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    • CommentAuthorSimonH
    • CommentTimeOct 13th 2010
     
    Cor, spent a few months away from the forum (as I don't have a house at the mo) and seems like I've missed loads. The latest is a colleague just put me on to is "micro inverters" for PV systems.

    Rather than having a single "BIG" inverter, with a high voltage & high current strings running to them you take the output from each panel and switch it to 240V ac on the spot. Then you can remotely monitor each panel separately and report on any discrepanices for maintenance. Apparently system inverters are not lifetime - with usual life expectancy 10-15 years. Is this correct?

    So although there's a slightly higer install cost, it brings down total cost of ownership (not having to replace the big inverter) and improves efficiency (and hence FiT income) by not losing as much in the DC runs.

    It can also prevent damage to panels - where eg. one panel is a string goes poof - it can take out other panels or break your big inverter. Or you might just not notice - only 2 of your 3 strings are operting and you lose 1/3 of your generation.

    Any comments appreciatied.

    Here's some products & links I googled:

    http://www.enphaseenergy.com/products/products/micro-inverter.cfm
    http://www.redherring.com/Home/23609
    http://pcsolarpv.blogspot.com/2010/05/enecsys-to-reveal-solar-pv-micro.html
    http://en.wikipedia.org/wiki/Photovoltaic_micro-inverter
  1.  
    I think that this is an interesting development with the inverters integrated into the panel themselves. The key benefit for me is that it means that shading of one panel will not affect output from others as each panel effectively has its own MPPT. It should also help to reduce sizing mistakes, installation costs and make expanding an array incrementally very easy.

    Another useful indicator of the level of interest in this idea is: http://www.eetimes.com/electronics-news/4209343/Suntech-pushes-for-solar--smart-panels-semiconductor

    It also means that there is no need to find a location for the inverter in the house. As long as the panel itself complies with G83 then it should be reasonably safe.

    I would worry about whether the lifetime of the embedded inverter matches that of the panel - if the inverter typically fails early compared to the PV array then you will reduce the lifetime of the investment considerably.

    Certainly something to watch.
    • CommentAuthorevan
    • CommentTimeOct 13th 2010
     
    I think that the MTBF on decent inverters is over 20 years now. It's true that when it goes, the whole system goes off until you repair it, but they are repairable.

    When one of the micro inverters breaks (which is n times more likely), it's up on the roof behind a panel for a start - that could get seriously expensive if you are paying someone to access and replace it.
    Then the unit itself is probably encapsulated or not serviceable, so you end up throwing it away and buying a new one.

    "It can also prevent damage to panels - where eg. one panel is a string goes poof - it can take out other panels or break your big inverter." - I just can't see that happening at all.

    The other mooted advantages in terms of efficiency and so on seem pretty marginal.

    It may be the way things are going but I'm not convinced about the economics of it yet.
    • CommentAuthorCWatters
    • CommentTimeOct 13th 2010 edited
     
    Electrolytic capacitors (there are several in a solar panel inverter) don't have great life expecancy. Typically only 3000-4000s hours if operated hot. They last quite a bit longer if kept cool but it's still a problem if you want long warranty periods. The advantage of having lot of small inverters (rather than one large one) is that you can replace electrolytic capacitors with other more reliable types...

    http://www.solar-pv-management.com/solar_news_full.php?id=73388
    • CommentAuthorGavin_A
    • CommentTimeOct 13th 2010
     
    the only situation I can see this being useful for is sites with complex shading problems, as shading on one panel would only effect that panel not the entire string, but here are other ways of mitigating this issue.

    power losses in the dc cable are tiny in most situations as he panels are run in series, so the voltage is usually equal to or higher than mains voltage, with 4mm cables being the norm vs 2.5mm ac cabling, so I see no benefit in this respect.

    problems I can see would be that you're basically tied in this manufacturer for the life of panels, so if you ever need to replace an inverter then you have no choice of make / model, and if this manufacturer discontinues then you're screwed. Replacement work would also need to be done on the roof, possibly in the middle of an array of panels which could be very hard to get to, and I've no idea what this routine maintenance is they're talking about (in the enphase energy link).

    basically it seems like a bad idea in the vast majority of situations, though there could be a small niche in shaded ground mounted arrays without a convenient location for a separate inverter.
    • CommentAuthorSimonH
    • CommentTimeOct 13th 2010
     
    Wouldn't it be possible to run a small DC cable length into the loft - on most systems. And then site the inverters on a board mounted in the loft. Then they're all together - and don't need roof access. The module shown above look like they don't have to be "in" the panel, as they're separate. Avoid the cost of scaffolding etc - should a panel fail. Then again - of a panel fails - you'll need to be on the roof anyways. LOL
    • CommentAuthorGavin_A
    • CommentTimeOct 14th 2010
     
    I fail to see the point of that solution though, and it'd seem to mean lots of lengths of dc cable with very low voltages running through them instead of 1 length with a higher voltage, plus you'd presumably need at least a DC isolator for each inverter, and probably an AC one each as well to be regs compliant, never mind all the extra wiring.

