Solar Edge / Tigo, Are They Worth It?

Solar Edge / Tigo, Are They Worth It?

It would be surprising if you work in the UK solar industry if no-one had tried to sell you anything made by Solar Edge or Tigo recently. I’ve been approached numerous times by the manufacturers themselves and by their distributors.

If you haven’t seen them yet and don’t know what they are, these devices are MPP trackers that operate in individual modules. They are being touted as the next big thing in PV efficiency, and as a favourable alternative to micro inverters. They look very similar to the connection box fitted to the back of PV modules already, and actually several module manufacturers are starting to offer modules with the technology already fitted in place of the standard connection box (UpSolar and Trina as the most notable). They can however be fitted at the point of install or retrofitted afterwards (if you want to take the whole array off again and re-install it once these are stuck to the modules).


The way that they work gets a bit technical, so I won’t go into it in great detail (Although feel free to ask if you’re interested) but essentially they take each module on its own and ensure that it’s working at close to the peak efficiency that it can given its individual conditions (Irradiance / temperature etc) by changing the operating voltage of each module. Most importantly this means that the problems traditionally associated with module miss-match across an array are largely eliminated, so shading, poor module grading, temperature differences and such similar things won’t drag the efficiency of the whole array or string down which can be a serious problem, particularly on shaded arrays.

They also allow the modules to be individually monitored and to be isolated if required.

Ok, so far so good. I really can’t argue that these things seem to be a fantastic idea. The question begs however, are they worth the extra cost. Clearly these things aren’t going to be free so if you were to buy them, would you ever see the benefit or would they only payback in 30 years or so after the array itself was history?

From the advertised literature for Solar Edge for example, they say that for a heavily shaded array you would get around 25% extra yield, and for an unshaded array you would get around 2% extra yield. These are Photon figures from case studies so should be reliable. To my mind however, that doesn’t really tell you much past that they’re unlikely to be worthwhile if you already have a well positioned and designed array.

The difficulty I see here is that if you’re getting 25% extra yield from a heavily shaded array, that may still be an additional 25% onto a yield that was never going to be worth it in the first place. How do you quantify the improvement? well, one issue here is that the software tool recommended by the manufactures to do simulations using this technology is PV-Syst, which is expensive and not terribly user friendly. It’s a very powerful tool and should give you good results for these types of systems but it can take quite a long time to model anything, which will eventually add to the cost of the systems delivered.

If you take the cost of the optimisers to be approximately £50 each as installed then for a 16 module system, the additional £800 or so for the array install is adding something like 15% to the cost of the install at present. Ok, the inverters are cheaper as a result of not needing their own MPP trackers, but not by much (About £40 in this example compared to an SMA equivalent)

Let’s do a simple worked example using some back of an envelope figures.

First let’s look at the really big Central Inverters.

Firstly the unshaded case

If we take a 4kWp array costing £6,000 installed. It’s in a fairly good location with a good aspect so gives an annual yield of 950kWh/kWp this would give a payback period of about 6 years and an 20 year IRR of 18.9% (Assuming 3% RPI and 5% electricity price inflation)

solar_pv_commercial_arialIf we installed the Solar Edge system at an additional cost of £800 we would get a yield increase of 2% giving 969kWh/kWp. in this case you would increase the payback to 6.6 years and the IRR would reduce to 17%. Ok so not a great deal in this case.

What about the shaded case? If we assume that the same array is fairly heavily shaded and so would give an annual yield of 600kWh/kWp then we would get a payback without the optimisers of 9.4 years and an IRR of 11.5% With the optimisers (Assuming the 25% increase in yield) the system would yield 750kWh/kWp giving a payback of 8.6 years and an IRR of 12.9%. If these figures were correct then they would be worth installing for this system but it would be very site and system specific.

It essentially seems to me that for a traditionally designed and installed systems in a decent location, it’s never going to be worth the extra expense. For sub-optimal systems with shading issues it may well be worth it, but if you don’t have PV-Syst and the time or expertise to construct detailed simulations then it will be difficult to justify the expense and the customer may end up with a PV system that never performs as well as they thought it would.

This example is clearly a bit rough and costs will come down, especially when they’re integrated at point of manufacture. The problem will still remain that it will be difficult to quantify the benefits unless better software tools are developed. Eventually however I’m sure that PV*Sol will include support for these devices, or that the manufactures will develop their own.

