no of modules to a string?

[edexlab]

Hello all I'm new to PV can anyone tell me what the procedure is for determining number of modules to a string, I know the ideal is to keep voltages down to 120v or less ,is this the norm?

 

[Markc]

Hello all I'm new to PV can anyone tell me what the procedure is for determining number of modules to a string, I know the ideal is to keep voltages down to 120v or less ,is this the norm?

Hi welcome along.

The answer to your question is dependant on several aspects. Forget the 120V or less also. Recent inverter I fitted didn't even start to generate until 180V and could drop to 150V before it stopped. Maximum voltage on this particular inverter is 400V. This is DC voltage also.

Aspects to consider are: Maximum voltage output of the Module, Maximum open circuit current, Maximum input voltage of Inverter, No of strings the inverter is capable of receiving.

There is no hard and fast rule on models on a string. It is solely on design, module type, make etc and inverter requirements. Arrangement of strings, series or parallel or a combination of both.

Mark

 

[edexlab]

so its up to the designer! . I've done the NICEIC PV course which gives limited/basic info (not too impressed!)
So i've been reading a lot, and this was the main concern after reading DTi pv in buildings re; <120v I've done a couple of installs using sanyo 230's 2 strings of 5
which measured 190v each on to Sma 2500, although the supplier insisted we should
put all 10 on one string ,did this just to see and found array produced 380v (very good clear conditions)
I decided to stick with having 2 strings at the lower voltage for obvious reasons
I'm thinking about doing a proper course possibly at CAT machynlleth
any feedback or suggestions?

 

[Markc]

Hi Edexlab.

Interesting reading your last post. I tried putting your design through PVSOL but couldn't find the Sharp panels you mentioned. Any chance you could post the panel part number?

I've has issues before on a Sunny Boy inverter but that was due to low voltage (and also a larger inverter than what you have used)

As a panel heats up it's voltage drops and to be at 190V (and I assume peak) it may drop of the generation parameters when hot or light level is less than perfect.

Are you monitoring the total generation and if so how. The sunny beam is a good investment on any system in my opinion. What is your total output of the system and is it grid tied?

Another issue with any inverter is more of a night time if there's lightening about. A sudden bright lightening bolt can put enough light energy into the inverter. It will not start generation as the 3 minute rule prevents it (G83) but it can over voltage the inverter. With more strings this is limited but it is only a real concern if running close to the total voltage allowances of the inverter.

I would be interested to hear back and run it through the design programme to see what comes out. Not knowing your panel I can only guess.

Cheers

Mark

 

[edexlab]

sanyo 240's 2.4 kw.
no monitoring as yet except meter readings although i have discussed it with the firm i'm doing this for ,they are also new to pv but non electrical backgrounds started with solar thermal( Mcs in both).
went to commision system today looks like i will be following you're advice and using one string as the 190v per string (x2) equals 190v for the array (just went off and forgot all about ohms law ,idiot!). sunnyboy display reads" mode waiting",
so i checked ratings and mpp range is 224 to 600v so am i right in thinking theres not enough voltage from the array?
pv not as easy as some think, actual install is fine but the design is a steep learning curve

can you recommend a good rail system?

 

[Markc]

Hi Edexlab.

It is what I feared. The sunny boys are good inverters but they do have a slightly higher generation voltage. I try to use SB where I can. (Or if I can get one!)

If I can give one tip. Avoid like the plague anyone trying to sell something from China. Most of their gear that is MCS accredited you will get through a UK agent and is good stuff in the main. But I get inundated with emails from none English speaking sales teams trying to offer us a "unique opportunity!" Two years ago we went over to a trade expo in China. I can't remember the name of the city but needless to say I couldn't spell it anyway!

Lots to see in the renewable market and we looked at the PV more than anything. We weren't MCS then and a bit naive to the industry. We were offered a system which looked OK as long as we could commit to a container full. We very nearly did it but on our return to the UK and doing some web searches I discovered it was well below MCS requirements and didn't pass any form of wind shear tests.

