Inverter choice help needed

synergy power · Jan 14, 2012

Hi Everyone,

I have a PV system i am going to install for a customer but i am a little unsure about the inverter configuration.

The job is a SE facing, 30 degree, no shading system using 16 SANYO HIT 250 modules.

I have ran the figures through PV SOL and it recommends i install it through 2 strings of 8 modules and use a SMA SB 3300 inverter.

What are you opinions on this? Would any of you choose something different that you feel would work better?

Thank you,
Ryan.

powervan · Jan 14, 2012

well first thing WELL DONE TO GET A JOB WITH QUALITY GEAR! i would run 2 strings back to sunnyboy 3800! my first system was a 4kw with sunnyboy 3300 (suppliers spec) well it works out if temp ever drops to -15 and sun comes out it prob blow inverta??? sma chap i spoke to said 3300 was a no no!! even though supplier had no doubts about it?? i now no what kit to use but as it was first job i went with there advise ! ive since learnt THAT SUPPLIER WAS CRAP! then again so are a few of them! hope there sat in office with phones very silent at mo

synergy power · Jan 14, 2012

Thanks for the help, i did think the same in that the power of the system may just be too much for the inverter given the right conditions. I will probably ask the same question to my supplier just to see what answer i will get from them as well. Thanks.

SpitfireW'sale · Jan 17, 2012

You could run 2 strings of 8 panels connected to a SolarMax 4200S inverter (Sputnik Engineer). The systems is very efficient resulting in good annual yield. The choice of Panels is excellent. I think we need to focus on efficient PV Panels if we want to keep the payback period short. Do not hesitate to contact with us, if you need further assistance with the inverter choice. Thanks.

meeb · Jan 17, 2012

3300 and 3800 are pretty much same inverter but the closer to the array size you can get the inverter the more of the generated power you can use. Bare in mind that your whole array will only hit its top performance maybe 4-5 times a year.

But try explaining that to a customer...

starcott · Jan 17, 2012

I am somewhat confused about this matter of matching the size of the array to the inverter. Can you explain, in layman's terms, why the closer you can get the two, the more the amount of generated power you can use?

I have just read a quote from Technical Service Support at SMA UK: 'only issue with oversize is that you will pay more".

Also one from Technical person at Powerone: "oversize (ignoring startup v) doesn't matter."

I have personally spoken to the Technical Project Engineer at Eltek who told me that their 4.4 inverter was very suitable for a 3.8 array, as long as the inverter was configured to the UK grid.

moggy1968 · Jan 17, 2012

if you go over a 3.6 inverter you will need to apply to the DNO so most people fit a 3.6 to avoid this. Inverters like to work hard so conventional wisdom is that oversizing an inverter means it's not running efficiently. In reality the difference in annual yield appears marginal between say a 3.6 or 4.0 inverter, but slightly in the favour of the 3.6. A 4kW system won't kick out 4kW bewcause of the losses in the system components, which is why a 4.0 inverter would be regarded as oversize.

In my neck of the woods (south coast) a 3300 is very undersized for this system. My preference would be a fronius 3.6 which you could run as a single string or an Aurora 3.6OTD if you really want 2 strings. If you wanted to match the inverter size to the array size you could use a SMA 4000TL.

PV sol comes out with some weird ideas sometimes! better to use your own expertise and experience TBH! the segen website has useful info on undersizing inverters and why.

It's worth pointing out that SMA had no decent inverter between the 3000HF, 3000TL and the 4000TL they had nothing in that crucial 3.6 bracket which slips into the G83 16a limit. That may be the real reason why SMA say oversizing isn't an issue, or is that me being cynical?! Power one are the principal importer of SMA into the UK so the same applies.I believe though they are soon bringing out an inverter to fill that gap, which would be good because I like their products and especially the sunnybeam monitor which is simplicity itself.

MorganPVI · Jan 17, 2012

moggy1968 said:
Power one are the principal importer of SMA into the UK .

Power One - Aurora manufacturer? Are your sure they import SMA to the UK?

We have a few systems using Sanyo 250w and SMA3300 very good match in my opinion, not shared by all posters in this forum. Power One 3.6tl are a good choice for any panels - well priced too.

SMA have launched the 3.6tl model, Wind and Sun were/are stocking them I believe (or some supplier that spams my inbox) There is an SMA 3.6tl and it is due for the UK if it is not already available.

FB. · Jan 17, 2012

starcott

An inverter which can output 2~3kW might reach peak efficiency (mid-90's percent conversion of DC to AC) at just 0.5kW output, whereas a 3~4kW inverter might not reach peak efficiency until it is outputting 1.0kW.
Basically; when the DC current is only just trickling into the inverter on a dull day, a smaller inverter is a few percent less wasteful than a larger inverter.

What would be ideal would be a 4kWp array with a 4kW inverter for summer and a 2kW inverter for winter - or, even better; a 4kW inverter which was actually twin 2kW inverters, of which one of the twins would shut down on dull days to improve efficiency.

My own panel array has a nominal maximum output of about 5% more than the inverter (3.75kWp array, 3.6kW inverter), but since the inverter will waste at least 5% during the AC/DC conversion (and probably a couple of percent DC cable losses), 3.75kWp is likely to become 3.6kW output at most - and even that maximum potential could only be achieved on a handful of bright summer days each year - if ever!