small grid tie inverter questions

Hello all, new guy here. My background - I’ve been using solar in sailboats for years (and an analog EE).

First and related to the question I have.. I live in Denver CO and have a house that does not have air conditioning so have moderate electrical needs. Our big energy expense is heating and the house I live in was not designed with passive solar in mind but this place has a great location on the S. side for solar. Last year, my neighbor had there roof re-done and tore off a nearly 30 YO air heating system and I got one of the air heating panels and put together this system

I used it all last winter, I never went back and looked at power company bills to see what it saved but it definitely makes the house more comfortable during the day when the setback thermostat would normally drop the house temp.

Anyhow... this may get me in trouble right off the bat.. but I have two applications where I am thinking about installing a 220V AC socket on the house AC distribution. I would then go and buy maybe 200 to 400 watts of solar panel and what ever micro grid tie inverters to pair with the panels (from someone like the sponsors of this web site) and just plug the output of micro grid tie inverters into the 220 VAC socket. These would of course have the "island" protection. But I would NOT get the power company involved in this since I’m guessing that this dramatically complicates things (possibly new meter, etc). Remember, I am only talking about a very small maybe 250 watt system.

In one application, it would be similar to the system in the link above (this has an 80 watt panel and a micro grid tie inverter simply plugged into the house 110 AC socket). In this case, the meter never even comes close to running backwards.

The second application (different house that is seasonally used) would likely have the meter run backwards (meter is likely original - installed about 1990)...

What about the legal or sensible issues of doing this DIY? Seems with folks selling this stuff and making it easy to buy, this type of install is going to happen.


  • mike95490mike95490 Solar Expert Posts: 9,581 ✭✭✭✭✭
    Re: small grid tie inverter questions

    bootleg, plug-in grid tie installs are done all the time. But you won't find the plug-in panel kits at wind-sun, as they are not legal to install on a insured structure. They have no UL certification and will void your house insurance. Most of them are also poorly made and wont produce their nameplate power.

    Meters, some older ones will run backwards, some have a 1 way ratchet and won't. And if the electric company senses a 10% reduction, or even total backfeeding, will chop your power off in a second, if they discover a bootleg install.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    Re: small grid tie inverter questions

    There are two major issues with doing it "right"...

    One is the building permit... In most areas, it is something like $500-$1,000 maximum, and in many rural areas, there is no permit required. If you have a smaller system (less than ~3.5 kWatt array) and a relatively modern main panel (say 125 amp service minimum)--You can usually add a solar power system using the existing main panel. If you need to replace the main panel, it may cost you $2-$4,000 for the panel upgrade itself

    Second is the power company... As Mike says, the "meter issue" is one (there are a wide mix of utility meters out there--Older ones may do exactly what you want--slow down and even turn backwards at times). And there are other meters (typically newer meters) that will not turn backwards or may even "turn forward" if you back feed power (some people were turning their meters upside down in the socket for 1-2 weeks a month to steal power). A few new digital meters may even "phone home" and report you that you have GT solar on your home (if they can detect it).

    In California, the utility has the right to pull the meter and the local building department will "red tag" the home.

    In any case--If you are thinking about solar power--Look at conservation first. If you have never tried "extreme conservation" before--You may be able to reduce your power usage by upwards of 50%. The typical North American home uses around 1,000 kWH per month. Getting down to 300 kWH per month (assuming no electric heat/range/water heating/etc.) pretty easily.

    Get a Kill-a-Watt type meter and start measuring your power usage--Appliances that are no 24x7 (desktop computers, entrainment systems, refrigerator/freezers, etc.) are good candidates for replacement with new/energy efficient devices.

    There are whole house monitoring systems too (like T.E.D.).

    Lots of insulation (especially attic insulation), double pane vinyl windows, using Heat Pump for heating/hot water, Mini-Split Heat Pumps vs central heat/air conditioning, etc. can all dramatically reduce electrical consumption.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waltnawswaltnaws Registered Users Posts: 2
    Re: small grid tie inverter questions

    thanks for the responses, useful to me. Better to find out on a forum that the power company would "not be happy" about that rather than just try it.

    Great forum, Ive been browsing around a little, found the answer to another question I had about how much power you lose with temperature rise.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: small grid tie inverter questions
    waltnaws wrote: »
    thanks for the responses, useful to me. Better to find out on a forum that the power company would "not be happy" about that rather than just try it.
    Good to hear. Needless to say, if you installed one of these things, caught your house on fire, and had your insurance company deny your claim because of it, you would "not be happy" as well.
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