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Would you do a solar roof in Western MA... Geothermal already installed, Model 3 on its way.

Hi all,

We just got a design for a solar roof on our house here in the Berkshires. We have a 3600 sqft house + 800 sq ft guest house where my mother lives (connected to power at the main house). Geothermal heats and cools the main house. over the past 12 mos. we used 32,083 kWh. The design for the solar roof says it would have a 48% energy offset. Our power usage is significantly higher in the winter due to the geothermal heat. Our bills tend to be twice as high in winter months ($980 last month vs. $5-600 in summer months and $4-500 in shoulder season months). We do need a new roof in the next couple of years, which I assume would be in the $20k range based on complexity and approx. 3000 square feet of roof.

Here are the pertinent details from the Tesla solar roof design estimate:


48% Energy Offset

$71,786.47 Net Cost

Solar​

  • 21.24 kW Solar
    $89,964
    48% Offset

Powerwall​

2 Powerwalls $19,000 0.5 Days backup power
Solar Roof $89,964.35
Roof Replacement $9,933.50
Installation Cost Included
Install Solar Roof + Powerwall together-$2,000.00
Deposit-$250.00
Total System Price $116,647.85
Down Payment - $11,689.79
Total Loan Amount $104,958.06
Federal Tax Credit - $27,810.73
ConnectedSolutions - $7,000.00
SMART Solar Incentive - $3,567.52
SMART Storage Incentive Adder-$5,733.13
MA Solar Tax Credit-$1,000.00
Net Cost $71,786.47

Est. Financing Details​

$11,689.79 down, 10 years, 2.99% APR
Est. Amount Financed $104,958.06
First Month's Payment $1,013.00 /mo
Term10 Year
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Screen Shot 2022-01-27 at 7.43.25 PM.png
 
Being above 10kW AC system size impacts your net metering, and from what I can find, it doesn’t look like National Grid has any cap space left (https://app.massaca.org/allocationreport/report.aspx). I don’t know what the sell/but rates are, but that’s probably going to sting.

How well insulated/air sealed is your house/guesthouse? Not as sexy as solar and batteries, but if you haven’t put a whole bunch into doing both, that’s probably where I’d start.
 
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Being above 10kW AC system size impacts your net metering, and from what I can find, it doesn’t look like National Grid has any cap space left (https://app.massaca.org/allocationreport/report.aspx). I don’t know what the sell/but rates are, but that’s probably going to sting.

How well insulated/air sealed is your house/guesthouse? Not as sexy as solar and batteries, but if you haven’t put a whole bunch into doing both, that’s probably where I’d start.
Hi, not sure what that means (looks like national grid doesn't have cap space left).

The house is an old house with plaster walls - i.e no insulation on exterior walls and from all of my research while it would obviously save us money on heating to insulate, old houses need to breathe. the attic floor is insulated at least. The guest house is also insulated fully (and that is heated by propane so not an issue on the electric bill for anything but lights and window a/c in the summer).
 
For the cap, if your system is under 10kW AC you automatically get net metering. If you’re over 10kW, you have to apply for cap space to get net metering. From that list, National Grid doesn’t have any cap space, so I don’t think you’d get net metering and therefore would have different sell/buy rates. While I have powerwalls, because my system is under 10kW AC, I can use the grid as a larger battery by getting basically the same rate selling excess solar during the day and buying from the grid when the sun isn’t shining. If (for example) you could only sell at .10/kWh and still had to buy at .27/kWh, you’d need to send 2.7kWh to the grid from solar for every 1kWh you wanted to pull from the grid later.

I still think your better bet is on insulation. Have you had a Mass Save assessment (https://www.masssave.com/en/saving/energy-assessments/what-is-a-home-energy-assessment)? Getting your energy usage down is probably the better longer term investment.
 
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For the cap, if your system is under 10kW AC you automatically get net metering. If you’re over 10kW, you have to apply for cap space to get net metering. From that list, National Grid doesn’t have any cap space, so I don’t think you’d get net metering and therefore would have different sell/buy rates. While I have powerwalls, because my system is under 10kW AC, I can use the grid as a larger battery by getting basically the same rate selling excess solar during the day and buying from the grid when the sun isn’t shining. If (for example) you could only sell at .10/kWh and still had to buy at .27/kWh, you’d need to send 2.7kWh to the grid from solar for every 1kWh you wanted to pull from the grid later.

I still think your better bet is on insulation. Have you had a Mass Save assessment (https://www.masssave.com/en/saving/energy-assessments/what-is-a-home-energy-assessment)? Getting your energy usage down is probably the better longer term investment.
We had a mass saves assessment done when we bought the house but at the time it was practically gutted so it really meant nothing but still we had to do it for the loan for geothermal and to get the credits for areas like the attic that we did insulate. And as much as I’d like to better insulate it, I’ve been advised by old house experts not to as it can lead to a ton of problems down the road.
 
Ok, makes sense. To your original question, I wouldn’t recommend a solar roof, but that’s more due to the horror stories I’ve read here about Tesla’s customer service. I can understand not wanting panels on the roof of a historical house, do you have space for a ground-mount system? Might be able to offset more than 50% of your usage.
 
And as much as I’d like to better insulate it, I’ve been advised by old house experts not to as it can lead to a ton of problems down the road.
Who told you that?- National Grid? Unless you have moisture problems your best investment would be to gut the house one room at a time, and seal, insulate, and plumb new electric (if possible). Your main problem looks to be heat loss.
 
If you are looking to generate as much kWh as possible to offset your better solution is traditional panels. Makes more financial sense in today’s market.

Being in the northeast, having the panels aimed south and at the right angle is key in the winter months when the sun is low.

Being in the Berkshires, do you have space for pole mount traditional panels someplace on your property? Very popular in VT for the above reasons.
 
If you are looking to generate as much kWh as possible to offset your better solution is traditional panels. Makes more financial sense in today’s market.

Being in the northeast, having the panels aimed south and at the right angle is key in the winter months when the sun is low.

Being in the Berkshires, do you have space for pole mount traditional panels someplace on your property? Very popular in VT for the above reasons.
We really don't have room for pole mount panels that wouldn't be an eyesore in the yard. We looked into traditional panels but based on our roof design they wouldn't actually work as well as we can get more coverage with the tiles than panels so even though they are less efficient, the fact that we can fit more of them on means that we can get more kWh out of the roof than separate panels. At least that's what Tesla says.
 

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