Benefits of Centralized Energy Storage Aggregation
Energy storage systems can provide benefits for both the system and individual owners through aggregation. Fig. 1 shows uncoordinated operation of EES by private owners for their own benefit versus centrally coordinated EES for maximizing system benefits. A sizing exercise has been performed to minimize life cycle costs taking into account electrical, thermal and aging models.
Cost
Many storage technologies have been investigated in order to smooth Direct Wave Energy Convert- er (DWEC) farm production, such as supercapacitors or flywheels. However, very few studies have investigated their impact on the life cycle cost of a DWEC system. This is due to the fact that the underlying electricity production is highly variable. This results in large power fluctuations at the output of the DWEC that must be smoothed in the energy conversion chain.
Grid integration of some renewables such as wave energy is a major challenge and requires the installation of a large amount of energy storage. This has a significant impact on power quality and reduces the potential of new generation technologies such as wave energy converters. The power variations induced by DWEC are also large and may result in flicker. This is all the more important for DC power sources such as the DWEC.
A policy implication of this study is that the system operator should make public the existing capacity of storage in the system and planned new storage installations, together with statistics about the fraction of these resources that are centrally coordinated as this significantly impacts the savings of consumers. This would improve consumer confidence in the technology and might facilitate deployments. From a modelling method perspective, the findings imply that models of the electricity system should take into account the trade-off between private and system benefits of energy storage aggregation.
Flexibility
The centralized control of the energy storage system allows a smaller device and lower energy cost. However, this entails more power fluctuations at the output of Centralized Energy Storage System each device and therefore more losses in the inverter and farm cables. This impacts the life cycle cost of the ESS, which should be determined by considering investment, replacements and losses. Moreover, centralized energy storage will require the involvement of a community to make it viable. This will involve the consumers/prosumers, PV utilities and the community energy storage operator. It will also require a communication network between these players.
Centralized coordination offers greater savings to prosumers than distributed coordination, especially under time of use tariffs. The value of home batteries depends on the need for flexibility in the long term, and centralized coordination is better suited to this requirement than distributed operation.
The impact of centralized energy storage coordination on electricity costs increases with the ratio between variable Centralized Energy Storage System renewable capacity and flexible supply capacity, and is inversely proportional to the size of the aggregation of these resources. However, the savings to the consumer are relatively small compared with the overall electricity cost under this scenario.
Efficiency
Centralized coordination of energy storage offers greater savings to prosumers, especially under time of use tariffs. However, it is important to consider the trade-offs between private and system benefits of energy storage aggregation. For example, it is essential to understand the impact of centralized coordination on power prices and on consumers’ electricity bills.
Several storage technologies have been investi- gated to limit total power fluctuations, such as supercapacitors or flywheels. However, little work has been done to demonstrate the technical and economic value of these systems for wave energy grid integration. This is particularly important for the Direct Wave Energy Convert- er, where the large power fluctuations produced by the device may have a negative impact on power quality.
In the present study, we compare the impact of distributed and centralized control on ESS sizing and management. We also investigate a management strategy to optimize the aging of a DWEC-ESS for each size by minimizing the life cycle cost and respecting the flicker constraint. The results show that the centralized control reduces the average aging speed and improves the power quality by reducing the fluctuation magnitude of the output.
The centralized scheduling of demand-side storage allows the system operator to utilize this flexibility in a more efficient way. As a result, peak electricity prices in the wholesale market are reduced. This benefit is shared by all consumers, including those without distributed technology. In contrast, the distribution of EES scheduling results in lower system-level benefits and higher electricity bills for consumers.