March performance

Actual vs. Projected for 2012

March madness, the weather that is. March was freakishly warm and much sunnier than February (33% less heating degree days, 31% more sun). This partially resulted in 23% lower energy usage in March. Our daily average usage was down 28% from February. We generated a 345 kWh surplus in March, the first since we moved in Jan 1st.

All values in kWh (except HDD) Jan 20121 Feb 20122 Mar 20126 Apr 2012
Solar PV generation 369 597 860
Usage 873 666 515
Net usage or (generation) 504 69 (345)
Average daily usage 28 23 17
HDD (base temp 68F)3 1,2124 1,0455 7045

1 January values based on meter reads.
2 February values based on TED data.
3 Heating Degree Days (a measure of how many outside degrees in a day it is below a target inside temperature)
4 Downloaded from, Station ID: KALB (Albany International Airport).
5 Calculated from my HOBO outdoor weather monitor hourly data.
6 March values based on meter reads. (TED died March 1st, eMonitor installed March 16)

The chart at the top of the page illustrates our actual performance for the first three months of the year, and our projected performance for the rest of the year based on estimated output of our array and historical heating degree days for the last 10 years. The usage numbers are a complete guestimate, but based on these numbers we could be net positive at the end of the year by 242 kWh. In any case, it will be interesting to track actual values against the projected values.

We’re also happy to report the TED folks accepted our return last month without incident and we’re enjoying our new eMonitor circuit level monitoring. Although we don’t have a full month of data for March, we are able to share the 15 days of data we did collect. It is available at You can now view solar, usage, net usage, temperatures and HDD for all of February and circuit-level data for 15 days in March. We’ve included a few snapshots below.

Heatmap composite including all options

The composite image shows all the high-level data heat maps. You can see very easily that the third week was warmest and sunniest days of the month that we collected data.

Air source heat pump mapping and day chart

The above snapshot shows March 16, the first day we started collecting circuit-level data. It wasn’t a particularly cold day, temps were in the mis 40’s, but there was very little sun as evidenced by the relatively flat solar curve. This required the heat pump to kick in enough to make it the most active out of the recorded days. This is a bit misleading because if you compare March to February, power use that day was quite low. Now that we have multi-month data, we’ll have to find a better way to compare across months.

If you have any questions or spot any math errors drop us a note in the comments.

1 Response to “March performance”

  1. 1 Steve Toomey 3-April-2012 at 10:00 pm

    This is really nice work, both in terms of the house’s energy performance and the array of data visualizations. Thanks for taking the time to prepare and share your real-world numbers – they are encouraging for those of us designing houses with similar performance goals in mind.

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