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Virtual Event Virtual Event

Solar & Heat Pumps Virtual Tour

October 1 @ 12:00 am - 11:59 pm - January 15, 2023 @ 12:00 am - 11:59 pm

Solar Panels

In 2016, my wife and I concluded that the fight against climate change would have to revert to the states and localities for a while – the federal government clearly was not going to do anything. Luckily, we had a large, south-facing roof with the ideal pitch for solar panels and had  a 7.37 kilowatt hour array installed in the fall of 2017. It required some creative financing but my analysis showed that this investment would pay us big long term dividends, in addition to being the right thing to do for the climate. The following is based on an example I constructed for someone with an average monthly electric bill of $150. I showed that they could finance the purchase of a solar array and still save money on their bill from their solar output, all without exceeding their pre-solar monthly cost for electricity of $150. I used my actual solar output data, Massachusetts Department of Energy Resources cost data and Hingham Municipal Light Plant rates in effect at the time. Incentives will vary based on your location and when you sign your contract, so I’ll just note that state, federal and utility rebates and incentives will cover between 40% to 60% of the total project cost. In other words, you will get an immediate return on investment of 40-60% in the first year alone – an amazing deal.

How Do I Get Savings on My Electric Bill?

  • Electricity produced by solar array goes to breaker panel and is available to power your home, reducing kWh’s you must buy.
  • Even if your panels produce less than what you consume, your electric bill is still reduced for each kWh you generate.
  • If your panels produce more than what you could immediately consume, you receive a credit on your bill for each excess kWh.
    • The Hingham Municipal Light Plant (HMLP) “Energy Credit” is the number of solar kWh’s in excess of what you used times HMLP’s average “wholesale” cost.
    • In effect, you become a supplier of electricity to your electric utility.
  • This is HMLP’s “net metering” policy.

Solar Panels Produce Two “Streams of Value”:

  1. The kWh’s produced by your solar array that you are able to use immediately and therefore do not have to buy from HMLP:
  • You’d have to pay HMLP $.17256 per kWh to buy that kWh from them.
  • So “avoided” purchases have a value to you of $.17256 per kWh.
  • @ 53% of my solar output is used immediately and represents avoided cost

2. The kWh’s produced by your solar array that you were not able to use immediately and fed back into HMLP’s grid for others to use:

  • In effect, you become a supplier of those kWh’s to HMLP .
  • HMLP credits you at its average wholesale cost per kWh: $.10756 per kWh
  • @47% of my solar output is sold back to HMLP

Total savings over 20 years due to installing solar array: (2018 data):     $46,273.83 – calculated as follows:

  1. Total 20 Year Effective Cost of Electricity with Solar: ($10,273.83) This is a negative number because you actually saved this much on your electric bill, even after paying for the solar panels. Plus,
  2. Total 20 Year Cost of Electricity Without Solar: $36,000 (without solar panels, you would have spent this much with an average monthly bill of $150.00 over 240 months)

So: Total savings over 20 years due to solar panels, after paying for them: $10,273.83

Plus: What you would have spent on electricity if you had not installed solar panels: $36,000.00 

Total savings over 20 years:  $46, 273.83

  • Plus, for years 21 through the end of guaranteed life of the solar panels (25 years), you continue to generate savings of $103.00 per month from the “two streams of value” of solar.
  • Using the guaranteed life of panels of 25 years, this is worth an additional $6,179.86
  • Total savings over guaranteed life of panels (25 years) thus is: $52,453.68
  • Compare these savings to cost of electricity you would have paid without solar over 25 years: $45,000 ($150/month X 300 months).
  • Instead of being out of pocket $45,000, you actually receive $52,453 in total savings from your solar panels.




In the fall of 2018, I installed an electric heat pump whole-house solution to heat, cool and dehumidify my home.

