The synchronous generators driven by steam turbines in solar thermal power plants have the intrinsic primary frequency regulation capacity needed now
CSP engineers tour Abengoa’s Cerro Dominador solar thermal energy project in Chile during construction
The COIIM (Official College of Industrial Engineers of Madrid) considers it essential to launch as soon as possible an auction program with CSP quotas for solar thermal energy.
Spain is a global leader in this type of power generation, both in installed capacity and technological capacity, with 50 plants totaling 2,300 MW of power installed between 2007 and 2013.
Since then, the sector has been in a state of impasse in Spain until the Integrated National Energy and Climate Plan 2021-2030 (PNIEC) included the deployment of 5,000 MW of solar thermal energy by 2030 in its proposals. This would allow our country to have approximately 7,303 MW of installed power capacity from this technology, three times the current capacity.
Storage
“The main reason why the PNIEC has chosen this technology is its storage capacity, being able to provide electricity to the system even during nighttime hours,” emphasizes Jaime Segarra, an expert from the COIIM.
Photovoltaic plants can achieve similar manageability by installing additional batteries with a significant number of hours of capacity. However, this entails a cost per unit of stored electrical energy several times higher than the storage systems of solar thermal plants, which are typically carried out through the storage of heat in molten salt tanks.
The experts from the College indicate that “it is necessary to promote the incorporation of more efficient innovations and designs with a greater potential for cost reduction.” An example is the central tower technology, which should benefit from improvements in its technical and economic conditions thanks to the new auction program for solar thermal plants, making its cost competitive compared to the best international references.
“Deserted” auction
The Government established a schedule of auctions for the allocation of the economic regime for renewable energy, indicating the minimum volumes of accumulated power for each technology in the period 2020-2025.
However, the minimum volume set for solar thermal was only 600 MW for that period, with 200 MW in 2021, 2023, and 2025. “This schedule made it practically impossible to meet the objectives of the PNIEC of 5,000 MW by 2030, especially considering the long project execution times for solar thermal projects, which are a minimum of three years. This would leave only two years (2026 and 2027) to initiate projects for a total of 4,400 MW,” points out Segarra.
With a one-year delay, in October 2022, the Government called for an auction for the first time with power quotas for technologies, reserving 200 MW for solar thermal.
Unfortunately, the auction was deserted regarding solar thermal, as the offered prices were higher than the reserve or cutoff price expected in the auction, prices that have not been made public.
Substitution with Batteries
If the Government wants to achieve the decarbonization objectives of the PNIEC regarding the contribution of 5,000 MW of installed solar thermal power with around 50 or 60 GWh of associated storage capacity, beyond the proposal of the College to build new plants of this technology, it would have to be replaced with other equivalent solutions. The most similar solution would be an equivalent power capacity of photovoltaic plants with additional storage through batteries or pumped storage, which would compensate for the uninstalled solar thermal storage capacity.
“This would mean multiplying the storage capacity planned in the PNIEC through batteries and pumped storage to 2030 – 6,000 MW, without specifying its energy capacity – with much higher specific costs per unit stored and probably higher overall costs of electricity generated in periods without sun, which would increase the projected average generation costs of the system in 2030,” points out Segarra.
Another option would be to give more prominence during periods without sunlight to existing combined-cycle gas power plants, with generation costs that are unpredictable but can be very high, and this would have to be added to the consequences of possible non-compliance with commitments to the EU.
Advantages of Solar Thermal Plants
The College considers that the commitment to solar thermal energy as indicated in the PNIEC is correct, although the pace of penetration of this technology is clearly insufficient. The highly likely reduction in the average generation cost provided by solar thermal plants compared to other alternatives already presented is just one of the significant additional advantages of this type of plant:
The fraction of added value in Spain from its investment costs would be much higher than in the case of photovoltaic plants and batteries, reducing the negative impact of large investments required in the balance of payments, which would later be compensated by the reduction in natural gas imports.
The installation of several state-of-the-art solar thermal plants in Spain, using central tower technology, should have a highly positive impact on Spanish engineering and construction companies, potentially placing them back as world leaders in this solar technology, which is still in the phase of commercial consolidation.
Their synchronous generators driven by steam turbines would have intrinsic primary frequency regulation capacity, surpassing even combined-cycle power plants in this aspect.
They would offer the possibility of using their surplus storage capacity in autumn-winter and on any other day with low solar capture to store low-priced surplus wind power through resistors. This would increase the overall storage capacity and therefore enhance the electrical system’s ability to manage energy supply, reducing its average generation cost.
They would offer the possibility of future hybridization with gas turbines powered by H2, biomethane, or natural gas to ensure their electrical power output even on completely
