German company Consolar offers a heating system called SOLAERA, which combines a heat pump with a specially designed solar collector and a heat storage space using the latent heat released when water freezes to ice (see photo). The solar heat pump system with 18 m² of collector area, a 300 litre ice storage space and a 1,000 litre buffer tank provides enough energy to heat a well-insulated building in Germany. In a field test by a local environment group, Lokale Agenda 21, it achieved a Seasonal Performance Factor (SPF) of 5.6, putting performance even above prior simulations. The SPF describes the ratio of delivered heat to electricity consumed over the entire year. Consolar sold about 160 solar heat pump systems in total, mostly in Germany but also in Denmark, the UK, Switzerland, Belgium, France and Italy. The systems there achieved SPFs between 3.5 and 6, depending on collector field size, maximum flow temperature and heat demand.