GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

10KW PV. 100+% ROI before I turned it on!

thrifttrust | Posted in General Questions on

This isn’t a question but I feel close to the GBA community and wanted to share. I commissioned my 10KW photo voltaic system a week ago. It being fall in Michigan so far I’ve consumed significantly more power than I’ve produced. This condition should persist until Lake Michigan cools around February, but with net metering, next winter I should be golden.  A year ago the utilities applied to end net metering but promised existing installations a ten year grace period. I got my net metering approval in time. My hip roofed house has poor solar potential so I built a 28′ X 14′ 1 1/2 story shed in back. A 10 in 12 roof pitch closely matched the recommended solar angle for my region.  20′ rafters and modest overhangs provided the necessary 20′ X 30′ area for 27 72 cell solar panels. 27 X 370W equals 9990W.


Marten almost convinced me that this was overkill. I scaled back my plan to 24 60 cell panels, but first I had to convince my electricity provider that I can use the power I produced. Eventually the house will get a energy retrofit with mini splits, but for now it’s heated with gas. Hot water was provided by a gas tankless. To boost my consumption I installed a used 30 gal electric water heater in series with the tankless, then turned off the gas unit. This is fine for our two person household but I when guests arrive I can turn the tankless back on for endless hot water. This provided nowhere near enough power increase to justify my proposed solar installation so we bought an off-lease 2015 Chevy Volt. I was surprised that our electric consumption more than doubled. I applied for and won a net metering contract for the 9990W system.


Utilities are notorious for being difficult to deal with, but DET Energy was anything but. Our power line was illegally close to the shed roof so we had it placed underground. I had them leave the last 20′ of the trench unfilled so we could put our solar cables in as well. DTE was responsive and courteous. At $390 I consider it a bargain. The co-generation application process is complex and really geared toward commercial installations. However, they provide a phone number for help. Someone always answered. By the time I was ready to turn the system on I only had a month before I’d lose my contract. In spite of the glut of people trying to beat the net metering and Federal tax credit deadlines they worked assiduously to accommodate their customers. They gave me the go-ahead with weeks to spare. The city was equally responsive. The code was written mostly with single inverter systems in mind so the requirements for microinverter systems are vague. Plus, PV systems are rare here so the inspectors are not fully up to speed. This was also my electrician’s first system. He brought and laid out the code manual to the inspection. It was fun to watch him and the inspector discuss and figure out which and where to put the various warning stickers.


So why was my system free? Two years ago when I first began research I quickly decided I wanted a microinverter system. I liked the shade tolerance and the inherent safety of no of high voltage DC lines, and that the system completely shuts down if grid power is lost. As far as wiring the array, everything is standard 220 VAC. The only additional components are a roof mounted fusebox that combines 3 20A microinverter strings into one 60A circuit and a shutoff switch near the meter. (Some states don’t even require that.) If system monitoring is desired a device is installed that talks to the microinverters individually. It communicates through the power line and a current transformer on one of the array power lines. It connects to the manufacturer through wifi. I installed mine near the electrical load center so it could monitor my total electrical production/consumption via optional current transformers on the main. As far as I know Enphase is the only company in the USA making such a system. I checked them out and was impressed with their products, support and stated company goals. I looked into their stock and it was trading at $1 a share. I bought a thousand. In spite of a big drop recently I’ve still made enough to more than cover the cost of my system. My next goal: buy a used Tesla Model Y and pay for it with my Tesla stock 😉

Douglas Higden

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    BILL WICHERS | | #1

    The volts will use about 12kWh to fully recharge their battery, and you may be adding that much every day if you drive a lot. It adds up! I’ve had a 2012 model since the end of 2011. The newer volts with more battery range probably use More kwh for a full recharge due to having more range.

    You’re in an interesting situation if net metering ends. You could potentially play with using multiple electric water heaters as a battery, heating that water with your excess solar capacity during the day and helping to heat your house at night. Might be something to think about.

    For anyone else: the end of net metering doesn’t mean solar systems aren’t possible, it’s just that the payoff schedule becomes more difficult. You end up needing to either downsize your system to near your daytime load, or do creative things to store any excess power. The end of net metering just means your home can’t get into negative load territory where you produce more power than you consume. You can still use solar systems to “cancel out” your daytime load.


