Photovoltaic supporting energy storage requirements

Energy storage requirements in photovoltaic power plants are reviewed. Li-ion and flywheel technologies are suitable for fulfilling the current grid codes. Supercapacitors will be preferred for providing future services. Li-ion and flow batteries can also provide market oriented services.

As a solution, the integration of energy storage within large scale PV power plants can help to comply with these challenging grid code requirements 1. Accordingly, ES technologies can be expected to be essential for the interconnection of new large scale PV power plants.

In addition, considering its medium cyclability requirement, the most recomended technologies would be the ones based on flow and Lithium-Ion batteries. The way to interconnect energy storage within the large scale photovoltaic power plant is an important feature that can affect the price of the overall system.

Nonetheless, it was also estimated that in 2020 these services could be economically feasible for PV power plants. In contrast, in, the energy storage value of each of these services (firming and time-shift) were studied for a 2.5 MW PV power plant with 4 MW and 3.4 MWh energy storage. In this case, the PV plant is part of a microgrid.

To sum up, from PV power plants under-frequency regulation viewpoint, the energy storage should require between 1.5% to 10% of the rated power of the PV plant. In terms of energy, it is required, at least, to provide full power during 9–30 min (see Table 5).

As explained above, these services do not require storage technologies as they can be provided by PV inverters together with classical central power plant controllers. Note that the use of ES for taking profit of the energy lost due to the power reduction is considered as an economic approach (time-shift). 9.2. Under-frequency regulation