# new system designed by myself

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Solar Expert Posts: 29
I have been building solar trackers for over 2 years now ,got a 520w Kyocera tracker working perfect.
A good friend has asked Me to design and install 5kw system.I know I am up to the challenge and have a good understanding of equipment available.I think.

I have detailed plans and specs as below

30 x Sharp 175w 24v panels
1 x SMA SB4000-TL 20 Inverter
1 x SMA SB 3000-TL 20 Inverter

I decided that because the sun moves from East to West around the building it was going to have 3 strings of 10 panels using 2 inverters.

The SB4000 would run 2 strings of 10 panels while the SB3000 would have 1 string of 10 panels.The Sb4000 would handle two parallel strings(balanced inputs with separate MPPT on each string as the specs say.)
The SB3000 is single string only so 10 panels only.

The sharp 175w panels peak at 35.4vdc so I thought 385.4vdc each string.
MPPT works from 125vdc to 450vdc but headroom on the inverters is 550vdc.

My question is Do this sound right? Are my figures right ?
I have limited room on the main flat roof for 20 panels maxium on the East flat roof,the west flat roof could take 16 if needed but I want to start with a total of 30 panels.
I will be buying the items from Holland in Europe as its a ferry there and back and it cheaper by loads than in the United Kingdom.

I will answer more questions no problem

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Re: new system designed by myself

I believe SMA has a string calculator... But I will use the Xantrex one for now as it is one that I know and understand its output...

First, really need to know the exact panel model number or Vmp, Voc, Imp, etc... Since you are planning on 10 in series--any errors can get multiplied by 10x.

Using the Xantrex Calculator--And Sharp NT-175U1 panels, Set your min/max temperatures for your region (say -5 to 35 C) (and you can pick any Xantrex inverter around the wattage of the SMA--we just want the numbers):
Max Power Voltage - Vmp 35.4 Vdc
Open Circuit Voltage - Voc 44.4 Vdc
Voltage Temp Coeff - Vtoc -0.144 V/°C
STC Rating - Pmp 175 Wstcdc
Max Power Current - Imp 4.95 Adc
PTC Rating 154.2 Wptc
Looking at the Max/Min voltage chart (for -5 to 35C):
```[FONT=Fixedsys]
Max Voc Min Temp    Min Vmpat Max Temp(Vdc)
==========================================
8 Modules    389.76    231.36
9 Modules    438.48    260.28
[B]10 Modules    487.2    289.2[/B]
11 Modules    535.92    318.12
12 Modules    584.64    347.04[/FONT]
```
The Voc (open circuit, -5C) voltage for 10 panels is 487 volts--looks good.
The Vmp (maximum power 35C ambient) for 10 panels is 289 volts--looks good.

So, I don't see any issue in your sizing/string setup.

Sounds like you are roof line limited--So, you don't really have to question if you get more before noon or after noon sun (optimum collector placement) and you did not say what kind of billing you have (flat rate or Time of Use--Flat rate, setup for maximum power collection--Time of Use typically charges more for afternoon power--so optimum is to setup panels for more afternoon collection).

Mount panels at around 5-6 inches off of the roof (or more) for better air circulation (cool panels generate more voltage, P=I*V so higher V means higher P-power).

Most panels (at least in the US) come with MC type connectors--you should get a tool/parts to mate to them, or get Male/Female pig-tales you can cut in half (plug to panel, hardware to your system wiring).

Note that PTC and CEC (from the Xantrex support page) are ratings used by California (and probably others) to rate GT systems for their "more realistic" average output (rebate calculations) vs the "marketing" STC ratings that panel mfg. use.

-Bill

PS: I am sure you are aware of shading... Difficult to tell from picture, but you may have significant shading in the winter (sun low in sky)...
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 29
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Re: new system designed by myself

Thanks BB for the info

In the UK we still don't have a rate to sell to the grid but its coming in 2010 but we probably will have a new government.Only got solar on domestic houses last April as permitted development ( no paying the council money for permision to put up your own system.)

I have 30 male solarline 2 connectors and 30 female and 50m of cable from my last purchase from solarline UK and I will be buying the connector tool this time but its £300 but I will not be paying this time so.

