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Solar Panels?

Solar panels and electrocution?

  • Is there any chance of being electrocuted by solar panels? Is there a risk for firefighters when they enter a building where there is solar power and stand in a puddle of water if there is short between the solar panels and the water. They cut normal power before entering buildings, but do you get enough juice from residential solar panels to consider this as a risk?

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    solar panels are usually 12 or 24 volts for the smaller ones, and those voltages are pretty safe. larger arrays can be connected in series or parallel, depending on the battery configuration. It's likely for a large installation to produce 48 volts or even higher, and those voltages can be dangerous. Higher voltages are used on large installations to cut down on the cost of the wiring. But, any solar array has an inverter somewhere, running off a battery, and that will output 120 or 240 VAC, and that is definitely dangerous. So this raises an interesting point. Should all solar panel installations include a cutoff switch accessible to fire fighters? It looks like they should. The switch has to cutoff the voltage from the array, and also turn off the inverter. edit: but switching off the voltage from the array is not enough, as the array is still putting out power (assuming the sun is shining). One possibility is to use a multiple pole relay located very near the array to open both + and – leads from the array. Thus there is no path for the current to get to ground. If water got everything wet, the array would short across itself but still be isolated from ground. But what if the relay fails? Max, you seem to have the idea that it takes a lot of current to be dangerous. No, 20mA can shock you, 50mA can kill you, and there are a lot of arrays that can put out 48 volts at many amps. edit2: "edit: you could place a normal off switch on the solar array and hook it up to the fire alarm for industrial systems, the switch should open even when power fails. And you are correct in saying that it is the current that kills, but you still have to have enough volts to get a decent current trough a human (no mater what the max current output is). The real question is then do solar panels have a fixed current output (then its dangerous) or a fixed voltage (then with max 50 volts is even wet not a problem)" sorry, 50 volts IS a problem, lots of people have been killed from 50 volts. I admit it is not as likely as with 100 or 200 volts, but it is still possible, specially with a lot of water around. I don't remember the UL spec offhand, but I think it is somewhere around 20 volts. solar panels have a variable voltage, dependent on the amount of light on them. You have to plan on the highest possible voltage. The current output is usually in the tens of amps or higher, more than enough to kill, so it is the voltage that will determine the current through your body. edit3: dividing up the world into constant voltage sources and constant current sources is meaningless, as neither exists in real life. All voltage sources are a imperfect voltage source or an imperfect current source or something in between. .

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The big grid-tied solar arrays intended to power a whole house, or a substantial part of it, must generally be installed according to the National Electrical Code (you can see a copy in the reference section of your library). Article 690 specifies several things intended to enhance safety. One of the first things to remember is that the panels themselves are waterproof, intended to be out in the elements for decades. If installed right, you can spray a hose at them - top side, bottom side, any of the junction boxes, wiring, or conduit, and nothing will happen. Second, the wiring practices for panels are the same as for other wiring, so there is no more danger than that of normal house wiring. Third, the code specifies that there must be a warning label or directory of power sources placed at the service panel. A firefighter going into a damaged house will go to the service panel to turn stuff off first, and will see the warning. Also, in most places, there is a requiement for at least one disconnect switch, and often that the switch must be visible from the service panel and within 10 feet. A firefighter will flip this switch when they see the warning label. A rooftop system can have voltages of 600 volts, although 450 is probably a more realistic maximum because of safety margins. It could be 10 to 20 amps, so is plenty enough to be dangerous.

roderick_young

it's a very low risk. Residential solar panels are very low power, considering they are only powering one or two houses, and pose very little threat. They run at low amperage, and produce fairly low voltage as well (you could probably stick your tongue on the leads). The transformers and batteries are more of a risk, but again no more dangerous than standard house electrical (120v). The voltage the panels produce shouldn't be your top concern safety-wise, i've been hit with a 600,000 volt stun gun - its unpleasant, but the amperage is what will stop your heart. Also, firefighters wear rubber insulated boots and gloves, and have been trained extensively, making their risk of electrical shock next to nothing.

Max

For Max: my rooftop system is delivering 500 V, 3500 Watts, I'd like to see you stick your tongue to the leads :) But I wonder if we're discussing the correct issues. When you would take both leads, one in each hand, you'd be dead since current will flow from lead A to lead B through your body. But when a firefighter stands in a puddle of water and touches a lead or is connected to a lead somehow, where would the current flow to through his body? There is a large potential difference between leads A and B coming from the panels, but there is no potential difference between the panels and the ground, I'd think. So no reason why he would be electrocuted. Unless lead A would be grounded and lead B not, and he'd touch lead B. But I don't see why they would ground one of the leads, I suppose that the whole installation is floating. And when the water from his hose touches both leads A and B, it would simply short circuit the whole system, making some fuse melt and anyhow the current would flow directly from A to B without passing through his body, because it takes the least resistance. Anyone comments on this?

Luc J

Since they are of very small power units, no such dangerous is expected.

krk

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