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How important is voltage for a solar PV inverter?

Posted by Chris Rudge on 22 June 2011 at 9:20 am

Q: I am thinking of installing a solar electricity system. I believe that the inverter is a key element. One company is peddling an inverter that operates at half the voltage of others. Is this an important factor when deciding which system to go for.

A: All inverter manufacturers have a different set of parameters they are designed to work with. All are good and will have applications for different peoples PV system designs. Broadly, it does not matter too much what the maximum power point (mpp), voltage range is for an inverter, but for longer DC cable runs it would be best to try and keep to high voltages.

As a couple of examples, the Sunny Boy range of inverters have a mpp voltage range of 200 to 450 (approx). This may not suit an application for a smaller system, so an alternative such as a Steca 2010 unit could be used which has an mpp range starting below 100v.

As long as the designer of your pv system keeps the array mpp voltage matched within the rated range of the chosen inverter, then the system will work at best efficiency. 

About the author: Chris Rudge is a qualified electrician who specialises in renewable energy.

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

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Comments

17 comments - read them below or add one

Ludgateman

LudgatemanComment left on: 15 July 2013 at 1:18 pm

We had a Solar PV system installed in November 2010, comprising 18 Romag 185 panels in two strings on our south facing roof, feeding a Sunnyboy 3300 Inverter, and have been very happy with the performance to date. This weekend, however, I realised that the inverter was no longer feeding the grid. The green indicator LED showed "Waiting", with a Pac. reading of 0w, and VPv showing between 238volts & 255volts.

What factors might have contributed to the failure to begin generating, & what can be done to remedy this? Unfortunately our intaller (Green-Sun Ltd of Farnborough) is no longer trading. I have sent an enquiry to the inverter manufacturer direct, and am awaiting a reply.

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ibvp

ibvpComment left on: 26 November 2011 at 10:08 pm

I have had a 2.35kw system installed in october 2011, this has 10 x Shuten PC-60 panels feeding a Sunnyboy 2000HF inverter. Since the announcement FIT cut in December i have decided to have 2 x additional panels (235w each) this will provide a gross output of 2820 watts. I have been told by the installer that the HF2000 inverter will be fine and will produce the extra output in excess of 2kw that I currently achieve in optimum conditions . I'm not sure if this is correct, I would appreciate any comments, should I have an additional inverter fitted?   

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Rogers

RogersComment left on: 28 September 2011 at 11:17 am

Hi

Forgive me if I am asking a question in the wrong place but new to this!

I am currently looking at getting 16 solar sanyo solar panels using a SMA sunny boy inverter however I am completely perplexed by the placing of the inverter - I can see the reason not to place it in the attic/loft - however one company has suggested I place in on a north facing outside flat roof - I can see the benefits but surely the inverter is then subjected to extreme elements from the outside - can someone please advise me if I should or should not place the inverter outside - there is another option of placing in on an inside wall with ample ventilation

 

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kpol

kpolComment left on: 28 July 2011 at 3:18 pm

Hi Norrie

The warmer the pv panels are the less efficient they become. The panels should have air circulating over them to cool them down , and some models even have cooling pipes on the back of them , which is then used as a form of solar thermal heating.

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Cathy Debenham

Cathy DebenhamComment left on: 28 July 2011 at 1:31 pm

Hi Norrie

Have a read of this blog: Why solar panels don't work so well in the heat. It should answer your question.

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sj-construction-sl1-6ee

SJ ConstructionComment left on: 28 July 2011 at 8:55 am

Hi , this probably could do with its own subject heading but I'm unsure how.

I'm after some clarification of the definitions of , Total Installed Capacity TIC and Declared Net Capacity DNC.

If you look at the DECC definitions you could come up to the conclusion TIC=DNC and it seem from Ofgem data of systems registered so far most do , therefore maxium AC ouput of inverter = DNC = TIC

So fitting 4.2 kWp of panels on say a 3.6 kW inverter would fall into the < 4kW band of FITs tariff .

Clearly using total panel peak wattage DC as TIC may be an error.

any thoughts anyone ?

