Energy sources are scarce in the chilly, high mountains of the developing world, Solar-assisted biogas digesters have recently been adapted to this climate providing an alternative cooking fuel for some rural families, but little is known about the thermal performance of these digesters. Internal slurry temperature is one of the important design factors in bio-digesters. This study conducted a series of field experiments on an experimental bio-digester in Cusco, Peru to investigate the thermal performance of these affordable bio-digesters. The study further improved and validated a one-dimensional thermal computer simulation model using the experimental results. A set of design recommendations for small-scale, cold-climate digesters is presented based on parametric analysis of the validated model for several key design parameters. (c) 2015 Elsevier Ltd. All rights reserved.