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Solar PV Inverter: Should you replace it?

Posted by Faisal Hussain (HIES Scheme) on 21 March 2018 at 10:10 am

Here at YouGen we’re producing a blog series which look at some examples of ‘mis-selling’, used by a small number of rogue traders in the renewables and energy efficiency industry. Although mis-selling is a trend which appears to be on the increase, there are also rising numbers of reputable organisations which are attempting to eradicate this form of bad practice by making sure customers stay informed. Here is a blog written from the perspective of Faisal Hussain from HIES which covers what you need to know on the subject. 

HIES is a consumer protection organisation and operates a Consumer Code for the renewable sector which is approved by the Chartered Trading Standards Institute (CTSI).

We are aware that an increasing number of homeowners, who already have a solar PV system, have been approached about replacing their inverter. In fact, many consumers have been cold called from companies who are offering a service to check their system is working correctly and then afterwards start talking about the inverter needing replacing, even where it doesn’t.

We have seen examples where consumers have been advised that replacing their existing inverter (even where it’s still working) could increase their solar PV system’s performance significantly and hence generate more money from it.  As with all of these types of claims we would advise you to be cautious; especially where the claims seem too good to be true!

Other consumers have been informed their existing inverter isn’t working properly (and needs to be replaced – when it doesn’t) and also that the inverter could potentially be a fire hazard.  This last point is difficult as all electronic and electric equipment may be susceptible to fire. 

We would therefore like to help consumers, who have an existing solar PV system, understand whether replacing the inverter is the right decision for them.

The cost to replace your existing inverter can vary depending upon the type of inverter you go for. This could be anything from £500 to upwards of a few thousand pounds and therefore it’s important that consumers make an informed decision.

For those of you who have a solar PV system and are either approached by a company or are looking to replace your inverter, we have developed a four-point guide which will help assist with your decision whether replacing your inverter is right for you:

1.What type of existing inverter do you have currently?

An inverter is an important part of a solar PV system. Its job is to convert the DC electricity generated from your solar panels to AC which allows you use the electricity in your home or export it back to the national grid.

To identify the type of inverter you currently have you can have a look at the existing inverter paperwork as it should explain the type of inverter it is, contact your original installer or the inverter manufacturer in the event you are not able to contact the installer who installed your solar PV system, or complete your own research via the internet.

There are three main types of inverter systems:

String inverters – most installations will have a string inverter installed alongside your solar panels.

  • Traditionally string inverters were sold into the UK market.  Usually installed in the attic or loft space, string inverters are usually fixed to a wall or other mounting board.
  • String inverters are ideal for a solar PV system which isn’t affected by shading during the day and the solar panels are not facing in different directions.
    • Your solar panels are arranged into groups connected by strings. Each string of panels is connected to a single inverter. You can also have multiple strings going to a single inverter. If an installation uses a string inverter and even if one panel is shaded it will reduce the performance of rest of the solar panels on the same string to the struggling panel’s level.
    • String inverters usually work most efficiently when all of the solar panels are operating under the same conditions – for example they are all facing the same direction and none are shaded by objects like trees or obstructions such as other buildings or chimneys.
  • String inverters usually come with a manufacturer’s warranty between 5 and 10 years (5 years was commonplace).

Micro inverters – are a more modern development than string inverters.

  • Micro inverters (or microinverters) are much smaller in size and capacity than string inverters. This means each panel has its own small inverter. These are attached to the back of each panel which converts the DC electricity generated by that individual panel to AC.
  • As each panel has its own micro inverter as the effect of any shading is reduced as only the performance of any individual panel impacted by shading are affected.

Power optimisers – are often considered a hybrid between a string inverter and micro inverters.

  • Co-located with each solar panel, power optimisers increase energy output from the panels using technology that constantly tracks and maximises the output of each panel.
    • This technology is called “Maximum Power Point Tracking” (MPPT).
  • As an additional bonus, power optimisers usually have built in monitoring as standard, which means that the performance of each panel is constantly monitored and consumers can see and compare the individual performance of one panel to the next.  This also enables faster fault identification and fault finding.

