Archive for the 'Performance' Category

We’re NOT net positive in 2018! What happened?

Year summary: We used 7,356 kWh and generated 7,256 kWh for a net of -100 kWh for the year.

2018 is the first year we have not generated a solar surplus. In short, we produced 15% less solar than average, and used 5% more than average. That tipped the scales just enough to break our 6 year net zero running streak. On the long view however, we’ve  generated a surplus of 9,157 kWh over the last 7 years since the house was built.

Chart showing solar and usage values for last 7 years

We were performing fairly normally until Q4. Let’s break down the numbers.

Q4 2018 summary: 7% colder, 12% more usage and 28% less sun as compared to Q4 2017.

In Q4 our total usage was 2,264 kWh, a 12% increase from our 2,022 kWh in 2017. We also generated 417 kWh less solar.

October through December was also the coldest forth quarter since we started recording temperature data at the house.

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

Charts comparing Q4 and YOY usage, solar and HDD

2017 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 2,022 1,466 556 22.0 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
2018 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 2,264 1,049 1,215 24.6 2,459
Oct 527 469 58 17.0 505
Nov 799 234 565 26.6 883
Dec 938 346 591 30.2 1,071
All values in kWh (except HDD which is base 65°F).

Year-over-year comparison

Here’s our progress for the first 7 years in the house.

Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 49,447 58,605 (9,157) 19.3 46,163
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 6,838 8,910 (2,072) 18.7 6,381
2017 7,198 7,966 (769) 19.7 6,452
2018 7,356 7,256 100 20.2 6,800
All values in kWh (except HDD which is base 65°F).

Circuit-by-circuit 

2018 was our third warmest year in the house (displacing 2017 to 4th place), although we continue to see wide extremes in temperature ranges (see temperature ranges below). The ASHP used 32% of the total as opposed to 27% last year, due mainly to the last 3 months being unusually cold and dark. Vampire loads decreased slightly this year. We cooked more in 2018 as the induction cooktop & stove vampire loads decreased in comparison to use. The combined vampire load for the stove, ASHP and solar inverter was 130 kWh in 2018, about 7 kWh less than last year.

Net-zero moment(s)

Our first ‘net zero moment’ this year occurred on July 15 at 7am. Then sadly, on Dec 12 at 7pm, our curves reversed again. We had 31 days this year where the solar panels generated less than 1 kWh, mainly because they were covered in snow. We had 23 days last year and 13 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.

In 2018, 28% of our power needs were supplied by our own solar generation directly. The other 72% was supplied from the grid. Of the 7,256 kWh we generated in 2018, we only used used 28% ourselves. The other 72% we sold back to the grid at a greatly reduced price. We’ve tried various strategies to consume energy when the sun is shining, but the largest energy consumers, hot water and heat, don’t amend themselves easily to this type of use.

I track our net energy use by the calendar year since we moved in Jan 1, 2012. But the electric company tracks our yearly solar anniversary in June. Although we didn’t net out Jan to Jan, we did still produce more power June to June. This year we sold roughly 694 kWh back to the grid and earned $27.26, about $0.04/kWh from the power company. I’m going to bet we will not generate a surplus by June. We’ll have to wait till the Q2 report to find out.

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 $9,124 over the past 7 years for the 49,448 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 64% payback. At our current rate of use and the trending price of power, it will take us another 4 years to break even in simple terms.

Air-Source Heat Pump performance

Chart of ASHP usage values Oct-Arpril, 2012-2018

We started the 2017-18 heating season (thick blue line) about normal, then ramped up more than usual in December through mid February before ducking under the 2014-15 heating season curve. We finished up that season as the second highest energy use in the last 7 years. We used 2,328 kWh for heat in 2018. At the average electricity price this year, $0.19/kWh, that would be about $442. With 6,800 HDD in 2018, that is $0.065/HDD.

But the real shocker is the thick black curve showing the start of the 2018-19 season. Two things could be happening, it was colder than usual, and/or the ASHP is running inefficiently. I don’t have a good way to analyze the efficiency of the ASHP so I’m going to have to say it’s a colder than usual forth quarter. I already knew it was the coldest quarter we’ve recorded at the house. We turned on the heat October 23, earlier than ever before and left it on. Second earliest was Oct 25, 2014 and that was only for a few days. Since we are a passive solar house I also wanted to look at how sunny it was this last quarter so I pulled together a new chart showing solar (proxy for solar heat gain, except when covered by snow), heating degree days (HDD) and ASHP energy usage.

Chart showing ASHP, Solar and HDD together

Notice the divergence of the HDD and solar lines in 2018, the largest we’ve experienced since 2014. In general, the higher the HDD the more heat required, but solar heat gain can lower our heat energy requirement as it did in 2012, 13, 16 and 17.

