Voltages of various inverter systems

[shet]

Trying to figure out the voltage on the roof for various inverter types. My thoughts below. Could you please share your insights too? This is for Northern NJ with PSEG as utility supplier

1) String: Seems like all the panels are connected in series and then it goes to inverter. So if say 20 panels then each generates 30V DC(is 30V DC right, btw?) then total voltage coming down from roof is 600V DC which then goes to 600V to 110V AC (probably two phase) inverter on ground and then to AC grid.

2) Micro-inverter: At each panel 30V DC is converted into 110V AC (single or two phase) and then it goes straight to the grid. (No other central inverter on way to grid? Not sure? ) So power coming down from roof is 110V AC (single or two phase, not sure)

3) SolarEdge SIngle Phase Inverter (say SE3000A) with Power optimizer: How does this work? No idea at all. Is this string inverter variation or more of micro-inverter? It does have a big central inverter on the ground with power optimizer connected to each panel. Does the optimizer do any DC to AC conversion?

[ButchDeal]

1)string inverters have voltage limits so you often do some modules in series and then parallel. The inverters often have a minimal voltage to turn on the inverter and a max voltage (residential usually 600V). Some have 2 (or even 3 ) MPPT inputs but that often confuses the string length. you have to look at the type of modules and local weather conditions to find a string length that is viable the majority of the time (modules put out different power at different temperatures).

2) micros do not do 110V, they only do 240V (BTW, there is no such thing as two phase). You have a limit of the number of micros on a string so you have AC combiners, disconnects, etc.

3)SolarEdge (all inverters) have optimizers (a form of MPPT) on each module. They combine to generate upwards of 350V, depending on needs of the inverter and conditions on the roof. The optimizer does not do any AC conversion and the central inverter does not do any MPPT. You can have multiple strings of optimizers to maintain the limit of at least 8 and no more than 5250watts per string (6kw 3 phase 208V and 12.75kw for 3 phase 480V)

[shet]

1)string inverters have voltage limits so you often do some modules in series and then parallel. The inverters often have a minimal voltage to turn on the inverter and a max voltage (residential usually 600V).

That is not good. 600V DC on the roof. 240V AC is bad enough. 600V DC is even worse.

2) micros do not do 110V, they only do 240V (BTW, there is no such thing as two phase). You have a limit of the number of micros on a string so you have AC combiners, disconnects, etc.

Isn't the power coming from PSEG into the house the two legs/phase from the 3 phase/legs each of 110-120V on the poles ? i.e. House 1 Get say Leg A and Leg B, House 2 gets Leg B and Leg C, House 3 gets Leg C and Leg A, House 4 gets Leg A and Leg B and so on?

3)SolarEdge (all inverters) have optimizers (a form of MPPT) on each module. They combine to generate upwards of 350V

So it is around 350V DC on the roof.

So out of the three, micro-inverters is the least dangerous in terms of voltage.

[ButchDeal]

That is not good. 600V DC on the roof. 240V AC is bad enough. 600V DC is even worse.

This can be dangerous for self installers. The modules can cause some arcing even when the inverter is off.
Also there are bimodal systems which are generally under 150V though there are a few higher voltage Charge controllers (Schneider for one)

Isn't the power coming from PSEG into the house the two legs/phase from the 3 phase/legs each of 110-120V on the poles ? i.e. House 1 Get say Leg A and Leg B, House 2 gets Leg B and Leg C, House 3 gets Leg C and Leg A, House 4 gets Leg A and Leg B and so on?

you are describing a commercial system where you would split up a 3 phase system into several 208V lets. A + B =208V, B + C = 208V, and C+A = 208V

residential is generally single phase 240V which you can split, leg A to ground is 120V and leg B to ground is 120V , This is single phase system.


Micros only put out 240V (they can not handle splitting). The Grid handles the splitting and provides the 120V to the house.

I am simplifying but sure some master electrician will add some.

So it is around 350V DC on the roof.

So out of the three, micro-inverters is the least dangerous in terms of voltage.

I would say that SolarEdge by far is the least dangerous.
They have a shutdown system such that each optimizer will only put out 1V when the inverter is off, limiting the strings to under 30V.
This safe voltage is the same when you have a battery (Powerwall) connected as well.

[SunEagle]

That is not good. 600V DC on the roof. 240V AC is bad enough. 600V DC is even worse.

This type of wiring is pretty common to all existing systems with String type grid tie inverters so not really that dangerous if you do not touch any exposed wire terminations.

Isn't the power coming from PSEG into the house the two legs/phase from the 3 phase/legs each of 110-120V on the poles ? i.e. House 1 Get say Leg A and Leg B, House 2 gets Leg B and Leg C, House 3 gets Leg C and Leg A, House 4 gets Leg A and Leg B and so on?

Most homes are powered from single phase transformers that provide 120/240volt power. 240v between Leg A and Leg B as well as 120volt between Leg A and the neutral/ground or Leg B and the neutral/ground. I seriously doubt PSEG has 3 phase power to homes.

