The Biggest Mistake People Make When Going Solar


One of the free services I offer is taking a look at people’s solar estimates to give them an unbiased and informed opinion. And, surprisingly, almost all of them make the same glaring mistake that costs them thousands of dollars.What is it?

There was a time when the biggest mistake people made was not getting micro-inverters. But with the release of power optimizers that optimize each panel’s output with a single inverter, this has become less and less of an issue.

The most common mistake I see people making is getting a system that is larger than they need. And if you think of the reason why, it becomes obvious: the solar panel installers are the ones making the estimates and the larger the system, the larger their profits.

With incentives as high as they are, they can still justify maximizing your electrical output because your breakeven point only shifts by months or a couple years. And once you’ve mentally committed to a 6-year breakeven, an 8-year breakeven doesn’t sound significantly worse.

But you’re still looking at paying thousands more than you need to and those thousands can mean the difference between getting solar panels or not.

So how large a system should you get? If you ask the solar installers, they’d recommend a system that offsets a full 100% of your electricity. However, I would recommend a system significantly smaller than that, depending on who your electric utility is, or was.

First off, I don’t believe any of the utilities will pay you if your electric bill for the year is negative. You are allowed to keep the credits in your account or even donate them to another account, but they will not cut you a check. But please don’t take my word for it – you should contact your utility to confirm. I only know that this is the case for people who formerly had NStar and National Grid.

If you formerly had NStar, then you are eligible for the Time-Of-Use rate and should opt for a system that is between 70-75% of your annual usage. The additional 20% you’ll save from switching to the TOU rate will allow you to offset around 84-90% of your electric bill.

If you don’t have NStar and cannot take advantage of a TOU rate, then you should size your system to offset between 85-90% of your electric bill.

So why not go to 100%? Easy. Because as household appliances continue to increase in energy efficiency, you will use less and less electricity each year. So while you may not exceed 100% of your usage this year, it becomes a very real possibility 5-10 years from now, even as electric cars become more and more practical.

These are things most solar installers will not tell you, as they’re trying to get you to purchase the system that’s right for them, not the system that’s right for you.


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4 thoughts on “The Biggest Mistake People Make When Going Solar

  1. Gary,

    I’m not sure I would agree completely on under sizing. I would agree that appliances over time are getting more efficient and this also includes heating with electricity. Specifically, the new ultra efficient mini split heat pump heaters/air conditioners and electric automobiles. Now that I may have caught your interest, I’ll recap my experience thus far and my thoughts going forward.

    I started looking at solar in early Spring 2012. At the time my electric use was a little over 1000kwh per month. The solar providers were giving me 2 quotes from the ~7.2kw system to a 9-10kw system using the newest&most expensive panels. Thinking about getting a system at the lowest possible kilowatt hour per dollar I went with the 7.2kw. It was supposed to cover 63% of my usage, but I was also being told by people that my consumption was way too high so I started looking at my appliances; 2 frigerators, old dehumidifier, old water cooler, etc. By the time I was done replacing or eliminating some of these appliances, my consumption was down to 250-500kwh per month. Because of this I was consistantly having a surplus. I moved my hot water production from my oil boiler to an electric high efficiency unit… Still a surplus.

    So then my mindset changed, I started to think what energy was I paying for that I could move to free electricity (free once breakeven is hit, Oct2015) heating was still on oil. And while I usually use a woodstove for most of the winter, I still had to run the boiler when it was really cold to ensure the heating pipes did not freeze and burst. But I think this winter will be the last of time. This past winter I really didn’t use the woodstove I used small space heaters as an experiment to see if they could keep up with heating the house and while they did better than expected, their BTU output is” low. The mini split heat pump heater / AC units should produce the BTUs required at 3-4 times the efficiency.

    So you may be asking what does this really have to do with solar array sizing… My reply would be because I was over producing and my NSTAR account balance grew to almost $1,500 it motivated me to find additional improvement’s to use the surplus and further reduce my total energy costs. And oddly enough, the mini split system will cost less than replacing the 30 year old plate steel boiler that is what is this life expectancy.

    So with that in mind, I would say you can always use the surplus electricity somewhere else and if your happy with your heating system there’s always an electric car. I’m not sure today’s solar electricity incentives will be here too much longer so you might as well get solar now. I regret not getting the 9-10 kW system. I’m sure I would find a use for the energy in the future. Jb

      • Thanks Gary and John!

        I too have been sizing for a couple of years. Have even looked at a wholesale solar company out in CA for the best deal on panels and inverters.
        I’ve looked at cost/benefit of over sizing and switching to electric heat( I currently have oil) I also intend on purchasing an electric car..and hopefully, battery back up. I don’t want to go offgrid, but I’d rather do that keep paying for fossil fuel.
        This is a great site..I have it bookmarked.

        Thanks again,

        • Hey Daniel!

          Thanx for contributing to the discussion. My only warning is to make sure you use don’t invalidate your eligibility for SRECs by not following the guidelines. I believe you need to use Mass.-approved contractors to install your panels and I’m not sure if batteries are allowed. SRECs are still your biggest incentive and you wouldn’t want to lose them by trying to save a few bucks.

          And I assume you’ve already taken advantage of all the savings the MassSave program has to offer? It’s subsidized by the electric companies but reduced my oil consumption significantly at little cost to me.


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