The aim of this thesis is to increase the understanding of small-scale green energy technology development. In the transition towards a fossil free energy system, heat pumps are a low emission heating alternative. Contrary to other types of new small-scale green energy technology such as solar cells and electric vehicles, heat pumps are established on the Swedish market, with more than half the share of single family buildings. This makes it possible to study an example of a mature technology, and that knowledge could be used in the development and deployment of other technologies with similar small-scale green characteristics. The type of heat pump technology studied is ground source heat pumps, and their development is explored from an economic and performance perspective, using the concept of learning. Learning tracks how a product develops for each doubling of units produced. The results show that the efficiency has increased by a learning rate of 2.8 %. When the effects of a low-temperature heating system is included, the learning rate is even higher, 5.8 %. The efficiency improvement is mainly due to new and more expensive components, which has resulted in a price increase. Even if the price slightly decreased until 2008, it has increased with 29 % since. Nevertheless, the ground source heat pump is profitable compared to several other heating technologies. The most important factors underpinning the development are regulations, competition among manufacturers and research.