PV system together with battery storage : A case study of Uppsala's new city bus depot

In this thesis the potential benefits of combining a photovoltaic (PV) system with a battery storage are investigated. The thesis is conducted at the company WSP in Uppsala and the aim is to design a PV system for the new city bus depot that is planned to be built in Uppsala, estimate the PV system capacity and investigate whether a battery storage can increase the self-consumption of the system. The results of this study are that the most appropriate installation of the PV modules is to place them horizontally on the roof and by that one can achieve an installed power of 715 kWp and a total annual electricity production of 871 MWh. This corresponds to a self-sufficiency of 29 % and a self-consumption of 92 %, which indicate that overproduction of electricity sometimes occurs. How different battery storages, based on both lead-acid and lithium-ion batteries, affect the system is evaluated by developing a battery model in MATLAB. From the results of the battery model it is concluded that battery storages with a capacity of 0.3–0.8 kWh/kWp are most suitable to combine with the PV system and this applies to both lead-acid and lithium-ion batteries. The interval 0.3–0.8 kWh/kWp corresponds to battery capacities of 200–600 kWh and the self-consumption increases to 93–94 % for the lead-acid battery storages and to 93–95 % for the lithium-ion battery storages. The economic analysis show that it is generally more profitable to increase self-consumption of self-produced PV power than to sell it to the grid. However, the high costs that are associated with the battery storages eliminates the economic benefits of the increased self-consumption of PV power. Therefore, it is not considered possible to justify the installation of a battery storage at the bus depot