Solar thermal power generation, as a clean power generation technology, its environmental and social benefits are also important influencing factors. Solar thermal power plants use solar energy for power generation, without burning fossil fuels. Their environmental benefits are mainly reflected in the almost zero carbon emissions during the power generation process, without producing harmful substances such as SO2, nitrogen oxides, and dust. At the same time, with the constraint of total carbon emissions, enterprises need to obtain excess emission rights through trading for the excess emissions when their carbon emissions exceed the free quota. Therefore, enterprises with lower carbon emissions can trade the remaining carbon emission quotas to obtain certain benefits. The benefits obtained from reducing carbon emissions can be considered as an environmental benefit, which can lower the cost of electricity generation compared to conventional fossil energy generation. For the energy storage system of a solar thermal power plant, the environmental benefits in the t-th year can be expressed as:
In the formula, EB π‘ is the environmental benefit of the system in year t, $; π sys, π‘ is the power generation of the energy storage system in year t, kWh; π is the CO2 emissions per unit of power generation. According to the statistical analysis data of the China Electric Power Enterprise Federation, π is taken as 0.832 kg/kWh; Lin and Jia believe that lower carbon emission trading prices will weaken the carbon reduction capacity of the carbon trading market. They suggest that the current pricing for carbon emissions be $10 per ton, and then gradually increase for transition. Therefore, the trading price π ec for carbon emissions is chosen as $10/TCO2, which will increase annually at a rate of 3% thereafter. The present value of the environmental benefits of energy storage systems throughout their entire lifecycle is expressed as:
Another advantage of solar thermal power generation is that it can reduce social costs caused by carbon emissions. The social cost of carbon emissions is mainly used to represent the negative externalities caused by marginal carbon emissions through carbon cycling and climate systems, mainly affecting ecosystems, human health, and property losses caused by extreme climate change due to negative externalities. The social cost reduction brought about by reducing carbon emissions during the entire life cycle of the solar thermal power station energy storage system can be expressed as social benefits, which is equivalent to a partial reduction in the cost of conventional fossil energy generation. The social benefits in the t-th year can be expressed as:
In the formula, ππ‘ is the social benefit of the system in year t, $; πππ π π π π π π is a monetary representation of the social cost of carbon emissions, expressed in $/TCO2. According to the national level social cost of carbon emissions calculated by Rick et al. , the estimated social cost of carbon emissions in China is $24/TCO2. So, considering the reduction in social costs caused by carbon emissions, the present value of social benefits over the entire life cycle of energy storage systems can be expressed as:
These two parts are equivalent to the benefits of the entire life cycle of the energy storage system in a photovoltaic power plant, which can reduce the cost of leveling the system’s electricity consumption. Therefore, the LCOE model that considers environmental impacts can be expressed as:
By using a deterministic model, the LCOE results of different energy storage systems considering carbon reduction benefits can be obtained, as shown in the table. Through comparison, it was found that after considering the environmental and social benefits of carbon reduction, the levelized electricity cost of different energy storage systems has been reduced. Overall, for the dual tank molten salt energy storage system, under two development scenarios, the LCOE values of the system are 0.1971 $/kWh and 0.1385 $/kWh, respectively, which are 13.7% and 18.4% lower than those without considering carbon reduction benefits. For concrete sensible heat storage systems, considering carbon reduction benefits, the LCOE of the system decreased by 17.4% and 23.4% respectively in two development scenarios. For the packed bed energy storage system, considering the benefits of carbon reduction, the LCOE value of the sensible latent heat combined energy storage system is still the smallest among all alternative solutions. In two development scenarios, the LCOE values of the system are 0.1283 $/kWh and 0.0874 $/kWh, respectively. Compared to the situation without calculating carbon reduction benefits, the LCOE values of the system have decreased by 19.6% and 26.3%, respectively. This indicates that the energy storage system of solar thermal power plants can benefit from carbon pricing, existing in the form of environmental and social benefits, which is the advantage over fossil fuel based power generation technology. Meanwhile, reducing the cost of system leveling can enhance the economic competitiveness of energy storage technology.
Set the carbon emission price π ec to follow a uniform distribution, with a minimum value of $10/TCO2 and a maximum value of $20/TCO2. The social cost of carbon emissions follows a triangular distribution, with a minimum value of 4 $/TCO2, a maximum value of 50 $/TCO2, and a most likely value of 24 $/TCO2. The distribution of other parameters remains unchanged. According to the random model, information such as the distribution and variability of LCOE for different energy storage technologies considering carbon reduction benefits can be obtained. The results under two development scenarios are shown in the box plots of Figure 1 and Figure 2.
Considering the impact of carbon emissions, the mean LCOE of different energy storage systems has decreased in both development scenarios. In the Blue Map scenario, the average LCOE of the dual tank molten salt energy storage system is 0.2105 $/kWh, and the average LCOE of the concrete sensible heat energy storage system is 0.1621 $/kWh, which is a 23.0% reduction in the levelized electricity cost compared to the dual tank energy storage system. The average LCOE of the sensible latent heat combined energy storage system is the smallest, with a size of 0.1378 $/kWh, which is 34.5% less than that of dual tank energy storage.
In the Roadmap scenario, considering the benefits of carbon reduction, the overall LCOE values of different energy storage systems are still lower than those in the Blue Map scenario. The average LCOE of the dual tank molten salt energy storage system is 0.1379 $/kWh, while the average LCOE of the concrete sensible heat energy storage system is 0.1036 $/kWh, a decrease of 24.9% compared to the dual tank system. In the packed bed energy storage system, the average LCOE of the sensible latent heat combined energy storage system is the smallest, at 0.0864 $/kWh, which is 37.3% lower than the standardized electricity cost of the traditional dual tank molten salt energy storage system.
After considering the positive externalities of carbon reduction, compared to the previous situation, the average LCOE of the C-X1 energy storage system decreased from 0.1756 $/kWh to 0.1378 $/kWh in the Blue Map scenario, a decrease of 21.5%. In the Roadmap scenario, the average LCOE of the system decreased from 0.1242 $/kWh to 0.0864 $/kWh, a decrease of 30.4%. For a single phase change packed bed energy storage system, the distribution range of LCOE values in the system is reduced, and the degree of rightward tailing is reduced, indicating a possible decrease in the maximum value of LCOE in the system. At the same time, in the Roadmap scenario, the average LCOE reduction of the C-X1 energy storage system is slightly higher than that of the dual tank molten salt energy storage system in the Blue Map scenario, indicating that one way to reduce LCOE is through system scale effect. The capital cost of energy storage systems will decrease with the increase of installed capacity. Utilizing economies of scale can potentially reduce marginal investment costs and increase power generation, thereby reducing the system’s power generation cost.