Energy storage systems integration into PV power plants
Authors:   , Beltrán San Segundo Héctor 
Published: July 2023

The boom experienced by renewable sources in recent years has changed their consideration as a marginal component of the electrical system mix into a major player with an important role in the demand coverage in many countries. Regarding the PV technology, its weight within the electrical systems in countries such as Germany, Spain and Japan suggests that integration problems may arise if the current installation trends are maintained. Most of these problems are connected to one of its main handicaps: its stochasticity and its high level of intermittency, both characteristics clearly dependent on weather.
This work is dedicated to the analysis of one possible solution to achieve a higher penetration rate of the photovoltaic technology in the grid which is, according to the literature, the introduction of an energy storage system in parallel with PV plants. The ultimate objective in the study reported in this Thesis dissertation is to provide PV power plants with the ability to generate solar energy in a controlled and, if possible, constant way so that these could access both the day and intraday electricity markets.
The analysis of the storage system characteristics , focusing the interest on the amount of energy and power that this system would require when operating the photovoltaic plant in accordance with a specific energy management strategy while avoiding saturations, requires a good knowledge of solar resource. At present, there has not been any major and exhaustive campaign to measure the radiation with sampling periods below 15 minutes. Therefore, the solar resource can only be estimated by using statistically-based data and weighted averages. These data come from sources in the space (satellites) and from meteorological stations in the Earth's surface. This work uses information extracted from one of the most accepted solar radiation databases, the PVGIS database developed by the European Union. Moreover, real data measured in a particular place in the south of the Iberian Peninsula, where the analysis of the energy storage requirements has been centered, are also used. Both data sets have been cross validated in order to verify their credibility and agreement degree.
On the other hand, there are multiple energy storage technologies that can be currently identified as potential candidates to be included in photovoltaic power plants to integrate future hybrid plants with controlled production. A review of these technologies, along with a description of their main features highlighting their strengths and limitations, is included in this Thesis work. Using the comparison as a method, which has been performed considering various factors associated to the storage technology itself (geographical dependence, state of development, energy and power rated levels achieved by each technology) but also taking into account the operation conditions at which the storage will be subject in a photovoltaic power plant, one technology is highlighted as the candidate to be used in this application.
Finally, this Thesis proposes various energy management strategies to control power production in photovoltaic power plants integrating an energy storage system. Some of these strategies are directed to incorporate the plant to the electricity market while others simply pretend to reduce the variability of the production. For each of them, an estimate of the energy storage system required energy capacity has been obtained. These estimates allow having a rough approximation of the energy requirements, as well as an estimate of the additional cost, that this solution would imply. Among the various energy management configurations proposed, some of them provide results technically feasible on the one hand and, on the other hand, also interesting outcomes from an economic point of view, as the regulatory framework governing the electricity markets becomes gradually adapted to the new and evolving reality of the electric power system.