Experimental studies on the contribution of solar energy as a source for heating biogas digestion units

The main drawback of heating biogas digestion systems based on solar energy is its unavailability overnight and at different times (days and months). To circumvent this problem, a hybrid system(solar and electricity) powering the heat digester could provide the required mesophilic conditions. The present study aimed to evaluate the technical and design feasibility of using solar energy to assist in heating the digestion units. Also, measured and determined the contribution of solar energy to heat the system. This study was conducted in the central area of Coastal Delta, Egypt (30.5 ∘ N, 30.6 ∘ E; 8.5 m a.s.l.). Results show that the contribution of solar energy to biogas production was 75.21%, 60%, and 53.58% when using three settings temperature of (37, 40, and 45 °C) of the energy consumed via cattle dung solution heating. Furthermore, increasing the set temperature inside the horizontal and vertical digesters from 37 °C to 45 °C augmented their daily average volumetric biogas production by 87.12% and 59.45%, respectively. Finally, the current study says that solar energy has reduced energy consumption by 61.28%. Also, the economic analysis indicates that the estimated return profit was $ 177.41 (USD), which represents 45.15% of the total income per operation.