My situation at the time: 

  • Old New England farmhouse built in 1880; 1,804 square feet
  • Balky, inefficient, noisy, uncomfortable, dangerous gas-fired steam heat and window air conditioners
  • Two floors, unfinished basement, pull-down stairs to attic
  • Limited closet space and low ceiling in basement – no room for ductwork.
  • Two of eight rooms do not communicate with basement or attic.
  • Several rooms have unique heating/cooling characteristics (e.g., solar gain) and need to be their own zones.
  • Fire safety a major concern in old wood frame house
  • Wanted to take advantage of $5,000 electricity credit for solar panels from Hingham Municipal Light Plant.
  • Self-financed/limited budget

Proposed Solutions

Two prominent contractors specified variants of the old standbys:

  • Two gas-fired furnaces/AC compressors located in basement and attic with air exchangers feeding ducts.
  • Extensive ductwork!
  • Many large holes in 2nd floor ceilings and 1st floor floors for registers
  • Kluged solutions for the two isolated rooms (small heat pumps or electric radiant heating). Still would need window air conditioners!
  • What about my $5,000 Hingham Municipal Light Plant credit for electricity for solar panels?
  • Bids were  $56,500 and $37,353
  • Four contractors proposed Mitsubishi air-source heat pump solutions:
  • Bids were $42,487, $29,790, $22,955, $22,800

The Winning Proposal

  • Two Mitsubishi “hyper heat” external air-source heat pumps:
    • For 4 larger rooms on south side of house –  36,000 BTU heat pump
    • For 3 smaller rooms on north side –  24,000
    • Total capacity: 60,000 BTU’s
  • “Branch box” in basement for optimal routing of refrigerant lines
  • 4 wall-mount internal air exchangers
  • 3 floor-mount air exchangers
  • Coastal Heating and Air Conditioning in Quincy MA submitted winning bid; Casoli Refrigeration was very close second. I was impressed with both outfits’ expertise and responsiveness.
  • Total Final Cost: $22,390
  • Time to install: one day!


Notes on Comparing Gas and Electric Power

  • Total energy usage/costs in New England are driven by heating requirements.
  • How do you compare a gas system to an electric system? Here’s how:
  • One Therm of natural gas equals 29.3 kWh’s of electrical energy.
  • To get electrical kWh equivalent of gas, multiple Therms times 29.3.
  • Example:
  • Total Therms used in 2018 :                   1,853.0
  • For kWh equivalent, multiply by:           X    29.3  kWh’s
  • Result:                                                  54,292.9 kWh’s, or “units”
  • Enabled analysis of energy used by gas boiler vs. electric heat pumps.

Comparison – Before/After Heat Pumps

Period 1: 2018 (Oct. 2017 through Sept. 2018 – pre-heat pump)

Period 2: 2019 (Oct. 2018 through Sept. 2019 – post-heat pump)

Total Energy Used –gas and electricity – expressed in “units” of kWh’s decreased dramatically in 2019.

2018 usage was 2.59 times 2019 usage!

2018:  63,500 units  (Most of the energy used was gas)

2019:  24,520 units  (Most of the energy used was electricity – greener/more efficient)

However, Cost per Unit almost tripled (electricity costs more than an equivalent amount of gas):

2018 Average Cost Per Unit:      $.0640

2019 Average Cost Per Unit:      $.1720

Despite this, annual operating costs increased by a relatively small amount – only $152.80 – a 3.76% increase which was more than offset by the $9,000 savings in initial outlay for the heat pump system when compared to the lowest cost gas-fired solution.

Total energy costs:

2018: $4,064.18

2019: $4,216.92

Increase, 2019 over 2018: $152.80

% Increase in operating cost: 3.76%


  • Electric heat pumps also cool and replace window AC. No more replacing failed air conditioners.
  • Most of the energy used during both periods was for heating.
  • Average monthly temperature analysis showed the two periods were almost exactly comparable.
  • Winter temps of the 2 comparison periods entailed equal heat loads.

