Pie chart showing circuit usage YTD
Pie chart showing circuit usage YTD
Bar chart showing circuit usage per month
Bar chart showing circuit usage per month

Year Summary

We’re net positive for 2012! We used 5,601 kWh and generated 8,856 kWh for a net surplus of 3,256 kWh. We used an average of 15.3 kWh per day.

We’re within 6% of our projected energy use of 5,950 kWh for the year. It also looks like we used about 80% of the estimated 2,440 kWh for hot water energy. It’s too early to tell how we’re doing against our heat energy estimate since we missed recording the primary heating season. We should know better by mid-March.

But we can calculate the current BTU/SF/HDD, which is a common measure to compare the efficiency of houses of different sizes and climates. First we need to know the total heating degree days (HDD) and heat energy usage for the period we have data. We recorded 5,885 HDD (base 65F) for 2012. 3,434.800 HDD were recorded when we had circuit level data for the ASHP, which used 277.331 kWh for heating in that period.

Now we convert kWh to BTUs,  277.331 kWh * 3412.14163 (kWh to BTU conversion factor) then divide by 1408 SF and divide again by 3,434.800 HDD (March 16-Dec 31, 2012) = 0.196. This is not a completely accurate number as it does not include Jan 1 through March 15, but soon we will have a full year of circuit level data and a more representative number.

We used an average of 56 gallons of water per day. 34% of our total water usage was hot water.  For the time period we have circuit level data that works out to 258 watts per gallon of hot water. I’ve found some estimates on the web that say we should be using about half that wattage to heat our water, so we’re going to do a bit more investigation.

December Summary

In December, we used 668 kWh and generated 302 kWh for a net deficit of 366 kWh. We had nine consecutive surplus months. This is the first month since February that we used more than we generated.

We used 152 kWh for heat, a 227% increase over November. Dividing 152 kWh by 979 HDD we get 155 watts per HDD. That’s a 182% increase from November. Not only are we using the heat more, but the heat pump has to work harder because it’s colder outside. Heating accounts for 22% of the month’s total usage. Hot water accounted for 32% of the energy for the month. We used 65.9 gallons of water per day, up 7% from the previous month.

The largest energy increase in the last few months has been in the All Other category, followed by the water heater, ASHP and the stove. Most of this makes sense. We’re spending a lot more time indoors. The holidays bring visitors, more showers, more laundry and lots and lots of cooking!

We generated 302 kWh, roughly half of November’s production. It was down 24% from the estimated December value of 399 kWh. A very cloudy and snowy month. In fact we only generated 116 watts the last 5 days of the year due to snow blanketing the collectors.

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 target inside temperature)
  4. Calculated from our HOBO outdoor weather monitor hourly data, unless otherwise noted.
  5. January HDD data downloaded from degreedays.net, Station ID: KALB (Albany International Airport).
  6. March values based on meter reads. (TED died March 1st, eMonitor installed March 16, 2012)
  7. Values based on eMonitor data.
Usage Solar PV Net usage or (surplus) Avg. daily usage HDD 3,4
Total 5,601 8,856 (3,256) 15.3 5,885
Jan 1 873 369 504 28.2 1,125 5
Feb 2 666 597 69 23.0 957
Mar 6 515 860 (345) 16.6 619
Apr 7 925 378 (538) 12.9 535
May 309 867 (558) 10.0 170
Jun 325 939 (614) 10.8 97
Jul 319 970 (651) 10.3 17
Aug 315 1,018 (703) 10.2 31
Sep 292 883 (591) 9.7 168
Oct 433 511 (78) 14.0 357
Nov 498 615 (117) 16.5 830
Dec 668 302 366 21.6 979

Next month we’ll start including information gathered from our two additional temperature/humidity sensors. We will now be able to see how temperatures differ from floor to floor.

You can see heat maps and detailed charts of temperature and electrical usage at netplusdesign.com. 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 December.

Happy 2013 everyone!