    I'm afraid I don't get this concept.
    • CommentAuthorstephendv
    • CommentTimeOct 14th 2010
     
    I can see some advantages to micro's in rare cases, e.g. strange shading patterns all over the array or multiple panels at different orientations. But IMO a high voltage DC system with a high efficiency transformerless inverter would be better for most installations because of smaller wiring size, lower overall cost and better efficiency.
    •  
      CommentAuthorDamonHD
    • CommentTimeOct 14th 2010
     
    Actually, lots of roofs have strange shapes and uneven lighting, for which microinverters could be just the ticket.

    Rgds

    Damon
    • CommentAuthorDavipon
    • CommentTimeOct 29th 2010
     
    Just finished an install using microinverters on an upper and lower south facing roof and an upper and lower west facing roof, system is a bit fiddly to fit but does have benefits; costs of multiple inverters with possible multiple failings and versatility of microinverters does make sense.
    • CommentAuthorstephendv
    • CommentTimeOct 30th 2010
     
    Choosing micro-inverters doesn't have to be an all-or-nothing decision. You could use a normal inverter for all the unshaded panels, and then just use micro's for those that are shaded.
    Best of both worlds.
    • CommentAuthorchuckey
    • CommentTimeOct 30th 2010
     
    I think that having external cables with 230V AC on them is asking for trouble. The idea of using micro-inverters in the loft seems to offer all the benefits without this disadvantage. The main downside could be the number of holes in the roof if the panels are put onto an existing roof. Can these micro-inverters be synchronized with the incoming mains to sell power to the board?
    Frank
    •  
      CommentAuthorDamonHD
    • CommentTimeOct 30th 2010
     
    The expectation is that these micro-inverters *are* full grid-tie. And 230VAC is quite possibly less of a hazard than the (higher) DC voltages in normal strings.

    Rgds

    Damon
    • CommentAuthorSimonH
    • CommentTimeJan 28th 2011
     
    Thought I should post an update on this.. the guy who sits next to me had his system comissioned yesterday. 3.9kW. He went with enecsys inverters in the end and bought his own 20 x 195W CEEG panels, and then got an MCS installer and enecsys came along to train the installer for the microinverters. After a small hiccup where the system kept tripping the main RCD - it was sorted this morning. It just needed a differnt MCB which has an intergral RCD feeding in the to the main circuit board.

    Each inverter has a wifi link to your router and continuosly outputs its data to a central server. They suplpy you with a web login and where you can see real time data for each panel plus overall system data - or have it shown by day/month/ytd or lifetime. I think this on it's own is worth the extra cost - we're currently seeing between 145 and 0 watts coming of his 195W rated panels... In January! Now to those zeros - 4 of the 20 panels aren't outputting. So the cost of the inverters has probably paid for themselves already. Imagine if these had been wired in series on a string - it could have been months before they had figures to suggest the system wasn't outputting what it should.

    The other benefit as far as we can tell is that even when the panels are working there's upto 40W difference between the panels - (Someone can correct me here - but as I understand it) if they were on a string they would be limited to the lowest output panel so maybe 120W per panel instead of 120, 125, 130, 130, 130 and 145. So the generation potential is raised by having separate inverters. Its amazing to see the effect of passing clouds over the panels. e.g panel 1 might be 130W and panel 2 90W. Then it will flip. And then they'll both settle at 130W again. It's seeing this kind of effect that has me convinced on their potential for extra units of generation - and at 41p per unit - it's worth it!

    The software is good - easy to use and very graphical. There's a couple of bugs when some of the accumualted values reset to zero when you flip tabs - but go the main page and back and its ok. Main thing is no crashes (and it's still only beta!). A really useful option is to hilight several panels (which are laid out on sceren as they appear on your roof). You can then compare the output from a couple of panels on a vertical bar graph - so you can spot any imbalances by looking at what they've output for the day/week etc.

    The system at 12:30 - peak for today is showing peak power for the day is 1.9Kw - that's with 20% of the system missing - and the bottom row shaded by the scaffolding. Not bad eh!

    The final comment - his installer decided to space the panels rather than close fitting them. This way - of one ever fails - it can be replaced with whatever is available at the time. It doesn't have to be an exact match to the rest of the system. Eg - you might be able to get 500W for £50 in 10 years time. ;-) Wonder if DEC have thought of that - people upgrading their supposedly 4kW systems?

    Note - this might sound like an ad - but it's not - I'm just really really impressed and when I get round to owning a house again I shall be going with the microinverters.

    Simon
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 28th 2011
     
    Simon
    Sounds like the 'guy who sits next to you' or GWSNTY has a well sorted system and an installer than understands things.

