Originally posted on MassSolarInfo.com. Reprinted with permission. (Thanks, Gary!)

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 EndingPeak
Aug 22, 2013-173233-$9.94$26.2426.4%
Sep 23, 2013-181253-$9.81$28.0429.3%
Oct 23, 2013-129146$0.94$8.4411.0%
Nov 24, 2013-11240$36.67$6.8412.1%
Dec 23, 2013144283$74.26$1.145.8%
Jan 23, 2014125313$79.08-$1.91-8.2%
Feb 24, 2014134272$77.70-$5.68-25.8%
Mar 25, 2014-182169-$9.99$14.5417.7%
Apr 24, 2014-21668-$31.31$14.1215.4%
May 26, 2014-202114-$21.93$14.4015.2%
Jun 24, 2014-190130-$28.92$25.9025.0%
Jul 24, 2014-207181-$29.84$32.2928.7%
Overall-1,088 kWh2,402 kWh$126.91$164.3618.7%


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.