Ok, now on to the interesting part, at least to my mind. What devices of this type open up are a large range of non-traditional system design options that would have been at best impractical before but that should be relatively simple now. The main things are:-

  • – Different module orientations and pitches on one inverter
  • – Different module sizes and types on one inverter

One of the largest expense for any PV installation is mobilisation. The process of selling, designing, and sourcing the array and then of getting the equipment and installers safely up onto the roof to fix it all there. There are clearly economies of scale then to be had in maximising roof coverage once you’re on the roof.


Installations like those shown above have always been possible. You would just have to use individual inverters for each aspect that the modules were in. This can make the project very much more expensive both in materials terms and the labour required to install them. With optimisers installed you can just use one (Or a few) large inverters making the whole thing much simpler. It’s even possible to install different sizes of module onto one inverter so you could maximise roof space where it is limited by filling in all the corners with smaller modules. That wouldn’t have been possible at all before except by using micro inverters.

solar_pv_arialThis use for the technology does make sense to me because it opens up buildings for PV installation that wouldn’t have been economic before.

However. We still run into the problem of how exactly you quantify that without software tools that can cope with the fine resolution offered by this technology. You could just use PV-GIS-CMSAF modelling, or the new MCS guidelines which don’t take different technologies into account at all, but they’re a bit rough, and the new MCS shading analysis doesn’t work for systems like this as it compensates for the large miss-match losses caused by shading which should be eliminated here.

Ok, I think I’ve waffled on for long enough now. Time for a conclusion.

In my opinion, these are a brilliant innovations who’s time hasn’t quite come yet. The cost is improving but still too high, and I think most importantly, the industry standard simulation tools have yet to catch up with this technology so the benefits are very difficult to quantify. Once these things catch up. I think this will become ubiquitous in the PV industry. I certainly see them as a far better alternative to Micro Inverters.

If you have any questions I’d love to hear from you, please leave a comment or send an email.

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  • Gerald Brady

    I have been contacted by Solaredge and their rep assures me that my unshaded system will benefit by at least 20% if I fit their optimisers to my panels. This seems unlikely to me. What do you think? The modification would cost £4,295.
    Gerald Brady

    • Chris Roberts

      Dear Gerald

      Thanks for your post on our website. We’d be surprised if this was SolarEdge themselves. We do a lot of business with them and it would be unusual for a manufacturer to be selling direct. This is most likely another installer. 20% is highly unlikely if your system is unshaded. We’d say around 2% which is achieved because the optimisers overcome the natural variation between modules. £4,295 seems very pricey too.

      You’d be better spending that money on a battery storage system. We’d be happy to advise.

      • Gerald Brady

        Dear Chris,
        Thank you for your answer. You are correct that it wasn’t solaredge directly that made the 20% claim. I hadn’t realised that as the rep gave his contact details on a solaredge pamphlet instead of a business card.

  • Sarah Hadley

    I had a meeting with a rep yesterday offering to retrofit these power optimizers + a replacement inverter to my 4 year old system. I was assured that I would achieve at least 25% improvement as that is their experience with an unshaded system, and I have some shading issues caused by a chimney. I understood how the system worked, and appreciated it could help, but the cost quoted to me was also £4295.00 after allowing a discount of £300.00 as a trade-in against my current inverter. I was also left a Solar Edge leaflet – although with a business card clipped onto it – so likely the same company.
    Where we then came to a rather more confrontational discussion was when I realised that their experience of a 25% improvement was primarily based on fitting new systems, where the 25% improvement was based on comparison with the SAP predictions on new installs – not on retrofit systems. By the reps own admission, he said that SAP figures (particularly like mine based on the 2009 SAP calculations) were quite cautious estimates, and it was routine for a customer’s installation to perform better. Mine has been performing better by about 10% to date ……..
    So I then suggested that on that basis, if my system had already achieved a 10% improvement, then his figures of 25% over a SAP baseline would mean that I would achieve maybe a 15% improvement – a much less attractive number when based on the installation cost. The rep couldn’t seem to understand this view, and kept reiterating a 25% saving based on my current production rather than the SAP figures, which to me (simplistically) means he was suggesting a 35% improvement over the SAP figures!!!! But he could (I guess understandably) offer no guarantee of such a saving, not even a guarantee of any saving at all! His reasoning being that no one could guarantee the weather. True, but it seems to me that year-on-year the variance in PV performance due to the weather isn’t that big – more in the region of 5-10% in either direction, so not enough for them to hide behind. (The rep then made things a bit worse for himself by also stating that 2015 have ben the best PV year for a while, so thereby making his quoted new install rates of + 25% compared with SAP look less amazing LOL
    Anyway, the upshot is that I think it is far too expensive with no guarantees, and I am investigating instead removal of my chimney that does do some shading of the system, as that seems a better use of money and I know for sure it will improve performance. Then when my current inverter gives up the ghost, I can review the state of technologies to see if adding Power optimizers would then be cost effective.
    In fact the biggest appeal to me was that they were offering a guarantee of 20 years on the inverter, and 24 years on the optimizers meaning that in combination with the 25 year warranty I have on my panels, then no more capital outlay would be needed in the future to maintain the existing system. That did sound attractive, until I then realised that if technology has changed so much in the 4 years since my system was installed, what might happen in another 5 or 10 years?

