Until recent years, storage was often still hindered by its high costs and was mostly reserved to small scale R&D pilot projects. However, following the recent price reduction of storage modules and technical innovations in the field, a number of commercial wind and PV projects have been carried through in the last few years. Some of them have now been operational for almost 2-3 years and 3E has acted as lender’s technical advisor or as owner’s engineer on a number of them. With the current technologies, storage allows to stabilize wind or PV project production as well as the grid frequency by injecting extra active or reactive power.
Storage is especially good for the grid when associated with a short term forecast system, and it can solve the biggest part of a grid operator’s challenges with renewable projects: the production variability, especially for wind projects. At present load shifting, i.e. storing part of the production of a PV plant during the day and injecting it during the night, has only been realized on very few projects. With the latest developments however, this could become the industry standard within 5 years.
Though wind and PV projects with storage will thus become increasingly mainstream, they should not be considered in the same way as traditional projects. The main difference is that the storage unit connects the production units (wind turbines, PV panels) to the grid, and to some extent, it controls the power output of these units. Technically, batteries and transformers need to be adequately sized to ensure compliance with grid codes. Assessing long term energy yield also becomes slightly more difficult as the behavior of the battery charge/discharge cycle needs to be taken into account.
From a contractual point of view, the storage system performance ratio needs to be guaranteed over the project lifetime and be in accordance with the PV or wind production unit supply and O&M contracts. Financially, it’s important to size the battery system adequately, to make the project economically viable; a wrongly sized battery will also degrade faster than required during the project lifetime, which will increase the operational costs significantly.