Since this year is atypical, I thought I’d show our ASHP usage broken down by temperature buckets in comparison to our 2017 numbers. Clearly the elevated 20-30, 30-40 and 40-50 degree ranges for 2018 are heavily weighted by this last quarter.

Chart showing kWh used by ASHP in 10 degree buckets

Chart of temperature buckets year-over-year

The same is visible when we compare all the hours the ASHP has operated each year by 10 degree buckets. 2018 stands out for the 20-50 degree range.

But it’s the following chart that makes me think the ASHP is working just as efficiently as the last 6 years. This chart plots HDD vs kWh used over the last 7 years, using yearly data.

Chart that correlates HDD with energy used by ASHP

If the data point was severely out of sync with the regression line, then I’d be more worried. I’m not a data scientist, so I’ll have to proceed until we get more data (or I get smarter).

Temperatures

The temperate bucket chart I usually create for the ASHP made me wonder what the general temperature buckets are and which buckets are increasing over the last 7 years.

Chart showing which temperature ranges are most frequent

The ‘snowbirds’ know that our area has a large number of hours in the 60-70 degree range, followed closely by the 30-40 degree range and then the 50-60 degree range.

Chart showing temperature buckets with trend lines

Chart showing rate of change for temperature buckets

The 30-40 and 50-70 degree ranges may have accounted for the most hours in the last 7 years, but the 50-80 degree range is increasing more quickly overall in comparison to the <50 and > 80 degree range. In particular, the 50-60 degree range is increasing at a rate of 29%. Upstate NY is the new Florida (based on a small sample of 7 years temperature data). 
Temperature ranges by monthChart of average temperate, year-over-year

We experienced our largest temperature range this year out of the last 7 years, 115.9°. Our coldest temperature was -17.1° on January 7th at 7am. Our high was 98.8°, the highest recorded since we moved in, on July 2 at 1pm.

The average temperature for 2018 was 48.9°, 0.5° down from 49.4° in 2017.

Water

Chart comparing water usage 2012-2018

We have been fairly consistent in our hot water usage. Over the year we averaged 17.2 gal/day. That hot water requires 243 watts/gallon to heat. We used a total 21,725 gallons of water in 2018, 59.5 gal/day, as compared to 22,406 gallons of water in 2017 and 26,735 gallons in 2016. It took 55 kWh to pump that water out of the ground. Our water pump used about 2.6 Wh/gal this year versus 3.1 Wh/gal last year. Pump is doing well. 🙂

Happy 2018 everyone.

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

Third quarter 2018 performance

Q3 2018 summary: 33% warmer, 1% more usage and 7% less sun as compared to Q3 2017.

This is part of our quarterly home performance reporting. All data is posted at netplusdesign.com

Nothing exciting to report, which is normal for 3rd quarters.

At 7am on July 15th we became net positive for the year. As of the end of September, we have a surplus of 1,115 kWh heading into the final months of 2018. That’s about 211 less kWhs than last year at this time. Overall for the year, our solar production is down about 7%.

Overall, here’s how this quarter compared to 2017.
Chart showing usage, solar, net and hdd

2017 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 1,045 2,657 (1,611) 11.4 254
Jul 322 848 (527) 10.4 39
Aug 377 944 (567) 12.2 73
Sep 347 864 (517) 11.6 143
2018 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 1,056 2,483 (1,427) 11.5 171
Jul 386 986 (601) 12.4 28
Aug 317 809 (491) 10.2 17
Sep 353 688 (335) 11.8 126
All values in kWh (except HDD which is base 65°F).

Water usage was down 7%. Hot water usage down 13%.

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

Second quarter 2018 performance

Q2 2018 summary: 18% colder, 2% less usage and 4% more sun as compared to Q2 2017.

This is part of our quarterly home performance reporting. All data is posted at netplusdesign.com

Overall, here’s how this quarter compared to 2017.

Q2 Comparison 2017-2018

2017 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 1,421 2,258 (837) 15.6 847
Apr 531 758 (227) 17.7 421
May 514 692 (178) 16.6 315
Jun 375 807 (432) 12.5 110
2018 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 1,396 2,349 (953) 15.3 997
Apr 627 660 (32) 20.9 724
May 470 850 (381) 15.2 162
Jun 300 839 (540) 10.0 111
All values in kWh (except HDD which is base 65°F).

Quite a bit cooler this quarter. The last day we used heat was May 1. That’s about 2 or 3 weeks later than usual.

Here’s our breakdown on energy use and cost for the last six winter seasons.

Winter season Heat kWh Est. Cost
2012-13 957 $144
2013-14 1,804 $271
2014-15 2,200 $330
2015-16 1,305 $196
2016-17 1,804 $271
2017-18 2,103 $315
Est. cost based on $0.15 kWh.

We would have spent about $1,527 (if we paid for electricity) for the last six winters.

