In recent years we have witnessed a growing interest in 'green energy'. Numerous applications are offered that enable energy to be obtained from freely available sources, among which photovoltaic panel installations are the most popular. Their prices have dropped to levels that permit installation even in small summer houses. When building such systems, it is important to understand the specific nature of the energy source – the photovoltaic panel or turbine – as well as to consider the challenges faced by the manufacturers of devices powered from such sources.