the 34 European countries that are part of the Eurelectric synchronous regions, has a total installed capacity of 35 GW.

At a global scale, other utility scale storage includes thermal storage (e.g. concentrated solar thermal) at 1.7 GW, which assuming 6 hours storage equates to around 10 GWh. Other storage includes electro-mechanical (e.g. flywheel) at 1.4 GW, battery at 0.75 GW, and hydrogen at 0.003 GW (United States Department of Energy (DOE) 2016).

The storage capacity of most PHS facilities in the US, Japan and China range from 8 to 25 GWh per GW of installed capacity, corresponding to a typical daily arbitrage cycle with spare capacity. In Europe, the storage capacity of 2,500 GWh is dominated by Spain with 1,530 GWh. US storage capacity equates to around 545 GWh.

Australia’s PHS

Australia has 3 PHS storage plants – Wivenhoe, Shoalhaven and Tumut 3. Wivenoe usually operates with about a 0.8 GWh pump cycle, Shoalhaven about 0.7 GWh, Tumut about 1.5 GWh. Tumut 3 capacity is 1,800 MW (after being upgraded from 1,500 MW in 2011), but only 3 of the 6 generators have pumps. These plants total about 3 GWh total storage but the actual capacity may be greater. Pumping power capacity is Tumut-3  473 MW; Shoalhaven 240 MW; and Wivenhoe 550 MW. To get a sense of scale, the NEM supplies about 600 GWh of energy per day.

The role of PHS

PHS has historically operated in unison with coal and nuclear baseload. In the US, the deployment of PHS was relatively slow until the 1960s, but developed in parallel with nuclear during the 1960s and 70s, and subsequently slowed in the 1980s when nuclear deployment came to a standstill. Since the 1980s, PHS has been superseded by gas turbines (i.e. utilising stored sunlight), which have a low capital cost and quick build time, and present lower risk for investors.

Baseload-PHS usually operates with a daily arbitrage cycle between overnight off-peak and daytime peak. The daily cycling maximises energy throughput for a given storage capacity and underpins the economic return for PHS. Since the deregulation of electricity markets, the use of pumped hydro has expanded to cover a range of additional services. PHS can also be used for load following intermittent renewables, provided that continuous power is available for charging. In Australia, PHS charging is simply utilising whatever generation is available – whether it be coal, gas, wind or solar. In practice, PHS is more likely to be relying on overnight coal baseload, and surplus wind at increasing wind penetration.

Utilisation of Australia’s PHS

Interestingly, Australia’s PHS plants aren’t used that much. There was only 118 GWh and 172 GWh consumed in pumping by these plants in 2014 and 2015 respectively (I’ve uploaded my spreadsheet here). Total capacity for these is about 1,391 MW giving a capacity factor of 1.0% and 1.5% respectively. Given the sunk cost, I’m not sure why these plants aren’t used more and whether price gaming may be part of the explanation. More likely, these simply require a much higher arbitrage than often assumed. Traditionally a low off-peak and high peak price supported PHS but price volatility is also seen as being essential with greater penetration of renewables. South Australia has a more volatile market which improves the volatility economics for the potential seawater scheme on the Spencer Gulf, but may not provide the certainty for a regular arbitrage cycle. The problem with relying on volatility of course, is that additional supply cannibalises its own economics.

The proposed Tantangara-Talbingo scheme

I contacted Peter Lang, who did an estimate at BraveNewClimate for a much larger Tantangara-Blowering scheme in 2010. The current proposed scheme is for a similar but smaller scheme linking the Tantangara-Talbingo reservoirs. The topology is that Tantangara (1,230 metres above sea level) sits near the top of the hill and Talbingo (550 metres) is upstream of Blowering (379 metres). 


Peter put together some rough costings for the proposed Snowy PHS –

Tantangara-Talbingo (TT) head is 686 m versus average head 850 m for Tantangara-Blowering (TB); the generating capacity of TT is stated to be 2 GW versus 8 GW for TB.  But with only the three tunnels used for generating.  8 GW/3 x 80% = 2.1 GW.  This implies the tunnel diameters and flow rates are the same in the two projects.

Tantangara-Talbingo tunnel length is 27 km v 53 km for TB – i.e. about half the tunnel length.  This should reduce the cost of the tunnels by about 40% and reduce the project by about 24%.  That is, about $1.5B in 2010 A$.  Therefore, based on my 2010 estimate for TB, the $2 billion for 2 GW for TT seems roughly reasonable.  

But it does not fit with overseas experience – US costs for PHS are around $3 to 4 billion per GW.  UK DECC (p57) gives a figure of GBP 3.4 per GW.  That’s around A$5.5 B per GW (using GBP 1 = AUD 1.6).  Of course there are differences (no dams, no land reclamation; on the other hand, three tunnels but only one productive and highly inflexible because of the tunnel length and the mass of water in the tunnels that has to be accelerated and decelerated).

What does it all mean?

What does all this mean for the Snowy upgrade? More storage has got to be better as more intermittency is added, but is it economically viable? Why aren’t the existing PHS facilities being used more and why is the proposed expansion going to be better? Is the market structured for merchant storage? Is there too much emphasis on intermittent renewables rather than low-emission baseload or dispatchable renewables? What scale of PHS will be required at higher penetration of intermittent renewables? 

As I see it, the bigger problem is that we simply don’t have markets that are designed to work with a changing market mix and storage. Markets can work if given the right long-term signals and policy stability but require technology agnosticism. Some progress might be on the horizon with the proposed AEMC rule change to reduce the settlement period from 30 down to 5 minutes. This will provide greater value for fast ramping generation that can capture market transients over OCGTs. But how do we value storage in an energy-only market?

These are interesting questions requiring resolution.

Thanks to Peter Lang for information and insights on Australia’s pumped hydro.