The benefits of these newer types of inverters are that:

  • The performance of the solar PV system using newer technology could increase between 5% and 25% over the lifetime of the system (based on information from manufacturer of these inverters) but it should be noted that the uplift in performance will only occur in certain circumstances (see point 3 below).
  • The solar panels operate independently meaning if one panel is affected by shading, dirt, debris, bird droppings etc, then it doesn’t affect the performance of the other panels.
  • You can monitor each panel’s performance and check for faults with these.
  • They could be more reliable than a string inverter, as if one solar panel fails, the others won’t usually fail with it.
  • They are safer because you won’t have comparatively high voltage DC power on your roof.
  • They often come with a longer manufacturer’s warranty, than a string inverter, typically 20 or 25 years.

The drawbacks of these newer types of inverters include:

  • They are more expensive than a more traditional string inverter and also replacement costs are higher (i.e., when compared against similar sized string inverters).
    • As with most technologies though, this higher cost could come down in time.
  • They are only really best suited with solar PV systems which have significant shading issues.

2.What is your motivation to replace the inverter?

Your motivation to buy should be key to your decision-making process. Depending on the type of inverter you choose it could cost you up to £5,000, so the reason(s) for replacing your inverter is important.

If you are concerned that your existing inverter is a potential safety hazard then contact the original installer (assuming that they are still trading) or the manufacturer of the inverter in some instances to highlight your concerns. And our advice would be that you should also contact the Microgeneration Certification Scheme (MCS) for assistance.

If you have received information from an installer advising you the installation of power optimisers or micro inverters on your solar PV system will increase its performance by 25% resulting in you getting your money back over the next 10 to 20 years then you should check this yourself or obtain independent advice.

It is important you don’t rush into a decision and carry out your own research to establish whether this is correct for your solar PV system.

Power optimisers and micro inverters are more beneficial when your solar PV system suffers from significant shading and then it is possible that you could increase the performance of your solar PV system by up to 25% not a blanket 25% increase.

Think of it as the Boxing Day sale from a high street retailer – just because they advertise a sale of up to 50% off, it doesn’t mean every item on sale is 50% off. If your solar PV system doesn’t have significant shading problems i.e. most of the day your solar PV system isn’t overshadowed by nearby trees, chimneys etc, then power optimisers and micro inverters will have little impact.

Point 3 below provides you with a quick checking mechanism you can utilise to see if power optimisers and micro inverters are right for your solar PV system.

3.How much shading does your Solar PV system experience?

Shading is an important factor affecting how your solar PV system performs. The more shading you have affecting your solar panels the less electricity your system will generate.

If you have little or no shading then replacing your inverter with a string inverter seems sensible. If you have some shading then micro inverters or power optimisers might be suitable.

The simplest way to check whether your solar PV system is affected by shading is to go outside and look at your solar panels and see if there are any objects (like trees, chimneys, lamp posts, neighbour’s roof’s) that could cast shadows between the sun and solar panels. If these objects are in the way for most of the day, then you could have significant shading. Our advice is to check your solar panels for shading every 2 hours in the day.

Another option, which is quite technical, is to look at your contractual paperwork which should state how much shading was taken into consideration by the installer at the time of the contract. If there was little or no shading then the Shading Factor (SF) on the contract will be “1” which means power optimisers or micro inverters will have little effect on increasing the performance of your solar PV system. If there was some shading identified, then the SF should be less than “1” which means there is some shading. For example, if the SF was “0.9” then you have 10% shading (1 – 0.9 x 100) affecting your solar PV system. Therefore the installation of the power optimisers or micro inverters would potentially increase the performance of your solar PV system by up to 10%.

If you have been told by the company giving you a quote that your solar PV system will increase its performance by 25% or more with the installation of power optimisers or micro inverters, then you could be mis-sold. You may want to contact the Energy Performance Validation Scheme (EPVS) who can guide you on how to establish whether the power optimisers or micro inverters will increase the performance of your solar PV system and how much this could equate to in monetary terms.

4.How can you check whether it’s the right decision?

If you have little or no shading, then spending up to £5,000 on replacing your inverter with power optimisers and micro inverters doesn’t seem like the right decision especially if you wanted to recoup that money back over the next few years.