( Norrie,  Pv panels reduce in efficiency as temperature increases , the rated panel figure, in watts, is at standard test conditons of 25 deg. C , likewise efficiency will increase as temperature drop below this point )

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Norrie

NorrieComment left on: 22 July 2011 at 5:17 pm

I have recently had a solarPV system installed on my South facing garage rood.   It is working well.   In full midday sunlight it produces the maximun 2500w but I noticed that in continuous sunshine this dropped to just over 2000w.   I suspected that this reflected the fact that resistance in wiring increases with temeperature and that the heating up of the units was responsible.   I read this up on the net and sure enough came across the observation that solar panel efficiency drops the warmer they get.   I also noted that if a cloud came over for long enough to allow the panels to cool the efficiency recovered.   There is nothing one can do about this.  One still gets the best input even if the efficiency drops.  It drops more in cloudy conditions.   I shall be interested to see what happens on sunny days in frosty conditions...

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Current Energy Solutions Ltd

Current Energy Solutions LtdComment left on: 6 July 2011 at 10:49 pm

Hi Glyn Owen and Carragwenv

If your modules are placed on two roofs facing different directions your installer should be recomending a dual input inverter such as the SB400tl of Steca 2010+, there is no need to go to the additional expense of two inverters. 

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ItalicSix

ItalicSixComment left on: 6 July 2011 at 7:18 pm

Hi Royh

I've run your system through the SunnyDesign software with a 2000HF inverter and it comes back with a nominal power ratio of 95% so you can never expect to achieve your full potential. Don't blame your installer though as this is the best match available and it is rare to ever come back at 100%

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ItalicSix

ItalicSixComment left on: 6 July 2011 at 7:01 pm

Hi Glyn Owen and Carragwen

Having your panels on two orientations is far from ideal as if one panel in a system is shaded then it will bring down the efficiency of the whole system (imagine squeezing a hose pipe reducing the flow along the whole hose). Using two strings will help a little, but is far from ideal (and may not be possible) so the best bet is to use 2 inverters.

Don't forget the panels do not need to be on your roof. If you have space in the garden then why not put some railway sleepers down and have the panels on A-frames? Make sure the inverter is mounted by the panels and the AC cables run back to the property (SunnyBoy's are weather tight). Make sure your installer has experience of this.

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Cathy Debenham

Cathy DebenhamComment left on: 6 July 2011 at 3:38 pm

Hi Glyn Owen and Carragwen

You'll find the answer to your questions in this blog: Solar PV across different facing roofs

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Carregwen

CarregwenComment left on: 6 July 2011 at 11:52 am

If panels are placed on 2 different facing roofs - WSW and SSE - are 2 inverters required or is there an inverter that  both arrays can be plugged into? Getting different answers form different installers when quoting.

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Glyn Owen

Glyn OwenComment left on: 5 July 2011 at 7:22 pm

Hi,

I amm currently getting quotes for a PV system, I had wanted some panels on the south facing roof and some on the west facing roof.  The "best" quote is from a company saying that a system facing south and west would not work! are they correct? why?  They are offering an 8 Sanyo panel with Sunny Boy invertor.

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royh

royhComment left on: 30 June 2011 at 4:20 pm

What size inverter would you recomend for a solar panel array of 9X245 sharp. The system is rated at 2.205Kw but the inverter ( a Sunnyboy) is rated at 2000w. Over the last two weeks the reading has maxed out at 1.999Kv so it appears that I am not running at full efficiency. Friends locally with systems are acheaving peak values and more over same period.

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flerbs

flerbsComment left on: 29 June 2011 at 11:28 am

My salesman (PV solar uk) also stressed importance of inverter starting at lower voltage (120V) which seemed to make sense as producing electric with less light. However when installed engineer set inverter (Power one Aurora PVI3.6) at 190v saying efficiency impaired if set too low. My system is 3.29Kw divided into two circuits. Noticed that inverter read 180v per circuit at 8.30pm on bright June evening so not producing electric. What are advantages of higher voltage setting to inverter?

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JamesPage

JamesPageComment left on: 25 June 2011 at 4:39 pm

In my experience the efficiency can vary a lot with voltage, even within the MPPT range, especially with some of the very small inverters. Some publish nice contoured graphs for different voltages. If not you should ask the supplier to get one!

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David Hunt

David Hunt from Comment left on: 22 June 2011 at 5:47 pm

Good response Chris, 

 What I would say is there are a LOT, and I mean a LOT of solar PV companies out there that have sales people, and installers for that matter, that do not know what they are talking about, and will try and 'blag' customers, or 'blind them with science'. If they can't explain clearly what they are offering by way of product, and how that directly benefits you and your system then I'd be concerned. 

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