Community storage for small urban units including dwelling and small businesses

This dissertation focuses on analysing the effect that aggregation of demand and photovoltaic (PV) generation of building units, from commercial and residential sectors, and the use of battery storage systems have on the self-consumption rate, the self-sufficiency degree and the profitability of the system, by analysis of the internal rate of return and the payback period. For the residential sector a condominium consisting in the aggregation of 14 or 7 dwellings was considered as a single building unit. Regarding the commercial sector, three different building units were studied: a bank branch, a restaurant and a hotel. The control strategy considered that the generated photovoltaic electricity is primarily used to fulfil the consumption needs of the units. If there is a storage available, if the generation is higher than the demand, the excess power is fed to the battery. If the photovoltaic production is insufficient to meet the consumption, the difference will be provided by the battery, if charged, otherwise it will be supplied by the grid. The system configuration was tested for installed PV powers in the range up to the contract power (when the peak power equals the maximum consumption). The hypothesis that the aggregation of electricity consumption, from different users with different consumption profiles, will lead to an improvement of the collective load diagram, in the sense of being better adapted to the photovoltaic generation profile, was confirmed and supported by the results. In general, the aggregation of different residential and commercial units and the use of a battery system, reflects an increase on the self-consumption rate. A battery storage capacity of 0.5 to 1 kWh per installed PV power reflects an increase of approximately 12% to 20%. For a 1.5 kWh/kWp ratio the increase was from 25% to 30%, and from 30% to 36% for a 2 kWh/kWp. The result also show that single sites feature lower self-consumption and lower self-sufficiency and less interesting economic value than aggregated units. The hotel is the exception to this premiss as, by itself, it achieves a high level of self-consumption, up to 90%, depending on the storage capacity. Another result of this study is that even without batteries, self-consumption rates of photovoltaic systems increase with aggregation since the excess energy point is higher for aggregated units. When aggregating building units (the restaurant in comparison with condominium, bank and restaurant in a no battery scenario) our study shows an increase up to 30% in self-consumption. Self-sufficiency degree suffers a negative, albeit less pronounced effect, caused by the aggregation of users. The results show that the restaurant, or any aggregation including the restaurant, hardly returns the investment. All other system configurations feature positive internal rates of return, with some being higher than 5%, again confirming the benefits of aggregation as it leads to higher returns. The values of payback period underline the conclusions from the analysis of the internal rate of return. All buildings and aggregated units, except for the restaurant, feature values between 8 to 18 years, with lower values for aggregation units and with a optimum for the no-battery configuration.