So it is around 350V DC on the roof.

So out of the three, micro-inverters is the least dangerous in terms of voltage.

Again this is one way to run the wire from a solar pv system. IMO it is not necessarily any safer than a String inverter or Micro Inverter system but does meet the new NEC rapid shutdown requirements.

See my comments in BLUE above.

[shet]

See my comments in BLUE above.

So there are exposed wire terminations on the roof? When it is raining then there is a path for electricity to flow from the roof to the ground along the exterior wall?

Which inverters will meet the NEC rapid shutdown code (starting 2017 onwards I believe). I thought Micro Inverter and SolarEdge inverter will meet it (or rather already meet it). String inverters will "not" meet it. Am I right?

I am in NJ. Where is this transformer which does the split from 240V to two legs of 120V. I don't see anywhere near my house main panel. Are they on the pole on the street? In which case every house has one transformer allocated probably.

[ButchDeal]

So there are exposed wire terminations on the roof? When it is raining then there is a path for electricity to flow from the roof to the ground along the exterior wall?

no there should not be any exposed wire terminations on the roof. SunEagles is talking about during the install, when someone is creating the system.

Which inverters will meet the NEC rapid shutdown code (starting 2017 onwards I believe). I thought Micro Inverter and SolarEdge inverter will meet it (or rather already meet it). String inverters will "not" meet it. Am I right?

String inverters require a rapid shutdown disconnect box on the roof mounted close to the array to meet the code. This adds cost and complexity.
Rapid shutdown is not starting in 2017, it is already in effect in most locations.

I am in NJ. Where is this transformer which does the split from 240V to two legs of 120V. I don't see anywhere near my house main panel. Are they on the pole on the street? In which case every house has one transformer allocated probably.

On a pole near your house or ground box in the neighborhood. Depending on the size of the transformers, they support multiple homes.

[shet]

You guys have been awesome in sharing your knowledge. Thanks for it.

I wish somebody comes up with a inverter system for residential purpose where each panel's 30V DC or so is taken down to the ground (means 40 wires for 20 panels) and then converted to 240V AC. There will be lot of transmission loss though at that low 30V DC voltage over long length (not to speak of extra cost in wiring).

Just from safety purpose so far as voltage is concerned, micro-inverter looks better than optimizer-inverter model (for single family homes). Lets say a scenario where a squirrel chews a wire and exposes bare wire on the roof. I am not saying 240V (micro-inverter) on the roof is safe either. Do they use metal or PVC conduits on the roof?

[SunEagle]

You guys have been awesome in sharing your knowledge. Thanks for it.

I wish somebody comes up with a inverter system for residential purpose where each panel's 30V DC or so is taken down to the ground (means 40 wires for 20 panels) and then converted to 240V AC. There will be lot of transmission loss though at that low 30V DC voltage over long length (not to speak of extra cost in wiring).

Just from safety purpose so far as voltage is concerned, micro-inverter looks better than optimizer-inverter model (for single family homes). Lets say a scenario where a squirrel chews a wire and exposes bare wire on the roof. I am not saying 240V (micro-inverter) on the roof is safe either. Do they use metal or PVC conduits on the roof?

Each solar installer uses what is available and compliant with the local code. Most pv panels just have their wiring protected under the unit. All of those wires must have insulation rated for outdoor wet locations and be sunlight resistant. Still most AHJ will not allow any wire(s) to be run along the roof and exposed to the elements including sunlight so they are required to be put inside a "raceway" or "pipe" for protection. That is why you usually see a single "conduit, pipe, raceway" coming from the roof area to the inverter.

[shet]

Pasting below contents from the "Safety" section in the link from Australia http://www.solarquotes.com.au/blog/m...ption-is-best/

Around the world the risks of High Voltage DC continue to be debated. When everything is done perfectly, great gear is used and maintenance is regularly conducted, HV DC is just fine and very efficient. However, the reality is that often isn’t the case and so rooftop safety is a growing issue. HV DC and 240V AC both present electrocution risks, but HV DC is more prone to creating fires when it all turns bad.

The major optimizer manufacturers almost all talk about their roof mounted units being able to recognise fault conditions and having the capability to isolate individual panels in the case of a fault so even though the HV DC cabling is still present they seem to have that in hand. What I don’t like is that you still need DC isolators which are the number one cause or problems in Australian solar systems. I also note that some optimizers require an optional device to enable this functionality in some circumstances, leaving room for error.

Micro inverters don’t let the DC out; it’s converted immediately to 240AC. Generally speaking it’s also true that electricians are more familiar with AC. Theoretically based on of all of the above, the risk is slightly lower with micros I think.

Win to micros.

[ButchDeal]

You guys have been awesome in sharing your knowledge. Thanks for it.

