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Leonard residence

October 8, 2023 @ 12:00 pm - 4:00 pm - October 8, 2023 @ 12:00 pm - 4:00 pm
Leonard Family Home, 600 Main Street, Hingham, Massachusetts Solar System Output and Home/Vehicle Usage

Our home was built in 1780 in the middle of hostilities between the English and colonials. Originally heated by firewood and not anything close to an airtight house, we had it air sealed and insulated. We highly recommend Jason Taylor of Carbon Cutters in Cambridge, MA. He made extensive use of blower door testing to determine where the air losses were coming from as well as extensive viewing and mapping out of the house with an infrared viewer. In old post and beam homes, there are diagonal braces throughout the structure. Without infrared monitoring during our blown-in cellulose process, we would have had a fair amount of insulation voids. The vast majority of insulation companies will probably not be doing this procedure for old houses. From a rough guesstimate of 4-5,000 Cubic Feet per Minute (at 50 pascals depressurization) when we did our first go-round of sealing and insulating, we got it down to 1,818 CFM (.5 air changes/hour) by the time Jason was through. That would be classified as a moderately leaky house—a little better than halfway between a leaky house at above 3,000 CFM and a tight house below 1,200 CFM.

Our house was the first in our historic district to be approved for solar panels. There was a bit of reluctance by some of the Historic District Commission to establish precedent for solar panels over 10 years back. Foliage largely screening the particular roof from street view and the lack of opposition by our neighbors proved essential.

We have two rooftop solar arrays, 16 panels installed in 2011 facing south on the garage roof and 26 more in 2021 on the east and west roof slopes over the rooms connecting the house and garage. The panels help power our home and plug-in Chevy Volt.

The 2011 array was paid off in eight years with a large amount of help from Massachusetts Solar Renewable Energy Credits (SRECs), version 1. The cost of solar panels has gone down over half for us from $7.74/Watt in 2011 to $3.40/Watt in 2021.  We expect to have the newer 2011-installed solar array paid off sometime in 2026.  Hingham Municipal Light Plant currently offers a $5,000 maximum rebate on solar panels, up from an original $3,000 maximum in 2011. HMLP was kind enough to give several customers who filed with the State in spring 2021, in addition to the normal Town utility rebate, the amount of a State rebate that the State had run out of money to pay.



In 2011, we installed a 3.68 kW system with SunPower panels with an SMA central inverter

In October, 2021, we installed a 9.49 kW system with LG panels with Enphase microinverters

We have combined system installation size of 13.17kW with a 2022 output of 13,742kWh



6799kWh 2022 electrical usage  (including the 87.4% electric fuel portion of the Chevy Volt)*

9,446kWh  equivalent of the 682 gal. average annual heating oil usage** in our air-sealed, insulated home, constructed in 1780

270kWh    equivalent to 23.5 gallons of Volt gasoline.  That comprised 12.6% of Chevy Volt fuel that it ran on for 989 miles.***

549kWh    equivalent to average workshop propane usage of 60 gal.

800kWh    equivalent to average annual GMC pickup truck usage of 164 gal. 

17,864kWh    Total


We produce the equivalent 76.9% of our combined house AND CAR usage energy****


We produce the equivalent 92.2% of our house usage (not including car energy usage).  Our non-vehicle usage totaled out to 14,912kWh

If you wish highly detailed financial and electric information, please drop a line to:



*2002 Volt mileage: 7803 miles of which 87.4% of that was electric.  6892 electric miles and 989 gas miles.  Electric usage was (.273 kWh x 6892 miles) 1882kWh

**assuming 1 gal. heating oil = 138,500 BTUs  and  1kWh = 10,000 BTUs

*** 0.273kWh x 989 miles = 270kWh

****4917kWh used for household, 1882kWh used for Volt

Photo Tour


October 8, 2023
12:00 pm - 4:00 pm UTC+0
Event Category:


Leonard residence
600 Main St.
Hingham, MA 02043 United States
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Sustainable Features
Solar PV - Rooftop, Electric Vehicle(s), Electric Vehicle Charging, Energy Efficiency, Energy Monitoring
System Size (in kW):
Tour Site Type

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