Renewable Energy Innovation

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re-innovation was asked by EvoEnergy to provide a test unit for their solar photovoltaic installations.

 

 

 

During the winter months, solar PV installations may finish after the sun has set. All PV installations should be tested to check that the solar PV panels are working correctly, the cables are good and that the PV inverter (which connects to the grid) is working. It was usually possible to test the PV panels before the sun has set and it does not matter if there is sunlight to test the cables but on a number of occasions the sun had faded before the inverter was powered up and tested.

To solve this problem, re-innovation were asked to produce a unit which would power a PV inverter and act like the PV modules so that the inverter could be commissioned.

To do this we supplied a low power (100W) isolated DC power supply. This unit could be plugged in to a local AC socket and would provide a DC output which would act similarly to a string of PV panels. This can be plugged into the DC side of the inverter and used to power up and commission the inverter.

The final device is shown here:

The unit is wired up as shown here:

Wiring diagram for inverter test unit

The basic wiring diagram is here:

Inverter test unit circuit diagram

Disclaimer: This unit is at a dangerous voltages. Do not build this circuit unless you are fully trained and competent with both AC and DC supplies.

The main design is a rectifier on the input AC to give around 320V DC. There is a resistor in series with the output cable which, as the inverter draws current, will cause the DC voltage to drop. The inverter will follow the maximum power point and hence pull the voltage down. The resistor will be dumping power, equivalent to the power supplied to the inverter, around 50W. This means that resistor must have a large heatsink and a fan to ensure it does not get too hot. The transformer provides galvanic isolation. The parallel resistor discharges the smoothing capacitor on the output.

These units were supplied with an instruction manual and the installers were trained in its safe use.

Comments   

 
#5 Guest 2014-05-22 21:44
I do not think this would work the sunnyboy because they need 175vdc newer needs 150vdc to startup and 150vdc newer 125vdc to keep running.
Thanks for the schematics will have a look and see if I can make something up for my sunnyboy 4000tl.
Will have a read on the isolation of the CPSU, I do nto buy the cheap Chinese things but more the over £150 versions top end PSU, but have a spare so might give it a go after the reading and trying to get my head around it.
Thanks for the great article.
 
 
#4 Matthew Little 2011-07-25 19:08
Quoting andy:
hi there i have made this curcuit and have tested it on an sma 3000kw inverter, in replacement of 14 sungrids 215w panels, but unfortuantly the inverter just keeps fllashing and doesnt match grid and draw watts. wot could be wrong. thank u andy.


Hi Andy, Sorry this design is not working for you. Is the inverter the SunnyBoy SB3000 or the SB3000TL transformerless? I've not used this with transformerless inverters, so might be a problem there, although I don't know why it would be.
To fault find the unit, please check the output voltage of the inverter test unit without anything attached. This should be around 320V DC (Note: safety!). If you can check this when the inverter is attached it should power the inverter. The voltage should stay around 320V. The inverter should wait 3mins for G83 connection, then the voltage will drop as the inverter tries to do maximum power point tracking. The voltage should rest around 150V DC, but only be able to supply around 40-50W (maybe too low).
What is happening in your case?
Please let me know how it goes,

Matt
 
 
#3 Matthew Little 2011-07-25 19:01
Quoting Shaun Fido:
Hi can you please tell me if this item is available for purchase if so where can we obtain price & availability from ?

Many thanks

Shaun


Hi Shaun - Yes, we can supply these units. Please email me at matt_at_re-innovation.co.uk and I can give you a quote and lead time. Might be good to know which inverters you are using so I can check the voltage ranges.
Regards, Matt.
 
 
#2 Shaun Fido 2011-07-20 07:21
Hi can you please tell me if this item is available for purchase if so where can we obtain price & availability from ?

Many thanks

Shaun
 
 
#1 andy 2011-07-11 20:08
hi there i have made this curcuit and have tested it on an sma 3000kw inverter, in replacement of 14 sungrids 215w panels, but unfortuantly the inverter just keeps fllashing and doesnt match grid and draw watts. wot could be wrong. thank u andy.
 

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