Thread: Solar panels on metal shed - ideas

Originally Posted by Wrongwayfirst

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.

I know about him .This is a result of people trying to get the minimum cost system.
It seems some sharks will offer the cheap option to make sales. I was aware of the crappy component scam and have specified that each component of the system be the best that my installer can obtain.He has been through them and I believe the contactors and switches are German Seimens.

We have even covered hailstorms and electrolysis. with aluminium frames on Colorbond . Its all covered in the quote docs that it will be set up for avoidance of electrolysis.

Grahame

Grahame, then you already had the chance to orient the new slab for maximum sun exposure. Now you could choose a steep pitched roof to directly install the solar panels onto the corrugated iron at optimal elevation angle. We had a flat roof, and they quoted us 12% extra for frames to elevate the panels. A steep pitched roof costs more than a standard shed roof though. You have to balance roof cost against frame cost against efficiency loss if the panels lay flatter than optimal..... Also it is harder to walk on a steep roof, and you definitely want access to the panels - if only to inspect and clean (from dust, mould, soot from a nearby chimeny, bird droppings, lichens, twigs.... depending on surroundings and the make of panels you choose). If your shed is very close to a public road you may have to consider against stone throwing vandals... best bet may be to take out insurance.

The roof pitch was already locked in at 15 degrees. This was already locked in before I signed up for the solar array. We are almost on the tropic of Capricorn so sun exposure is not going to be a problem.

Most of my research on solar started here :

Canadian Solar's tutorial on solar power systems, solar PV panels and solar PV cells - Solar Choice There's quite a bit of reading to be done there.

As far as UV on the conduits ,there's 14 meters or so under ground and the rest under cover of a building roof, there remains a couple of meters that run up walls but I guess the installer might use something similar to the PVC ducts they use on external wall A/C cabling.

Grahame

Originally Posted by Grahame Collins

As far as UV on the conduits ,there's 14 meters or so under ground and the rest under cover of a building roof, there remains a couple of meters that run up walls but I guess the installer might use something similar to the PVC ducts they use on external wall A/C cabling.
Grahame

As far as I know, conduits of any color that are medium duty or heavy duty are UV stabilized. With light duty ones you have to check with the maker.

Originally Posted by cba_melbourne

If your shed is very close to a public road you may have to consider against stone throwing vandals... best bet may be to take out insurance.

I would have to be very unlucky. I live at the end of a Cul de sac so almost no foot traffic .The shed roof will be 3,5 metres above street level and its not visible from the street 60 meters plus, away. I doubt if panels cam be seen, let alone reached with a stone throw. Dust is a problem here, both from the sugar harvesting period and from the coal terminals.I think I'll be able to stand on the ground and Gurney the panel tops to clean panels on a regualar basis.Shouldn't be too much of a pressure problem from 3 or 4 metres back.

There closest tree , a Bowen mango is 10 meters from the shed roof and was topped when the tree mob took out the palms . Glad to see the palms go, -too much picking up and disposal of the fronds. We have about 3 minutes of mowing in the back yard . Yahoo! and a little more than that at the front .Overall the shed carport and BBQ , solar areas will improve our lifestyle significantly.

Grahame

Bowen mango. You just through that in to tease ’em, right ?

Originally Posted by dabbler

Bowen mango. You just through that in to tease ’em, right ?

Yep!

Hi Grahame,

Steel sheds wont cause you any more problems than than any other sort of structure be it brick, timber, mud brick, straw bale or compressed earth.

The majority of failures come from cheap equipment. There are currently recalls on 4 brands of DC isolating switches. I have seen pictures of panels with discolouration in the centre of the panel caused by heat generated in the panel or under it. I don't remember the brand of those panels. I have also seen one inverter which did not turn off when the power went off.

Plastic conduit comes in comes in heavy and medium duty (I think?) On our solar system the DC is run in heavy duty orange underground conduit. The installer uses this as it is cheaper than heavy duty grey plastic conduit. None of the conduit is exposed to the weather or UV so the colour and UV stability of of the conduit is not an issue. The standard for the DC wiring is heavy duty conduit.

I am of the opinion that while the panels are earthed the actual DC output from the panels is not. ( I could be wrong about this). Thus if the panels experience some sort of failure and liven up the steel shed there will be no risk if you were to lean against it. Unlike AC where the neutral is earthed and an active to shed fault would be dangerous.

Solar systems capable of exporting to the grid will cause a rise in voltage, not a voltage drop. The calculations for voltage rise or fall are the same and require the cable size, circuit current and length of the cable to be known. The suggested use of 50mm cable seems a bit over the top to me. The maximum short circuit current for 2.5kW of panels is usually under 10 amps. I am always amazed by the current ratings people reckon a given cable size will give them. 6mm will supply anywhere from 8 to 58 amps depending on how it is run. That does not take into account voltage drop or loop impedance or harmonics currents in the circuit.

Sites with some shading might be better served with micro-inverters. These systems have a small inverter on every panel and only those panels in shade suffer a drop in output. With a conventional system one panel in shade will kill the output from the entire string.

Roof angles and orientation are less critical than I originally thought they would be. To overcome a less than ideal site you can add extra panels.

Battery storage systems are the coming wave. They use "intelligent" battery charges and inverters directing power where it is required. There are issues with the battery bank around location, access and enclosure designs There are a couple of Australian Standards on the issue. I can't recall the numbers at the moment. Because batteries are expensive you can design a system with less batteries and more solar panels, that way even on dull days there is enough to recharge the batteries. Why the coming wave? Mains power is around 28 cents per Kwh and climbing plus whatever the network fees are in your part of the country (also climbing). Battery backed solar is 29 cents per Kwh over the life of the system and falling in price. If you need to run mains power any real distance then the capital costs will also bite you. In Queensland it is also possible to get permission to install 30Kwh of panels on a non exporting system without having to jump through lots of hoops.

