A Word with Thomas Altmann
Thomas Altmann, Vice President of Innovation & Technology at ACWA Power
Is CSP the answer to clean water desalination? In this interview with Thomas Altmann of ACWA, we explore the opportunities and possibilities of CSP for desalination.
Interview by Lila Neuberger
L.N. What is the current role of solar power in desalination?
T.A. We are in the early stages of solar driven desalination. For example, currently we are seeing several pilot plants operating during the day in the Middle East, Spain and India. There is also a small-scale commercial CSP desalination plant operating in Port Augusta, Australia which provides electric power and desalinated water for tomato greenhouses. However, in this case the end product is not water or power, but tomatoes.
It’s just a question of time before the right project environment is created to run a 24-hour large-scale solar powered desalination plant.
Figure 1: Solar-Desalination at Port Augusta
L.N. What countries would you say have the most potential in solar power for water desalination?
T.A. For a country to become a leader in CSP for water desalination, there are several factors to be taken into consideration. These include a high growth in demand for water, a lack of alternative fresh water sources, suitable solar resource, access to sea water, and a costal population as consumers. All these factors play a significant role in countries in the Gulf which currently don’t have an alternative to desalination and also choose to export fossil fuels at high prices rather than internally consuming them.
Besides the Gulf, other Middle Eastern countries, Australia, India, South Africa, Namibia, China and Chile also possess potential when it comes to solar powered desalination.
L.N. What are the viable processes for turning saltwater into fresh, drinkable water using solar power and more specifically CSP?
T.A. For a desalination plant to be viable, it needs to run 24 hours a day.
The simplest process would be to use PV technology alongside reverse osmosis, as well as to utilize the grid for night supply or as storage. In the latter case, you would need to ensure the PV plant is much larger than you’d need to run just the desalination plant. You can then dispatch the extra energy produced throughout the day to the available grid and the grid would then return that energy to keep the desalination plant running during the evening and night. Through this methodology, it is possible to produce the full amount of energy for a reverse osmosis plant using PV. This is also probably the cheapest solar option. There also exists a more expensive PV option with batteries to supply 24 hours.
CSP offers a more flexible option for desalination and is another interesting option. You could produce electricity to run a 24-hour reverse osmosis desalination plant due to the integrated thermal energy storage (TES). Depending on tariffs for optimization, you can use only CSP with TES or alternatively; a combination of CSP and the grid supply for during the night. The best option would depend on the specific project circumstances.
Figure 2. First Solar-Desal plant in India
L.N. One of the problems of using CSP for water desalination purposes is the costal location. Why is that and what are the possible solutions?
T.A. Desalination plants need to be close to the coast, which poses a potential problem to CSP powered desalination plants. On the coast you have limited land availability (CSP requires a lot of space), high costs of land and lower irradiation than sites at higher elevations due to humidity and other factors.
The ideal location for a CSP plant would be away from highly populated areas with less emissions and aerosols and low humidity where CSP conditions are optimal to produce electricity which can then be transported via transmission lines to power the desalination plant. However, the downside of doing this is the losses in the transmission lines.
A trade-off study would need to be done to determine the best solution for each specific project.
L.N. Is the use of CSP technology for water desalination competitive with other technologies?
T.A. First of all, CSP has a higher capacity factor than PV meaning it can run all night and has a higher annual generation. Also, the volume of steam required for desalination is less in comparison to that needed for generation, i.e. lower temperature and pressure, meaning that CSP plants for desalination can be built at a lower cost using less robust, less precise and bulk materials at lower cost.
The energy consumption of desalination is still decreasing due to better performing membranes and optimization, combined with less stringent steam conditions. I see a lot of room for system integration, hybridization and further optimization. We are just at the beginning of this journey.
L.N. What needs to happen for it to become more competitive?
T.A. We are seeing a trend of decentralization and decarbonization. This trend fits well with several solar-desalination plants along the coast close to the consumer without the need of power transmission or gas supply lines. This is an advantage for solar desalination. And of course, decarbonization allows a company to apply for carbon credits and accredited companies access to low-cost financing.