Thread: Solar panels on metal shed - ideas

Contactor/ on/off switch is the gremlin I am led to believe causing the fires. Typical shortcut, we can save a few cents on this here thing what does it matter. Oh hindsight.
i digress. Um putting panels on your shed/house/freestanding building/frame in the middle of your backyard it all depends on which gets the most sun which reduces your payback period. Also distance to connect said panels back to the grid is why most are put on houses. Eg easy access to the meter box
that said if you are not interested in payback on the panels disregard the distance to meter box
cheers

Hi Grahame,

I haven't been there, but have a 12x16m all metal barn and looked into it fairly carefully when we had the barn built, but council changed the planning scheme later that year and we could not trim trees that were shading the areas where the panels would be placed. (Actually have to get a planning permit from council to cut up fallen trees to clear them, or leave them to be grown over with grass and get a fire clearance demand from council in December, which exempts us from permit requirements but gives us 14 days to clear the branch(es) and surrounding fire hazard grass.)

In 2006, before this planning zone was created, we could have installed panels etc on the barn without issues, we actually had the site inspected and obtained quotes to do so. However because of the shading issues created by the revised planning zone, we did not go ahead. However we anticipate selling up within the next year, and rebuilding on a property 2 km away which has been in my family for 100 years. I have therefore been keeping a watch on the technology since then and regularly read and participate in solar related forums so have good general knowledge of the topic.

Intrinsicly, approved quality panels should be safe provided they remain intact and are correctly installed and wired to meet the appropriate standards. There have been issues in the past relating to damage to the panels, caused by the glass face panel being broken by hail or other impacts, faulty connectors on shoddy imported panels, installers not fully seating connectors when connecting panels in strings, and similar problems. The only issue that I foresee for an all metal shed that would not exist for a metal roofed house is that the entire building may end up live, rather than just the roof. However, if the building is fully metal framed (rather than metal clad over timber frame) the entire shed should be earthed, so should not become live.

Based on that, the panel mounts attached to the roof and the panel housing should also be earthed and the panel internals should be isolated from the housing. The standards stipulate appropriate cable size and conduit requirements, and require DC isolation switches and fusing installed between the panels and cable, with an additional DC and AC isolation switches located at the inverter, and suitable retention of all cabling (interpanel and output to inverter). Provided that these standards are complied with, there should be no opportunity for leakage to the metal cladding, unless a substantial fire within the building causes heat damage the cabling and cable retention in some way, at which point the solar installation is not a primary contributor to the fire situation.

I recently did see some photos of a rooftop panel with a hail damaged face which had water stained and charred zones on the active panel below. This was provided in the context of an enquiry about reduced outputs from the system, the string including the panel had reduced output substantially, and it was obvious that there was very localised overheating at points where cracks in the face met, however the unit had continued to operate at reduced output for some time without catching fire or doing anything similar until the drop in output was investigated. The localised overheating within the panel substrate was attributed to localised corrosion as a consequence of water ingress through the cracked glass face, or possible damage to the substrate from the hail directly, or from splinters of the glass face when it was fractured.

Re Wrongway's reply, distance is an issue, but can and should be compensated for by choosing appropriate cable sizes for both the DC and AC cable runs. Your installer should be able to decide which (AC or DC) is most critical based on the number of panels, their arrangement, the inverter etc, and optimise the cabling to suit the installation and inverter location requirements.

Hope this helps

According to my sparky and the wholesaler he uses, there is conduit available thats suitable for roof mounted solar setups. Big deal you say, but after seeing how quickly the conduit on my electric hotty perished...

You certainally wouldnt want your live cables protected by the crap they used on my install.

Know the "solar suitable stuff" is dearer to buy when I enquired.

Hi Graeme,

I'm gradually accumulating bits and pieces to do something very similar, I plan on running the workshop lighting with off-grid solar.

So I'm interested to follow the discussion. I've been getting bits and pieces from Buy solar panels | solar modules and cells | solar panel information

And I'm currently looking at how to do the panel mounting. It's a colour bond decking roof. I'm going to be mounting a number of 250W panels and I;m hoping I can get a frame setup in such a way as to allow more panels to be added as I can afford to add them.

Still don't have batteries, but I'll probably start with lead-acid.

Ray

Graeme, if it is your intention to feed (sell) power back to the grid, the distance to your meter box matters. It can be quite expensive if you have to lay a new underground cable - unless you can use an existing cable, or regulations in your area allow to use an above ground cable.

It would also matter if you intend to benefit from government subsidies. They need to be satisfied that the system they are subsidizing is going to last for long enough to save enough carbon emissions. If your shed was already a bit rusty that may be a problem.

Another problem is, you mention batteries. Normal home solar systems use an inverter to transform DC current from the panels into 240VAC. The inverter also synchronizes the frequency and phase with the grid. And this is the important thing, the inverter also switches itself off in case of a blackout of the grid. This is to make sure your solar inverter does not keep running and feeding power into the grid whilst linemen work on the blackout. It could kill them. Now if you intend to use batteries at a later stage in the hope of having power during a blackout, it is likely that another type of grid feed inverter could be needed. Better look into this before forking out money.

