How to Increase Your NStar Solar Credits by Almost 20%!


Sometimes you have all the facts in front of you and can analyze the pros and cons of a particular venture. And sometimes you just have to go with your gut. Oftentimes it’s the latter that yields the greatest rewards.

Such was my experiment switching to NStar’s Time-Of-Use (TOU) rate from their typical residential R-1 rate. Briefly, TOU charges one rate during peak hours and a second lower rate off-peak. Since my solar panels do most of their generating during peak daylight hours, it seemed to me that I would be getting larger credits at the higher peak rate and pay a lower rate when I did need the electricity during the off-peak night hours.

But there was no data out there for this. Even when I signed up for it, there was only one other Mass. resident with solar panels who was doing the same thing and NStar understandably wouldn’t tell me what their electric bill looked like. The concern was that once you signed up, you had to commit to it for one full year since NStar had to install a special meter to capture not just how much electricity you generated and used but the time as well.

If I found out after the first month that I had made a mistake, I was still stuck with it for the entire year. My original post about my TOU experiment details how it looked like I had made just such an error. However, what I didn’t know then was that NStar hadn’t fully set me up on the new program. At the time of that post, I was still getting my original bill that was taking account of my usage at the different rates, but didn’t include my generation credits. Less than a month later, the original bill was zeroed out and my account was closed. They opened a new account for me and I got a new bill which went into much more detail about my peak vs. off-peak usage and generation.

And instead of saving $91 that month due to my solar panels, that new bill showed that I had saved $125, a huge increase! Here are the numbers after my first full year on the TOU rate:

Period Ending Peak
Aug 22, 2013 -173 233 -$9.94 $26.24 26.4%
Sep 23, 2013 -181 253 -$9.81 $28.04 29.3%
Oct 23, 2013 -129 146 $0.94 $8.44 11.0%
Nov 24, 2013 -11 240 $36.67 $6.84 12.1%
Dec 23, 2013 144 283 $74.26 $1.14 5.8%
Jan 23, 2014 125 313 $79.08 -$1.91 -8.2%
Feb 24, 2014 134 272 $77.70 -$5.68 -25.8%
Mar 25, 2014 -182 169 -$9.99 $14.54 17.7%
Apr 24, 2014 -216 68 -$31.31 $14.12 15.4%
May 26, 2014 -202 114 -$21.93 $14.40 15.2%
Jun 24, 2014 -190 130 -$28.92 $25.90 25.0%
Jul 24, 2014 -207 181 -$29.84 $32.29 28.7%
Overall -1,088 kWh 2,402 kWh $126.91 $164.36 18.7%

These savings are estimates based upon the last rate I had when under R-1, which was 16.1 cents per kWh. This rate has since increased, which only increases your savings above what I have here.

Notice that in August and September of last year that I used significantly more electricity than I generated but I still had a negative bill. This is because the peak rate for June through September is 2.3 times higher than the off-peak rate (it is about 1.8 times higher the rest of the year). So the energy I’m generating during the day is worth 2.3 times the energy I’m using at night. Pretty cool, eh?

And while on the year I still used over 1,300 kW of NStar’s power, I paid less than 10 cents per kWh for it!

As you may have guessed, I would highly recommend switching your rate to TOU if you have NStar. Or, if you haven’t purchased your solar panels yet, you should decrease the size of your array below what your installer has recommended since you can now generated a full 100% of your electricity cost with a smaller sized grid. And NStar won’t mail you a check if your bill is negative so you don’t want to spend extra money on a system that is too big for your usage.


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13 thoughts on “How to Increase Your NStar Solar Credits by Almost 20%!

  1. My understanding from our United solar installation person (May 2014) was that Nstar would not issue a check for excess production, but would allow us to credit somebody else’s bill. Can you confirm this?

  2. That is correct, Jean. Which is why I recommend smaller installations, targetting say 80% of your usage rather than 100%. Don’t forget that your electricity usage in general will *decline* over time as you upgrade your appliances and purchase more energy efficient models.

  3. Pingback: Solar Production - Summer 2013 and Time-Of-Use Experiment | Massachusetts Solar Information Blog

  4. Gary,

    Thanks for posting this info as it looks very promising as a way to increase the return on our solar systems without any increase in costs.
    I have tried to estimate my savings using National Grid rates for Time of Use (R-4) rates ( and get very low savings (<$1 for August for a 10 KW system.) I have also tried to reproduce the number you posted using the NG rates and get unusual results ( high cost per kWh ) To help me resolve this , can you confirm from a recent bill that NG is charging you ( as notes on the above website)
    -Customer Charge $20.87/month
    -Peak Rate $.10985/kwh
    - Off Peak Rate $0.04797/kwh
    or some other set of charges for these items?

