Background to phes
It is often assumed that to mitigate the worst effects of climate change we need an energy revolution incorporating a raft of new ideas. However, the core technologies needed to decarbonise the power sector already exist in the form of renewables, with wind and solar now the fastest-growing sources of new generation.
One major problem, as critics are quick to point out, is intermittency. If that problem could be solved, the energy sector could be transformed within a few short decades. And, as it happens, several countries are betting that we already have the answer.
In pumped hydroelectric storage (PHES) there is a tried-and-tested technology that not only fits the bill but has been doing the job for well over a century. First employed in the 1890s, pumped hydro makes up 97 per cent of energy storage worldwide, with around 168GW currently installed. Excess off-peak grid power – theoretically from renewables – is used to pump water uphill, where it’s stored as gravitational potential energy. When electricity demand is high, water is released downhill to power turbines, the elevated reservoirs essentially acting as giant batteries to help balance the grid.
South Africa is in a fortunate position with regards to renewables in that the energy present in the wind and solar sources is vast. Solar energy per square metre is 50-100% more abundant in South Africa than in Europe where already significant solar capacity has been installed. The land required to install the capacity is available and would not be disruptive to the majority of the population.
The majority of electrical power generated comes from coal burning power stations which also happen to exist in the more densely populated parts of the country causing untold respiratory problems to the inhabitants who live there. The coal quality is in decline and the costs of extraction are increasing. The fleet of power stations is aging to the extent that most are in the tail-end of their life-spans. Globally there is agreement that coal generation is too costly to the environment and while existing plants may be allowed to perform to the end of their economic lifespans, any new builds would be strongly discouraged if there were alternatives.
Now as the country faces national load-shedding on a frequency that moves GDP growth into negative numbers, there needs to be some bold choices made on how we will ensure sufficient generation capacity for the near future and generations to come. The economics tell us renewables is the way forward, and yet the coal and nuclear lobbies will always reply citing the need for baseload; and they are not wrong on that point.
South Africa is no stranger to PHS with just under 3GW of installed capacity. China has 23GW with another at least 6GW currently under construction. The US has 14GW with eyes on 40 new sites to be developed. The technology is developed, the world is embracing it and its growing quickly with 165 GW installed globally. There is however a problem in the South African context: the country is largely arid and PHES requires large rivers or rainfall to ensure the water is available for power storage and generation. On timescales for lifespans of strategic long term generation assets together with less predictable weather patterns and increasing population demand for fresh water, it cannot be a sound choice to build more of the same fresh-water based power stations.
Taking all the above into account we have aimed to solve the renewables baseload problem in order to provide clear direction to stakeholders that we must now redouble our efforts to begin the energy transition, that the old baseload bogeyman of renewables has been slain, and that a massive national effort of diversifying our national grid away from fossil fuel baseload can begin.
The key component in the solution is the creation of a small inland seawater reservoir 22 by 5 kilometers in size, with a useable water level between 180 and 200 metres above sea level. Situated 7km from the sea the reservoir will hold a maximum of 2 billion cubic metres of seawater. With a usable capacity of 2 billion cubic metres of seawater held between 180 and 200 metres above sea level, the potential stored energy would be 980 GWh. For reference South Africa uses approximately 550 GWh per day, so this facility would have enough storage to power the entire nation for more than a day, if every other generational unit was switched off.
The location has been carefully chosen to not involve a river valley (which is environmentally difficult to justify), to utilise a naturally occurring depression which assists in delivering the potential for a large volume of water to be stored while requiring minimal dam wall building for a dam of this capacity. Furthermore the location is approximately 100 kilometers away from the inland areas of the country that have some of the most consistent solar power in the world.
Building a solar farm region in conjunction with the reservoir will together realise the renewable baseload. The idea would be for the project owner to implement a “plug and play” model where the project company acquires blocks of land, obtains all required government approvals for solar power generation and then awards contracts to solar power developers through auctions. The project company would then use the daytime generated solar power to pump energy into the dam to ensure it had sufficient reserves for the provision of night time power.
It is perhaps prescient that with Eskom finally moving towards unbundling into different units in order to survive that the potential for a large scale energy operator to enter the market and provide services to the national grid, it will be possible to work with the grid division of Eskom to feed this large power source into the national grid. The hydro plant can offer the grid Frequency Control Ancillary Service (FCAS), by being able to quickly draw or provide large quantities of power. It could also provide a System Restart Ancillary Service (SRAS) where in the case of a blackout, it could supply power to re-energise other power facilities so that their generators can synchronise and re-enter the market.
The hydro dam is not a net generator and relies on the availability of cheap solar power to recharge. Thus the dam, the solar/wind and connecting grid can be seen as part of the same system and should use a contracted model for project revenues. The use of firming contracts involving the hydro storage plant purchasing the variable output of the renewable energy providers and selling back a baseload or peak firm energy, firm to Value of Lost Load (VoLL). Alternatively, the solar plants could purchase the dispatch rights to PHES in order to firm up supply from renewable energy sources. Firming contracts could also be of interest to large industrial energy users, who see the appeal of purchasing low cost non-firm renewable energy and then firming it up to match their load.
In South Africa’s IRP2010 where they laid out energy procurement for the period 2010 to 2030 where 29GW of new capacity is called for, the addition of this PHES combined with solar could provide up to 10GW of that capacity with lower amounts also possible. Programs for ensuring a Just Energy Transition, allowing coal energy workers to move into new economic opportunities created by the new renewables energy infrastructure must be a key theme to ensure a smooth transition where all stakeholders are brought in and given a role.