Wednesday, November 25, 2009

Our New Grid-Tied PV System -- First Sun

The new PV system we have been working on putting in is up and running.  There are many pages of detail and a hundred or so pictures that go through the whole planning, design and installation process in mind numbing detail here...
Sections on performance and economics of the system are also included.


The system is a 2150 watt grid-tied system.  It uses the new micro-inverter approach from Enpahse -- so, each PV panel gets its own small grid-tie inverter.

The panels are ground mounted with our own mounting racks. 

We did the whole installation ourselves, and I've tried to include enough detail to be helpful to anyone who wants to install a PV system of their own.  I've tried to cover not only the details of the component installs and wiring, but also the stuff like deciding on what kind of system, locating the panels, doing a solar site survey, and going through the permiting and net metering process.  It should be enough reading to put you to sleep for a week of nights.


It was a technically interesting and fun project -- not having any previous experience with solar electric stuff, I learned a lot. 
But, the economics are also interesting.  Basically, the system cost was right near $10K or $4.65 a watt -- after rebates this gets down to $6.5K and $3 per watt.  Better than what I was expecting.  The $ saving per year if you pay 10cents a KWH would be $300, or about a 5% return on the $6,500 -- tax free and energy price inflation protected.
Not so bad, but when you compare our PV to well thought out conservation/efficiency projects, or to DIY solar heating projects its comes out a very very distant 2nd -- some examples in the Economics section.

I've fallen behind in getting other projects that people have sent in up, but now that the PV is done, I plan to catch up right after Thanksgiving -- so, keep the projects coming in!



  1. Hi Gary,
    Finally had an opportunity to read through the detail on your PV install. Very informative! It will certainly be of great benefit to those that are considering such a system. I got a kick out of some of the day your twisting wire in short sleeves and the next there's almost a foot of snow down. :-O A little cool today here in NS but we've been experiencing mid to low 50s the last few weeks. BTW. I always thought that a clean shop was a sign of a sick mind! ;-)

  2. Hi Rowland,
    Yes -- that is Montana weather -- we had a 22 inch snowfall in October, and I thought maybe the project was done for until the spring, but we ended up getting some good weather after -- just enough to get it finished.
    Had a nice day yesterday and collected 12 KWH.
    Well, if a dirty shop is a sign of a sick mind, my mind must be very healthy :)

  3. Gary,
    12 KWH per day is impressive. To put it in perspective, from the last power bill for my apartment, my average use was 5.82 KWH per day(averaged over the last 14 months). I used a couple of the tactics you recommended like power bars on the TV and computers. I have 2 incandescent bulbs left, one in the oven and the other in the fridge....the rest are CFLs and LEDs (for task lighting). I resist using the air conditioner until it's absolutely necessary...which is 3-4 weeks per year. I'm lucky in that my heat and hot water are supplied.
    For my home, my power usage is close to 3 times what I use here (my living arrangements are a long story...the short of it being I work 250 miles from my home). So, I could really benefit from a PV system like yours.

  4. This is an idea from Carl in an email.
    I put forward the idea in the Economics section of the new PV system writeup that if we could get people to live like off-griders, we could cut household power consumption a lot because people living off grid really value power, and conserve accordingly.
    Carl's idea for getting more of us on-griders to treat power usage with the same respect would be to use these PowerStat meters:
    Basically, you prepay for a known amount of electricity, and when that runs out, the electricity gets automatically shut off at the PowerStat.
    The PowerStat meter also gives quite a bit of feedback on how much power you are using -- I think that people on it would be much more aware of power usage. Especially if their power goes off if they use too much :)
    Not exactly a full solution, but an interesting idea. I guess the trick would be getting people to sign up for such a program -- maybe substantially lower electric rates if you sign up for a low level electricity usage on a PowerStat?

  5. Tha only problem there, would be what do you do with the fridge and freezer?

  6. Nice to see that you've finally taken the plunge into the wonserful world of PV. You always seem to have plenty of sun and I here that PV works best when cold so it's looking good.
    I was just wondering what the advantages are to having inverters on each panel??

  7. Hey John,
    Good to see you here.
    For those who don't know John, he runs the site, is (I think) the founder of the Yahoo Solar Heat group, and the inventor of the MTD collector.
    The claim that Enphase makes for the micro-inverters (and it seems right to me) is that with an inverter on each panel, each panel gets its own MPPT tracking, which can be helpful in partial shading conditions. It also seems to me that its easier to start small and expand -- you can literally start with one PV panel and one micro-inverter -- several places sell this setup. It also seems somewhat easier to wire.
    For me, one big advantage is that if I had used a single larger inverter, the best place to mount it would have been on the outside of the house, next to the meter. This works fine in some climates, but MT winters regularly get below the low spec temperature for the common big inverters. It may be that the inverter would handle this OK, but I got mixed opinions from the experts. The Enphase micro-inverters are rated down to -40F, so OK for our winters outside.
    But, I think either kind of system is fine and they are getting pretty easy to install.

  8. Gary,
    How has your PV system been performing since startup? I've noticed that the Enphase's Enlighten info for your setup hasn't updated recently. Are you monitoring instantaneous generation via a different device?
    Keep up the good work! Your site has some really good, useful information.

  9. Hi Monte,
    The system is fine, but our internet service is not working well for keeping the Enphase server up to date.
    I'm thinking about changing internet service, but we are a ways out of town, and its hard to get something that works well.
    I can still keep track of the system with the EMU unit -- it gives you some stats on the lcd display, and you can also hook up to it with and Ethernet cable and get more info and any error messages the inverters are generating. The nice thing about having the connection to the Enphase server is that they email you when anything appears to be wrong with the system.
    I need to add a note to the "live stats" webpage so people don't think there is something wrong with the system.


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