First post for me. Long time reader.

I'm in south west Massachusetts.

I just bought a new two-story home. 9ft ceilings. With garage, it is about 2,600 sq ft plus 2,000 square feet of garage space (one is a 3-car carriage house). I'm including the garage space because I wrench and build stuff year-round...it's important to me.

Property is 6 acres, and has 350' of southern-facing property line, unobstructed sunlight. Flat ground facing the sun on the edge of a farm field! Solar panels wouldn't be visible from the home. Blazing rays!

Would it make sense to convert this home, or add ancillary heating via electric heat with this potential?

I've never done solar, never thought I would be asking this, either. The future is coming whether we like it or not....

Is there a calculator, or algorithm to find feasibility for this type of thought?

What would the knowledgeable guys say?

Thanks in advance.

  • Compare (without assuming adding solar production) the cost of running cold-climate mini-splits (I'm an entire state North of you and they work fine well below 0 °F - not your old-skool heat pumps that crap out at 35 °F) to buying oil. Those are THE way to do "electric heat" since they are 250-400% efficient (COP - you supply power to move heat) rather then the mere 100% of resistance heat (you supply power to make heat.) Then look into solar production...
    – Ecnerwal
    May 14 at 19:39
  • Ecnerwal. Thanks for the response. I am unfamiliar with how that type of system would work....... Ideally, I want no energy bill at all, if it is possible.
    – Derek14
    May 14 at 19:45
  • 1
    I have installed a few systems the ones that were large enough to supply a 1500 sf home were in the 15-20kw range I know the pay back would have never been there unless government required payback at a higher rate on the power sold during the day and the gov kickbacks on the systems they did have an advantage at first but cells age and don’t produce as well then new cells. power will have to get way more expensive for solar to pencil out and you still need the utility at night or huge battery banks and way more maintenance requirements.
    – Ed Beal
    May 14 at 20:01
  • 2
    @EdBeal It's not only about money. And even if it was about money, it's foolish to assume today's fuel prices will be frozen forever. If it's 1952 would you really want to buy brand new steam locomotives? May 14 at 21:12
  • 1
    @harper, I am sure all the systems you have installed are still running, it is also foolish to be ignorant of the materials used the amount of material that are still not recycled and the maintenance required, larger systems increase the maintenance and and utility interaction. The largest system I installed was split and moved to another property for this reason. Also most folks don’t realize the power roll off with system age and I live in one of the least damaging areas when it comes to system life. Even those that have stated it was “for the environment” had many more reservations later.
    – Ed Beal
    May 15 at 1:10

OK, here's what you DON'T do. "straight substitution". Going "oh hey I don't like change so I'll just use all technology exactly as I'm accustomed to, except change this one thing and expect all that to work like magic".

In fact, we see anti-solar people take that attitude on purpose, to show how the new tech can't possibly work.

So you wouldn't just bolt-up solar to "old tech" electric resistance toaster heating. 20 years ago someone said to me "using solar to run a resistance heater isn't even stupid". Of course solar is much more efficient and cheap today, so maybe... but yeah lol... no.

NOT energy storage

One problem is that the solar doesn't run 24x7. To "time-shift" energy to when you need it, you need a storage method.

The prevalent storage method in use today is to sell your power to the electric company when the solar is running, then buy power back for your evening needs. Of course, that depends on the grid being up, doesn't it?

Here's the thing. At this point, solar is just a "bolt-on". In fact, really, "selling power to the PoCo from your solar" is really a separate transaction from "buying power from the PoCo for household use". (except they may punish you on rates if you generate more power than you use, since rates like "net metering" are more of a courtesy).

So you don't really need to optimize anything else. If you have inefficient appliances, you don't need to care.

So you can separate it more. For instance, those panels would work much better in the Mojave Desert due to more solar hours... and electricity is worth more there. So yeah. You could actually stick the panels there, sell the power to PG&E, and use the dollars to buy power from Mass Electric.

Energy storage (grid-down capability)

The other storage option is, y'know, actual storage. The advantage here is it can stay up even with the grid down. Since most people don't have the facilities for pumped storage, "batteries" are usually it. That costs about $200 per kilowatt hour, using used Tesla Model S batteries, and that will usually end up costing more than the solar panels.

