Micro Inverters vs. String Inverters [infographic]

I’ve had a lot of people ask me about the pros and cons of microinverters recently.  I have written a long and detailed description of microinverters, but for those who would rather learn about them without ploughing through 1000 words of my ramblings (and who can blame you!) I created this infographic about micro inverters vs string inverters. Hope you like it 🙂

microinverters pros and cons - infographic

Micro inverters vs. String Inverters (AKA Central Inverters)

 

 

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About Finn Peacock

I'm a Chartered Electrical Engineer, Solar and Energy Efficiency nut, dad, and founder of SolarQuotes.com.au. My last "real job" was working for the CSIRO in their renewable energy division.

Comments

  1. Hi Finn, In the event of a power failure will the house still have available power from the solar panels with micro inverters as I hear from friends that it is not normally the case in a solar installation as a power failure causes the inverter to shut down. I have a friend in the Dandenongs area of Melb, subject to frequent power outs of long duration and this could be a deciding factor.

  2. Thanks for the ‘infographic’ (never heard the term before); one can never do better that ‘local knowledge’ / asking the man who owns one..
    Sounds like early-days yet for microinverters, but a promising development, which can only get better. I’ve never thought putting all one’s eggs in a single basket was very clever.

    From my rudimentary perspective the exposure to the environment on the roof might be the most critical consideration (including odd things like low-level static-electricity ….er, ‘unearthed’ on my roof recently!). Rather that connecting the inverter directly to the panel is there a prospect of mounting them in a well-ventilated spot under the eaves and connect them to the panels via an extended bit of cable? It’d certainly make working on them much simpler and safer.

    Will be watching with interest.
    Meanwhile, any

    • computer-glitch. Continued….. Meanwhile, any ideas/offers re circumventing the anti-islanding component of a grid-connect inverter ~ for use in a stand-alone system ~ will still be most welcome: by myself and others.
      eg …What do you mean by “fancy electronics to keep going in a blackout”?
      Speaking as a layman, how about some simple sort of magnetic-reed switch which ~ upon loss of grid-power automatically closes a circuit to a battery-bank?

  3. Has anyone done a truly independent comparison of overall performance because the sales pitch for micro inverters is always that they perform better when you have less than ideal conditions
    If you have ideal conditions so no shadows facing north etc which gives better performance and best roi

    • Colin – all the evidence I’ve seen points to about 8% extra power from micros on an ideal roof. This can be put down to: 1) clouds 2) manufacturing mismatch of panels 3) uneven soiling

  4. The infographic says that all solar panels have to point in the same direction with a central inverter.
    That is not true if you have a central inverter with two max power point trackers. In this case only each of the panel strings has to be oriented in the same direction.

  5. Hi Finn
    Have you heard of power optimizers instead of microinvertors

  6. Hi Clive, there are few concerning factors about microinverters that have been left out in the debate.
    – Most of them offer a 25 year warranty, but the companies have only been around 5 years or less themselves.
    – if a good string inverter has a failure rate of under 1%, then on a 5kW system with 250w micros, I.e. 20 microinverters vs one string inverter, the micros need to have a 20 times better failure rate than the strings inverters…..that’s a tough call with them sitting under the panels at 70’C.
    – if there is a microinverters failure, none of the microinverter companies reimburse for the labour costs of replacing a microinverter. Which is much more involved than changing a string inverter, for which one is at least compensated for labour.
    This article may be off interest to you…
    http://seekingalpha.com/article/1888141-enphase-anemic-revenue-growth-with-alarming-warranty-obligation-growth

    Cheers Nathan

    • Apologies, my message was meant for Finn. Got my names mixed up.

    • Would have been nice to get some kind of a reply to this post Finn.

      • Good brands of microinverters have very low failure rates for a new technology that sits in incredibly harsh conditions, and their reliability is improving very quickly. I predict that in 1-2 years reliability will be a complete non-issue.

        And Enphase provides an installer payment associated with a replacement in the event of a microinverter failure under warranty, as do many panel manufacturers that use Solarbridge micros pre-installed.

        Some more info on high temperature reliability of microinverters here:

        http://www.solarquotes.com.au/blog/wp-content/uploads/2015/01/Enphase_Extreme-Climates_Topic-Brief_AU.pdf

        • John Seymour-Griffin says

          Hi Finn

          Given we’re now three years on from your comment re reliability being a non-issue in 1-2 years, what are your thoughts now on micro inverter reliability?