I'm looking at the possibility of a battery backed 3 phase non exporting inverter arrangement as a way of getting 3 phase for my shed. One issue though is how the inverters stand up to the loads from VFDs etc.

Cheers

The Beryl Bloke

Originally Posted by Theberylbloke

The suggested use of 50mm cable seems a bit over the top to me. The maximum short circuit current for 2.5kW of panels is usually under 10 amps. I am always amazed by the current ratings people reckon a given cable size will give them. 6mm will supply anywhere from 8 to 58 amps depending on how it is run. That does not take into account voltage drop or loop impedance or harmonics currents in the circuit.

The orange conduit I have laid underground is 50mm.I seem to recall it was said that the cable is around 12mm. Its about 60m run from the shed to house sw/board-only 14 metres or so U/ground-rest is in the residence.
Anyway I shall soon see when( at last) I get the shed erected for the solar to sit upon.The company is from Cannonvale, Element energy. in speaking with him he said the thought the battery prices would be cost effective around 2016. I have asked for the system to be configured to allow battery connection when prices make it viable.

Originally Posted by Grahame Collins

The orange conduit I have laid underground is 50mm.I seem to recall it was said that the cable is around 12mm. Its about 60m run from the shed to house sw/board-only 14 metres or so U/ground-rest is in the residence.
Anyway I shall soon see when( at last) I get the shed erected for the solar to sit upon.The company is from Cannonvale, Element energy. in speaking with him he said the thought the battery prices would be cost effective around 2016. I have asked for the system to be configured to allow battery connection when prices make it viable.

Hi Grahame,

I have inspected well over a hundred of Element Energy's solar systems. They do a pretty reasonable job. You should not have any problems with them. Although local, I had a different contractor (also local) do our install. I chose the opposition due to the height of my roof (5.5 metres at the edge) and their use of a panel lifting system.

Cheers

The Beryl Bloke

The distance between the solar panels and the inverter has to be minimised because that is where large voltage drop takes place. After the inverters it doesn't matter really because its just like any 240V cabling, 60 meters is not a problem. This would mean that the inverter has to be installed on the external wall of the shed. The inverter has to be in the shade with good ventilation. Too hot or installing the inverter in the sun is asking for trouble.

I am making the assumption that the inverter would be near the shed sub panel which will be near the PA door.Really it can go any place inside the shed.

Its when the ( future) batteries will go in is where I will need to layout the place fairly carefully.I will definitely have a corner for welding & fabrication, so the batteries will need to the max distance away from that.

The neighbours have recently installed a PV system and their installer placed the inverter on the west wall in a position where it will always cop the summer afternoon sun.It looks like a Sunnyboy which is the a fairly good one I believe. Dunno how it will go in the high summer temps up here.


Thanks for all those who have contributed.

Grahame

Originally Posted by justonething

The distance between the solar panels and the inverter has to be minimised because that is where large voltage drop takes place. After the inverters it doesn't matter really because its just like any 240V cabling, 60 meters is not a problem. This would mean that the inverter has to be installed on the external wall of the shed. The inverter has to be in the shade with good ventilation. Too hot or installing the inverter in the sun is asking for trouble.

This is not necessarily true. Yes, each individual solar panel generates a relatively low DC voltage of nominal 12V, 24V or for the larger ones 48V. And yes, for any given power, transport losses are greater the higher the current or the lower the voltage.

Now you are assuming that the energy is transported between the solar panels and the inverter with the solar panels wired in parallel, at low voltage, requiring very thick wires to keep losses down. Lets assume there are 10 solar panels of nominal 24VDC and 200W each in an array, for a total of 2kW. If all are wired in parallel, you got to design your power line between panels and inverter for 24V and 83A. To keep losses down over a substantial run, that is going to call for pretty thick and expensive wire.

But what if we wire the same 10 panels in series? Now you have to design the same power line for 240VDC and 8.3A. For any given length, that is going to require 10 times thinner wire, 10 times less copper weight, and considerably less cost. As a further advantage, the inverter can be single stage, converting 240VDC directly into 240VAC. Which is a cheaper inverter than the more complex double stage inverter that would be needed to convert first 24VDC into 240VDC, and from there 240VDC to 240VAC. This is so, because unlike with AC, you can not use a transformer to increase a DC voltage.

There is a third option to serial and parallel wiring of solar panels. If every single solar panel is fitted with its own 24vDC to 240VAC micro-inverter, the ten outputs can be connected in Parallel. This is also the most failsafe solution, since one broken panel or inverter does not shut the whole system down, but only reduces output power by 10%. The downside is, cost of 10 microinverters is higher than one single inverter.

Originally Posted by justonething

The distance between the solar panels and the inverter has to be minimised because that is where large voltage drop takes place. After the inverters it doesn't matter really because its just like any 240V cabling, 60 meters is not a problem. This would mean that the inverter has to be installed on the external wall of the shed. The inverter has to be in the shade with good ventilation. Too hot or installing the inverter in the sun is asking for trouble.

Hi justonething,

There is a little difference with 240 volt wiring to inverters. If the inverter system is capable of exporting back to the grid it will cause a voltage rise on the entire grid. Only sometimes apparent on the high voltage network but certianly on the low voltage network the effects can be measured. The further you are from the transformer that supplies your property the greater the effect. The further your inverter is from your meter box, likewise, an increase in the effect. To prevent the low voltage network getting too high, voltage wise, inverters will trip off at 255 volts. That setting is built into the inverter and not user adjustable. It can be changed by the installer but woe betide him if he gets caught having done so.

The issue of voltage rise from inverters is not something people outside the distribution companies tend to think about.

Cheers

The Beryl Bloke