sunshine hours

A Net Zero Energy Year : February and March 2011

 

MillCreekNetZero

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:

 edmonton_sunshine_hours
(source)

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:

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

A couple of daily snapshots:

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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.

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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.