Possible danger with solar power

[maltaron]

Have been doing some minor changes to my electrics and switched off the double pole isolator on the CU. But then a thought, solar is connected to the live bus bar via a 20amp MCB and thus makes the bus bar live again but not connected to the incoming supply. Another reason for checking for dead methinks!

 

[westie101]

Approved solar systems cannot generate AC voltage without a parallel with the AC mains.
They will however continue to produce DC power on their outputs

 

[Lectrician]

Have been doing some minor changes to my electrics and switched off the double pole isolator on the CU. But then a thought, solar is connected to the live bus bar via a 20amp MCB and thus makes the bus bar live again but not connected to the incoming supply. Another reason for checking for dead methinks!

This shouldn't happen with an approved system installed correctly.

 

[endecotp]

Shouldn't there be a massive warning sticker telling you about that risk?

 

[flameport]

Shouldn't there be a massive warning sticker telling you about that risk?

Yes, and a massive isolator switch next to it to disconnect the solar inverter.

 

[Iggifer]

And even if there is no isolator for whatever reason, killing the 20A MCB will kill the backfeed.

 

[Risteard]

To prevent islanding and danger to DNO staff a grid-tied inverter will shut down very rapidly once the DNO mains supply is lost.

 

[kai]

Shouldn't there be a linked Four Pole Isolator controlling both the PV and mains supply, so that when it is OFF, all poles are broken, the Mains and the PV feeds??
Google WYLEX PV Consumer Unit to find out more.

 

[Risteard]

No. There will be an AC and DC isolator for the PV, but once mains supply is lost the inverter will shut down.

 

[ban-all-sheds]

Whilst thinking of these issues, spare a thought for firefighters. It's all very well having a GTI which shuts down, and all-pole manual isolators, but if the sun is shining then the panels will be generating electricity, and there's no off switch for the sun.

 

[maltaron]

Thanks for all the replies. I must admit I forgot that as soon as I switched off the power to the live bus the invertor would have shut down. I do have DC and AC isolators at the invertor and another AC isolator prior to the CU.

 

[SimonH2]

No. There will be an AC and DC isolator for the PV, but once mains supply is lost the inverter will shut down.

It should shut down, but assuming it's not got any fault, it's still not "off" for the purposes of safe isolation - for one thing, it may well still leak a small amount of power, and it'll still have a significant power into it and energy storage (large caps).

Whilst thinking of these issues, spare a thought for firefighters. It's all very well having a GTI which shuts down, and all-pole manual isolators, but if the sun is shining then the panels will be generating electricity, and there's no off switch for the sun.

Yes, and there was a link posted some time ago to research that's been done regarding that. IIRC the panels can be supplying up to about 800V DC, through possibly fire damaged cables, connectors, and equipment. They found that spraying foam over the panels had little effect, only applying a heavy light blocking sheet would shut the panels down - something that's not really very practical.

 

[JohnW2]

Yes, and there was a link posted some time ago to research that's been done regarding that. IIRC the panels can be supplying up to about 800V DC, through possibly fire damaged cables, connectors, and equipment. They found that spraying foam over the panels had little effect, only applying a heavy light blocking sheet would shut the panels down - something that's not really very practical.

Indeed - and I wonder why the problem has not been addressed. PV elements obviously only present a hazard when large numbers of them are connected in series. It would presumably be easy enough to have relays connecting the groups of cells which could be de-energised to render the PV array relatively harmless, or some such arrangement?

Kind Regards, John

 

[endecotp]

They found that spraying foam over the panels had little effect, only applying a heavy light blocking sheet would shut the panels down

If you measure the open-circuit voltage from a solar panel with a high-impedance voltmeter, it will tend to show a high reading even when the illumination is low. But it will be unable to supply any significant current at that voltage. As a first approximation you should think of a solar panel as a current source, with the current proportional to the incident light.

It would be interesting to know what the research you're referring to was actually measuring. Can you post the link?

 

[a546345]

The newer systems (Solaredge) with optimisers on the back of each panel fail safe. If there is no grid connection to the inverter, then the output of the optimiser at each panel drops to about 1VDC. The inverter communicates with each optimiser through the DC connection. Apparently it is worth telling the fire brigade if you have this system so they can store a note against the address.