Solar thermal power becomes competitive

Solar thermal power plants are far from being fashionable. In Central and Northern Europe, this may be down to the fact that they are a rare sight, given that they need much more direct sunlight than PV arrays in order to generate electricity efficiently. However, IRENA, the International Renewable Energy Agency, believes that, compared to other renewable energy technologies, CSP can still be considered in its infancy, in terms of deployment. CSP stands for ‘concentrated solar power,’ a term indicative of the principle behind it: bundle rays of the sun to heat the water-steam circuits found in coal, gas and nuclear power stations.

Investors’ initial preference of wind and solar PV farms is due to several factors: substantial subsidies in rich industrial nations such as Germany and the United Kingdom, which are not home to solar thermal power plants, and the at first minor demands placed on the availability of renewable energy. Moreover, failures like Crescent Dunes are a huge deterrent, owing to the substantial investments they draw. The solar tower power station in the Nevada desert is purported to have sunk nearly half a billion US dollars. After producing much less electricity than planned for technical reasons, it was shut down in 2019 at the end of just its fifth year of operation.

Significant drop in generation costs

But a lot has changed since then. The technology has advanced, enabling newer stations to produce electricity more reliably and, in turn, more affordably. According to IRENA, the average generation costs of solar thermal power plants plummeted from 29 US cents per kilowatt hour (c/kWh) in January 2016 to 18.2 c/kWh last year.

Relative to the global average, this still makes it some 50 percent more expensive than offshore wind energy and nearly three times as costly as PV power, but some investors now factor in much lower costs. Bids below eight US cents per kWh were successful in concession auctions for deliveries from 2021 onwards in Australia, the United Arab Emirates and Chile.

Record price in Dubai

One such project is Phase 4 of the Mohammed bin Rashid Al Maktoum Solar Park in Dubai. It consists of a parabolic trough power plant with an output of 600 megawatts (MW), a solar tower power station rated at 100 MW, and a PV array with 250 MW of installed capacity. The Dubai/Saudi/Chinese consortium is set to receive 7.3 US cents for every kilowatt hour put on the system by the solar thermal power plants. PV power is set to be remunerated at a rate of 2.4 c/kWh. According to Dubai’s state power utility (DEWA) these represent the lowest electricity costs for each of these technologies anywhere in the world.

In addition, DEWA claims that the two solar thermal power stations sport a further superlative: reaching 260 metres into the sky, the solar tower is the highest in the world. What is more important, though, is that the molten salt cavern can store heat for 15 hours, enabling the steam turbines to bridge even the longest winter nights if there is enough sunshine during the day.

Cost advantage: heat storage

For many experts, this is a key advantage of solar thermal power production over PV systems: heat storage is much cheaper than electricity storage. However, the latter is required by PV stations in order to supply electricity at night.

On completion of the five construction phases, the power plants of the Mohammed bin Rashid Al Maktoum Solar Park will have an installed capacity of five gigawatts. According to the German economic advancement company Germany Trade and Invest, they will power an electrolyser used to obtain hydrogen from seawater, among other things. In such costly plants, capacity utilisation is key to profitability. Thanks to solar thermal technology, in theory, the electrolyser could be operated 24/7.

Less dependent on oil and gas

Whereas the United Arab Emirates are apparently seeking to establish an export economy built on hydrogen production, other countries are attempting to reduce their dependence on energy imports. Morocco, for one, has been meeting its demand for energy nearly entirely with imported fossil fuel thus far. Based on the country’s current solar strategy, the power of the sun should account for 14 percent of energy supply someday.

The start is being made by the Noor solar hybrid complex: 80 MW PV and 500 MW solar thermal power with storage for at least five full-load hours are already making an important contribution to Morocco’s power supply.

A similar plan is being pursued by Israel, which so far has produced its electricity nearly entirely from imported coal (approx. 30 percent) and natural gas (approx. 65 percent). Although the country will probably cover its gas needs with its own sources in the Mediterranean in the future, coal will still have to be imported. This is why Israel is looking for alternatives – and not just for reasons of climate policy alone. One option are the two solar thermal power stations in the Negev desert in the south, which have been generating up to 242 MW of electricity since 2019.

Further cost reductions

Based on figures from the National Renewable Energy Laboratory of the US Department of Energy, some 120 thermal power stations have been commissioned in 23 countries, including research and demonstration plants. A total of 16 solar thermal power plants with a good 1.5 GW of combined capacity are under construction, with another 14 in the development phase. This is anything but formidable growth. In fact, the international Energy Agency IEA projects the need to increase electricity production from solar thermal power plants twelve-fold by 2030. But the technology is nowhere near this growth trajectory.

However, experts anticipate further declines in cost as expansion progresses – thanks to lessons learned in construction, the automation of plant management and economies of scale resulting, for instance, from parabolic mirrors being manufactured in larger numbers. Australia-based “Vast Solar” stakes this very claim: Reduce the construction costs of solar thermal power plants with attached storage through modular processes, while also making them more reliable. This construction method is to be applied for the first time to a 30 MW solar tower power station on Mount Isa, Queensland, designed to generate electricity around the clock.

Heat transfer fluids are another possible starting point for reducing costs. Studies involving silicon-based liquids, molten salts and dark ceramic particles that are able to absorb and transport much higher temperatures are currently underway. These solutions could be used to significantly increase the efficiency of steam power plants and heat storage facilities, thereby reducing electricity generation costs.

However, solar thermal technology is far from being perfectly engineered. Scientists at the Institute for Solar Research of the German Aerospace Centre (DLR) in Jülich are exploring how to make more efficient and multi-faceted use of the heat of the sun. Read Part 3 of our Solar Thermal Power series soon to learn about the innovations in the works there.