If you would like some independent advice on whether replacing your existing inverter is a good idea and which type of inverter is right for your solar PV system then trusted bodies such as the Energy Saving Trust, Yougen or HIES could help you.


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Image credit: John Swindells.


About the author:

The Home Insulation & Energy Systems Contractors Scheme (HIES) is a Chartered Trading Standards Institute approved Consumer Code for the renewable sector. The HIES Code of Practice requires that consumers are dealt with professionally, courteously and sympathetically.  Any products installed by HIES members must be fit for purpose, installed professionally and come with comprehensive guarantees which are covered by specialist insurance, providing consumers with a high level of protection and peace of mind. We aspire to deliver world class dispute resolution services and provide consumers with free access to our frontline complaints team, mediation, independent inspections (at our discretion) and free access to an independent ombudsman. For further information about HIES visit or follow us on Twitter or Linkedin.

If you have a question about anything in the above blog, please ask it in the comments section below.

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11 comments - read them below or add one


jensonComment left on: 4 March 2020 at 6:39 pm

HI all, one thing that has not been mentioned about upgrading from a string inverter to say a micro inverter is that even if you have not got any shading these will still product more generation.The reason is that on a string inverter all the panels will be brought down in generation to the solar panel that is producing the lowest generation. (which all solar systems with have this issue) The micro inverters works independent on each panel so each panel will pull the maximum generation it can without effecting it's brother panels.On top of that the new micro inverters need less electric to start them up so there's a saving AM and also a saving PM every day of the year.


If you have shading of some sort you can see from above there is a great saving to be had as long as you don't pay over the odds for the re-fit and you have got at least a 3kw system.

Hope this has helped as much as above comments


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perkiscComment left on: 15 February 2019 at 3:30 pm

Just had a company round fpr my "free system evaluation" they are trying to sell me a Solar Edge inverter with optemisers for £3800 and declaring  a 25% increase in output.

Reading this artical in seems as this in inaccurate as my system does not have any shading issues.

He also mentioned that with the end of the FIT scheme in March 2019 that if I changed the inverter after that date it would be classed as a system upgrade and I would loose the FIT payments so I needed to act fast. Does anyone know if this is true or just a pressure sale tactic

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monflyer58Comment left on: 6 January 2019 at 5:23 pm

I have been cold called by a company trying to persuade me to install solar edge optimisers and inverter.   I have a 3.4Kwp system with a SMA 300 inverter,  7 years old so getting me 52.75p/unit  FIT + export . A few of their claims seem a bit spurious, including

- even on a unshaded roof, optimisers can increase output by "up to"  15 % due to differential performance of panels, cloud shadows, dirt etc.   They claim this is supported by side by side installations.

- my SMA inverter is likely to fail any day, and as it is out of warranty, will be v difficult and expensive to get anyone to replace it ( original installer no longer in opertation )  as the new installer will have to check the whole installation,  and I will probably have to wait sveral weeks ( thus losing valuable FITS payments ?.

I guess with  most  of the initial rush of installations now reach ing the end of warranty periods for inverters  its a pretty common situation.

Welcome any comments on these points - Whats the ball park figure for straightforward  inverter replacement ?   


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JulesComment left on: 5 July 2018 at 7:38 am

Out of 16 enecsys microinverters, we have 3 which have stopped working ie are dead -- and it is definitely the microinverters,  not the panels.   We're finding it impossible to get enecsys replacements, so can we replace just the 3 with a different make, or would all 16  have to be the same make?   Fortunately, we're still able to monitor the working ones through a helpful website.

Many thanks for any advice -- we're sad to see all this sunshine going un-used!

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deeppurpleComment left on: 31 May 2018 at 12:38 pm

If you look at the event log on your system it should show the cause of the trips. The only trips I have ever had, and there were a few over a couple of days were all caused by the grid voltage seen by the inverter being above its max limit. I suspect that as we are on the end of a long overhead system where the normal no load voltage is set high (so that as a lot of load comes on and voltage droops it doesnt breach the lower voltage limits), and we also have a lot of pV systems on this line, then occasionally this might happen. 

