Performance Optimisation of a Hybrid Biomass-Solar Parabolic Trough Collector System for Industrial Tea Drying

Abstract

The rising global energy demand and environmental challenges calls for the adoption of sustainable and cost-effective renewable energy (RE) solutions. Despite the predominant focus on RE for electricity production, heat actually accounts for the largest share of global energy consumption at 50%, compared to 20% for electricity and 30% for transport, with industries consuming 51% of global heat and contributing 40% of Greenhouse Gas (GHG) emissions. In Kenya’s tea industry, a substantial 85% of total energy consumption is attributed to heat, primarily sourced from biomass boilers and occasionally supplemented by fuel oil. This reliance on wood fuel for process heat poses significant challenges, including increased production costs, GHG emissions, and deforestation, exacerbating climate change. However, global projections indicate continued reliance on fossil fuels and biomass, reinforcing the economic and environmental case for biomass–renewable hybridisation over standalone systems. The main objective of this study was to investigate how hybridisation of biomass with solar thermal energy from Parabolic Trough Collector (PTC) for tea drying can improve cost-efficiency, reduce firewood consumption, and enhance environmental sustainability. The methodology involved solar resource assessment and analysis of thermal demand and financial data from Toror tea factory. The study used the System Advisor Model (SAM) software to simulate the performance of different hybrid configurations. The model’s accuracy was confirmed through experimental validation against on-site measurements, employing a solar PTC prototype manufactured for this purpose. Results show that the most suitable hybrid configuration achieves optimal performance at Solar Multiple 1.8 and Thermal Energy Storage of 24 hours, producing 15,852 MWhₜₕ/year (above the plant’s demand of 14,286 MWhₜₕ), with a 92.5% solar fraction and 50.5% PTC efficiency. The system achieves Levelised Cost of Heat (LCOH) of 1.88 US cents/kWhth, which is a 30.9% cost reduction compared to biomass boilers, a Net Present Value (NPV) of USD 2.16 million, and 6 years payback period. Environmental benefits include reducing firewood use by 16,462 m3/year, cutting CO2-equivalent emissions by 9,817 tons/year, and conserving 23.49 acres of land that would have been used to grow trees for biomass fuel, enabling alternative uses such as expansion of tea production or other purposes. These findings demonstrate that optimised hybrid biomass-solar PTC systems can deliver reliable, low-cost, and sustainable heat, strengthening the tea industry’s competitiveness while also contributing to Kenya’s renewable energy and environmental goals.