I wish somebody comes up with a inverter system for residential purpose where each panel's 30V DC or so is taken down to the ground (means 40 wires for 20 panels) and then converted to 240V AC. There will be lot of transmission loss though at that low 30V DC voltage over long length (not to speak of extra cost in wiring).

Just from safety purpose so far as voltage is concerned, micro-inverter looks better than optimizer-inverter model (for single family homes). Lets say a scenario where a squirrel chews a wire and exposes bare wire on the roof. I am not saying 240V (micro-inverter) on the roof is safe either. Do they use metal or PVC conduits on the roof?

that is very impractical and would have quite a bit of loss in the wires as well as considerable copper.
The physical bulk of the wires would be cumbersom as well.

The SolarEdge is very close to this. When the inverter is turned off or any disconnect in AC the micros all drop nearly instantly to 1V as well as for DC arc faults etc.

Micro inverters don’t let the DC out; it’s converted immediately to 240AC. Generally speaking it’s also true that electricians are more familiar with AC. Theoretically based on of all of the above, the risk is slightly lower with micros I think.

It sounds like you are still debating the Edison/Tesla DC/AC wars.
doesn't much matter if it is AC or DC, the Amps will kill you and either one arcing is likely to start a fire.

[SunEagle]

Pasting below contents from the "Safety" section in the link from Australia http://www.solarquotes.com.au/blog/m...ption-is-best/

Around the world the risks of High Voltage DC continue to be debated. When everything is done perfectly, great gear is used and maintenance is regularly conducted, HV DC is just fine and very efficient. However, the reality is that often isn’t the case and so rooftop safety is a growing issue. HV DC and 240V AC both present electrocution risks, but HV DC is more prone to creating fires when it all turns bad.

The major optimizer manufacturers almost all talk about their roof mounted units being able to recognise fault conditions and having the capability to isolate individual panels in the case of a fault so even though the HV DC cabling is still present they seem to have that in hand. What I don’t like is that you still need DC isolators which are the number one cause or problems in Australian solar systems. I also note that some optimizers require an optional device to enable this functionality in some circumstances, leaving room for error.

Micro inverters don’t let the DC out; it’s converted immediately to 240AC. Generally speaking it’s also true that electricians are more familiar with AC. Theoretically based on of all of the above, the risk is slightly lower with micros I think.

Win to micros.

The sky is falling the sky is falling. Sorry i could not help it.

When it comes to electricity the voltage is only a part of the danger. It is the current that will kill you. So even a 120V AC circuit will blow you out of your socks if you touch it and a "ground".

Also fires can be started using a magnifying glass which has no voltage present.

An electrical system is designed to isolate the power if a short circuit occurs thus reducing the chance of a fire or "arc flash". If the circuit is 120v, 240v or 600v AC or DC it really doesn't matter as long as all of the terminations are secure and protected.

[jflorey2]

Around the world the risks of High Voltage DC continue to be debated. When everything is done perfectly, great gear is used and maintenance is regularly conducted, HV DC is just fine and very efficient. However, the reality is that often isn’t the case and so rooftop safety is a growing issue. HV DC and 240V AC both present electrocution risks, but HV DC is more prone to creating fires when it all turns bad.

That's great in theory, but in reality medium voltage DC (i.e. up to 600 volts) has been proven to be safe when installed and maintained to manufacturer's directions and to the rules of the appropriate AHJ.

Think about it this way. Let's say you have kids in your house. All they need is a fork and they can connect themselves to 120 volts AC. They are not going to be able to get near that 450 volt DC line that goes from the panels to the inverter.

Micro inverters don’t let the DC out; it’s converted immediately to 240AC. Generally speaking it’s also true that electricians are more familiar with AC. Theoretically based on of all of the above, the risk is slightly lower with micros I think.

Micros are nice. But they are more complex (24 inverters to deal with instead of 1) and require a lot more interconnects (which are failure prone.) So from a safety perspective you have pluses and minuses on both sides.

[shet]

When it comes to electricity the voltage is only a part of the danger. It is the current that will kill you.

Correct and incorrect. Current = Voltage / Resistance. Current kills you but voltage is the source (provided power source has enough power to provide the required amp [actually in tens of mA] which is fatal to the heart). A car battery is 12V but can supply hundreds of amps but will not kill you if you touch it because 12V divided by human body's resistance is not enough to kill you (assuming you are not all wet or you are not holding a metal wrench and then connecting across it's terminals). Voltage is not "part" of the danger. It is the "whole" danger itself.

I would say above 30 or 40V is fatal for humans.

[ButchDeal]

Voltage is not "part" of the danger. It is the "whole" danger itself.

I would say above 30 or 40V is fatal for humans.

eeh, yes and no. Electric fences are typically in thousands of volts and certainly not fatal.
Almost any electrician or handy man has been shocked by 120V AC as well, and still not fatal.
some even 240V.
12V or 24V or 48V battery banks (more amps than car batteries), can be very deadly. Biggest danger due to arc flash, but also to under sized wires, and lack of fuses.

PV is a bit funny in the voltage/current though.