Archive for January, 2014

Fourth quarter 2013 performance

Q4 2013 summary: 10% cooler, 22% more usage and 10% more sun as compared to Q4 2012.

Now that we are starting to collect our second year of performance data, I’ll be comparing our new data to the same period last year. Year-over-year comparisons should be more illustrative than comparing to previous months. I’m also switching to a quarterly reporting period to look for larger trends, but I will continue to post data monthly at

In Q4 last year our total usage was 1,599 kWh. This year is was 1,957 kWh, a 22% increase. Despite snow covering the collectors for a few days and cloudy weather, we still produced 10% more energy in Q4.

Overall, here’s how this quarter and the year compare to 2012.

Chart comparing Q4 2012-2013 energy and temperature values

2013 Usage Solar PV Net usage
or (surplus)
daily usage
Total 1,957 1,576 380 21.2 2,372
482 674 (192) 15.6 405
559 639 (81) 18.6 838
916 263 653 29.5 1,129
2012 Usage Solar PV Net usage
or (surplus)
daily usage
Total 1,599 1,428 170 17.4 2,166
433 511 (79) 14.0 357
498 615 (117) 16.6 830
668 302 366 21.6 979
All values in kWh (except HDD which is base 65°F).

We used 22% more energy (358 kWh) this quarter as compared to 2012. That’s about 3.8 kWh extra per day, or 158 watt hours per day more than last year. The last two quarters we’re been running 4 to 5 kWh higher per day. Last quarter I predicted this quarter usage would also likely be up 4-5 kWh/day from Q4 2012. It looks like we stuck to the lower bound, same as last quarter.

One noticeable difference this quarter was our heat usage. Q4 2012 our air-source heat pump used 205 kWh. This quarter we used 438 kWh, a 114% increase. It was about 10% cooler than Q4 2012, but we also had 10% more sun.  It’s not really clear to me at the moment what is causing the increased usage. I’ll have to do a bit more detective work. Overall for the year we would have paid $180 to heat and cool our house, if we paid for electricity.

Chart of ASHP usage values 2012-2013

Cumulative plot of ASHP usage values for Q4 2012 and Q4 2013

Water-wise our usage is down 5%, and our hot water usage is down 13% from Q4 2012.

Year over year comparison

Looking back over 2012 and 2013, most circuits we track stay about the same over time, excluding heat. The one set of circuits that have changed a lot over the last two years are in the category of ‘all other circuits’, meaning the circuits we do not measure individually. This category counted for 43% of our overall usage in 2013. This includes plug loads, lighting and ventilation. (Ventilation is only used from late fall through mid spring.) Plug loads include the home office, the TV, stereo, refrigerator, freezer, coffee maker, incubators and heat lamps for chickens in the spring, the Prius plugin, barn lights, electric fence, water bucket warmers, etc.

Chart comparison of 'all other circuits' 2012-2013

You can see that this category has steadily grown from 100 kWh/month to peaking in April at 330 kWh/month. I’m hoping we’ve leveled off, averaging around 250 kWh/mo. We will still have a peak in the hatching season, until the chickens take over this work for us.

Happy 2014!

You can see heat maps and detailed charts of temperature and electrical usage at View hourly, daily and monthly values for solar, usage, net usage, temperatures and HDD.

We’re net positive for 2013!

Pie chart of energy usage by circuit 2013 Stacked bar chart of energy usage by month 2013 chart of monthly temperature ranges 2013chart of temperature buckets with ASHP usage overlay 2013chart of water usage 2013

chart of grid vs solar supply mix for 2013

Solar we were able to use directly vs. solar that was sent back to the grid

Year Summary

We’re net positive for 2013! We used 7,206 kWh and generated 8,575 kWh for a net surplus of 1,368 kWh. We used an average of 19.7 kWh per day. We used 29% more energy and generated 3% less than last year. 2013 was 16% cooler than 2012. The coldest day of 2013 was Jan 3 at -7 degrees F, and the coldest day overall was Jan 24 at 60.8 HHD.

We’re 21% over our projected energy use of 5,950 kWh for the year. We used about 85% of the estimated 2,440 kWh for hot water energy. We used 26% of our heat energy estimate for the year.

Our BTU/SF/HDD is 0.425. BTU/SF/HDD is a common measure to compare the efficiency of houses of different sizes and climates. We recorded 6,810 HDD (base 65F) for 2013. The ASHP used 1195.782 kWh for heating in that period. Converting kWh to BTUs, 1195.782 kWh * 3,412.14163 (kWh to BTU conversion factor) then divide by 1408 SF and divide again by 6,810 HDD = 0.425.

We used an average of 66 gallons of water per day. 33% of our total water usage was hot water.  It takes about 264 watts to heat each gallon of hot water and 2.644 watts to pump it from the well.

That’s it for 2013. Happy 2014 everyone!

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