Scientists from Finland have built an experimental system that allows the drying of woody biomass with solar thermal energy and a heat pump. They claim PV may play a complementary role in the proposed setup.
Researchers from the VTT Technical Research Centre of Finland have demonstrated a hybrid system for drying woody biomass that utilizes both solar thermal energy and a heat pump.
“We have indeed considered the possibility of powering the heat pump with PV,” corresponding author Tomi Thomasson told pv magazine. “However, relying solely on PV is not deemed feasible, given the limited solar hours in the Nordics. Grid electricity is essential to ensure an adequate number of annual operating hours and sufficient drying quantities.”
“We recognize that PV can play a complementary role in this setup,” Thomasson added. “With local PV production, we could avoid electricity transmission costs and potentially increase the feasible operating hours for the heat pump. Furthermore, local PV production could help reduce investment risks associated with the price volatility in the electricity market.”
The scientists built an experimental setup consisting of two freight containers. In the first, they installed a 24 kW heat pump, a condenser, an evaporator, a heat recovery unit, a heat exchanger, and 12 flat-plate solar heat collector modules. The second container consists of a drying chamber for fresh wood chips in size classes P16 and F15.
“The main role of the heat pump is to remove moisture from the drying air, but it can also provide additional heat at the beginning of the drying process since, to work efficiently, the drying air temperature must reach at least 20 ◦C before switching the heat pump into a drying mode,” they added.
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The researchers then used some collected data points to build a model that can assume drying rates and power consumption under different operating conditions. Those estimation methods, which used a gradient boosting model and a multiple linear regression model, received an average mean absolute error (MAE) of 0.27 (deviation of 5.9%) for the drying rate and an average MAE of 0.88 (deviation of 8.9%) for the power consumption.
Then, the researchers fed the results of this model, along with weather and market data, into an optimization model.
Experimental and techno-economic analysis of solar-assisted heat pump drying of biomass,” which was recently published in Energy Reports.
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