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Juha Koskela: Electrical energy storage affects the profitability of using photovoltaic in residential buildings

Tampere University
LocationKorkeakoulunkatu 1, Tampere
Room TB109, Tietotalo building, Hervanta campus, and remote connection
Date17.5.2024 9.00–13.00
Entrance feeFree of charge
Photo: Sanna Kapanen, Foto-Kapanen Oy
The electrification of the energy system and increasing local production create challenges for the electricity grid that could be answered by storing electrical energy. In his doctoral dissertation M.Sc. Juha Koskela investigated the factors affecting the profitability of electrical energy storage and developed methods for efficient use of electrical energy storage in connection with photovoltaic systems in residential buildings.

The production power of photovoltaic varies depending on weather conditions, time of day and season, so that only part of the production can be used for own consumption. Typically, replacing purchased electricity with own production is profitable, because in addition to the purchase cost of electrical energy, the costs caused by transmission and electricity tax are avoided. On the other hand, selling the surplus to the grid is not profitable when the investment costs of the system are considered. According to researcher Juha Koskela, sizing the photovoltaic system can affect how much of the production can be used for own consumption.

“Storing electrical energy can increase the amount of production used for own consumption and at the same time reduce the amount of energy transferred between the customer and the grid in both directions. This could reduce the need to strengthen the grid and thus curb the increase in network service fees,” Koskela states.

In practice, in residential buildings, electrical energy can be stored in a battery, or the consumption profile can be modified by controlling the loads.

“The obstacle to the widespread use of batteries has been their high prices and, on the other hand, poor knowledge of their utilization possibilities,” says Koskela.

Various earning opportunities have not been effectively utilized in the management of commercial storage systems. Koskela researched how to get the best financial benefit from storage, and he developed control methods based on forecasts for this in his dissertation.

In addition to increasing the self-use of photovoltaic, the battery can be used to decrease the peak powers if a tariff that includes a power fee is used, and to minimize the cost of purchasing electricity by using market price-based electricity contract.

“However, without intelligent control based on forecasts, the benefit can be lost when different control targets are combined,” Koskela points out.

In addition, Koskela developed a sizing method for photovoltaic systems from an economic point of view and observed how storage and flexibilities affect sizing.

“Often the profitability of the battery is considered separately alongside the dimensioned photovoltaic system, and it is not considered that the storage capacity directly affects the dimensioning of the photovoltaic system. Utilizing storage can in many cases significantly increase the size of a profitable photovoltaic system,” Koskela states.

Koskela's dissertation is very timely considering the ongoing energy transition, where fossil energy production is being sought out and the electricity grid must withstand the effects of the transition. One example is the transition from hourly to quarter-hour periods in electricity measurement, which Koskela found to have little effect on the profitability of solar electricity, but the profitability of storage increased because of the shorter measurement period.

Koskela lives in Kurikka and works at the Tampere University.

Public defence Friday 17 May

The doctoral dissertation of M.Sc. Juha Koskela in the field of electrical energy engineering titled Utilization of Electrical Energy Storage in Residential Buildings with Small-Scale Photovoltaic Production: Techno-economic research perspective will be publicly examined at the Faculty of Information Technology and Communication Sciences at Tampere University in room TB109 of the Tietotalo building (address: Korkeakoulunkatu 1, Tampere) at 12:00 on Friday 17 May 2024.

The Opponent will be Professor Jero Ahola from LUT University, Finland. The Custos will be Professor Pertti Järventausta from Tampere University.

The doctoral dissertation is available online.

The public defence can be followed via remote connection.