    1. Reid Baldwin | | #7

      The end of net metering doesn't even mean that you cannot send power back to the utility some of the time. The replacement for net metering in Michigan is an inflow/outflow billing setup. Inflow is billed at the normal rate. Outflow is credited at a lower rate. Both rates are set in a rate case with the public utility commission. The payback period is longer under this system than with net metering, but hopefully by so much that continued cost reductions can't keep pace. There is a proposal in the legislature to put net metering back in place, but I would never advise anyone to make decisions based on legislation that is merely proposed as opposed to passed.

      1. Expert Member
        BILL WICHERS | | #8

        That’s interesting, and I hadn’t heard about it. This might even be a more fair system since the net metering system really was (is) an issue for the utilities. I’d like to see a “time of day” type of rate for the power-to-the-grid direction too, where solar could be used as a peak load supply (since peak grid load and peak solar output tend to be close together in time), which would pay a higher rate for on-peak power than for off-peak power when excess capacity isn’t as valuable.


  2. thrifttrust | | #2

    I imagine most cars average fewer miles per day than the all electric range of the Volt. As such they use as much electricity as a pure EV. This gets me to thinking. Consumers seem to demand EV ranges north of 200 miles, but if they actually go less than 50 miles per day there would be a huge margin for utilities to use cars for grid storage once vehicle to grid technology matures. I can imagine a day when you buy a car but lease the battery from an energy provider, for free. When they degrade they replace it and use the used battery for dedicated grid storage.

    The demise of the Volt is a shame, not only because we are losing a great car, but soon there will be no vehicles assembled in the city of Detroit. The Detroit/Hamtramck Assembly Plant was built in the 80s to much fanfare and controversy. Within walking distance of the then and current GM world headquarters, it was to be a flagship plant, building GM's first front wheel drive midsize cars "done right". The controversy was that to build it they demolished Poletown, one of the few viable neighborhoods in Detroit. With the demise of the Volt, Impala and Cadillac CT6 the plant was to be shut down next year, but really the shutdown was a bargaining chip for the UAW contract negotiations. They've now announced that they will be building an electric truck there.

    In a decade when my net metering ends I hope the Enphase plug and play "AC" battery will have come down in price, allowing me to save daytime solar power for use at night. Enphase is also introducing a system that can be retrofitted to my microinverters that can provide power when the grid is down. I suspect this will be popular in California with their strategic blackout issues. It could also allow one to go off-grid. When there is not enough solar power you could charge your car remotely to power your house. Heck, with an autonomous EV your car could go get charged by itself.

    1. Expert Member
      BILL WICHERS | | #3

      The original volt had a rated range of 32-35 miles, but usually could do a little better than that. The typical driver, per insurance industry info, averages 12,000 miles per year. That’s why typical car leases are for “12,000 miles per year”. If you divide 12,000 miles/year by 365 days/year, you get an average of about 32.9 miles per day. The designers of the volt didn’t arrive at those design daily range numbers by accident :-)

      The reason for the big range numbers people want to see is that people are used to going around 250ish miles per tank of gas so they all think they “need” that much range. They don’t realize that the typical daily commute is something less than 40-50 miles or so, and if you can “refuel” at home in your garage every night, going to the gas station too much becomes a non-issue. Some people are worried about occasional road trips, but even with a limited range EV you could always rent a car for that occasionally trip.

      I’m not a big fan of in-home batteries for “grid storage”. There are better ways to do it, and it makes more sense to do storage in large-scale facilities. The economics of the little home batteries isn’t generally very good. Using an electric car’s excess battery capacity is an interesting idea, but would eat into the cycle life of current battery technologies so there is a downside.


  3. thrifttrust | | #4

    Funny thing, Our off-lease Volt came with dealer follow up service. It went in with 42 mile range and came out with 44. There must have been a software update that freed up some reserved battery power.

    I think batteries will be an essential part of most residential solar installations. Many people will get batteries without solar. Net metering doesn't make sense. There is little upside and a lot of downside for the energy provider. It was a useful incentive to grow the solar market but now the industry should stand on its own. Similarly, Fixed price electricity's time has passed. In a given day, providers pay wildly different prices based on immediate supply and demand. the irregularity of renewables, and in the future, the heavy demand from EVs exacerbate the problem. Time of use pricing is starting and eventually will be universal, and that's a good thing. It makes the consumer more aware of their energy use. They will run their dish washers, laundry equipment and charge their cars when power is cheap, AND they will use batteries when power is dear. Companies like Tesla and Enphase will make simple automated systems. When needed, they will charge their batteries and turn on car chargers when prices are low. This will even out overall demand making it easier for providers to manage the grid and reduce reliance on expensive peaker plants.

