Hybrid Energy Storage Systems (HESS) from renewables have begun to gain traction. As the share of solar, wind, and battery storage technologies in the energy mix increase and their respective LCOE continues to decline; hybrid systems are gradually penetrating the market.

A HESS typically combines two or more energy generation technologies with on-site battery storage, providing multiple benefits such as reducing the intermittency of power dispatched. These systems can be off-grid or connected to the grid. Nevertheless, this article will focus on the latter.  

Even though these systems can be comprised of various technologies such as solar CSP, biomass, geothermal, hydropower, or fossil-based energy sources, the coupling of wind and solar has become one of the most researched and implemented to date.

As wind and solar generation fluctuates due to its variable nature, dependent on weather conditions and solar irradiation, hybrid systems with integrated battery storage are enabled to behave like a conventional power plant.

Successively allowing the hybrid power plant to enter new and attractive revenue streams. Including capacity markets and ancillary services to provide grid stability and reliability. This marks a shift from the traditional energy market revenue models, which primarily consist of Power Purchase Agreements (PPAs) and Feed-in-Tariff structures. This triple configuration has the potential of providing a “baseload” supply, as well as meeting grid peak demand [1].

For example, in a PPA, power plants aim to dispatch the full capacity of kWh into the grid and resort to curtailment when supply is high or demand is low. On the other hand, the hybrid and storage system aims to dispatch energy at optimum times.

Hybrid plants with integrated storage have gained the interest of energy developers and investors as they can potentially maximize the profits of their assets by combining them. In this way, the total costs of the power plant decrease by incorporating an additional technology, such as wind, into a solar farm [1].

Combining these technologies presents a viable opportunity to reduce capital costs by using the same land, permitting fees, and shared infrastructure such as roads, connections, substations, etc.  

Several HESS power plants have been developed or are in the pipeline in the US, Germany, the Netherlands, and the UK [2]. One of these is the Haringvliet Zuid hybrid power plant developed by Vattenfall in the Netherlands, a forefront runner in the innovation of these systems. It combines a 12 MW Li-ion storage system, with 22 MW of wind and 38 MW of solar capacity [3].

Vattenfall’s largest hybrid energy park

Even though HESS offers many benefits to the developers and investors because of the aforementioned reasons, the battery systems could be underutilised for an extended period of time and could provide optimal services if located close to load centres depending on its intended use.

Moreover, these systems are still in the demonstration stages, and their design and operation are more complex than a stand-alone generator. If the right market and regulatory conditions, which currently determine the project’s financial feasibility, are put into place, HESS might soon become the standard. As green hydrogen is expected to gain ground in the coming years, electrolysers will likely be integrated into hybrid systems [1].

Overall, HESS offers a compelling case for energy developers and investors to reduce financial risk by complementing different technologies, reducing costs through economies of scope, and providing fundamental capacity and ancillary services. The scale of its implementation will widely be influenced by the continued reduction in technology costs and facilitating regulations and incentives from local and national governments.

[1] https://www.nrel.gov/docs/fy20osti/75026.pdf

[2] https://www.evwind.es/2021/05/06/combining-wind-power-solar-batteries-and-in-future-even-electrolysers/80646

[3] https://group.vattenfall.com/press-and-media/newsroom/2020/vattenfalls-largest-hybrid-energy-park-is-taking-shape-in-the-netherlands

Isaac Elizondo Garcia

MSc. Energy Systems at University of Oxford

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