Typical DC input voltage of solar inverters?

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Although I don't have solar panels myself, I see a lot of houses with them nowadays.

That got me thinking, what DC voltage normally goes into the inveter from the solar panels on a bright sunny day for example?
 
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12 -36 volt is typical for for small systems charging batteries etc

8 kW at 12 volt would require 667 amps from the panels


200 to 300 volts is more common in the domestic solar arrays.

In the USA it can be as high as 600 volts where the building code allows for such high DC voltages in domestic property. Some areas limit to about 300 volts DC,
 
I think it's 12v but about 8kw

No, its much much higher.

4 kW (the max size for a domestic array) would need a current of 4000/12 = 333A.... that's just not practical!

The panels are connected in series/parallel groups to get a string voltage of around 200 - 400V DC.

edit: beaten to it!
 
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Can't remember where - could have been here - I saw it, but someone posted a link to a Fire Service document where they'd been looking at the risks of solar PV installation to their people.
With no load (inverter failed, damaged by fire, shut down due to failed main, whatever) the DC voltage could be a LOT higher than suggested.

IIRC they then went on to say that other than covering the whole array with a thick (opaque) tarpaulin, there wasn't really anything practical they could do to reduce this voltage.
 
IIRC they then went on to say that other than covering the whole array with a thick (opaque) tarpaulin, there wasn't really anything practical they could do to reduce this voltage.
Indeed - such is PV, and you can't change physics/chemistry. However, I would have thought that spraying with something sticky and opaque would be more practical (and safer) than trying to position a tarpaulin - particularly if the building were on fire.

Kind Regards, John
 
It mentioned that spraying with their standard foam had little effect. I suspect that getting something that's sprayable (especially by someone stood on the ground and aiming at a roof on a 2/3 storey house), and is sticky enough to stay put, and is opaque enough to do any good - would be quite a challenge !
 
they are connected to the inverter with some kind of fire-resistant cable. The inverter will turn off if connection to the grid is lost, so I suppose the cables to the inverter will continue to be live until the fire starts to damage the installation on the roof, but it will not make the house circuits live after inverter shut-down.

I thought I had heard the OC voltage could go up to 800V but don't remember where.
 
I think the issue was the risk to fire fighters spraying water over cables (that may be damaged) carrying up to 800V DC and with no way to switch them off. Not to mention, if they fail to see the cables and lean a ladder against them.

Also, while many installations run the cables down the outside of the building, I can see that they may well encounter them inside where some forward planning has been done and/or the householder prefers a bit of making good inside to having washing lines down the side of the house. Thus a fire fighter groping around in a smoke filled room could potentially come across live wires with 800V DC on them.

Of course, post fire, the risk remains (assuming the fire didn't "take out" the installation on the roof) making it a risk to anyone involved in the investigation or cleanup.

Looking at my brother's installation the other day. The inverters are in the cellar. So while the cables come down the side of the house, there is an internal run - in a space that would have no light once the power is off.
 
It mentioned that spraying with their standard foam had little effect. I suspect that getting something that's sprayable (especially by someone stood on the ground and aiming at a roof on a 2/3 storey house), and is sticky enough to stay put, and is opaque enough to do any good - would be quite a challenge !
Indeed it would - but so, I imagine, would any of the alternatives (e.g. tarpaulins) represent a major challenge!

Kind Regards, John
 
Wouldn't it be nice if people who'd put solar panels on their roofs found that they could no longer get buildings or contents insurance against fire damage.
 
It mentioned that spraying with their standard foam had little effect. I suspect that getting something that's sprayable (especially by someone stood on the ground and aiming at a roof on a 2/3 storey house), and is sticky enough to stay put, and is opaque enough to do any good - would be quite a challenge !
When I joined the fire brigade back in the 70's we used a protein based foam that has some thickness to it and on a flat, horizontal, surface could be several inches thick. It would never have stayed put on a pitched roof.

However this was replaced by AFFF (Aqueous Film Forming Foams) which, from memory, was as good as transparent and when applied formed a thin water layer and thin film over it. That too would never have remained on a pitched roof apart from not blocking out any light.

Only other form of foam used was HiExpansion which consists of concentrated compound, similar to washing up liquid, mixed with water using a large fan, driven by the water used. Looked exactly like bowlful of soap suds.

Perhaps good news, not, is comment on BRE website
There is currently no national UK guidance specific to fighting fires involving PV systems. In most respects, fires involving photovoltaics are little different from any fire involving live electrics, however, PV systems do present some new risks to fire-fighters:

Indeed it would - but so, I imagine, would any of the alternatives (e.g. tarpaulins) represent a major challenge!
Fire Brigade ones are plastic so might be feasible after the fire but not during. Installing on a normal house might be OK if there was access for hydraulic platform, or similar but otherwise there is still going to be a danger of electric shock.
 

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