Passive houses have exceptionally low space heating demands (less than 10 Watts per m2).

When the energy demand is as low as this, it is possible to meet the majority of the space heating needs of the house using solar energy in combination with an interseasonal energy store.

A house constructed to the Passivhaus standard, situated in Co. Galway, Republic of Ireland, has seen the heating season for the dwelling drop from a predicted 8 months to two months.  This is achieved through a combination of a solar combi system and an integrated Inter Seasonal Energy Store (ISES).  The Passivhaus has a (low) demand for heating between October and May of 1842 kWh, and a year round demand for domestic hot water.  To meet these needs a 10.6m² evacuated tube collector was installed on the south-facing roof.  This feeds theDHW tank, underfloor heating and a 23m² sensible seasonal store buried in the garden. 

The house has been monitored for two years.  As a result of observations, changes have been made to improve operation and reduce losses.  The solar system provided a DHW solar fraction of 93% and a space heating solar fraction of 56% for 2010.  The seasonal store provided 556kWh of energy, despite losing 50% of 1111kWh of the peak stored energy through sensible heat losses.  The financial analysis show that the solar heating combined with ISES is the most economical solution for heating especially when the RHI incetive is considered.