- Scientists from Lappeenranta-Lahti University of Technology (LUT) in Finland have investigated the conversion of a Finnish oil-heated townhouse into a carbon-neutral building across four energy efficiency scenarios.
- They dimensioned an off-grid PV-powered heat pump system using waste heat recovery from a hydrogen storage system and calculated its life-cycle cost.
- They shared their findings in “Power balance control and dimensioning of a hybrid off-grid energy system for a Nordic climate townhouse,” which was recently published in Renewable Energy.
- They concluded that the solution is less profitable than grid-connected systems.
The team considered four scenarios for improving the energy efficiency of the building in Lahti, southern Finland, consisting of 18 apartments with a total heated area of about 1,100 square meters. A scenario with a 45 kW air-source heat pump and a 78 kW electric boiler (EEO); another with a 45 kW ground-source heat pump and a 33 kW electric boiler (EE1); another with a 79 kW ground-source heat pump (EE2); and finally a scenario with a 15 kW ground-source heat pump, 16 kW electric boiler, 15 kW heat recovery ventilation, and additional insulation of the roof, as well as renewal of windows and doors (EE3).
They simulated an off-grid PV-powered system with a fuel cell, battery, and hydrogen energy storage (HESS) for each scenario and studied the impact of waste heat on the dimensioning of the system’s components. The researchers created a calibrated energy simulation model of the current building with the IDA ICE 4.8 building performance simulation software. The PV generation was simulated in PVsyst, while the entire system modeling tool was created with Excel and MATLAB.
The fuel cell is supposed to act as a secondary energy source in winter when solar PV generation is reduced or inexistent. The waste heat generated in both the fuel cell and the HESS electrolyzer is intended to be recovered for space and domestic hot water heating. “The primary heat source in the tool is waste heat, followed by a heat pump and, if necessary, an electric boiler,” the academics said, noting that waste heat is prioritized because its temperature more closely matches the temperature requirements of domestic hot water.
“Waste heat recovery from the fuel cell and the electrolyzer reduces the need for heat generation by other heat sources, which affects the electricity consumption when the heating is based on a heat pump,” the scientists explained. “As a result, the load profile of electricity changes, and both the peak powers and the energy demand of electricity are reduced.”
The team calculated that the 30-year lifecycle cost of the off-grid systems would be between €2.3 million ($2.5 million) and €4.3 million and concluded that “the cost is very high and unprofitable compared with a grid-connected system.” They also noted that special safety considerations must be taken into account if a HESS is used in a residential setting.
Author: Beatriz Santos
This article was originally published in pv magazine and is republished with permission.
