question

kevinc avatar image
kevinc asked

System Check, grid tied UK system

I am in the process of getting a system installed.


Currently i have 7.2 kw of solar panels (i would like to increase to 15kw in the future)

and

4 x pylontech US5000 batteries on order ( i am open to adding more batteries in the future)


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This is the system template that i am working from

https://community.victronenergy.com/storage/attachments/24658-aa8e5611-87cb-46e8-ab05-7536ca42a2b6.jpeg

1665678733881.png


I am now looking to order the Victron products

VictronMultiPlus48/5000/70-50
MPPT smart solar controller. 250/100 MC4 VE.can Bluetooth

Victron Lynx Shunt

Cerbo GX Controller

ET112 Energy meter ( to be installed closest to the grid, to monitor grid use)

Victron Lynx Distributer 1000A Busbar




I have a number of questions


1. With the Multiplus 2, is the 5000 size large enough? is the 3000 and 5000 the only ones passed by regulators to use in the UK


2. How much power can this draw and send to the grid as i plan to take advantage of Octopus Agile 30 minute tarrifs


3. Is the size of MPPT correct


4. Is the Shunt needed or is it an optional extra


5. Do i need to buy anything alse in addition to what i have listed?

Multiplus-IIPylontech
1665678733881.png (476.1 KiB)
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Craig Chamberlain avatar image Craig Chamberlain commented ·

Something to be aware of is that, as of right now, Multiplus-II inverters are not G99 type tested for new UK installations. Have a read of this thread to get the details.


https://community.victronenergy.com/questions/160177/victron-inverters-no-longer-approved-for-uk-dno-gr.html


This should be a temporary situation and will hopefully be resolved in a few weeks but it throws a spanner in the works for the DNO G99 application in the meantime.

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wkirby avatar image
wkirby answered ·

In the MultiPlus II range, only the 3kVA and 5kVA models have type testing certificates for UK grid parallel operation. G98 notification for 3kVA and G99 application for 5kVA model.
There is also a 8kVA or 10kVA Quattro which have G99 certificates and are suitable for 4x US5000 batteries.

MultiPlus II 5kVA can charge from the grid at ~3.5kW (70A charge current).
Inverter can make 5kVA

That is a 100A MPPT, it can charge the battery at 100A maximum which is ~5kW. Your array is a bit over sized for that. It won't damage the controller, but the controller can only take ~5kW from the array. You'll also need to take care to arrange your array in series / parallel strings so as to stay below the 250V maximum input Voltage of the controller.
As you plan to increase your array size even further then perhaps a MPPT RS 450/200 would be better, although the limit is ~10kW with this model.
To take advantage of the full 15kW of your current and future arrays then three 100A controllers would be the answer and your arrays would need to be split up into three separate arrays for each controller.

Don't include a shunt, this will only add confusion. The US5000's will provide the necessary information using their own built in shunts.

All sorts of cables, fuses, ancilially connectors and fasteners will be needed to finalise the installation.

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kevinc avatar image
kevinc answered ·

Thanks for your reply wkirby


regarding the MPPT


I have 18 JASolar 405W panels, i think in 2 strings (but i will check this)

https://www.jasolar.com/uploadfile/2019/0529/20190529105240378.pdf

If that is the case i think it would be best to have a MPPT for each string (do you agree?)


I am new to these calculations

9 x 405 = 3645 Watt so just over 70Amp


So to size the Mppt i want just over 70 Amp


What about volts


is it 9 x 41.46= 373 volts


I am guessing i have got this volts part wrong?


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wkirby avatar image wkirby ♦♦ commented ·

Thank you for the additional information.

Your calculations are correct. Re panel Voltage, that is at 25ºC, so on a crisp, cold, sunny morning this Voltage will be higher.
18 of these panels gives us some tricky problems to deal with.
We can have the panels arranged in 1x18, 2x9 or 3x6. 1x18 won't work as it's over 700V.
2x9, as you have calculated is 373V, no good for a 250V controller.
3x6 would be 248.76V. This is awfully close to the maximum for a 250V controller and a little below 25ºC this Voltage will exceed 250V.
6x3 would bring the Voltage down to a level acceptable for even a 150V controller.

So 2x3 into a MPPT 150/45 would be pretty much perfect. 6x panels would be capable of 48.6A at 50V. A 45A controller would be not be losing much for the incredibly rare occasion that the UK weather offers us full power. This arrangement would need to be tripled of course.