If you are not looking at feeding power back to the grid it would be a different story. You would essentially setup your own independent power supply. Just like if you had a diesel generator.

I did look into solar panels some years back, but I was not prepared to sacrifice trees to get a sufficiently long sunshine duration onto the roof to make it pay off.

I am watching with interest Grahame. I have signed up for a solar system previously and then pulled out when It became apparent that the installer was so overloaded with work prior to the deadline when it came crashing down that I was not getting correct information. I was told 6mm² cable for a run of 95m from the panels to the meter and a number of equally silly things.

I don't want to chase you away but if you want solar info then Whirlpool Forum is the place to go. That was where I discovered that the info I had been given was complete rubbish. There were a number of Solar Installers on Whirlpool who are happy to advise.

If I ever get around so solar electricity then I will have to do a ground based array. I don't have any roofs that are suitable. Too many trees. The main culprit is a massive Red Gum just North of the house/shed. Any installer worth using will provide a camera designed to determine angles of sunlight if there is any doubt at all. This is just a camera with a fisheye lens with nearly 180 deg coverage. It just needs a lens that will cover the angles that the sun will produce viable power from. A computer program can then determine suitability based on shading etc. This came from Whirlpool and other research. The installer Yer, this looks ok.

Wrongwayfirst,

What is the problem with these switches?

Malb,

One of the things that my installer missed out on completely was the ac/dc side of things re cabling. The facts as I know them. Ac has a slight edge over dc regarding conductivity, so all other things being equal, use ac current for long runs. But, all other things are rarely equal. In my situation the installer wanted me to fit the inverter in my implement shed close to the array and then have 240v ac from there to the house, 90m away. Bad mistake. 480v dc will cover that distance much easier. The 6mm² cable I was advised to use for this run? An online electrical wire size calculator gave me a value of 25mm² cable and an installer on Whirlpool suggested I go up to 50mm² cable. Then start asking whether an earth conductor should be run or if an earth electrode at each end would be suitable. That opened a real can of worms. You may recall one or two of those sort of questions here from time to time.

jatt,

What is wrong with the standard orange heavy duty conduit? That is what I was going to use and nobody had any issues with that. Most of my cabling was going underground tho.

Any worthwhile installer will have these issues covered, but it cannot hurt to check. They may be cutting corners where you would prefer to have a long term reliable setup. Who knows, maybe if one asks the question on Whirlpool, it may be your installer that replies! I am sure that most of them are honest and reliable. My situation was caused by the impending end of the glory days of government subsidies, and installers employing all sorts of people to get signatures on paper before the deadline.

I wish there was more long term stability for infeed pricing. My understanding of the situation in Victoria is that the energy companies are not impelled to pay for infeed power. They do pay $0.08 for it, or thereabouts, but there is no law against them saying one day, sorry you're stuffed. It is better for retired people or those that work from home. They can make some use of the power when it is produced. I work days for 87% of the year. I cannot make use of the power then. SWMBO can use some. I have to laugh when the govt talks about being able to save money by deciding when to use electricity based on the cheaper tarrif periods. This would be suitable for indoor hydroponic systems at least.

I also am waiting for the magic battery system.

Dean

Hi there,

Now I don't assume to know much about solar installations other than a basic knowledge of electrickery. 50mm or even 25mm cable seems pretty big, unless you have to run it 100's of metres or you have a 20Kw system. It's my understanding that voltage drop for a given system is purely dependent on the current. So obviously the higher the voltage you run over the long distance then you are minimising that current (for a given power). The power cables to my house run about 60M from the street and they are 35mm square, which I assume would give me an 80A power circuit to the house. I'm of the opinion that with mains, the allowance is a maximum of 5% voltage drop and so cable sizes are calculated taking into account maximum 5% voltage drop at the maximum current. I guess with solar installations it's a little different in that ANY voltage drop will affect your return as it will affect the MPPT inverter and power production but I guess you need to draw the line on a compromise somewhere, but 50mm square cable? What current do they assume will be flowing through that and over what distance?

Watching this thread with interest in any case. At one stage I had toyed with the idea of powering my shed with solar (still yet to have dedicated power to the shed) but it soon became obvious (to me) that it would not provide satisfactory results without spending lots of money. The biggest issue was running my welders from an inverter. No one could guarantee it would work or what size I needed. Then there was the massive battery bank I would have needed to allow 1 or 2 days of intermittent power with no sun.

I think running the lighting from solar is a great compromise, certainly in my situation. I'm seriously considering running 3 phase to the shed but it will mean 110M of cabling from the street (power meter is in the front pillar of our driveway) direct to the shed. An online calculator shows I can get away with 16mm (3 phase) cable for a 40 (maybe 48A at a pinch) circuit but like I said, I'm no electrician. Sick of buying a VFD every time I buy another machine!

