Use PV to offset non-renewable energy use

Some of the housing renovation projects studied included a PV roof. Decisive is the price at which the local utility is required to buy back the solar electricity. For example in Switzerland as of Jan. 1, 2009 electricity providers must buy back solar power for 25 years for all approved pv installations built since Jan. 1, 2006. For systems <10 kW the buy-back rate for attached PV systems is €0.46 and for systems integrated into the roof or facade €0.56. [9].

An exemplary project where PV was part of a comprehensive renovation is the apartment building in Staufen. The 110 m2 PV installation on the south-facing roof (fig. 1) has a nominal output of 14.7 kWp. In 2006 it fed 14’300 kWh into the grid. The motivation of the owner, Guido Erni, was to provide retirement income. Also part of the renovation were insulation of the attic floor (140 mm), facade (200 mm) and basement ceiling (100 mm); a new ventilation system with 85% heat recovery and replacement of the oil furnace by a heat pump. The results: primary energy use for space and water heating was reduced 65% from 154 to 54 kWh/m2 [10].