2x9 work into a MPPT RS 450/100. Each string of 9would even get it's own tracker - which is nice. Power would be capped at ~5kW though.
2x9 would also work into a MPPT RS 450/200, each string having it's own tracker with two more trackers available.The full power of the 18 panels would be realised. Indeed the full powerof 3x9 strings would be realised.
The remaining 9 could go into the last free tracker of the MPPT RS 450/200 but you'd not see the full 15kW from the 36 panels.
This is not usually a problem here in the UK because it is rare to see full power anyway, most of the time you'll be seeing 25% - 75% of nameplate power.
If you really care about seing the full power of your array then the ramining 9 could go into a 3x3 arrangement to feed a 150/70 controller. You do need to fuse each string of three before combining them.

Lots of options, hopefully not too confusing.

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kevinc avatar image kevinc wkirby ♦♦ commented ·

Hi wkirby


I was going to purchase the MPPT RS 450/100 but Bimble Solar are saying we should use the Voc which is 49.81V As soon as the temperature drops below 25C the Voc will increase and destroy the MPPT.


That being the case what would you reccomend 3 x 6 in the MPPT RS 450/200?


you also wrote


6x3 would bring the Voltage down to a level acceptable for even a 150V controller


i guess this would not work now with the new voltage, any other thoughts?


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Jason - UK avatar image
Jason - UK answered ·

@KevinC I've a 5kva 48v Multiplus II that meets 99% of my energy usage. On the odd moments I cant meet the demand, it takes a little from the grid bit its minimal.

Link to my VRM real time info below so you can see how it performs on a 5 bed detached house using a ASHP for HWS as well. Photos of the install in the menu as well.

https://vrm.victronenergy.com/installation/171934/share/db6807bb

1665744051875.png


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kevinc avatar image
kevinc answered ·

thank you again for your answer wkirby you wrote


2x9 would also work into a MPPT RS 450/200, each string having it's own tracker with two more trackers available.The full power of the 18 panels would be realised. Indeed the full powerof 3x9 strings would be realised.
The remaining 9 could go into the last free tracker of the MPPT RS 450/200 but you'd not see the full 15kW from the 36 panels.


I am thinking towards thhis solution MPPT RS 450/200

So if i follow you correctly my current 2 strings will attach to this.


Do i understand you correctly that i could connect a 3rd string to this unit and get the full power of 27 panels, but not a 4th string?

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wkirby avatar image wkirby ♦♦ commented ·

The MPPT RS 450/200 has four trackers.
So you could easily connect your current array to this device in two strings of 9, each string on its own tracker.

You could then connect another string of 9 to the third tracker (for a total of 27 panels) and get the full power of all 27 panels.

You can connect a fouth string of 9 to the fourth tracker for a total of 36 panels.
You'd only miss out on cold sunny days. For the other 95% of the time these 36 panels will not cause the controller to limit the power and they would work very well.

In the UK it is not a bad design to "over panel" the charge controller or PV inverter because it's so rare that the conditions allow for full power. The UK is cloudy most of the time. This last summer it was sunny for several weeks in a row, but it was also hot which causes the panels to under perform too. When it's 30ºC outside the panel temperature is even higher and output can be 75% of nameplate.
The over paneled controller would max. out at ~10kW. You'd need to decide if that would be problematic for <5% of the year.

If you really do want to take advantage of the brief full power moments then three strings of 9 into a MPPT RS 450/200.
The remaining 9 into a MPPT RS 450/100 leaving you with a spare tracker for another array.
Or the remaining 9 into a MPPT 150/70 in 3x3 arrangement.

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kevinc avatar image kevinc wkirby ♦♦ commented ·

Thanks again wkirby, I will go with the MPPT RS 450/200.

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kevinc avatar image kevinc wkirby ♦♦ commented ·

Can i ask another likely silly question.


Lets say i have

36 panels all wired into the 4 trackers of the Mppt RS 450/200 and it is outputting more than 11kw.


Now say the batteries are fully charged.


If i have

1x VictronMultiPlus48/5000/70-50


Does this cause a serious problem as the mppt is sending 11kw but only 5kw can canverted to AC and passed through the Multiplus.


Does the remaining 6kw cause a major issue with the equipment?


With more panels i will get more than 1 multiplus but just wanted to know what happens if there is more power being sent to it than the multiplus can handle.

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philippem avatar image
philippem answered ·

you should be aware that all those power electronic products are very sensitive. I would not do a installation like that. I always put at least 2 MPPT and 2 inverters so in case a product is defect you still get some power. Usually Victron is very fair concerning the warranty put it will take several weeks to send back the product, have it tested and replaced, please take this aspect in account.

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