Friday, July 12, 2013

Energy Consumption at Mid-Year

We've made it through half of our first calendar year in the house and have some additional energy usage information to share.  First off, on May 6th, we became net producers of electricity for the calendar year.  From January 1st to June 30th, we produced 6580 kWh of electricity and consumed 5220 kWh, a net surplus of 1360 kWh, which at $0.14/kWh is worth $190.  Our HERS rater estimated that we'd produce about $400 surplus of electricity for the year.  We seem to be on track to realizing that.  The chart below illustrates our experience.

In the beginning of the year we consumed more electricity than we produced.  There were two drivers of this.  One, fewer daytime hours means less electricity produced by the PV panels on the roof.  And two, colder outdoor temperatures means that we need to consume more electricity running the heat pumps.  You can see in the chart above that this trend was reversed in March as evidenced by the orange "Net" line in the chart above starting to slope upwards.

In April, May and June we produced significantly more electricity than we consumed.  We see the same two drivers at work again.  One, more daylight hours means more electricity produced by the PV panels on the roof and two, warmer outdoor temperatures means we consume less electricity because we need to run the heat pumps less frequently.

It'll be interesting to see how often we need to run the heat pumps for cooling in July and August.  We have seen the house heat up pretty quickly to 83 or 84 degrees when it's 95 outside.  Fortunately, there have only been a couple of days like that and as a result, we've hardly used the heat pumps for cooling.  They seem to use 10 to 15 kWh per day or $1.40 to $2.10 at $0.14/kWh.  We've had them on the last couple of days more for dehumidifying than cooling.  It's been so wet and humid around here lately that turning on the heat pumps has been a better option than opening the windows at night for cooling the house.

It'll also be interesting to see how our PV panels perform the rest of the year.  So far they are performing very close to the estimates we received from the company we bought them from, Aegis Solar.  You can see from the chart below that we produced more electricity in April than in June.  This probably has something to do with the 34 degree angle to the horizon of the panels on our roof being better suited to the sun being somewhat lower in the sky.

Stay tuned to see what our stats will be in July and August, the hottest months of the year.

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