1. Welcome Hearth.com Guests and Visitors - Please enjoy our forums!
    Hearth.com GOLD Sponsors who help bring the site content to you:
    Hearthstone Soapstone and Cast-Iron stoves( Wood, Gas or Pellet Stoves and Inserts)

PV micro inverters vs power maximizers

Post in 'The Green Room' started by Vic99, Jun 13, 2012.

  1. Vic99

    Vic99 Minister of Fire

    Joined:
    Dec 13, 2006
    Messages:
    842
    Loc:
    MA, Suburb of Lowell
    I've had 2 companies give me an estimate on photovoltaics for my roof. I want about 125% current electricity capacity because in 4-5 years when a car dies I want replace it with a plug in electric to charge off of my house. Going grid tied. To get125ish % would have to get 327 watt panels.

    Both outfits told me I'm at 80% for sun. I had one tree cut down and a few branches trimmed. Roof faces almost dead south. Most of paneled area would be at 28 degree pitch.

    Company A said get central inverter Power maximizer
    http://www.tigoenergy.com/data_sheets/MM_ES_datasheet.pdf.

    Co B said get micro inverters instead and get creative with a couple different string set ups.

    Anyone have any experience with either? Don't want disappointment due to shading knocking down productivity because lots of panels are tied together.

    Helpful Sponsor Ads!





  2. Jags

    Jags Moderate Moderator Staff Member

    Joined:
    Aug 2, 2006
    Messages:
    15,254
    Loc:
    Northern IL
    From my limited understanding, this is where the micro-inverters shine. Also as time goes on and panels change, get better, cheaper (or one of yours dies 5 yrs down the road), you can mis-match panels if each one has its own inverter. Partial shading of a panel or two will also have little effect on the whole system.
  3. denjohn

    denjohn Member

    Joined:
    Jul 25, 2010
    Messages:
    40
    Loc:
    Prairie Farm, WI
    I'm not real clued in on this, but your link says:
    Isn't that basically a micro inverter?
  4. Jags

    Jags Moderate Moderator Staff Member

    Joined:
    Aug 2, 2006
    Messages:
    15,254
    Loc:
    Northern IL
    It does appear to use a module at each panel then sends it to a centralized unit.
  5. GaryGary

    GaryGary Feeling the Heat

    Joined:
    Jul 12, 2010
    Messages:
    291
    Loc:
    SW Montana
    Hi,
    Not an expert on this, but I do have a system that uses the Enphas micro inverters.

    Just looking at the Tigo manual, it appears that while there is a Tigo ES unit at each PV module there is also a central inverter that they don't provide. So, (I guess) the Tigo units play with the output of each PV module to mazimize its power output, but the output from the Tigo modules is DC and the modules are strung together in a series string and go to a standard string inverter. The advantage is that each panel gets its own optimization (which could be quite helpful for mixed shade), and you get the internet reporting and monitoring of the system right down to the individual PV module.
    Install manual for Tigo: http://www.tigoenergy.com/manuals/install_manual_maximizer.pdf

    With the micro-inverter system, a micro inverter goes on each PV module, and it converts the DC output of the PV module to grid ready 240VAC, which goes right to your circuit breaker box. Each micro inverter is a complete grid-tie inverter.

    One thing you could do with the micro-inverter approach is you could initially go for just 100% of your electrical demand, and then add the additional modules when you get the EV. With the micro-inverters, you can use whatever PV modules are the best deal at that time -- they don't have to be the same as the original PV modules. The Tigo system may also allow mixing modules (don't know). A lot of net-metering setups won't pay you for power you produce over what you use on a yearly basis -- they let you accumulate excess power in summer months to apply to low winter months, but at the end of the year its all zeroed out and you don't get paid for your surplus at the end of year. But, it depends on what your utilities rules are.


    As far as I know, the Enphase mico-inverters (the most popular brand) only handle PV modules up to 260 watts, so not sure how that's going to work with the 300 watt panels?

    Wonder what "getting creative with a couple different string set ups" means? When installers start talking about "getting creative", I get worried :)

    This is my system -- it will give you an idea how an Enphase micro-inverter system goes together: http://www.builditsolar.com/Projects/PV/EnphasePV/Main.htm
    This is Doug's bigger Enphase system that uses the new cabling system: http://www.builditsolar.com/Projects/PV/DougEnphase/DougEnphase.htm

    It does sound like you have a mixed shading issue, and a system that has optimization for each panel would be a definite plus for you.
    This is a bit with my own experience with shading: http://www.builditsolar.com/Projects/PV/EnphasePV/Shading.htm
    Very minor in my case, but there is some info there on the differences between how a string inverter and micro-inverters cope with mixed shade.

    Gary
  6. Vic99

    Vic99 Minister of Fire

    Joined:
    Dec 13, 2006
    Messages:
    842
    Loc:
    MA, Suburb of Lowell
    Thanks for the info. Been on vacation, sorry didn't get back sooner.