Simon

Originally Posted by Oldneweng

I am watching with interest Grahame. I have signed up for a solar system previously and then pulled out when It became apparent that the installer was so overloaded with work prior to the deadline when it came crashing down that I was not getting correct information. I was told 6mm² cable for a run of 95m from the panels to the meter and a number of equally silly things. I don't want to chase you away but if you want solar info then Whirlpool Forum is the place to go. That was where I discovered that the info I had been given was complete rubbish. There were a number of Solar Installers on Whirlpool who are happy to advise. If I ever get around so solar electricity then I will have to do a ground based array. I don't have any roofs that are suitable. Too many trees. The main culprit is a massive Red Gum just North of the house/shed. Any installer worth using will provide a camera designed to determine angles of sunlight if there is any doubt at all. This is just a camera with a fisheye lens with nearly 180 deg coverage. It just needs a lens that will cover the angles that the sun will produce viable power from. A computer program can then determine suitability based on shading etc. This came from Whirlpool and other research. The installer Yer, this looks ok. Wrongwayfirst, What is the problem with these switches? Malb, One of the things that my installer missed out on completely was the ac/dc side of things re cabling. The facts as I know them. Ac has a slight edge over dc regarding conductivity, so all other things being equal, use ac current for long runs. But, all other things are rarely equal. In my situation the installer wanted me to fit the inverter in my implement shed close to the array and then have 240v ac from there to the house, 90m away. Bad mistake. 480v dc will cover that distance much easier. The 6mm² cable I was advised to use for this run? An online electrical wire size calculator gave me a value of 25mm² cable and an installer on Whirlpool suggested I go up to 50mm² cable. Then start asking whether an earth conductor should be run or if an earth electrode at each end would be suitable. That opened a real can of worms. You may recall one or two of those sort of questions here from time to time. jatt, What is wrong with the standard orange heavy duty conduit? That is what I was going to use and nobody had any issues with that. Most of my cabling was going underground tho. Any worthwhile installer will have these issues covered, but it cannot hurt to check. They may be cutting corners where you would prefer to have a long term reliable setup. Who knows, maybe if one asks the question on Whirlpool, it may be your installer that replies! I am sure that most of them are honest and reliable. My situation was caused by the impending end of the glory days of government subsidies, and installers employing all sorts of people to get signatures on paper before the deadline. I wish there was more long term stability for infeed pricing. My understanding of the situation in Victoria is that the energy companies are not impelled to pay for infeed power. They do pay $0.08 for it, or thereabouts, but there is no law against them saying one day, sorry you're stuffed. It is better for retired people or those that work from home. They can make some use of the power when it is produced. I work days for 87% of the year. I cannot make use of the power then. SWMBO can use some. I have to laugh when the govt talks about being able to save money by deciding when to use electricity based on the cheaper tarrif periods. This would be suitable for indoor hydroponic systems at least. I also am waiting for the magic battery system. Dean

There is something seriously, seriously wrong with your cable cross section calculations. I have a 90m run of 6mm2 3 phase cable going from my house to my dam and the voltage drop over that distance is the SQRT of sod-all. It's conservatively rated at 20A per phase and could easily carry 32A. I use 16mm2 cable for carrying 90A over 30m. All my wiring is to code. Just how many amps @240V did you use in your calculations????? PDW

Hello

I have 12 panels on a tin roof, been in situ for 4 years, all German panels and controls, have not paid for a power bill in that time, receive credit from the power utility. No problems as of yet.

DD

Orange conduit. My understanding is orange is for underground only. However I am not a sparky.

He did tell me off however, for having solid orange plastic above ground and exposed without a cover. Where the cables exited out the end above ground is out of the elements, so the abuse was mild for this guy

He likes things to be done right, that's fine by me.

Hello,

My sparky mate tells me that Orange conduit is for in ground only. It have better mechanical strength but has no/little UV stabilisers, whereas the grey stuff is for above ground and has some/more UV stabilisation in it. I think you have to change from orange to grey before you pop up out of the ground.

Simon

Originally Posted by simonl

Hello,

My sparky mate tells me that Orange conduit is for in ground only. It have better mechanical strength but has no/little UV stabilisers, whereas the grey stuff is for above ground and has some/more UV stabilisation in it. I think you have to change from orange to grey before you pop up out of the ground.

Simon

Your sparky mate might be confused. UV stabilized orange conduit is available. Several suppliers list it as a specification. It is my understanding that underground power had to be in orange.

Originally Posted by PDW

There is something seriously, seriously wrong with your cable cross section calculations. I have a 90m run of 6mm2 3 phase cable going from my house to my dam and the voltage drop over that distance is the SQRT of sod-all. It's conservatively rated at 20A per phase and could easily carry 32A. I use 16mm2 cable for carrying 90A over 30m. All my wiring is to code. Just how many amps @240V did you use in your calculations????? PDW

I can't help there. I wasn't doing the calculations and I don't remember the actual factors used at the time. It is old history now. My point was that it doesn't hurt to check the info.

Re orange conduit. There is orange type conduit that "pops" up out of the ground at work. I had not heard of having to change it to grey. I might have to remember that as the stuff I saw at work tonight is clearly not UV stabalised. It is also not orange any more.

Dean

Originally Posted by Oldneweng

I am watching with interest Grahame.

Wrongwayfirst,

What is the problem with these switches?

Dean

I am led to believe in qld there is an importer of contactors, used in solar installations as the main isolation switch, which has a higher than acceptable incidence of house fires.