Using building thermal mass energy storage to offset temporary BIPV output reductions due to passing clouds in an office building

Ongoing concerns about electrical grid stability and existing economic interests create unattractive conditions for grid-injection of renewable energy produced in building integrated photovoltaic systems (BIPV). As a result, BIPV often fails to use the full potential of the building envelope and site. An effective approach to increase BIPV size is maximizing self-consumption of the generated renewable energy through building demand flexibility and energy storage. Unfortunately, in cooling dominated office buildings with BIPV, shading by passing clouds can increase grid demand as the building maintains its energy demand in a moment when BIPV output is reduced. This paper analyses the effectiveness of turning off the heating ventilation and air conditioning system (HVAC) to offset temporary reductions in BIPV output due to passing clouds. Analysis of cloud duration in different climates shows that, on average, clouds last 20 min and occur predominately in the afternoon. When HVAC is off due to cloud shading, the building thermal mass limits indoor temperature increase to 2 degrees C in the first 50 min. Simulation based analysis of HVAC control-based energy flexibility shows that it is possible to maintain acceptable thermal comfort while reducing HVAC grid energy demand by 60% during the cooling season.