Luca Cioccolanti
The amount of electricity generated by wind increased by almost 273 TWh in 2021 (up 17%), 45% higher growth than that achieved in 2020 and the highest among all renewable power technologies. Wind remains the leading non-hydro renewable technology, generating 1’870 TWh in 2021, almost as much as all the others combined. According to IEA solar was expected to account for 60% of the increase in global renewable capacity in 2022 trained by large projects encouraged by national policies in China and Europe. Hence, both solar and wind energy sources are envisioned to play a key role in the transition towards a 100% renewable energy system. However, the large penetration of solar and wind power technologies brings some concerns since it may result in reliability and stability issues of the grid which is not designed to deal with the fluctuating nature of renewables such as solar and wind.
Indeed, they often suffer from rapid changes in power or prolonged periods of low availability which are also known as energy droughts. Furthermore, these two variable renewable energy sources are characterized by significant temporal complementary.
Therefore, the combination of two or more renewable energy technologies has attracted significant attention to promote a sustainable development while assuring a more reliable energy supply. In particular, hybridisation of solar-wind, solar-hydro, solar-wind-hydro and wind-biomass has been investigated in literature by many researchers. Most of these studies assumed the use of photovoltaics (PV) to convert solar energy to electricity. However, compared to PV solar thermal technologies like concentrated solar power (CSP) offer additional benefits like partial-dispatchability and thermal energy production. The thermal energy storage (TES) of a CSP system, indeed, can store the excess power production from the wind and supply back the users at the time of its request. In this way, it is possible to prolong the operation of a CSP plant also in case of poor radiation and provide ancillary services to the grid while solving reliability and stability issues related to the excess of power production.
Figure 1. Scheme of the integrated hybrid system under investigation
So far, the hybridisation of CSP with wind turbines has been studies with reference to the large scale. Indeed, the low competitiveness of CSP plants at small scale makes these systems not much attractive. However, in the transition of the current energy system towards small-energy communities CSP technology may play a key role also at small-scale by compensating the variability of other intermittent renewable technologies.
Therefore, based on the experience gained within the EU funded project ‘Innova Microsolar’, which dealt with an innovative CSP system for households applications, a group of researchers have investigated the dynamic operation of a Linear Fresnel Reflector solar field in combination with wind turbines for the provision of combined cooling, heating and power to 10 residential appartments.
The proposed hybrid trigenerative system consisted of a 440 m2 collector area Linear Fresnel Reflectors solar field, a 20 kWe/100 kWt organic Rankine cycle unit combined with a latent heat thermal energy storage system, an absorption chiller, and a 20 kWe wind turbine.
Read also Monocrystalline silicon solar cell, new record for JinkoSolar
An advanced dynamic model was developed by the authors and the operation of the systems evaluated with respect to three different Italian locations having different solar radiation and wind energy availability. The results have shown that the hybridisation can extend the thermal demand coverage by renewables for all the investigated locations by increasing the operation of the organic Rankine cycle unit, especially in wintertime. In particular, the energy production from wind turbine contributes more to meet the users’ energy demand compared to the separate configuration. Furthermore, a sensitivity analysis of some design parameters revealed also that the size of the water thermal energy storage tank does not have a significant impact on the electrical and thermal coverage of the hybrid system.
However, it is worth to notice that despite sending the power surplus from wind turbine to the TES of the CSP system adds flexibility to the integrated plant their full integration is still not taken for granted. Indeed, power surplus from wind turbine could be used also for other scopes like hydrogen production in electrolysers or heating provision through power to heat systems. Therefore, a thorough economic assessment of such a solution is needed for deducing an overall comprehensible conclusion.
Nevertheless, in the perspective of a 100% renewable energy system CSP technology may play a key role even at small-scale.