Eltek 3800s and Sunnyways 4200 questions

[starcott]

I've just had 16 Sanyo N240 panels installed with an Eltek 3800S.

I asked for 2 strings because I understood that as the Eltek has a max DC voltage of 780 v and that as 16 Sanyos would have an open circuit voltage of 838 v, the wiring of the panels would need splitting into 2 strings of 8. However, the 2 electricians doing the job insisted that the max power voltage was the figure to use, and that this came to 699 v for the 16 panels, therefore only one string was needed.

We consulted with 2 different technical members of staff at Eltek. The first one said only use it with 2 strings of 8. The second one put the 3800 through a feasibility study and reported that the Sanyo system need a 4200 model, with no mention of 2 strings.

The installer has left us with only 14 panels on one string until the issue is resolved. He has suggested a Sunways NT 4200 to replace the Eltek.

So I am looking for comments on the Sunways 4200, or help me get some clarity on the situation. I can find very little reference to the Sunways on the forum.

John

 

[sharpener]

I've just had 16 Sanyo N240 panels installed with an Eltek 3800S.

I asked for 2 strings because I understood that as the Eltek has a max DC voltage of 780 v and that as 16 Sanyos would have an open circuit voltage of 838 v, the wiring of the panels would need splitting into 2 strings of 8. However, the 2 electricians doing the job insisted that the max power voltage was the figure to use, and that this came to 699 v for the 16 panels, therefore only one string was needed.

No, because in any situation where the inverter is drawing no current the input stage will see the full o/c voltage and this may damage it. Also you have no margin for cold weather, the voltage per panel will increase by 0.131V per deg temp drop below 25C which might add another 80V.

You also need to check that in hot weather two strings of 8 will still be above the MPPT min voltage in low light levels. Otherwise I can't see any reason why the 3800 inverter should not be OK but I have no personal knowledge of either make.

 

[starcott]

Thank you for that response. The installer is obviously still keen for us to keep the Eltek despite Eltek's own software, Theia Site Designer, indicating two problems.

Firstly, The MPPT range of the inverter is 315 to 630v, but the MPP input range from -5 to +40 degrees C is 233 to 305 volts.
Secondly, Max DC current of inverter is 12.0A but the Mac current of the PV Generator is 13.54 A.

Would you consider these 2 findings to be serious enough to insist the 3800 is not suitable for our setup?

 

[sharpener]

Thank you for that response. The installer is obviously still keen for us to keep the Eltek despite Eltek's own software, Theia Site Designer, indicating two problems.

Firstly, The MPPT range of the inverter is 315 to 630v, but the MPP input range from -5 to +40 degrees C is 233 to 305 volts.
Secondly, Max DC current of inverter is 12.0A but the Mac current of the PV Generator is 13.54 A.

Would you consider these 2 findings to be serious enough to insist the 3800 is not suitable for our setup?

Don't understand yr figures, from e.g. http://www.sanyo-solar.eu/en/servic...data-sheets/?eID=dam_frontend_push&docID=1234 the MPP current at STC is 5.51A per string and voltage 349.6, these are nicely within the limits and look fine to me, is this the panel you have (the o/c voltage agrees with yr OP)?

Looks as though the s/w has used panels with fewer, bigger cells giving more current and less voltage, check they have used the correct type.

 

[starcott]

Thank you again for that information.. I had made a mistake inputting the max power current value and voltage on the software.

With the correct values, max current shows as 11.02A, which is just below the max current of the pv generator at 12A.

 

[daytona600]

cant send reply to your message - i included contact detail;s

 

[starcott]

We have had further developments this afternoon.

The installer has offered to replace the Eltek 3800S, because 'once the ambient temp rises above 28 degrees, the inverter could fail to reach the MPP input range.'

The suggested replacement is a Theia 4.4 HE-t. I am now looking for views on its suitabilty with reference to its size.

We have a 3.84 kWp system. The 4.4 HE-t has a nominal DC power of 4600 W , a max recommended PV power of 5750 W and a max input current of 21.0 A.

