Costs and benefits of using parabolic greenhouse solar dryers for dried herb products in Thailand

Parabolic greenhouse solar dryers have been developed to overcome product quality and postharvest loss problems. It uses solar energy, a renewable source of energy. Due to their high investment costs, economic feasibility and the potential of carbon dioxide (CO₂) mitigation were investigated. Owners and managers of 17 enterprises, producing several varieties of herb products, investing in different sizes of solar dryers and using various traditional drying methods before investing in solar dryers, were interviewed in depth to create a data set. The net present value (NPV), internal rate of return (IRR), payback period and CO₂ mitigation were evaluated. The enterprises with annual production capacities higher than 1,200 kg or the annual revenues higher than solar dryer investment costs tended to have positive NPV indicating that the investments were attractive. Most enterprises showing CO₂ mitigation higher than 130 tCO₂e over 15 years had positive NPV. The annual production capacity, annual revenue and the amount of CO₂ mitigation could be used to assess investing in greenhouse solar dryers.