          Thanks

          • Ronald Brakels says

            Hi John, Ronald here.

            Finn is out, so I’ll give you my thoughts. Personally, I’d say Enphase microinverter reliability has been pretty impressive. While they are not perfect, failures do appear to be rare. Enphase’s competitors don’t have a great deal of market share and so it is harder to form a clear picture. In some cases microinverters have worked fine but communication links have failed.

            Falls in cost and improving reliability of string inverters has meant that microinverter use has not increased in the way some expected it would a few years ago. Enphase still says they can get their cost per watt down to that of string inverters, and I hope they do, but with the low cost of panel string optimization, which I wrote about here:

            https://www.solarquotes.com.au/blog/maxim-just-killed-microinverter-dc-optimiser/

            Along with (generally vague) promises to improve fault detection with string inverters, microinverters face some stiff competition.

  7. How much did you ge paid for this hogwash Finn? DC switchgear more costly? Multiple inverters = possible multiple failures, monitoring only available by computer, shading can be an issue but most systems wouldn’t have to deal with this, where does the extra 8% per annum yield come from? Are most of your clients using micro inverters now?

    • No-one paid me to write this. But thanks for questioning my independence.

      The 8% extra comes from soiling, clouds, temperature difference across cells, and panel mismatch. Yes – good DC isolators cost more than AC last time I checked.

      I monitor my micros on my phone personally.

      Most of my clients still offer DC only.

  8. John Salisbury says

    Hi Finn. I’m presently trying to decide which is best….A conventional system( 16 panels/Renasolar and Aurora inverter) or micro inverter system(12 panel JA Solar and Enphase ) Very little difference in price.Your thoughts please and thank you in advance.

  9. Rowan Reynolds says

    Hi Finn. Couple of questions. Are ‘standalone’ microinverter solar panels available i.e. keep outputting with out a grid connect voltage? What varies in low light conditions, voltage current or both? Could the output from an array of microinverter solar panels be fed to a variable speed motor drive with the output speed varying with the available input from the array. If so how might a feedback loop to the drive be established?

  10. Rowan Reynolds says

    Hi Finn. Are non grid microinverter solar panels available? In low light conditions what varies – the voltage, the current or both? Could the output of an array of microinverter panels be inputted to a variable speed motor drive with the output of the drive adjusting to suit the available solar input? If so how might a feedback loop be established to vary the drive?

  11. Finn this article was written back in Dec 2013 any new developments in technology that you would update this info graph or is the micro inverter still as you mention above. I am really thinking micro (enphase + sunpower panels would be a good match?) your thoughts ?

    • Hi Michael,

      I would say that the ifo still applies. The main thing that has changed is that the good microinverter companies have intensified their high temperature torture testing and are super confident in the reliability of their devices.

      Sunpower make funny sized panels (327W), so a 250W Enphase may be a bit undersized to take full advantage of the panel’s output. But Sunpower have just bought Solarbridge micro inverters so expect a Sunpower AC panel to appear in the next 6 months.

      Any Tier 1 250-260W panel with Enphase should make a really good solar system if you don’t want to wait.

      Hope That Helps,

      Finn

      • michael chapman says

        Thanks Finn , yes I saw your article on solarbridge and sunpower the other day, might wait and see what they come out with probably price will be the inhibiting factor.

        Regards
        Mike.

        • Yes the Sunpower/Solarbridge AC panels will most likely be heart-stoppingly expensive! But when you factor in the ‘proper’ 25 year guarantee and the extra power generated over their lifetime they should look a little more attractive 🙂

  12. Finn,

    on your infographic of shading I think you might have over simplified and made an incorrect assumption. I think if an MPPT used a “dumb” algorithm then what you suggest could be correct. But in reality, a module string and an MPPT operate far more intelligently than the graphic gives credit. I’d recommend watching this short YouTube clip about how a modern MPPT works. I understand that This operation be true not just for SMA, but also for other “high quality” inverter manufacturers.
    https://www.youtube.com/watch?v=bxIi4GiZakE

    Interested in your thoughts

    There also an interesting blog post from SMA on their view of when each of the technologies (String & Micro). The sell both products (Micro and String) so I guess at least there is less of a vested interest when one technology is suggested over another compared to a pure string or pure micro inverter company.
    http://en.sma-sunny.com/2015/10/05/string-versus-micro-which-is-the-right-choice/

    Again, interested in your thoughts.