    1. Expert Member
      BILL WICHERS | | #6

      >”Similarly, Fixed price electricity's time has passed. In a given day, providers pay wildly different prices based on immediate supply and demand. the irregularity of renewables, and in the future, the heavy demand from EVs exacerbate the problem. ”

      That’s not exactly true. Most supply pricing is handled by long term contracts for what is known as “base load”. That is the bulk of the supply, and tends to be pretty stable over time since many contracts are for periods of at least a year. Peak time can be expensive, but it’s only part of the supply that is subject to that, basically whatever amount is over the contract amount, which is usually a pretty small percentage of the total.

      I agree that time of day rates are a good thing, and I’m on such a rate at my own house by choice. I save a good amount of money with that rate and have my volt setup to charge during off peak times. I also have my thermostats setup to take advantage of the much lower off peak rate. I don’t think batteries are a good way to do energy storage on grid scales though, pumped storage is better especially in terms of maintenance needs. There was another poster on here several months ago that posted a link to a very different type of battery that shows some promise, but that technology isn’t widely used yet.


  4. walta100 | | #5

    “I looked into their stock and it was trading at $1 a share. I bought a thousand. In spite of a big drop recently I’ve still made enough to more than cover the cost of my system.”

    You did not say what price you sold the stock at. You do not have a profit until you sell the stock. It sounds like you have a paper profit that could change tomorrow.


  5. thrifttrust | | #9

    Yes Walter, that's the way the stock market works. I'm definitely a hobby investor. I bought my first stock at the depth of the financial crisis. I didn't believe they'd let GM go bankrupt. They did. However, since the Obama administration did a brilliant restructuring job, I consider my loss money well spent, but I can be sanguine, I also took a position in Ford which more than cushioned the blow. It's difficult to pick stocks. It takes a full time commitment to do it well scientifically. I came to a philosophy of investing in companies that I admire. It's worked. Two years back I sold everything but Tesla to help buy my forever home. Then I got Enphase. I have no intention of selling either. I really admire these companies.

    In the 70s, on the drive to our favorite camping spot the west Michigan coast, we'd pass a nearly 3 mile long earthen berm that I assumed was a really big landfill. Turns out it was the world's largest pumped storage facility, but Michigan is still building gas peaker plants. In spite of there being many places where bluffs tower hundreds of feet above Lake Michigan. The difficulties of securing real estate and clearing regulatory hurdles makes it unlikely that Michigan will build any similar pumped storage projects. It can take a decade to get a pumped storage facility built. Tesla can install a battery system in weeks, anywhere.

    There are so many proposed energy storage technologies, flow batteries, flywheels. molten metal batteries, dragging weights up inclined rails and many more. I hold great promised for Aquion salt water batteries, but after failing to gain traction they filed for bankruptcy and were sold to a Chinese holding company. Maybe It's just the force of Elon Musk's personality, but it seems only lithium ion batteries are making real inroads. Seeing that feeding our Volt tripled our electricity consumption puts into perspective how much energy transportation demands. I have to believe that EV batteries will play an important role in grid storage.

  6. thrifttrust | | #10

    We've reached a milestone. Our solar system has been live for 6 months and we've finally produced more power than we have consumed. It's been a cloudy winter. (Probably normal but seems excessive when you check your solar stats each day.) We're now banking power with our ten year guaranteed net metering. (Having our Volt parked in the drive for the past two months has helped.) Our last two electric bills have been $8.75, the minimum hook up fee.

    I looked at our little stock portfolio today for the first time in many weeks I was delighted to find that Enphase and Tesla have recovered to nearly their all time highs, just before the shutdown. Now the profits from our Tesla stock could more than cover the the price of our solar and we could buy a Tesla with the increased value of our Enphase.

    1. STEPHEN SHEEHY | | #11

      I wonder what Musk's recent Trump like rant about having to abide by shutdown rules will do to Tesla stock. He sure blew a lot of goodwill.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |