Akkujärjestelmät aurinkosähköjärjestelmän tukena suomalaisissa asuintaloissa

This thesis discusses the use of battery energy storages (BES) with photovoltaic (PV) systems and, in particular, their use in domestic residences in Finland. The main objec-tive is to determine which battery technology is the most promising to add to Naps Solar Systems’ product portfolio for home battery energy storage. The benefits of using the chosen product in parallel with photovoltaic systems is analyzed. The cost savings and other benefits for residential customers are thoroughly analyzed with simulations. The thesis discusses the theory behind photovoltaic cells, and describes their current rate of market penetration. It presents a techno-economic comparison of the three most commonly used battery technologies, i.e. the lead-acid, lithium-ion and nickel batteries. Although the study focuses on battery energy storage for residential, grid-connected customers, it also gives an overview of other energy storage technologies. It examines possible topologies, control systems and the benefits to be gained from battery energy storages, particularly with regard to their profitability. The thesis concludes that battery energy storage based on lithium iron phosphate seems to be the optimal solution for residential PV use. Lithium iron phosphate is one of the safest lithium ion battery technologies, and its cycle lifetime is by far the longest. Therefore, simulations were performed using lithium iron phosphate batteries with capacities ranging from 4-16 kWh. Differently-sized PV systems affect the profitability and operation of a BES system, and these effects are reviewed, as is the impact of having an electric heating system. At the moment, battery energy storage is not a particularly profitable investment. However, most PV-BES systems will reach payback in their lifetime, and they do have a positive net present value. In Finland, the possibility of time-of-use-shifting, coupled with high differences in the spot market price, does indicate some future potential for battery energy storage. At present, these systems are more likely to be bought for ecological rather than economic reasons, and these factors are also considered when recommending the product for Naps Solar Systems