For all you energy nerds out there, we now have two+ years of energy performance data from our real time energy monitors at Painters Hall (, so here’s a little treat. Below is a graph that shows two comparative years of both consumption and production. From May 2010 to April 2011 (pink line) total building consumption was 15,291kWh. From May 2011 to April 2012 (the darker red line) total consumption was 19,838kWh. The big increase was the result of much more activity in the building (more events, Cafe use, etc.). The solar PV pretty much stayed the same; 2010-11 was 21,548kWh and 2011-12 was  22,234kWh.

However what looks like a pretty innocent increase in energy consumption has a pretty big impact on our 12-month net energy performance. Based on PGE net metering reports going back to October 2009 when the 20.2 kW system was installed, after our first 12 months of occupancy, we over-generated 11,000 kWh worth of energy, about double what the building consumed during the same period. All excess power was used (traded with PGE) and counted against the pumping of our ground-source geothermal loop, through a program called Aggregate Metering. As Painters Hall activity increased, so did energy consumption, reducing our excess net (as you can see below) taking it all the way down to where we are now, at about 3,000 kWh of excess net for the year. For example, we added the espresso machine in June 2010, but because this is a 12-month equation, the impact isn’t immediately noticeable unless we compare Sept of 2010 with Sept of 2011 (11,000kWh and 4,000kWh)* note: the espresso machine, we have learned through energy monitoring, consumes about 5,293kWh per year!! whoa! We’ve since ordered a smaller replacement).

This graph shows how delicate the Net-Zero Energy balance really is. It is hard to size a PV system for NZE when there are so many variables and uses (office, Cafe, classroom, event venue, etc). For buildings that want to achieve NZE, a swing of of 8,000kWh is huge, in our case about 40% of total PV output for the year. The data also shows how much can change as occupancy and the building mature and develop over time.