If it is a voltage issue then you can talk to your grid owner who will measure the voltage and if it persists I believe that there are ways of resetting the PV system over voltage limit, but I think this is a fairly diffocult thing to achieve and requires the grid owner to be aware of it.

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GaryComment left on: 14 May 2018 at 6:43 pm

I am no expert but understand this can happen if the inverter senses that the grid limit has been reached and switches off for a while.  This can happen on good days, especially if there is a lot of PV in your area.  You could try searching the "

The Green & Ethical MoneySaving Board

" forum on moneysavingexpert. com where i know it has been discueed.

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BobAComment left on: 8 May 2018 at 5:26 pm


Bob Axford‎ to YouGenUK Yesterday at 12:35 ·   

A perfect weekend for generating solar PV. I had the perfect bell shaped curve on Saturday, but on Sunday I noticed mt system was not generarting continusously - it looks like my system 'tripped out' twice. Does anybody have this probelm and know how to resolve it.


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DuncanComment left on: 19 April 2018 at 10:19 am

Really useful and timely artical.

Only yesterday phoned yet again by some company offering  my  'entitled free PV system health survey'!! --

Totall agree with comments above and thank you Gary for really  showing how long the likely payback period would be.

I have a Sunny Beam display for my system and as long as that shows a peak of 2.52kW on sunny cool day - same now as when new 8 years ago -  and the daily bar graph looks 'normal' I'm happy all is OK.

If it aint broke don't fix it.

Where are these companies buying 'our' contact details from? Doesnt GDPR now stop this ?

Could this artical be made available as a pdf for down load and saving please?

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Sussex Solar Ltd

Sussex Solar LtdComment left on: 10 April 2018 at 6:40 pm

Just received a marketing mail shot from a company called ESE in Liverpool. The letter is offering a "free health check" as the inverter warranty is about to expire.

They are selling replacement inverters with a 20 year warranty, but fail to mention that its a parts only warranty and you will still have to pay for scaffold to replace the optimizers on the back of the panels when they give up.

As mentioned above, I recommend waiting til there is a problem, your inverter may last for 15 - 20 years, why replace it now!!

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GaryComment left on: 2 April 2018 at 6:37 pm

Interesting and useful artical. 

In my opinion it's not worth replacing an inverter until it breaks, even if you have a string inverter and suffer from some shading.  After all, you would have been aware of the reduced production resulting from the shading when the system was installed, so why now chase marginal improvements at significant (unecessary) cost? 

Also, if shading is not an issue, you need to consider that inverters have been 95 to 98% efficient for many years now, so is it realistic to think that a new inverter alone can produce any noticable increase in performance?

I have 2 systems and one (1750kWp) suffers from more shading than I expected as the sun casts a bigger than expected shadow from our chimney.  On sunny days during the summer months I have estimated that the shadow costs me 2 to 3kWh of production per day.  Let's say that is 3kWh and let's assume that happens on every other day throughout the year, i.e. 180 days.  This is a worst-case scenario but useful for costing purposes.

So, that's about 550kWh per year at about a net 20p per kWh for my FIT and export rates.  That works out at about £110 "lost FIT" per year and possibly a small (very small) amount of own consumption.

If we assume that retro-fitting power optimisers with an inverter would cost between £1,000 and £1,500 (seemed reasonable a couple of years ago when i did the maths) then it would take 10 to 15 years just to break even! 

in my view that makes it uneconomical to even consider an "unnecessary" change.  However, as an when that inverter packs in, it would be sensible to consider the cost difference between replacing the inverter like-for-like and doing something to deal better with the shading at that time.


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deeppurpleComment left on: 29 March 2018 at 10:34 am

The first step to see if your inverter is performing well or not is to plot a graph of monthly output of your system against the theoretical output. The theoretical output can be calculated using tools such as 

If your system is working well then you should be getting about 10% more than the theory averaged over the year, this may go down slightly with system age but my experience is that over 8 years I am still pretty much the same.

This technique will also enable you to take action against anyone who sells you new technology on the basis of increased output which fails to be achieved. At least you will have evidence which is vital if you are to succeed in getting your money back.




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