    • Chris Roberts

      Hi Sarah, thanks for your post. We do not believe it makes sense to scrap (or trade-in) a perfectly good inverter. We like to SolarEdge system but it’s not worth it until your existing inverter fails.

      It is also a little cheeky to include some of your existing over-performance (in comparison to the original SAP calculation) as a benefit for you when you’re already getting that benefit. MCS selected the SAP calculation at the time (I chair the technical committee that took the decision) because it was known to be conservative. We didn’t want installers exaggerating performance to the extent people were left disappointed.

      It’s difficult to predict the improvement you’ll get as I don’t know the extent of the shading from your chimney but I’d agree you’re probably best removing the chimney if it’s no longer required and then consider options when (if) your existing inverter fails. The SolarEdge might then give a 2% to 5% improvement over a normal “string” inverter.


      • Juan Carlos

        Depending on the conditions of your system, you could always Retrofit Poweroptimizers from Tigo, using the TIGO TS4-R-O to optimize the panels that are shaded and only those, it has to meet certain conditions but definitely posible. Without change of invert or anything and you can probly get that problem solved and get that extra production with you spending a couple hundred dollars.


  • Peter Barlow

    I’ve also had a similar experience to Sarah and Gerald. A sales rep visited me to sell me the benefits of a Solar Edge upgrade on my 5 year old system. I was initially told that I would see at least a 20% improvement however they were unable to guarantee this and as I have no shading was unable to understand how they were quoting such a percentage for my unshaded roof. A value of £4,495 was stated and like Sarah I could see that the warranty upon the invertor would mean no additional capital outlay during the FIT period. I am unable to see what benefit this is going to be as technology moves on and I expect a more advanced invertor will appear on the market before mine ceases to work. Think I will definitely be doing more research in a couple of years time as I was initally given a 7 year life expectancy on the invertor. Does anyone have any experience of how long an invertor generally lasts>

    • Sarah Hadley

      With regards to inverter life-span …. My Delta Solivia monitor did pack up after 2 years 🙁 It was replaced FOC under warranty without any problem with Delta as such. BUT unfortunately, in tandem with the inverter failing, the monitoring software that is supposed to send me E-Mail alerts also packed up prior to this unnoticed by me, so it was 6 weeks before I noticed! (having had the system installed by 2 years at that time I was not routinely checking output sadly). Then to add to the problems, the company that had sold me the system had gone out of business. Luckily the actual installers who had done the work were still in business and did agree to install the replacement inverter with them being able to claim (some?) of their costs from Delta. So that was great.
      Although unfortunately the installer who came was not an experienced installer, and whilst the inverter was easy to swap out, when he turned it on he only turned on one of the two strings, so it was another month down the line when I realised that whilst I was generating, it was lower than previously! Oops! With a bit of help from Delta, they told me how to turn on the 2nd string (an easy change just turning one switch on), and the installers did agree to pay for the loss.
      So support was overall good in the circumstances.
      My inverter has a 5 year extended to 10 year warranty, so I am covered for another 6 years.
      I have been told that the older string inverters do have a limited life due to the extreme heat generated when power is generating, so that means that I can expect this inverter to break again sadly at some point. However, if it is within warranty, hopefully I will spot the issue more quickly and get another replacement, 🙂 If it is out of warranty at that time, then I will look at what is available at that time. The Solar Edge system did look good, but without any guarantee of improved performance, it wasn’t an option for me.
      Currently getting quotes to remove the chimney stack that does give some shading, but that too is expensive – about £1,100.00 due to the need for scaffolding! But it seems that getting the maximum out of my system to benefit from my higher FIT seems a good idea.
      As an aside, I spoke to another supplier a few days ago (another cold-call) and they are offering an alternative upgrade of the inverter, but this time without power optimizers, but including a 5kw battery storage system. Again with a 20 year warranty for the inverter and battery storage systems, with a promise that any replacements would be to the latest technology available at the time! (The person I spoke to also rather naughtily suggested that if a big improvement came out and my kit was working fine, then I should ‘spill’ water on it to force it to break to get a replacement! Naughty man 🙂 ) Anyway, their quote was for £2,800.00 fully installed.
      So it seems lots of companies are looking at a way to keep doing something with solar but concentrating on upgrading older systems due to the almost complete collapse of new business since the FIT dropped to only just over 4p a couple of months ago. Plus there is also now a capped amount of new install money available each year, so a new install might not even get that from Day 1, but have to wait until the following year.
      So it is all very challenging to know what to do for the best. I have looked at systems like Immersun that redirect unused solar to your hot water tank to heat the water. A good idea, but for me living alone, I don’t use that much hot water, so again I decided not cost effective for me – but a good idea to make maximum use of your solar power.
      Hey-ho – what fun.
      .(w for except that it had to come from Germany

