In 2004 the Government of the Principality of Liechtenstein published its wide-ranging and ambitious Energy Strategy 2013. Its contents included the stated aim of reducing greenhouse-gas emissions by more than 8 % over the 1990 level by 2013. This is to be achieved by selective and subsidized thermal refurbishment of existing buildings or increasing to more than 10% the share in overall energy consumption of renewable energy sources such as hydropower, solar energy and geothermal energy.
The "Renewable Energy" series of stamps is devoted specifically to these energy sources, which are characterized by being self-renewing and thus sustainably available resources. The first part of this series highlights "Hydropower" (face value CHF 1.00), "Wood" (face value CHF 1.40) and "Near-Surface Geothermal Energy" (face value CHF 2.80) as such renewable energy sources.
A distinctive feature of the stamp series is the use of heat-sensitive ink. Imprinted on each stamp is a pictogram representing the particular recoverable energy. This symbol is hidden by black thermal ink which becomes transparent only when a finger is pressed on it, revealing the coloured pictogram. This philatelic novelty thus symbolises the flow of energy.