Grid-tied Size Advice (MA)

[Himeji]

Summary:
I'm trying to decide to either get 10 panels or 20 panels for a net metering solar install in MA. 20 panels is the max my roof can fit. The difference is roughly $10k in price. 10 (400w QCell w/Enphase microinverters) panels will provide %135 of my current electrical needs. 20 panels will be well over double what I currently need. My initial goal was to have no gas or electric bills. Even with 20 panels I don't think that's possible so is it even worth it?

The Details:
I live in MA, which has 1:1 net metering. Last year I used 3,700kw of electricity for a 2,100sft house. My roof is pointed south with no obstructions. The house uses gas for heat, water, oven, range, dryer.

My gas furnace is old and I thought I would switch to ground source heat pump since it should be more efficient than air source heat pumps. I've had various companies inform me that the electrical usage of a ground source heat pump for my house would range from 3,000kw to 6,000kw per year.

My electrical use would then range from 6,700kw to 9,700kw. 20 panels are estimated to annually produce roughly 9,680kw, which might be enough to offset the electricity bill. That's just switching heating from gas to electric. If I switch all the other gas appliances I'm not so sure I'll be able to be bill free. Gas is relatively cheap in MA where as electricity is on the higher end in the US at around $0.24/Kw.

If I forego the ground source heat pump I really don't need 20 panels. I thought I'd then get 14 panels to have a bit more head room. If I needed more for expansion then I could get 6 more panels added then. The installer though says that at a minimum they need to install 8 to 10 panels for it to be worth their time the second time around. Most likely that will be 10 panels as time passes. That then gets me to using either 10 or 20 panels.

10 panels will meet my current needs. If I go with a gas furnace in the future I don't foresee a major increase in electrical use. I would like an EV but I don't see it happening anytime in the next 5 years. After 10 years the panels degrade to 90% production. I should still be over producing and meet 120% of my current needs. The ROI is around 8 years factoring in electricity price increases.

20 panels though would allow me to take advantage of the 26% tax incentive this year as well as being cheaper to install doing it all at once. The ROI though would be close to 17 years. Over production will keep building credit on my account with NationGrid. From what I've heard, in MA those credits never expire so I could build up credits for years if I don't use them. I think I'm able to cash out the credits, but it would be at the wholesale rate, which is probably a few pennies per kw, instead of the retail rate.

The cost difference is $10k. That $10 either goes into solar panels with a long ROI or I could invest that in the market. I'm pretty sure the market will have better returns after 17 years.

My heart wants to do 20 panels, but I'm having a difficult time justifying it. Most likely I will get 10 panels but it will bug me that if I ever expand it's going to be a headache and be overall more expensive. If I go with 20 panels is there any way to use the extra production that can shorten my ROI? I looked into mining but my extra production would only be a drop in the bucket with what mining requires.

 

[BentleyJ]

Based on your detailed examination posted above, I would have to go with the lower number of panels. Simply max out ONE 20A breaker for your Enphase system. I believe that's going to be 13 or 14 panels.
One consideration you didn't mention or is not yet an issue in your state relates to NET metering charges for excess production. In Ca they now have a $10 per month minimum meter charge for every month that you have excess production. The excess production does still get credited on a 1:1 basis so it can be used later for AC or any heavy demand months but basically we are paying $10/mo. for the privilege of using SCE as a battery. If we finish the year with excess production we get 3 cents per KW hour, its a joke.
IMHO, there is no reason to give the utility company FREE electricity. Just size your system for what you need. If they get nasty like in Ca and try to go with Time-of-Use rates then you can add batteries and do peak load shave and self consumption.
Lastly, KEEP your gas appliances especially for heating your home and water, its the most cost effective at least for now.

 

[Shinebox]

I live in MA too… I would go with the maximum you can fit in your roof. First off, you want to have the option to install a heat pump, ground or air sourced. The other angle here that your missing is that you WILL be driving an EV sooner rather than later. All new cars sold in MA will be EVs by 2030. That’s no time at all. As you point out, rates are already sky high in MA (for Dec-March I averaged about $1200/month). Rates will only go up as they do in general, but also as grid demand increases with EV adoption. Widespread adoption will roughly double the current demand on the grid, and this is going to lead to equipment failure as the utilities as a rule are never proactive in making necessary upgrades. They will always wait for things like transformers to blow up and then decide to act. This will lead to further rate hikes beyond the normal steady increases.

 

[onokai]

For me I would go big and think about mini splits for heat and cooling-I have two mini spits and they are extremely efficient heating and cooling with low amp draw. I know of no one who has to much power-the always get more stuff that uses power -like an electric car and mini splits or hot tub.

 

[Shinebox]

I guess it depends on the construction of your house. My house is fairly old and reasonably well insulated, but it could be a lot more efficient, and I plan on making it so. The old oil furnace that came with the house was 50 years old and on the way out, so knowing I was going to go with a mini split for a number of reasons I did so before weatherizing my envelope to modern standards. That said, in the coldest months, my system is by far the largest draw on energy. It can easily pull 8-10000 watts during the evening. I’ve seen 25kw draw with the car charging on a cold night. While my bill is high before my array gets fully installed later this month, I’m still ahead of what I would have paid for heating oil and vehicle fuel during the same period.