      • Chris Roberts

        Hi Sarah,

        Interesting comment on the battery storage system. £2800 sounds a very keen price for a 5kW system but it’s storage capacity that matters and that’s where the cost is (the battery capacity).

        Using a car as an analogy, a car that can do 200mph and only costs £10,000 might seem like a bargain. But if it only has a tiny fuel tank such that it can only travel a couple of miles then it’s about as much use as the proverbial chocolate fireguard.

        If you’re considering a battery storage system (which are great with solar but don’t yet stack up financially) then you need to ask the battery capacity you’d be getting for your £2800 (the 5kW might just be the maximum power output). We have a very good guide published by the UK’s National Solar Centre available for free download from our website (with a contribution by yours truly). Click here


    • Chris Roberts

      Hi Peter and thanks for posting.
      It’s difficult to know with certainty the lifespan of inverters as the majority have only been installed in the UK over the past 6 years or so. Therefore it could be argued those that have failed are the ones which have prematurely failed and so are no guide to the average lifespan.

      Many manufacturers now offer a 10 year warranty so I’d expect the average lifespan to be at least that if not 12 to 15yrs or more especially if a good quality one such as those made by SMA, Fronius or Power One (now ABB).


    • Gordon

      My ABB Aurora 3.6 invertor only lasted 4 years. Fortunately it was replaced very quickly by my installer under warranty and in November I lost very little generation

  • Wayne Campbell

    We are converting systems over to Solar Edge technology but were certainly not charging anything like that.As Tesla Energy certified installers we are looking at the best way to add the Battery to existing systems. Some customers want to do the changeover and add the Battery but were also letting customers know that the Batteries will come down in the next couple of years so by installing Solar Edge you will gain more generation up to 25 % depending on all the above factors – and there system is then battery ready. We charge £ 1600 – 2000 for a Solar Edge conversion okay we don’t make a lot of money but we have made a future market for ourselves as we know customers don’t want to give away their electricity for free and buy it back at 14p.

    • Matt Harvey

      Hi Wayne, what is your company called? I was quoted £4300 but with no shading i’m not sure i’ll see the return on investment at that price.

      • Wayne Campbell

        Hi Matt We are Alba Heat and Power small company Father and Son based in Fife Scotland . What exactly are the quoting you for – is this a full system – is your existing system difficult to get to ??

        • Wayne Campbell

          If you have no shading it is probably not worth doing unless of course your inverter is around 5 year old as they start to lose the efficiency about this age. The one thing it will do is get the maximum out of each panel by tracking the individual panel to its optimum and you can check each panel for underperformance or even a faulty panel. If you are thinking about a storage system like the Tesla PowerWall this can be retro fitted to your existing system without the need to do any upgrade.

      • Chris Roberts

        Dear Matt, in our view a conversion to SolarEdge, even at £2000 is unlikely to be worthwhile. Unless your system is heavily shaded then the improvement in output is unlikely to be little more than 2% to 5% as all it is doing is correcting the loss from module mis-match and uneven degradation. It might be worth considering when (if) your existing inverter has failed out of warranty but otherwise you’d be disposing of a perfectly good inverter (and we do not agree that efficiency degrades much over time)

        Battery systems may be a better bet sometime but to get the best solution to match your system and usage, it’s helpful to monitor your system to see how much you export on a typical day (an Owl Intuition PV is a great low-cost monitor for this). The Tesla Powerwall is a great product but isn’t suitable for every situation. If you’d like to investigate more we’d recommend you read a guide published by the UK’s National Solar Centre (there’s a download link on the battery storage page of our website). We’d especially direct you to the questions at the back written by our MD, Chris Roberts.

