If you missed Part 1, please have a look at it first and then come back here to read Part 2.
At this meeting, the manager refused to provide any assistance with regard to the problem. The optimisers were clearly not the cause of the interference, he claimed. However, Tigo Energy itself publishes a repair guide, which is considered confidential, on how to successfully repair a system that is affected by interference. In this manual the optimisers are certainly presented as a potential source of interference.
To eliminate the interference frequencies, so-called folding ferrites are to be attached to the connections to the optimizers. No technical or financial assistance was offered by the Tigo manager. Just this much: If the customer wanted to demount the equipment, he would refund the purchase price. However, the dismantling would have to be done at the customer's expense. Tigo also sent a threatening letter through their lawyers.
Following the conversation in Munich, Jochen Freisinn and his installer were left empty-handed. It is known from other such cases that the inverter must first be excluded as a source of interference. Freisinn installed a new Solarmax inverter and protected it with special filters on the DC side.
Transformerless inverters are naturally less protected against interference on the DC side than devices with integrated transformers. This repair shows no change in the interference levels, so the cause had to be found in the strings.
Wiring plated and twisted
Then it was time to fix the cabling on the roof: "We twisted the solar cables and laid them in metal cable ducts to protect them from emissions," says Freisinn. "All roof modules were fitted with ferrite cores at the access points to the optimisers to reduce any interference from the electronics." This is in accordance with Tigo Energy's repair instructions. Nonetheless, the company continues to deny all responsibility.
He initially left the fourth string of vertically installed modules on the surrounding terrace and on the facade unchanged. "First I wanted to know if the repair solution really worked as stated by Tigo," he explains. "Only then could we restore String D. Taking the modules off the facade is very, very complicated."
Like a youth science festival
Jochen Freisinn feels that photovoltaics and the solar energy transition are very important. That's why he took it upon himself to repair the installation. "I feel like this is the Swiss Youth Science Festival," he admits. Without any technical help from Tigo - apart from the aforementioned PDF document - he was actually left to fend for himself. The manufacturer does not offer repair kits, so the system operator must find out for himself which ferrite cores and which filters need to be installed to attenuate the interference.
Fortunately, his installer has agreed to share the costs. As of the beginning of March 2020, two roof strings had been repaired and their interference levels had dropped significantly. The third roof string still had interference from the optimisers despite metal ducts, twisted cables and ferrites.
The complexity of the matter can be illustrated by a sample of the operator's e-mail correspondence with his installer. In it, he refers to recommendations of an EMC expert whom he has since consulted. This expert has checked the system with special testing equipment. Now he recommends further ferrite cores for additional damping:
Very complicated repairs
"He determined during the tests that opposing currents are still forming and these also need to be eliminated. This is done by taking the two matching plus and minus conductors together and also shielding them with a ferrite. You could also take four conductors together, as discussed before, but they then fall into saturation and therefore you take the two conductors that belong together (two to the module and then the two along the string out to the next optimiser). So that means four ferrites per optimiser, or six ferrites in a double optimiser (i.e. two ferrites per two wires). So overall it adds up to just under 120 ferrites (60 MRFC-13 and 60 FRFC-13).
See also:
"Power adapters and PLC may interfere"
The EMC expert had announced that he would be available in mid-March 2020 to carry out the outstanding work. After that the Bakom comes over for the final testing. Based on the results of that test, it will completely or partially shut down the installation. Or approve it if the repairs are successful. " Maybe the weather will be bad, then the Bakom can't take any measurements," Freisinn says with gallows humour. "Then I have a little more time. One last reprieve."
So far, he has taken the solar modules of the roof system off and remounted them three times, and the next time up to the roof will be number four. Each day of the installer's work costs 1,600 Swiss francs. The ferrites combined cost around 1,500 Swiss francs. With the sheet metal ducts for the string cabling, the new inverter and the filters, it should eventually come out at around 20,000 Swiss francs.
Freisinn has written more than 300 e-mails in this matter, not counting the necessary costs and nerves.
And what will he do if the Bakom says no? "I guess I'll have to install micro-inverters," he says. "But then, in effect, we are looking at an entirely new installation. Which is going to make it even more expensive."
