Archive for December, 2012

Home Performance App Upgrade

I’ve updated our home performance app at,

Screenshot from new app.

Screenshot from new app.

At the beginning of the year I put together a simple online tool that displays our energy and temperature data on a daily and hourly basis. It gave me an easier way to track and visualize our energy usage on a month to month basis without a bunch of spreadsheet work. The heat maps provide an easy way to quickly find days of high energy use and see what else was going on that day. This helps me understand why usage might be high on a particular day.

Now that we’re coming up on twelve month’s data, I wanted an easier way to see across months and drill down from the macro to the micro scale. So I built some new views that would allow me to slice by time period (year, month) and dice by aspect (energy used, generated, heating degree days or a summary across all of them).

It’s a bit slow, I’m just a hobby developer, but give it a chance and let me know what you think. I’ve released all the code on Github under the MIT “Do what ever you want with my code, just don’t expect it to be bug free” License.

In a few days I’ll upload December’s data. Happy Holidays.

November performance

Chart showing monthly usage, generation, net and hdd

We used 498 kWh and generated 615 kWh for a net surplus of 117 kWh in November. This is our ninth consecutive surplus month. We’ve generated a surplus of 3,622 kWh so far this year, guaranteeing we’ll be net positive for our first year of operation.

The month proved to be sunnier than average. We generated about 63% more than predicted, despite the fact that it was about 12% cooler than average for the month. Usage was up 19% over the previous month. Lot’s of guests, cooking and laundry for the Thanksgiving weekend period.

We used 46 kWH for heat. That’s about 55 watts per HDD. That accounts for 9% of the month’s total usage. Compare that to hot water which used 38% of the energy for the month. We used 61.7 gallons of water per day, down about 9% from the previous month.

I’ve been updating some of the data reporting measures. This month I’ve moved to reporting all heating degree days at a base temperature of 65 degrees rather than 68. This should make it easier to compare performance to other homes that use 65 as a base temperature.

Month Solar PV Usage Net usage or (surplus) Avg. daily usage HDD3,4
Jan1 369 873 504 28.2 1,1255
Feb2 597 666 69 23.0 957
Mar6 860 515 (345) 16.6 619
Apr7 925 378 (538) 12.9 535
May 867 309 (558) 10.0 170
Jun 939 325 (614) 10.8 97
Jul 970 319 (651) 10.3 17
Aug 1,018 315 (703) 10.2 31
Sep 883 292 (591) 9.7 168
Oct 511 433 (78) 14.0 357
Nov 615 498 (117) 16.5 830
All values in kWh (except HDD).
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 base target inside temperature, 65F.
4 Calculated from our HOBO outdoor weather monitor hourly data, unless otherwise noted.
5 January HDD data downloaded from, Station ID: KALB (Albany International Airport).
6 March values based on meter reads. (TED died March 1st, eMonitor installed March 16, 2012)
7 Values starting in April are based on eMonitor data.

You can see heat maps and detailed charts of temperature and electrical usage at View solar, usage, net usage, temperatures and HDD for all of February and circuit-level data for 16 days in March and the full months of April through November.

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