When trying to make a house work on batteries, i.e. being grid-down-impervious, the #1 goal is to reduce energy usage. It's much cheaper to invest in efficient appliances than to invest in additional battery and solar needed to sustain inefficient ones.

Now we get out the sharp pencil and start crunching on efficiency tech.

Empowering tech: Heat pump

Where electric really excels for heating is the use of heat pumps. They take 1 unit of energy to pump 4-5 units. So they're just stupidly efficient.

You can see where that's a nice multiplier with solar heat.

Now, they do have a problem running in the very cold. Older ones just shut off, but newer ones at least can "do a defrost cycle" and keep running at all temps (at much reduced efficiency). You can end up in "coffin corner" as the aviation people call it: as air temperature drops, you need more heat, but you have less available due to lowering efficiency interchanging with -20F air.

So don't. Interchange with deep ground water that is 50-60F. This "ground sourced" heat pump is quite efficient and stays that way in the bitterest cold, because it doesn't feel the cold.

Empowering tech: Passive solar

This, unfortunately, requires a house built from the ground up for that. However a great deal of HVAC load can be removed altogether by designing the house to catch full effect from the winter sun, and have a great deal of thermal "energy storage" built into its bones. So now the bulk of your heating comes from solar gain, and you only need the heat pump for small adjustments.

There are many more, but that's just a few.

  • 1
    As commented, I'm at the southwest end of the state north of the state the OP is at the southwest end of (so, one state north, which is what I actually said) and air-source heat pumps work just fine here; the overall win is large enough that the defrost is not putting you in negative territory at temperatures we normally see. Ground source is better if you have the deep pockets for it, but it takes deep pockets to play there.
    – Ecnerwal
    May 15 at 0:39
  • @Ecnerwal I didn't say they didn't work. I said that the colder your heat source, the worse your efficiency (COP). I'm sure your system works just fine at a COP of 1.4, but if you had a ground source you'd be back up at COP 3-4 where you expect to be. May 15 at 1:49
  • Passive solar design can be applied to existing buildings... in fact passive solar was understood thousands of years ago - why were the south facing caves occupied in the north hemisphere...
    – Solar Mike
    May 15 at 6:01

I would suggest approaching this as two parts.

First, is converting from oil to electric heat. Here, you'll want a heat pump as opposed to resistance heat. I suggest leaving the existing oil furnace in place, in order to need a smaller heat pump system and having a backup for cold weather. This doesn't even need to cover the entire house. (Also consider the benefit of getting A/C during the summer.)

Next, is putting solar panels in for a direct reduction to your electric bill. You'll want to look up if you can get a negative power bill or not; this varies from place to place. (Also consider the benefit of retaining power if the grid connection goes down, depending on your location.)

Both of these can be treated as an investment. An X upfront cost results in Y savings per year, which is Z% "interest". Calculate out both of these individually, then do them if you like the interest rate. Even if you want to be energy conscious, just because you have space for solar doesn't mean that this is the best place to put solar panels. Your highest energy usage will be during the winter, when the solar panels will be at their worst, and at night, when your solar panels won't be doing anything.

I would also highly suggest getting an energy audit done. Many power companies will offer a free version to residential customers, and these people are able to look at your property in person, suggest things you might not have thought of, and will have knowledge of the specific tax incentives and the like available to you.

  • Energy Audit. I have a guy looking at the property via online map. Good suggestions! Thanks!
    – Derek14
    May 14 at 22:49

Use solar thermal panels to heat water directly - no need to use pv panels to run heaters.

For dhw you need roughly 1m^2 of solar collector per person. Then, depending on how many people the tank needs to be sized accordingly so for 4 people the minimum tank size needs to be 200 litres.

As for heating the solar thermal panels can heat a water tank and then run water underfloor heating from that - as it only needs 20 to 30 deg C it matches the tank temperatures well. But there is a three way valve to control the water temperature into the underfloor heating pipes.

The system we put in for a 4 bed house (but super insulated, triple glazed and passive solar designed) has 8m^2 of panels and a woodstove for 3 weeks of the year. It also has 2.7kW peak of pv panels to offset the electricity use.