    Regarding the variance in panel power, that sort of difference is not unusual and you may find that in different light conditions the variation between panels changes, the IEEE have looked into this for large scale installations.
    Bets way to find out is to allow others to access the data that shows minute by minute output in either real time (that can be saved) or as a downloadable text file that is downloadable. I would say that as I love playing with data, but many heads make for solutions.
    • CommentAuthorbillt
    • CommentTimeJan 28th 2011
     
    That does look interesting. How much do they cost compared to a standard inverter and how available are they? (I'm getting quotes for a system now, so it could be an option.)
    • CommentAuthorSimonH
    • CommentTimeJan 28th 2011 edited
     
    The prices are dropping quite rapidly - he was quoted £175 each last year, but when he came to buy them earlier this month they were £140 (you need as many as you have panels). But there's several sizes based on your panel output - so get some quotes.

    PS - we're both IT contractors - so he's worked out a scheme with his accountant where his payback is in 4 years!! By buying his own panels from a supplier, getting them installed on day rates, claiming back the VAT through his business, he lent the money to his business to buy the panels and he gets the loan payments back tax free - which are paid out of the FiT. I.e. he's made it as tax efficient and cost effective as possible. 4 years! Followed by 21 years of income! I'm looking into installing some on my dads house in Liue of the fact i'm between houses and renting at the mo.

    PPS - did you realise how much PV panel prices had dropped? When I first start looking about 12 months ago they were about £2.55 per Watt Peak. Now they £1.59. I have a spreasheet that shows you might get returns as high as 12% if you make the best use of tax relief.
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 28th 2011
     
    I'm not getting quite such as short payback period as I don't get the full FiTs due to being keen to do the right thing ASAP rather than wait for the FiTs... Grrrr... But I reckon somewhere between 5 and 10 years' clear payback which which I intend to do more PV ultimately to maximise the CO2 emissions that my capital can avoid...

    And yes, prices have come done a lot. There's a bit of a glut right now from curtailment of the German, French and Spanish schemes.

    Rgds

    Damon
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 28th 2011
     
    Damon
    Would you be financially better off selling what you have to some boat or caravan people and redoing everything on FITs?
    Regardless of initial reasons?
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 28th 2011
     
    No, I don't think so.

    Rgds

    Damon
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 28th 2011 edited
     
    have you looked on eBay to see what stuff is going for.
    Personally I think with the cut throat tactics currently going on the next year is a good time to re-evaluate. Mind you you do have some on FITs and some on something else.
    What is to stop you getting a 2kWp fitted and bolting your kit to it?
    With insulated spanners of course:wink:
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 28th 2011 edited
     
    I have some on pre-FiT and some one not-top-tier FiT because they deem the stuff that doesn't earn me FiTs nonetheless increases the installation size and so should reduce my FiT size. There's a word for that kind of reasoning; several in fact.

    Rgds

    Damon

    PS. Main obstacle to further PV expansion at home is domestic harmony.
    • CommentAuthorCWatters
    • CommentTimeJan 28th 2011
     
    Simon - Any chance of a rough cost breakdown for this system?

    20 microinverters at £140 each plus 3.9kw at £1.59/W plus installation at ?? Total of around £10,000 ??
    • CommentAuthordaveh
    • CommentTimeOct 15th 2011
     
    Anyone recommend a value for money supplier for the Enecsys microinverters for 250W panels?
    Also, any suggestions on sources of cheapest available Sanyo 250W (HIT-H250E01) panels?
    Dave
    • CommentAuthorwookey
    • CommentTimeOct 16th 2011
     
    A colleage here fitted an enecsys system recently. He was mostly sold by the shiny GUI :-) but he does also have some shading from trees in the afternoon and the panels split between two roofs at slightly different angles.

    He too noticed the large variance in panel outputs due to angle, clouds, and shading. There is reason to believe that you may get better utilisation overall this way.

    Chukey: why is 230vAC on the roof 'asking for trouble' but 400-600V DC OK? That makes no sense.
    • CommentAuthorSteveZ
    • CommentTimeOct 20th 2011
     
    As I mentioned in another thread on inverters elsewhere, I have decided to go for a different hybrid system which uses DC-DC converters with MPPT mounted on the roof panels, monitoring each panel and feeding a constant DC voltage to a simpler inverter in the garage. My layout is mainly due East with another four panels facing South, so quite an uneven split for a conventional dual inverter

    The inverter has the built-in capability to feed each individual panel output to my PC, which is one of the benefits of the Enecsys micro system and, not having the power point tracking circuitry, it should be more reliable and comes with a 12 year warranty. Inverter efficiency is quoted as 97.6%

    The DC-DC Powerboxes only pass 1 volt DC when the inverter is switched off, which makes the system safe by default, rather than relying on switching the DC off manually. Although they do the Power Point Tracking, they are relatively simple compared with the Enecsys micro. The efficiency is quoted as 97.7% with 25 year warranty

    PS Ecopen and SolarShop-Europe were fairly good for Enecsys prices when I was looking a few months ago
    UK Urban Energy Ltd have the Sanyo HIT around £1.60 per watt - not a recommendation, just info
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