Technical specifications:
Maximum power: 175 watt peak power Voltage at maximum power: 35,4 V x 10= 354vdc @ 5.028amps
Total 10.36 amps 3500 watts max

Current at maximum power: 4,95 A
Open circuit voltage: 44,4 V
Short circuit current: 5,55 A

Specifications:
Cell: mono 72 in series
Application: DC 24V systems
Dimensions: 1575 x 826 x 46mm
Weight: 17 kg
IEC 61730
IEC 61215

This is all I have until I collect the panels

I hope this is the start of a job for me as I fix pcs and install anything Audio video self employed from August this year but want to get into solar and wind power,
• Solar Expert Posts: 10,300 ✭✭✭✭
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Re: new system designed by myself

vanman,
in general a system like you propose will work and you seem to have the basic dilemma most of us have with no clear ideal unobstructed southerly views. as it rises, the westerly pvs will not produce and as it sets, the easterly pvs will not produce. hopefully you don't suffer morning fogs making the easterly arrays produce even less. hope it works well for you.
• Solar Expert Posts: 29
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Re: new system designed by myself

If I had my way I would put everything on Trackers but that's in a perfect world.
But over here we are well known for the wind so I have to build them strong 100% over the top for trackers.

Everything is a compromise

thanks again

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Re: new system designed by myself

Regarding your panels... Make sure they are rated for high voltage (at least in the US, that is usually 600 VAC minimum for the electric code) and have appropriate approval (UL, CSA, ETL, GS, TUV, BSA, or whatever is required for your area).

There are some panels that are designed for battery systems and not rated to put 10+ modules into series... Need the exact model number and spec. sheet (or look in Inspector's handbook) to ensure appropriate approvals (I don't think you have a problem/issue--but is a requirement for the panels to meet).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 29
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Re: new system designed by myself

Ok will make sure I get the correct ones before I take the trip to Holland

The chap called Marco is a director and so far he seems to know what is What .

I have just yesterday sent him a price I want to pay for the Kit.
He has not replyed yet so he is adding his Sums up. Should be Interesting.

I gave him a price of \$375 Euros per panel
SB4000 \$1850.00
SB300 \$1500.00 Euros

Hope I can deal with him Save some Money
• Solar Expert Posts: 1,571 ✭✭
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Re: new system designed by myself

Vanman,

Firstly, it's not legal to use (TL) transformerless inverters in the UK - currently UK requires transformer based inverters.
Secondly, it seems that the inverters are oversized for the given installation 7kW of inverter vs. 5kW of panel - was this deliberate to accomodate future expansion?

The Sunny Design tool available free of charge from the SMA website is really quite useful in speccing the inverters and string design.
For the east roof: 2 x 10 panels, the SB 3000 looks to be matched.
For the west roof: The SB 1700 comes closest but you'll need to go 2 x 5 instead of 1 x 10.

Disclaimer: I'm not a professional designer, so please double check this!
• Solar Expert Posts: 29
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Re: new system designed by myself

Clarification on the uk spec for the SMA SB4000-TL 20

This means the SB3000 and the 4000 /5000 are G83 Compliant

• Solar Expert Posts: 1,571 ✭✭
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Re: new system designed by myself
vanman wrote: »
This means the SB3000 and the 4000 /5000 are G83 Compliant

Dated 24/06/2009, Just after I completed the course at SMA then Thanks for the clarification. BTW, the Sunny Design tool doesn't have this info updated yet, so you'll have to check the "ignore country" in the inverter section in order to see the TL inverters in the tool.
From the letter, it sounds like SMA have made some changes to the configuration of inverters shipped to the UK -but which won't be applied to inverters you buy in the Netherlands. I'm sure they'll let you have the password to access those settings if you explain the situation.

What about the potentially oversized inverters?
• Solar Expert Posts: 29
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Re: new system designed by myself

All I can really say is German Engineering is beyond doubt the best in the World and I for one would buy anything German Just look at their cars to see why.

If they cannot get it right then it cannot be done
The Americans and Ruskies only got to the moon with German Scientists they stole from WW2.

This is a German model plane builder Loads of dedication needed.

This was posted on a Biodiesel forum I visit regulary

:D:D8)
• Solar Expert Posts: 1,571 ✭✭
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Re: new system designed by myself
vanman wrote: »
All I can really say is German Engineering is beyond doubt the best in the World and I for one would buy anything German Just look at their cars to see why.

Not sure I understand, was this a response to something I said in the previous post? or is it unrelated?
• Solar Expert Posts: 29
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Re: new system designed by myself

Sorry
What I meant is SMA make High quality equipment made in Germany

It seams generally that all switch mode psu,s are best to be oversized as they work a little bit harder than transformer types

The SMA SB4000-TL 20 has switches that the user can change himself to set the Country and selfs find the correct voltage cool.

MotoGP starting at 12.30pm so I will be back after the race