More results:

  • Reduced natural gas consumption from 1,853 Therms in 2018 to 45 Therms in 2019 – a reduction of 98%!
  • Solar panels produced 40% of all electricity used, further reducing carbon footprint.
  • Too many variables were at play in my situation to calculate a valid “Return on Investment” (ROI) or “payback period” that might be applicable to others.
  • However: lower initial cost of heat pump system compared to gas means electric wins in overall $’s.
  • $9,000 in project savings spread over 30 years = $300/year – almost 2X $152.80/YR increased annual operating costs.)
  • Alternative Energy Credits (AEC’s) for heat pumps further shift cost picture to favor electrical HVAC solution. (Utility Rebates of up to $4,500 or more are available now and Federal IRA legislation will add further incentives.)

Impact on Carbon Footprint

  • I used the House tab for the carbon footprint calculator at this link:
  • Entered “one person” to isolate house undiluted by occupancy.
  • For comparison periods 2018 and 2019, entered the total electricity (in kWh’s) and natural gas (in Therms) used each period.


  • 2018: (Pre-heat pumps) 45 Metric tons of CO2e**
  • 2019: (Post-heat pumps) 44 Metric tons of CO2e – almost 50% lower!


*  To preserve an apples to apples comparison, results shown are not distorted  by the output from  the solar panels installed in 2017, which I excluded from the analysis.

**Carbon dioxide equivalent (CO2e) “Carbon dioxide equivalent” or “CO2e” is a term for describing different greenhouse gases in a common unit. For any quantity and type of greenhouse gas, CO2e signifies the amount of CO2 which would have the equivalent global warming impact.

Performance and Satisfaction: Positives

  • Hingham Municipal Light Plant electricity is greener than natural gas and will get greener as HMLP makes further progress in renewable sourcing (currently at 50%).
  • Air exchangers make each room a separate zone. Heat, cool or dehumidify the air with room-specific flexibility as you use them.
  • Remote control for each unit provides flexibility in setting mode (heat, cool, dehumidify, circulate), temperature, fan strength and direction of air flow.
  • You can program each unit with optimal settings for night, day etc.
  • Units direct air flow optimally.
  • “Gentle heat” – it’s more comfortable.
  • Air exchanger intake filters trap dust and are treated with an antibacterial agent – the air you breathe is cleaner.
  • Cleaning filters is easy and a revelation – unbelievable how much dust circulates in a house.
  • Other heating systems can have a “long throw” and will initially overheat rooms 5 or 6 degrees more than called for by the thermostat. Then they cool down – and the cycle repeats.
  • Whisper quiet – no pipes clanging and radiators hissing; no window AC units chugging away.
  • Mitsubishi “Hyper Heat pumps” tested to 13 degrees below zero in Vermont – they work!
  • Technology used for many years in Europe, Scandinavia and Asia, especially in older (even ancient!) buildings in historic districts.
  • No schlepping window air conditioners! AC at the touch of a button
  • No chopping up house for duct work.
  • Refrigerant lines (only 1 3/8” diameter) can be routed with great flexibility.
  • “Branch box” (intake and outflow manifold) increases line routing options.
  • Safe, no combustion, fumes, or potential gas leaks. High-amp compressors located outdoors.
  • Great solution for an older house!
  • Massachusetts APS Renewable Thermal Program administered by Mass. Clean Energy Center (MassCEC) qualified my Whole House Replacement system for alternative energy credits worth $820.80.


  • No combustion devices now in cellar, before was toasty in winter, now 53°
    • We were wasting a lot of energy heating unfinished basement.
    • “Hybrid” heat pump water heater further cooled basement until we had plumber exhaust it into unused masonry chimney
    • We now dress warmly to use laundry, shop, exercise equipment.
  • Cold from uninsulated crawl space and basement makes floor above feel colder even if kitchen heated to 70 degrees. Will address in future phase.
  • You may need upgrade to your electrical breaker panel for the 40-50 amp/240 volt heat pumps (Relatively modest cost -hundreds, not thousands of $’s.)
  • Must learn mini-split remote control; “flexibility entails complexity”.
  • Some may not like the appearance, especially in older homes.



Photo Tour


October 1
January 15, 2023
Event Category:
Event Tags:


John from Hingham


Sustainable Features
Heat Pump(s), Solar PV - Rooftop
Solar Site Type


Heat Pumps & Solar Virtual Tour
Hingham, MA 02043 United States + Google Map

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