Optimal production and use of solar electricity in municipal nearly zero energy service buildings

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Insinööritieteiden korkeakoulu | Master's thesis
Innovative and Sustainable Energy Engineering
Degree programme
Master’s Programme in Energy and HVAC Technology
Like other EU countries, Finland must implement the EU Energy Performance of Buildings Directive (EPBD), requiring all new buildings to be nearly Zero Energy Buildings from the year 2021. Municipal buildings are required to be nearly Zero Energy Buildings from the year 2019. This thesis investigates municipal service buildings and the role of solar photovoltaics (PV) in improving their energy performance, in view of the future nZEB regulation. Three case study municipal service buildings from Tampere, Finland, are modelled and their energy performance is simulated. The service buildings include a day-care centre, a school and a renovated old people’s home. Simulation-based optimization is employed to find the optimal solar panel areas and inclinations for each case study building. The objectives to be minimized are net present value (NPV) of system life-cycle cost for 20 years and building primary energy consumption. A standard commercially available solar panel type is assumed. Electricity pricing is based on current rates. It is found that own solar PV generation can lower the service building energy performance considerably, if there is enough roof space for panel installation. With current electricity tariffs, PV generation is financially profitable in the old people’s home, where it can bring a maximum profit of 2,7–3,6 €/m2, depending on the main heating solution. The maximum profit occurs with 461 m2 of solar panels, with inclination angle of 48°, and combined with an air-to-water heat pump. With this arrangement, the primary energy use of the building is lowered by 13%. Generally solar PV production is a more profitable combination with a heat pump solution than with district heating. Solar PV generation does not create a net profit in the day-care or school building, because unlike the old people’s home, they are closed during the summer. The profitability of solar PV generation also depends on the basic heating solution, electricity tariffs, the future behaviour of real interest rate, energy price escalation and solar panel pricing. Sensitivity analysis and additional optimization cases reveal that even for the day-care and school buildings, financial profitability is not far away. If considering the measured electricity use from the whole property of the day-care centre, installing solar PV is profitable even at current electricity tariffs and installation prices, creating a maximum profit of 1,6–1,8 €/m2. Key recommendation for municipalities is to design new care housing buildings with enough south-facing roof area for a large solar PV system. Solar PV production should be first implemented in buildings that are occupied throughout the year, and can utilize as much as possible of the own generation. When considering the profitability of the solar PV installation, it is necessary to know the actual electricity consumption arising from the whole property, and not just the building. For educational buildings, solar PV is the best candidate for the buildings that are open also in the summer, e.g. those day-care centres that do not close for the summer holiday. Even if the future nZEB targets do not necessitate own solar PV generation in municipal service buildings, both the financial profitability and the energy efficiency improvements should encourage municipal solar PV installations, especially in nursing homes.
Sirén, Kai
Thesis advisor
Jokisalo, Juha
nearly Zero Energy Building (nZEB), photovoltaics, service buildings, multi-objective optimization, building simulations, life-cycle cost
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