In Spain there are 18 concentrated solar thermal power plants with storage, 17 of which are 50 MW and have a storage capacity of 7.5 hours at nominal power; another, of 20 MW, has a storage of 15 hours. In total, the equivalent electrical storage capacity is 6,675 MWh with a delivery capacity of 870 MW. These facilities take between 7 and 10 years to load and unload their tanks daily with total reliability and without signs of degradation.

Thermal storage of solar thermal power plants is, after conventional hydroelectric power plants, the technology with the highest installed capacity worldwide for electricity generation. Said thermal storage represents, at this time, more than 10 times in equivalent electrical terms, the installed capacity in lithium-ion batteries worldwide.

However, in practically no official document or in the presentations of the agents of the electric sector mention is made of this mature technology, of great capacity in terms of volume of energy, term and power of delivery, for the electrical generation.

These 6.7 GWh of storage capacity, which at the moment are exclusively linked to the routine operation of the plants, together with the additional 60 GWh associated with the 5 GW of new thermal power expected in the PNIEC for 2030, could offer services of extraordinary value to our electrical system over the next decade. For example, they could collect excess production from wind and photovoltaic power plants when demand is exceeded.

The solar thermal power plants would only need to add a simple electric heater to pass the molten salts from the cold tank to the hot tank, while that same capacity of about 70 GWh and 6 GW of delivery power, contemplated in the PNIEC, would require investments greater than 35,000 million euros in batteries and could even be higher in new pumping stations, depending on the complexity of the development of new sites.

With these levels of investments, business plans for battery installations or new pumps to store spills that would result in high expected levels of penetration of non-manageable renewables, would be absolutely unviable, as some consultancies have already shown specialized Nor could business plans for storage investments be justified with the expected differences in the future between the valley prices and the peak of electricity.

But, in addition to those possible applications for short-term dispatch, the storage tanks of solar thermal power plants can offer their capacity, not only for periods of hours or days, but for weeks or months, and can act as a firm strategic reserve. since they have partially available some volume of the hot tank that they do not use during a good part of the year. For this reason, they would be, in this sense, a technical alternative comparable to the pumping, in terms of capacity and term, but without the need for new investments.

In fact, the volume of the molten salt tanks is dimensioned so as not to have to fold mirrors from the solar field on the days with the greatest number of sunshine hours, corresponding to the months of June and July. In those months the stored energy would have to be dispatched within a few hours or one day, depending on the weather, but in the rest of the year, the stored energy could be kept indefinitely, without losses and without conditioning the daily operation of the plant, until it was more convenient to deliver it back to the network.

With this perspective, the solar thermal power plants could contribute to the firmness of the system by offering an availability coefficient similar to those of conventional power plants. In the periods in which the consumption peak is expected, which usually coincide in the last part of the year, solar thermal power plants could be prepared to supply their energy to the grid if required and, therefore, their availability factor could be assimilated to 100 %. Its capacity is so great that the reserve would not be exhausted in the moments in which they had to download and could be restored immediately on the next sunny day.

The storage is the crutch that is used to get out of step when the problems that the Energy Transition would face on the most unmanageable generation scenarios are put on the table. Solving them with battery or pump systems would be highly costly and unfeasible in a free market regime.

Therefore, a generation fleet in 2030 with a significant share of renewable technologies could significantly reduce the dysfunctions that auctioned us based exclusively on prices and whose problems are easily addressed.

Therefore, a generation fleet in 2030 with a significant share of manageable renewable technologies would significantly reduce the dysfunctions that auctioned us based exclusively on prices and whose problems are easily foreseeable. A balanced fleet with manageable renewables would also significantly reduce the level of discharges. If, in addition, these manageable renewables, in addition to their operation, are capable of offering storage services to the system, to ensure the guarantee of supply, as would be the case of solar thermal plants with the aforementioned approach, we could move more quickly towards the complete decarbonization of the electricity sector.

And all this with lower costs, not requiring high investments to solve problems that have arisen, inherent to some of the scenarios that are managed and whose problems we should, in any case, try to limit.

Luis Crespo, Protermosolar