        • Matt Harvey

          Thanks Chris, that is really helpful. We have no shade on our panels so I don’t think this is going to be for us until like you say the inverter fails on us. thank you for your reply. a+

  • Sue Symonds

    We had a visit from a rep yesterday who spoke very convincingly (as they all do!) about the benefits of fitting Solar Edge power optimisers. The cost has obviously come down – now £2800 +£140 VAT as we already have the panels and Samsung battery installed vat is only 5% currently. Our panels are completely unshaded but he spoke only of 25% minimum extra generation (which seems to be wrong/dishonest if I have read your article correctly). What he said about the benefits of the panels working individually rather than in a string makes sense and appeals to us – is it right that they all work at the same level as the lowest-producing panel, so that if one is obscured by bird droppings, for example, they all produce the same low level of power? No-one ever mentioned that we should get the panels cleaned regularly, but it seems that is a sensible thing to do?! There is an obvious film on our panels currently – they have been up for 39 months and never been cleaned and the annual generation has gone down from 3709 to 3523 to 3176. Could this be partly because of the dirt?
    Am I right in thinking you would say this is not a good investment, to spend yet more money on ou pv system?
    Thanks for your advice……

    • Paul

      Hi Sue
      Yes, I think that it’s very unlikely that investing £2800 or more installing optimisers would be worth it for you.
      We are actually very positive about the optimiser technology itself, and often install it ourselves, but only at first install generally when it’s a relatively cheap addition.
      Whilst in some circumstances it is possible for them to increase yields by up to 25%, (NOT minimum 25%) that would only be for systems that are already very heavily shaded. For unshaded systems you would probably only increase your yield by 5% and maybe not even that.
      This sounds like a case of either a poorly trained, or possibly a dishonest salesman unfortunately. but this isn’t uncommon at the moment. If you want some better information I’d recommend looking the SolarEdge website itself as they have some very good information about their products with no inflated sales talk.
      With regard to your dirty panels and reduced yield over the last three years, yes that could be the cause. I’d certainly recommend giving the panels a clean every few months as dirt build up can definitely reduce yields. Try asking your window cleaner if they can use a long reach sponge to give then a once over.
      If you’ve lost 15% yield over three years than that is higher then I would expect unless the panels were pretty dirty, so it may be worth contacting your installer to have them look over the system to see if there are any faults.

  • Janet in Oz

    I’m about to get solar panels on north (best for Southern Hemisphere) facing roof. Because of state heritage restrictions – four of the panels are being placed either side of a chimney which will put some shade on some of those panels when the sun is either very West or very East. The solar panel sales person suggested an optimiser when I asked what the chimney effect might be on the panels. But could not tell me what the percentage improvement was on… so I have no way to work out if extra $850 is worth it on an initial investment of around $10000 for a 4.72 KW system (16 panels, 4 of which are affected by the chimney shade). Date posting this – 6th June 2017… I don’t know if the optimisers’ time has come yet because there does not seem to be a date on the blog post. I like the info but it’s going to date over time as system prices come down and tech changes… it should have a date on it.

    • paul lukehurst

      HI Janet
      From your description, it does sound like the optimisers would be a good idea for your installation. If you don’t have them them the performance of all of the unshaded modules will be effected by the shaded ones to some degree.
      The installer should be able to tell you what the effect of them would be though. We use a piece of software called PV*Sol which is very standard in the solar industry across the world, and can model the effects of shade on the array and how much difference the optimisers would make.
      They do of course cost something and you want that cost to be justified, so I’d ask them to provide some more evidence of the performance advantages if I were you.
      We’ve installed a lot of them for customers of ours and they have performed very well generally, and do seem to justify the expense in most cases where there is some shading as long as they’re installed at the same time as the panels.

      • Janet in Oz

        Hi Paul

        Thanks for the info. If I expand my system then I will consider it but after the installer came out and actually measured the roof, it turns out I can fit an 8kWh system on the unshaded bit of roof with 28 panels – bonus. So I don’t need the optimiser thingies at this stage and they were not recommended. I don’t know how the sales person got the roof layout plan info so wrong before (measuring off google maps – my fault – probably didn’t help). But I think we’re on track now. And hopefully when my finances recover – I can get batteries – in the next 1 to 2 years. Mostly I want them because our electricity supply has become quite unreliable. posted 9th June 2017