Published Saturday January 30, 2016: Updated January 24, 2017

Misplaced Megawatt-hours

I seem to have misplaced 2.9 Megawatt-hours. Has anyone seen them?

Ever since June of 2014, our entire household and vehicles have been powered entirely by electricity. 

  • 2 electric cars, plus plug-sharing for visitors. 
  • Lighting of course
  • Appliances
  • Hot water heating
  • All home heating in the winter time (ground-loop heat-pump).
  • Central air conditioning in the summer time (ground-loop heat-pump)
  • Mom’s basement apartment
  • All cooking/food preparation – 95% of all our meals are homemade.
  • Grow lights in the winter time – Small indoor hydroponic herb/salad gardens. 

Based on our 2014 energy usage and the new PV solar array addition in March 2015, I estimated that all our energy usage for 2015 would effectively be 100% solar powered and there would be about 1000 kWh of excess of solar energy available for future expansion. 

Well, instead of an excess, my energy surplus ran out two months shy of the net-metering period end date. By the time late February comes around and I start building up energy credits again, our household will probably have consumed 1200 kWh (about $120 worth) beyond what the solar panels produced for the net-metering year. Energy credits are tabulated on a March 31st to March 31st calendar year. 

The solar array performed as calculated, so where did all that extra energy go?

 Year Solar Energy Production Energy Consumption
 2014   -9,440 kWh 14,706 kWh
 2015 -16,049 kWh (more PV added) 17,577 kWh
 Delta    2,871 kWh

That’s a difference of almost 2900 kWh for energy consumption between 2014 and 2015. I don’t see any extension cords running to my neighbors houses, although they joke with me that they are going to do it. So what used all that extra energy in 2015? 

To modify Lord Kelvin’s famous quote into my own, If you CAN Measure It you CAN Improve it. 

Thanks to the energy monitoring hardware installed in my home, I can keep tabs on how much energy my household uses and for the most part, know where it is going. Analyzing the data for 2015, here is were the missing energy has gone. 

Raj vs Geo EV:

In January 2015, I retired my beloved Geo EV and started exclusively driving Raj, my 2012 Nissan Leaf. Even thought the Leaf, being 100% electric is a crazy energy efficient car, my Geo EV had it beat. The Geo was a much smaller, lighter car and used about 40% less energy. So essentially after driving 9500 miles that year, I consumed about 1000 kWh more in 2015 than I would have had I continued to drive the Geo EV.
I average about 3.65 miles per kWh driving the Leaf as opposed to 6.04 miles per kWh in the Geo EV. These figures are based on total energy to charge the car's battery, not just energy consumed by driving the car. 

Note: Nissan Carwings energy data only accounts for energy used while driving. It does not account for charging inefficiencies or energy used pre-setting climate controls while the car is parked in the garage or away. For my conservative driving habits, Carwings reported energy usage 21% lower than what it actually took to re-charge the car. 

 Day TED CarWings % Error
 1/29/2016 14.2 kWh 11.4 kWh 19.7%
 1/28/2016 12.3 kWh 9.6 kWh 22%
 1/27/2016 10.1 kWh 8.2 kWh 18.8%
 1/26/2016 11.2 kWh 8.9 kWh 20.5%
 19.4 kWh 15.7 kWh 19.1%
 1/15/2016 18.8 kWh 15.0 kWh 20.2%
 1/14/2016 10.6 kWh 8.4 kWh 20.8%
 1/13/2016 12.6 kWh 9.5 kWh 24.6%
 Average   20.7 %

Additional Heat-pump Energy Usage:

The ground-loop lost some of its memory settings during a power bump. Some default parameters were used instead. Apparently this caused the heat pump to not operate as efficiently as it could have. Nobody noticed any difference in home comfort and I didn't think it would matter either so I ignored it until a year later during a routine service call when the correct fan speed settings were reprogrammed.
The technician also found the ground-loop pressure had dropped quite a bit, (12 psi down from 40 psi). The technician told me that while this would not make much difference in system performance, it could add to the energy usage of the circulation pump.

Colder Winter in General: 

It was 4.7 degrees colder in the winter time in 2015 than in 2014. 
Also in October 2015, I raised the home thermostat heat set-point from
70 °F to 72 °F. 

 Year Avg Outside °F  Inside °F Energy Usage
 Nov-Dec 2014 37.6 °F 70 °F 887.1 kWh
 Nov-Dec 2015 32.9°F   72 °F 1237.7 kWh
 Delta 12.5% colder 2.8% warmer 350.6 kWh more

Together the fan speed settings, lower ground loop pressure and raising the temperature throughout the colder winter, collectively added another 1000 kWh to our annual energy usage for 2015. 

Ironically, with increased heat-pump usage came increased free hot-water generation and a corresponding decrease in hot-water heater energy usage (-149 kWh), even though our tweenage children started taking more showers in 2015 than in 2014. 

 Year Electric Hot Water Heater 
 2014 1737 kWh
 2015 1589 kWh
 Delta -148 kWh

Electric Clothes Dryer

Until June 2014, the clothes dryer (our last remaining gas appliance) was still running on natural gas. Since then it has been 100% electric. For 10 loads per week and with hot attic air feeding the drier during the hot attic months, energy usage averages about 100 kWh per month or 600 kWh total for the remainder of 2014 and 1200 kWh for 2015. So for 2015, dryer energy usage would have been 600 kWh more. 

Apartment Space Heaters: 

The entire house is under one HVAC zone and my mom lives in a little basement apartment in our home. Since the basement is always colder than the upstairs, we added supplemental resistive heating so she can crank it 73-74°F while the rest of the basement hovers around 67-69°F through the winter months. This extra resistive heating adds about 3.5 kWh of energy usage per winter day, (~400 kWh each year).

My mom's electric fireplace, (solar powered of course).


I picked up 2 used hydroponic Aero-Gardens for a total of $40. While growing herbs and salad is really enjoyable and delicious, each garden consumes about 33 kWh per month. I started these in mid-December, so together they used an extra 33 kWh (for the last 2 weeks of December).

Add it all up:

Clothes Drying 600 kWh additional
Raj (2012 Leaf) 1000 kWh extra
Heat Pump 1000 kWh extra
Water heating energy -150 kWh (a reduction)
Resistive space heating 400 kWh extra
Hydroponic Gardens 33 kWh
For a total of 2883 kWh.

Okay! So that’s where my 2.9 Megawatt-hours went!!

2016 will be the first full calendar year with the new solar addition. I’m estimating that this year will be our first complete net-zero year, maybe even a net-positive one.

What a great time to be alive!

Update January 24, 2017:

I missed net-zero for the year by 1135 kWh. I'm blaming it on the kids and the older kids get, the more energy they use. More driving than ever, more showers, more laundry and more lights and appliances left on.
Oh well. Love them anyway right? 

I hope to be truly net-zero by 2018. However, together my wife and I are driving our cars an additional 7000 miles a year. Like I said, kids take more energy. 
Net-zero is a cool goal and all but the bar has been raised. 

Off-Grid By 2020

That is what I plan on achieving by the end of 2020. I will explain the specifics of how this will be accomplished in an upcoming article.