net zero energy house

A Net Zero Energy Year : April 2011


Energy use, MCNZH, April 2011. Negative numbers represent export of electricity.

Our Net Zero Energy Year finally turned around in April. We stopped heating the house pretty much as of March 31, and it’s been generally sunny ever since.

Here are the numbers for Oct 18, 2010 – April 30, 2011 (all units in kWh of electricity):

Consumption: 7643

Production: 2785

Net Consumption: –4858

We’re in the hole overall, but April was a net positive month. We exported 550 kWh to the grid!

A Net Zero Energy Year : February and March 2011



The above picture would actually be one of grey skies and snow if it represented March and February of 2011, but I’m not one to dwell on bad weather.

Barring a solar miracle, the Mill Creek Net Zero Home (MCNZH) will not be net zero in its energy consumption for the period of Oct 18, 2010 – Oct 17, 2011. The fact is, it was a tough winter for a passive solar house, with cold temperatures in February, and a very overcast March.  In 2010, for example, we virtually stopped heating the house by the second week of February. This year, it was April before the heaters stopped kicking in.

The results so far bring us back to some of the questions I asked when we started this little experiment. Although I have no sunshine data for this year, I’m sure that it was below average for insolation (how sunny it was). Here are some numbers on how sunny Edmonton has historically been:


The three-week period in March 2011 without a ray of sun makes me sure that we came well under these numbers this winter.

Here are the numbers for Oct 18, 2010 – March 31, 2011 (all units in kWh of electricity):

Consumption: 7333
Production: 1925

So we’re –5408 on a net basis for the year. Even though we’re just entering our prime solar production months, I don’t think we’ll cover the bet.

Here is a snapshot of the net power consumption for the months of February and March, 2011. Negative numbers represent exporting of power to the grid:



Our net energy use was higher in March than in February due to the aforementioned overcast weather.

A couple of daily snapshots:


March 28, 2011 was a terrible day for solar houses in Edmonton. The sun hadn’t shone for days, so the thermal mass in the house had lost its solar charge. The weather wasn’t that cold (low of –5, high of 0), but the heaters ran all day to keep the house heated.


On the other hand, February 25, 2011 was the kind of day that our house was built for: brutally cold (a low of –26, high of –9) but sunny. Notice how the energy use is much lower after 6pm than it was in the middle of the night. That is the residual effect of the day’s sun keeping the heating load down.

These days our PV arrays are really cranking out the juice. It will be interesting to see how close we can come to overcoming our deficit. 

A Net Zero Energy Year : Jan 15, 2011 - Jan 31, 2011

During the last half of January, the MCNZH consumed a whopping 957 kWh and produced a measly 121 kWh.

Here’s were we are so far on the year (starting October 18, 2010):



Electricity Consumption, MCNZH, Oct 18 2010 - Jan 31 2010

We've consumed 4943 out of an estimated 8000 kWh.



Electricity Production, MCNZH, Oct 18 2010 - Jan 31 2010

We've produced 845 out of an estimated 8000 kWh.

And here is how much of the year we have left:


Blue is how much of year has passed (Oct 18, 2010 – Jan 31, 2011).

105 days have passed. The warmest and sunniest days are ahead!

A Net Zero Energy Year : Dec 15, 2010 -Jan 15, 2011


During the past 31 days the house consumed 1810 kWh and produced only 152 kWh. OUCH!

Our total consumption to date (since October 18) is 3986 kWh, with total production at 724 kWh. Since our total annual consumption budget is 8000 kWh, we’ve burned through 50% of our electricity budget.

Sounds pretty bad right? The game isn’t over just yet. We’ve just come through three of the four darkest months of the year. By February 15, we will be getting as many sunshine hours as we do on October 27. Plus, last year we virtually stopped heating the house as of the second week of February (due to a sunny, mild month).

So we are still in the ballpark, but we will definitely need some luck for this to be a net zero energy year.

Some numbers and observations:  read more... »