    • Hi Steve,

      First, let me be very clear. SMA are a great company that make great products with really good MPPT algorithms. String inverters make a lot of sense over micros in a lot of situations.

      But optimising the MPPT to the global peak, not the local peak, is not particularly difficult or new. I think the SMA claim that it is ‘Groundbreaking and Exclusive’ is marketing fluff. The engineers back in Germany are probably cringing at the marketers getting carried away!

      I don’t care how intelligent an MPPT algorithm is: physics is physics. If you constrict the current though a solar panel with shade, the other panels in the series string will have the same current going through them. Of course this can be mitigated a little with bypass diodes, but it’s a very coarse fix.

      The video is also misleading, bordering on deceptive IMHO from the axis labels on the graph – as one of the Youtube commenters points out.

      If you have an array that has more than a little shade and you install a string inverter, I’ll bet my mountain bike that you’ll be disappointed in the performance compared to DC optimisers or micros.

      The blog post from SMA is pretty skewed to Central/string inverters too IMHO. I personally believe (just a hunch – no real evidence) that SMA really don’t want to see micro inverters gain too much traction. They are a string inverter company through and through. The fact that they make no mention of the dangers of HVDC compared to 240V AC is exhibit number 1 pointing to their bias! Exhibit number 2 is no mention of clouds or panel soiling.

      Also it is not true that it is impossible to do power factor correction with a micro.

      I’ll do some digging and see what performance people are seeing in the real world from partially shaded arrays with modern SMAs on them. But I think it will be hard to find an installer I know that has specced a string inverter on a shaded array!

      If you do decide to get a string inverter on a shaded array – get performance guarantees before you hand over any cash.

      Best Regards,

      Finn

  13. Thank you for your insight,i have gone with the micro inverters after talking with different installers and your advice and think i have done the right thing. VERY HELPFUL!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

  14. Rudolph Bucovaz says

    Hi Finn, thanks for your blog.

    With string inverters being more efficient I expect you mean under optimal operating conditions – (excluding bird droppings, shading etc.)
    So, are micro inverters more efficient over all.

    (January 13, 2015) It seems that the good micro inverter companies are improving their product every day.
    Would I be sensible to get a 3kW micro inverter system and then add extra panels when the system is more proven and the competition stronger between the micro companies?

    Also, what about a north facing 3kW String set up and East or West facing Micro set up to maximise the advantages of both?

    Cheers, Rudy.

    • Hi Rudolph,

      Yes – that’s exactly right. In perfect conditions string inverters are a bit more efficient. In the real world, the micros produce about 10% more energy due to shade and panel mismatch and no single point of failure.

      Enphase are very good now – they are getting smaller and cheaper all the time though.

      I wouldn’t mix and match. I’d go either a dual MPPT string with E/W on one input and North on the other:

      http://www.solarquotes.com.au/blog/an-eastwest-spit-of-solar-panels-on-a-single-string-can-work-well/

      Or all micro inverters.

      Mixing string and micros on one roof will be expensive and I don’t see any advantage.

      Hope That Helps,

      Finn

  15. David Barry says

    Hi Finn,

    I have 3 phase power and have room for approx 20 KW of PV on my roof. Should I go for micro or single inverter? I have the capacity to charge a battery, what brand would you recommend? How is your powerwall 2 going?
    my consumption is 65KWH/day.
    Cheers
    David

    • Ronald Brakels says

      Hi David, Ronald here.

      Microinverters or standard string inverters will both work fine, but for such a large system microinverters would be expensive. If you like the advantages of microinverters go for it, but if you want a lower cost per watt of capacity go for a string inverter. (But not necessarily the lowest cost string inverter. You may want to consider a Fronius as it is a reliable brand that allows for flexible installation.) If you have localized shade issue such as from a roof pipe you can work around them by putting optimizers on the affected panels.

      I don’t recommend any batteries at the moment as it’s not really possible to save money at their current price. But with your high electricity consumption you’d be closer to making a battery pay than most households as you could probably fully cycle a large one almost every day. So I suggest keeping one in mind when their price comes down. If you have plenty of money you could get one now for silent backup purposes, but generally a generator is cheaper.

      Finn’s Powerwall 2 is chugging along and he just wrote about it here:

      https://www.solarquotes.com.au/blog/heatwave-solar-power/

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  1. […] For a rundown of both the advantages and disadvantages of microinverters I’ve put together a summary infographic here. […]

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