We haven’t netted out energy-wise yet. We’re still 312 kWh short. In 2016 we netted out on May 31 after 8am. In 2015 we were 637 kWh short. In 2014 we netted out around mid-July. In years prior we were net positive by May or June.

Our overall water usage is down 6% from Q2 2017. It started out dry this quarter but the rain picked up. We only had to water the garden a few times. Out hot water usage was down 22%.

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

First quarter 2018 performance

Q1 2018 summary: 4% colder, 3% less usage and 13% less sun as compared to Q1 2017.

This is part of our quarterly home performance reporting. All data is posted at netplusdesign.com

I said it last year and I’ll say it again, it was a whacky winter. Lots of cold days, but also lots of warm days. It would be warm for a week or two, the ground would thaw, then we’d get snow.

We recorded a low of -17.1 on January 7, close to our lowest recorded temperature of -17.3°F on February 14, 2016. Our high was 77.6, higher than the 73.6°F last year. In 2012 we recorded a high of 82.4°F in the same period.

Overall, here’s how this quarter compared to 2017.

Q1 Comparison 2017-2018

2017 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 2,710 1,586 1,123 30.1 3,056
Jan 1,035 357 678 33.4 1,086
Feb 783 478 305 28.0 890
Mar 892 752 141 28.8 1,079
2018 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 2,640 1,375 1,265 29.3 3,173
Jan 1,093 375 718 35.3 1,294
Feb 768 399 368 27.4 894
Mar 780 602 178 25.2 985
All values in kWh (except HDD which is base 65°F).

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

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)
Avg.
daily usage
HDD
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)
Avg.
daily usage
HDD
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)
Avg.
daily usage
HDD
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

Circuit-by-circuit 

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.

Water

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
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 netplusdesign.com. View hourly, daily and monthly values for solar, usage, net usage, temperatures and HDD.

Third quarter 2017 performance

Q3 2017 summary: 33% cooler, 9% more usage and 7% less sun as compared to Q3 2016.

This is part of our quarterly home performance reporting. All data is posted at netplusdesign.com

Nothing exciting to report, which is normal for 3rd quarters.

At 1pm on July 17th we became net positive for the year. As of the end of September, we have a surplus of 1,326 kWh heading into the final months of 2017. That’s about 574 less kWhs than last year at this time. Overall for the year, our solar production is down about 13%.

Overall, here’s how this quarter compared to 2016.
Chart showing usage, solar, net and hdd

2016 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 957 2,857 (1,900) 10.4 191
Jul 300 955 (655) 9.7 32
Aug 330 934 (604) 10.6 27
Sep 328 968 (641) 10.9 133
2017 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 1,045 2,657 (1,611) 11.4 254
Jul 322 848 (527) 10.4 39
Aug 377 944 (567) 12.2 73
Sep 347 864 (517) 11.6 143
All values in kWh (except HDD which is base 65°F).

Water usage was down 6%. Hot water usage up 30%. I think that’s attributable to the chillier mornings this summer.

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

Second quarter 2017 performance

Q2 2017 summary: 15% warmer, 1% less usage and 15% less sun (412 kWh) as compared to Q2 2016.

This is part of our quarterly home performance reporting. All data is posted at netplusdesign.com

Overall, here’s how this quarter compared to 2016.

Chart showing usage, solar, net and hdd

2016 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 1,439 2,668 (1,229) 15.8 994
Apr 575 893 (317) 19.2 615
May 551 834 (283) 17.8 279
Jun 313 942 (629) 10.4 100
2017 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 1,421 2,258 (837) 15.6 846
Apr 531 758 (227) 17.7 420
May 514 692 (178) 16.6 315
Jun 375 807 (432) 12.5 110
All values in kWh (except HDD which is base 65°F).

Most noticeable is the lower solar generation, 15% down this quarter and 17% down for the combined first and second quarters. I think we’ll still easily remain net positive for the year, but this might be the lowest solar generation year for us since we got the panels.

The last day we used heat was April 11 for a total of 69.3 kWh this quarter. Last year we turned the heat off on April 17th and used 117.2 kWh that quarter.

Here’s our breakdown on energy use and cost for the last four winter seasons.

Winter season Heat kWh Est. Cost
2012-13 957 $144
2013-14 1,804 $271
2014-15 2,200 $330
2015-16 1,305 $196
2016-17 1,804 $271
Est. cost based on $0.15 kWh.

We would have spent about $1,212 (if we paid for electricity) in the last five winters. That’s still a lot less than many of our neighbors would spend in one winter.

We haven’t netted out energy-wise yet. Last year we netted out on May 31 after 8am. In 2015 we were 637 kWh short of netting out for the year. In 2014 we netted out around mid-July. In years prior we were net positive by May or June.

Our overall water usage is down 34% from Q2 2016. This has been a very rainy an cloudy season as evidenced by the lower solar generation numbers. Out hot water usage was up 17%.

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


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