    Thanks, Roy

  5. Hey Roy,

    I have NStar but am glad to see that National Grid also has a time of use rate. Here’s a breakdown of NStar’s rates for may latest bill dated August 29, 2014:

    Customer Charge: $9.99/mo
    Distribution Peak: $0.12528/kwh
    Distribution Off-Peak: $0.03895/kwh
    Transition: ($0.00277)
    Transmission Peak: $0.09234/kwh
    Transmission Off-Peak: $0
    Renewable Energy: $0.0005/kwh
    Energy Conservation: $0.0025/kwh
    Basic Service: $0.09379/kwh

    So it looks like you’re not taking the Basic Service item into account. I don’t know why NStar’s transmission rate goes to zero off-peak and National Grid’s doesn’t but you may want to give them a call and inquire.

    I’d love to hear what they say. Good luck!

  6. Hi Gary, Great post, I am very intrigued. I am also on Nstar, and am getting panels installed within the month. I spoke with NStar about this change, and from their information it is a little bit of a cumbersome process in that they have to change account numbers, create manual bills, and not allow for online access. What is your opinion as far as timing of the switch to TOU? I am leaning towards having the system installed, and up and running for a little while, to smooth out the transition, and then switching to the TOU in maybe two-three months after.
    What do you think?

    • Hey Brian,

      It is a cumbersome process on their end, but they’ve got some good people doing the manual billing so I’m sure they could figure it out. It did take a couple months to get me fully switched over and sorted out, but it’s been fine since then. Since they have to switch you to a net meter for your solar panels anyway, I would think they would want to switch you right to a TOU net meter rather than have to come out twice.

      Hope that helps!


  7. Gary, thanks for your informative post. I finally had my panels switched on in December – panels installed in August, btw. I am on R-1 and was under the impression that I would receive a 1 for 1 credit for kWh’s produced (like I did in California) – that’s incorrect of course. Nstar only gives credit for excess power generated – where did that 300 kWh of energy I produced in December go? I am wondering if TOU gives the 1 for 1 credit for production – do you know? I’ve asked Nstar, but since all their customer service reps barely graduated grade school you can’t get a full answer out of them.


    • NStar’s TOU does not give you 1-for-1 credit but it comes closer. Massachusetts takes a net metering approach to solar, where you will use the electricity your panels generate first and then receive a credit for any extra, the net difference. TOU also uses a net meter, but instead of calculating the net difference once per month, it calculates it once per hour. And since your panels generate their electricity during the daylight peak hours when most residents’ usage is reduced, you will get credit for more of your production, and at a higher rate than R-1.

      You will, of course, receive SRECs for all kWhs produced. There is no net SREC metering.

      Also, I have heard from a few people that they have had trouble reaching someone at NStar who was aware that you could combine solar and TOU. If you have any such difficulty, please contact me and I’ll put you in touch with someone that can help you out.


      • So I did some more research regarding power produced & power reduced off my bill. First, I incorrectly used the word “credit” as it has entirely different meaning wrt Nstar/Eversource. The net meter site claims a PV owner with a net meter receives 1 kWh off the bill for 1 kWh produced. I used “credits” to define the power I produced being credited to my overall power usage, thus when talking to Nstar/Eversource they couldn’t answer my questions.
        It gets tricky when one starts to produce more than is used. There is some mathematical equation Nstar/Eversource uses (to their advantage) to come up with “credits” on your bill. I am still befuddled as to why Nstar/Eversource will not reflect customer power production on the monthly bill? It creates doubt that they are correctly applying the power I produced each month to reduce my bill, e.g. this month they claim I used 1000 kWh (598 kWh produced + 404 kWh used), but that seems too high as I have not turned on my heat in 3 weeks.

        The power companies processes of measuring power production and subsequent crediting are very murky. I guess it is a work in process? The more PV arrays installed the more pressure will be put on Eversource/National Grid to better service Net Meter customers.

  8. Pingback: Net Metering and Solar Task Force "Minimum Bill" - Massachusetts Solar Information Blog

  9. WE have thought about this, too. However, Claire and I are aggressively orphaning any dependence upon fossil fuels (oil), and, so, switched to ductless minisplits (air heat pumps) for heating two years ago, and are going to switch to an electric (heat pump) hot water heater where the hot water is presently provided by the oil furnace.

    This affects our load profile, especially in winter, so I’m not sure TOU would be a win for us.

    Hopefully we’ll understand better what our load profile is now that we have solar and are monitoring closely.

    One other thing: The size of system installed also depends upon the environment. Our system is, contrary to your recommendation, a little oversized (though it might not be so with the hot water heater), and that’s because we have a lot of trees, and a relatively high western horizon. The trees are not over the house, but they do shade from one azimuth.

    But I predicted, and it has proved out, that in a sky with thick cirrus or cirrocumulus cloud cover, we capture a lot of light from the sky, with the light thereby getting around the trees. I imagine this may also apply to summer cumulus clouds at a distance. So our generation depends upon surface area, even if, at those times, we don’t approach nameplate capacity.

    We do have efficient panels: SunPower X-Series 345W apiece.

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