Have a look at Wind and Sun web site. Their rails are top notch and good value for money. They are also very helpful and you can go and have a look at their systems up and running. If you get a problem with any Sunny Boys they are the service agents.

 

[edexlab]

yes funnily enough we had an Irish bloke phone today with sma specials about 1/4 normal price "Direct from china " he could supply yinglis by the container we reckon a bit moody or fake , also heard on pv course i did, about someone who bought direct from a chinese factory and when they arrived they were glass over photocopied cells, would'nt be surprised if thats true! we'll stick with known distributors!.

do you fit surge protection on your installs or just on systems at risk from lightning
i'm looking at offering it as an option not just for pv but for ccu changes (after what happened in Bolton) .

 

[rorylondon]

so its up to the designer! . I've done the NICEIC PV course which gives limited/basic info (not too impressed!)
So i've been reading a lot, and this was the main concern after reading DTi pv in buildings re; <120v I've done a couple of installs using sanyo 230's 2 strings of 5
which measured 190v each on to Sma 2500, although the supplier insisted we should
put all 10 on one string ,did this just to see and found array produced 380v (very good clear conditions)
I decided to stick with having 2 strings at the lower voltage for obvious reasons
I'm thinking about doing a proper course possibly at CAT machynlleth
any feedback or suggestions?

Good day, nothing to do with the string calcs but I did a 7 day 2372 course with ableskills in Dartford, Pretty good and I am certain more detail than the NICEIC

 

[edexlab]

to be honest i would'nt recommend niceic or any scheme course i think C&G course is always going to be better, the one i did the electrician had never fitted pv and was'nt too sure with the answers ,when it came to the installing/ testing of pv, no hands on ,and they told us what to write on test /commisioning sheets, i never had to pay for the course but in my opinion it was only an introduction to pv and not an installers course .
ps how much did ableskills cost?

 

[kablue2000]

to be honest i would'nt recommend niceic or any scheme course i think C&G course is always going to be better, the one i did the electrician had never fitted pv and was'nt too sure with the answers ,when it came to the installing/ testing of pv, no hands on ,and they told us what to write on test /commisioning sheets, i never had to pay for the course but in my opinion it was only an introduction to pv and not an installers course .
ps how much did ableskills cost?

£995 was well worth it,Jim the tutor has had experience as a PV installer so was quite knowledgeable

 

[Markc]

to be honest i would'nt recommend niceic or any scheme course i think C&G course is always going to be better, the one i did the electrician had never fitted pv and was'nt too sure with the answers ,when it came to the installing/ testing of pv, no hands on ,and they told us what to write on test /commisioning sheets, i never had to pay for the course but in my opinion it was only an introduction to pv and not an installers course .
ps how much did ableskills cost?

To be honest I've also been in C&G course's that have done that also. I think in the main its up to the training centre and like most colleges unless you pass the course they don't get paid. Wrong I know but I have been on an electrical course (recently) and a fellow sitting two seats away was a cleaner who had never done a day on the tools in his life. He held the entire course up with stupid questions which anyone with practical knowledge would never ask.
I had a chat with him at coffee and discovered he ran his own cleaning business in London and was gaining qualifications so he could start his own Electrical Contracting firm. He quizzed me all about Part P and then said he wouldn't probably worry about that bit and see how it goes!
I don't think you can beat practical experience and the piece of paper with certificate written on the top is little more than a token symbol.

 

[amigo]

Hi edexlab,
the general rule is the higher the DC voltage - the better.
This way you have less current to the same amount of power,therefore you'll need thinner cables and you'll have less power loses due to the heat.
However,the guys told you,that all you need to worry about is the inverter side,as most of the PV modules can be connected in series up to 1000 V.
So try to get as close as possible to the top input voltage of the inverter and you'll be fine safe.
Good luck

 

[mmccx]

If you use a Mastervolt, Fronius or SMA inverters then you can download a sizing programme from there respective websites, this will tell you how many modules of any manufacturer and make you can put onto any of their inverters. I would guess other inverter companies would have similar programmes but I am not sure.