    My understanding is that the microinverters are not compatible with 327 Watt panels, otherwise I would go with that. If someone knows of a product that is, please chime in!

    I'm told they are designed for 240 W. If I just kept adding panels to make up the difference, I would start hitting roof area that is shaded with much more frequency. I already had a tree taken down and had a few others trimmed. I don't want to do much more because it would change the character of my yard. Plus, some of the shading trees are across the street in the neighbors property and realistically I can't do anything about that. Despite all that, I still get a lot of sun for 12 of the 19 panels. The other 7 would be decent, but adding another row of panels down would probably not be worth it due to the shade. I'll try to include a graphic below. A week after the photo was taken, I had a new roof put on my house.

    Company A said tigo power maximizers will work with the 327s and a central inverter.

    However, Co B told me to beware of the maximizers because the generation of maximizers that are out now is being discontinued in favor of a newer generation. This run would only have been out for less than a year and the new one will come online within a year, I think. Co B said their engineer thought it was a decent product from a technical standpoint on paper, but that short run caveat makes him a bit wary.

    I am also not sure if tigo power maximizer (PM) product would be as efficient as a microinverter (MI).

    If MIs are on 20 panels and 1 is shaded to 10% efficiency, then I understand that 19 panels would be operating at ~100% and one would be only at 10%.

    However, with a PM on each of 20 panels all running to a central inverter, if 19 are full sun and one is shaded to 10%, would I get 19 panels at 100% and 1 at 10%? Does that 1 shaded panel hurt all others because a central inverter is involved? Co A seemed to think it would, but not a lot. When I tried to get a ballpark %, I couldn't get a concrete # . . . . to be fair, I don't think the rep was trying to be evasive, I think he really didn't know because there are too many variables.

    I really want to go with 327s if I can, but don't want to be disappointed because shade hurts panels in full sun.
    What do you reckon?

    Attached Files:

  7. GaryGary

    GaryGary Feeling the Heat

    Joined:
    Jul 12, 2010
    Messages:
    291
    Loc:
    SW Montana
    Hi,
    Good picture.

    Again, I'm not an expert at all in this area, but I think that the panel by panel optimization is also helpful when some of the panels on a string are mounted at different tilt angles as it looks like yours are. And, the dormer and chimney may also do a little shading early and late where the panel by panel optimizers might help.

    If you are into Google SketchUp, it and you can make a model of your house and the trees, it will give you a minute by minute shadow pattern on the array. Obviously the tree shading would be approximate, but maybe enough to be helpful. SketchUp comes with a built in sun -- you just tell it where you are.

    I was offered a free solar survey Bright Harvest and took them up on it -- I was pretty impressed with what they did http://www.builditsolar.com/References/BrightHarvest/BrightHarvest.htm
    I'm not at all pushing them as the fee is pretty stiff, and it may just not be worth it.

    One last think is that there are some pretty heavy duty PV types the AZ Wind and Sun forum and it may be worth running the questions past them.
    http://www.wind-sun.com/ForumVB/forum.php

    Would like to hear how this all works out.

    Gary
  8. peakbagger

    peakbagger Minister of Fire

    Joined:
    Jul 11, 2008
    Messages:
    1,661
    Loc:
    Northern NH
    The Tigos are MPPT controllers that optimize each panels output. There is still a need for a grid tie inverter.I dont see them being on the market for long as they are an expensive option compared to microinverters which do the same thing and dont need a central inverter. I would consider reducing your output and going with microinverter sized panels. I expect if the larger panels are around for awhile enphase will come out with one rated for the large panels at some point. The current reality is put in the most cost effective system you can now and take advantage of whatever incentives you can get now. With budget pressures I dont see the 30% fed tax credt lasting forever and expect when the other ratepayers realize how much they are subsidizing renewable power that those subsidies will decrease like they have in Germany and Spain. Bascially whatever you install today is going to be borderline obsolete in 5 years. It will still work but I expect there will be better/lower cost technology available when you upgrade your car.

    If you could go with an adjustable pole mount you will get more output for less panels but that obviously depends on your site. Your roof pitch is not very optimal for anything but summer operation. In the winter the panels will build up snow and even if they are clear, the angle is way off what you really need to optimize the amount of generation. The new Allsun solar trackers made in VT have impressive output. If your utility has a feed in tariff versus a front end incentive trackers are the way to go.
  9. Jags

    Jags Moderate Moderator Staff Member

    Joined:
    Aug 2, 2006
    Messages:
    15,254
    Loc:
    Northern IL
    Don't stop now, guys. I am sucking this up like a fat kid eating doughnuts.
  10. begreen

    begreen Mooderator Staff Member

    Joined:
    Nov 18, 2005
    Messages:
    49,084
    Loc:
    South Puget Sound, WA
    Hmm, we may end up using you for virtual solar storage. ==c
  11. Jags

    Jags Moderate Moderator Staff Member

    Joined:
    Aug 2, 2006
    Messages:
    15,254
    Loc:
    Northern IL
    Most of my storage is reserved for beer.

Share This Page