I remember reading somewhere that it is not a good idea to have an inverter which is too powerful. I'm not clear what 'powerful' means.

Is the 4.4 too big? If so, how will it affect performance?

John

 

[jb2000]

HELLO ALL
ive got a 4kw system 16 panels sharp 250w with the theia he-t 4.4kw it has 3 string inputs but is only using two of them and im having trouble with connecting in to the laptop for monitoring it. have set it up as they say but still no joy would appreciate any help.

 

[starcott]

I can't help you with the monitoring problem since I haven't yet reached that stage.

However, I would be interested to know how your 4.4 is performing on a 4 kWp system.

Was it selected by an installer as being the most suitable for your system?

 

[jb2000]

i was expecting the sunnyboy but thay were out of stock and this was available it seems to be running fine and had no probs.It was the first they had fitted so will talk to them soon to see if they have sorted out how to connect it to the laptop. the inverter is very well built and looks like a very nice bit of kit with its own colour srceen and very easy to look at the data just as well its in the garage and not the loft !! Its been in for around 4weeks now and produced 62 units weather not been the greatest in sunny kent.Hope you get yours sorted out soon.
p.s. your installer might want you to keep the old one as i think the eltek is more money my installer did it for the same price but think it cost him.

 

[sharpener]

We have had further developments this afternoon.

The installer has offered to replace the Eltek 3800S, because 'once the ambient temp rises above 28 degrees, the inverter could fail to reach the MPP input range.'

The suggested replacement is a Theia 4.4 HE-t. I am now looking for views on its suitabilty with reference to its size.

We have a 3.84 kWp system. The 4.4 HE-t has a nominal DC power of 4600 W , a max recommended PV power of 5750 W and a max input current of 21.0 A.

I remember reading somewhere that it is not a good idea to have an inverter which is too powerful. I'm not clear what 'powerful' means.

Is the 4.4 too big? If so, how will it affect performance?

John

Again don't understand their calcs. With 8 panels in series the Voc tempco of the string will be - 1.05V/degC, on the figures above this means that to reduce from 349.5 to the 315 Vmppt min of the inverter the panel temperature would have to rise from 25 to 58 deg, is this likely given that in a 25 ambient the NOCT is 44 deg so you have 14deg in hand?

WRT the choice of inverter you would have to look at the efficiency curves but with 3840W array on a max 5750W inverter I would suspect you will always be some way below the optimum working point, and this may well be worse than accepting a minimal loss of output on extremely hot days, consider also where you are located and what are the probable wind conditions for cooling the panels.

 

[starcott]

These figures are from the tech spec sheet for the 4.4 HE-t

Input
Max DC Power 4600 W
Max DC Voltage 600 V
Max Input current 21.0 A

Output
Nominal output power 4450 W
Max AC Current 20.0 A

 

[dansk]

starcott - this is an easy fix - either do 2 x 8 panel strings on the 3800s - or another alternative is the 4301S and the power one 3.6 or ever solar 4000tl (capped at 16A) as suggestions - in my eyes this is the solution - plus you dont want the hassle of applying to the DNO to have an inverter over 16A ac output.

 

[starcott]

The 4.4 has the facility to be capped to 16A by using some sort of internal controller. That information is in the brochure.

We have been offered these 2 options, the 3800S or the HE-t 4.4, as both are available now.

What disadvantage is it to have an inverter that a max pv power well above that of the array?

 

[dansk]

As shapner stated above, it's best to undersize an inverter with the uk climate, Reason being we don't often reach peak performance days, and on the days it's dull it's best to have a smaller inverter therefore meaning it will be working at optimum when the days are less than optimum, the only downside is when we do have optimum days the inverter may max out, but that is a risk worth taking. Remember pv systems are "peak" performance and don't often run at maximum output for long, my view is we have more "less than optimum days" than we do optimum. Oversize inverters won't be running at there best. It like pulling away in second gear, not good but it works.