Archive for January, 2018

We’re net positive again in 2017!

We used 7,198 kWh and generated 7,966 kWh for a net of 769 kWh for the year.

2016 was our second highest net energy surplus year after 2012 and our highest solar generation year.

2017 was our second lowest net energy surplus year after 2014 and our lowest solar generation year over the last 6 years. We had a lot of cloudy days and snow covered panels.

Q4 2017 summary: 2% colder, 7% more usage and 5% more sun as compared to Q4 2016.

In Q4 our total usage was 2,022 kWh, a 7% increase from our 1,890 kWh in 2016. We also generated 65 kWh more solar.

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

Charts comparing Q4 and YOY usage, solar and HDD

2016 Usage Solar PV Net usage
or (surplus)
daily usage
Total 1,890 1,402 488 20.5 2,243
Oct 412 607 (195) 13.3 420
Nov 567 451 115 18.9 722
Dec 911 343 568 29.4 1,102
2017 Usage Solar PV Net usage
or (surplus)
daily usage
Total 2,022 1,466 556 21.9 2,295
Oct 375 724 (349) 12.1 262
Nov 585 505 80 19.5 780
Dec 1,062 237 825 34.2 1,253
All values in kWh (except HDD which is base 65°F).

Year-over-year comparison

Here’s our progress for the first 5 years in the house.

Usage Solar PV Net usage
or (surplus)
daily usage
Total 42,091 51,348 (9,258) 19.2 39,363
2012 5,601 8,856 (3,256) 15.3 5,885
2013 7,206 8,575 (1,368) 19.7 6,810
2014 8,108 8,348 (240) 22.2 7,063
2015 7,141 8,694 (1,552) 19.6 6,772
2016 6,837 8,910 (2,073) 18.7 6,380
2017 7,198 7,966 (769) 19.7 6,452
All values in kWh (except HDD which is base 65°F).

Year over year usage comparison


Pie chart - circuit breakdown

2017 was our third warmest year in the house, although we continue to see wide extremes in temperature ranges (see temperature ranges below). The ASHP used 27% of the total as opposed to 25% last year. Vampire loads decreased slightly this year. We again appear to have cooked less in 2017 as the induction cooktop & stove vampire loads increased in comparison to use. The combined vampire load for the stove, ASHP and solar inverter was 137 kWh in 2017, about 8 kWh less than last year.

Net-zero moment

Our ‘net zero moment’ this year occurred on July 18 at 7am. This was our third earliest time since 2012. Our solar curve remains fairly constant. Our usage changes the most from year to year, manly due to weather. We had 23 days in 2017 where the solar panels generated less than 1 kW, mainly because they were covered in snow. We had only 13 days such days in 2016.

Chart showing net-zero moment

Where did all that solar go?

Charts showing mix of solar and grid supplied elect. Charts showing mix of solar and grid supplied elect.

I still find it amazing that although we generate more energy than we consume each year, we directly consume only 1/3 of it, the rest is fed back to the grid. That means over 2/3 of the energy we use is still supplied by the grid. We would need battery storage to make use of a greater percentage, thereby lowering our demand on the grid.

In 2017, 29% of our power needs were supplied by our own solar generation directly. The other 71% was supplied from the grid. Of the 7,966 kWh we generated in 2017, we only used used 26% directly. The other 74% we sold back to the grid (at a greatly reduced price) so other people use it (if there was demand for it).

This make 6 full years not having to pay for electricity. We still pay the monthly connection fee, minus any rebate from the utility for excess electricity generated. This year we earned $45.35 or 0.0355 cents per kWh. That’s $28.27 less than 2016.

National Grid does not tell us how much electricity would cost if we bought it from them. They only do that if you actually use more electricity than you generate. So I have to go to the NYSEDA website to find the state averages. Using their data, we would have paid about $7,781 over the past 6 years for the 42,090 kWh we’ve used if we didn’t have solar. Our solar cost $14,320 to purchase in 2011. In very simple terms that puts us at about 54% payback. At our current rate of use and the trending price of power, it will take us another 5-6 years to break even in simple terms.

Air-source Heat Pump performance

Chart of ASHP usage values Oct-Arpril, 2012-2017

This was the third warmest fourth quarter since we moved into the house. We started off on a steep curve in 2017 but decreased our slope in January and February. We ended up using about the same heating energy as 2013-2014. We’re currently charting above the 2017 level as seen above. Overall, heating season 2016-2017 worked out to be our second highest energy use in the last 6 years. We used just over 1,946 kWh for heat in 2017. At the average electricity price this year, $0.18/kWh, that would be about $350. That is 6,452 HDD for $350. That is about $0.05/HDD.

My thermostat strategy this year is to just leave it at 68 degrees F. As the charts show below, leaving it at 68 every day incurred more vampire losses, but overall the energy use is not greater. Cleaning the filters every month also has a noticeable impact.

Chart showing kWh used by ASHP in 10 degree buckets

Chart of temperature buckets year-over-year

Similar to last year we saw a larger number of 30-40 degrees F days. The graph is almost identical to 2016 although we had more cold hours in the lower temperature ranges. Our last highest number of hours in the 30-40 degree range was 935 hours in 2014. This year we had 1,484 hours in this temperature range, only 88 hours lees than 2016. The ASHP ran 63 hours less than 2016 but used the second largest number of hours, it’s total usage was the second largest since we started tracking circuit-level data.


Chart comparing water usage 2012-2017

We have been fairly consistent in our hot water usage. Over the year we averaged 18.1, almost the same as last year. That hot water requires 242 watts/gallon to heat. We fared much better in out cold water usage in 2017 as opposed to last year’s spike. We used a total 22,406 gallons of water in 2017, 61.4 gal/day, as compared to 26,735 gallons of water in 2016, 73 gal/day, and 20,684 gallons in 2015. Oddly, it took the same 69 kWh to pump that water out of the ground, same as last year. Our water pump used about 3.1 Wh/gal this year versus 2.6 Wh/gal last year. Will have to keep an eye on the pump.

Temperature ranges by month

Chart of average temperate, year-over-year

We experienced our 3rd largest largest temperature range this year out of the last 6 years, 108°. Our coldest temperature was -13.2° on December 28 at 7am. Our high was 94.8° on May 18 at 1pm. Our highest recorded temperature in the last four years was 95.135°, set on July 19, 2013 at 3pm.

The average temperature for 2016 was 49.4°, 0.7° down from 50.1° in 2016.

Happy 2018 all.

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.

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