  • A) Each solar panel should tell you how much energy it can produce
  • B) An electric furnace should tell you how much energy it consumes
  • Make sure A is more than B
  • Calculate how many batteries you would need to power your heat source overnight
    • Note that 100% of energy does not get transferred into a battery so you'll have to upsize your panels
  • Realize that batteries are astronomically expensive
    • Cry a little if you so choose
  • Ditch the battery idea
  • Over-invest in panels to power your heat source during the day and sell back excess energy to the grid during the day
  • During the night just use energy from the grid
  • The second to bottom suggestion of your was my primary thought. I'm a business guy. This one makes most sense to me. Your response I appreciate, Sir!
    – Derek14
    May 14 at 22:51
  • Most schemes you can sell / buy power all year for your net balance. Much harder to manage daily in the short cold winter days, but most allow an annual balancing (and no payment for any excess generated over the year.)
    – Ecnerwal
    May 15 at 0:43

I have a solar array installed at my home that uses 50 PV panels and a single 15KW single-phase grid-tied inverter. It was installed in September 2018. There is no gas available in my area so my home was already 100% electric. I'm in the Indianapolis, IN area which is somewhat south of your location in MA.

Several factors to consider:

  1. What is the initial cost of the system? In my case the total came to approx. $30,000 which I had available so I paid cash for the system vs. financing the purchase. I also did all the site prep work, racking assembly, and PV panel installation myself. I worked with a local electrical company that has a track record of PV installations to do the wiring of the panels, installation of the inverter, and wiring into the home.

  2. What is your annual energy usage and how much of that do you want to replace? In my case that was easy since my electric bills for the preceding 12 months show that I used 70KWH daily on average. So the system was sized (the electrical company performed the calculations) to provide 70KWH on average. So far it has been pretty close to that so the calculations appear to have been good. In your case you have oil heat and so if you want to heat using solar, you will need to also factor in changing from oil to electric heat.

  3. What government incentives are available? In my case the federal 30% tax credit was still in effect and so $9000 of my expense ended up being rebated in 2019 when I filed my taxes. In my calculations of payback period, the installation would make no sense without this since the payback period exceeded the lifetime of the equipment. With the tax credit, however, the calculated payback period was about 6 years.

  4. What about net metering? In my location net metering was required by law and grandfathered in for 15 years. The energy utility (Duke) lobbied the Indiana Legislature and got them to phase out net metering. So today the installation might not make sense. Net metering is a BIG DEAL for all grid-tied alternate energy installations. What that means is that they pay the same price for the power as they charge me. So Duke acts like a huge "battery" and I don't have to store anything on-site. In many places today the utility pays wholesale and charges retail so you will be losing money for every KWH that goes off-site. But battery systems are quite expensive and may make the installation not worth the money.

  5. Equipment warranty and expected lifetimes. In my case the PV panels and the inverter are expected to last 20-25 years. While this is, of course, a statistics game, the warranty on the equipment is long enough to protect me through the payback period.

  6. Even though I'm an electrical engineer, I would never have been able to pull this off without the assistance and experience of the local electrical company. They sized and designed the system, ordered the equipment, pulled the permits, and installed all the electrical components and wiring. The total I paid them for service amounted to about $5000 and it was money well spent. They were very helpful at all points including working with Duke to get the system approved (by Duke) before it could be connected to the grid.

The system has been on since 09/2018 and I have not paid anything but the minimum billing ($11.44) to Duke since 12/2018. Right now there is a "surplus" of about 6000 KHW on my meter. Duke doesn't refund surplus energy until it reaches some threshold which I believe is 100,000KWH. So it just shows as a negative KWH figure on my bill each month.

Key decision factors:

  1. How much energy, on average, do you want to produce from your installation?
  2. How much is that energy worth in your location?
  3. How much will the utility pay for excess energy that goes onto their grid?
  4. How much in the way of incentives will offset part of the cost?
  5. How much money do I have available to fund this? Financing will change the break-even point!
  6. What is the lifetime and warranty of the equipment?
  7. How sure am I that the location will remain unobstructed over the next 15-20 years? (i.e. do YOU control the site or does someone else? In my case the array is located on the north edge of my property so I own the property south, east, and west of it.)

I recommend you find a local company who has an established track record of these types of installations and who is willing to work with you to get a system installed that meets your needs. Those "solar today for no money down" outfits are generally scam artists.

Good luck! My system was an interesting journey and a lot of work but it's been working flawlessly for going on 3 years. Since energy rates have been going up here every year, that has the effect of shortening the payback period. I also like having a $11.44 electric bill vs. the $300-$400 bill I used to receive.

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