AndyH
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Re: Is this Solar Deal good??

Wed Nov 14, 2012 9:03 pm

Mothernaturesolar wrote:Saleem,

With Enphase M215 inverters, you'll get-

1- 20% better performance. Each inverter takes the highest amount of electricity that is available from each panel. But a DC inverter can only pull power at the rate of the slowest panel. IE, if you have 3 panels putting out 190, 195, and 200 watts, the DC inverter will only pull 190 watts from each.
Yes, if someone violates the standard practices of PV planning, microinverters can provide such a performance improvement.

In the world outside of marketing, however, one installs the same panel brand/type/size in any one string. They do that because those PV panels will be within 1% or 2% of each other. In the real world, microinverters will not provide "20% better performance" compared to a string inverter on the same array.


Mothernaturesolar wrote:5- Safety for your family, as the Enphase inverters shut off the electric flow from the panels to the electric main panel when the breaker is shut off, not so DC inverters. If you have a house fire, the DC panel system is always hot with dangerous high voltage DC electricity.
Yes, this "can" happen, but is not likely to for code-compliant installations. All inverters must go off line immediately when main power is disconnected (anti-islanding). So neither inverter type is 'superior' to the other in this instance.

The PV combiner box is supposed to be near the array. There are combiners that are roof mounted (with the array) that have disconnect switches at ground level.



Either method is just as safe for families and emergency personnel.

Get a price quote that separates the panels from the balance of system and installation. You can likely get a much better price this way. Sunelec Miami has top of the line panels from about $0.60 per Watt, for example.

Good luck!
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QueenBee
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Re: Is this Solar Deal good??

Wed Nov 14, 2012 9:57 pm

AndyH wrote: Yes, if someone violates the standard practices of PV planning, microinverters can provide such a performance improvement.

In the world outside of marketing, however, one installs the same panel brand/type/size in any one string. They do that because those PV panels will be within 1% or 2% of each other. In the real world, microinverters will not provide "20% better performance" compared to a string inverter on the same array.
I'd agree that 20% is very much marketing but if there heavy shading involved NREL's testing shows a 12% increase. It would be interesting to see a comparison for non-shaded.
AndyH wrote:
Mothernaturesolar wrote:5- Safety for your family, as the Enphase inverters shut off the electric flow from the panels to the electric main panel when the breaker is shut off, not so DC inverters. If you have a house fire, the DC panel system is always hot with dangerous high voltage DC electricity.
Yes, this "can" happen, but is not likely to for code-compliant installations. All inverters must go off line immediately when main power is disconnected (anti-islanding). So neither inverter type is 'superior' to the other in this instance.

The PV combiner box is supposed to be near the array. There are combiners that are roof mounted (with the array) that have disconnect switches at ground level.

Either method is just as safe for families and emergency personnel.
I completely disagree that one is just as safe as the other. Sure I consider both to be safe but with microinverters the fire department can pull your meter and now there is no high voltage in your house. With strings of PVs there is no way to disable the high voltage DC being created by the sun.

From a self install point of view the idea of not having to deal with high voltage DC was huge. Enphase makes the install very much plug and play with simple standard AC wiring from the panel to the roof.

For people that know what they are doing I imagine figuring out DC wiring size, string size, inverter size, etc. is a no brainer but trying to learn that stuff is not fun.

AndyH
Posts: 6388
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Location: San Antonio

Re: Is this Solar Deal good??

Wed Nov 14, 2012 10:40 pm

QueenBee wrote:
AndyH wrote: Yes, if someone violates the standard practices of PV planning, microinverters can provide such a performance improvement.

In the world outside of marketing, however, one installs the same panel brand/type/size in any one string. They do that because those PV panels will be within 1% or 2% of each other. In the real world, microinverters will not provide "20% better performance" compared to a string inverter on the same array.
I'd agree that 20% is very much marketing but if there heavy shading involved NREL's testing shows a 12% increase. It would be interesting to see a comparison for non-shaded.
Absolutely - shading will cut performance regardless. If there is no way to get around it, and the owner absolutely needs the 'best case' power from the affected panels, then microinverters should perform better. It really depends on the installation, though - the same benefit might be obtained by splitting the array and using two string inverters. I don't think there's any 'one size fits all/best answer' for any system.
QueenBee wrote:
AndyH wrote:
Mothernaturesolar wrote:5- Safety for your family, as the Enphase inverters shut off the electric flow from the panels to the electric main panel when the breaker is shut off, not so DC inverters. If you have a house fire, the DC panel system is always hot with dangerous high voltage DC electricity.
Yes, this "can" happen, but is not likely to for code-compliant installations. All inverters must go off line immediately when main power is disconnected (anti-islanding). So neither inverter type is 'superior' to the other in this instance.

The PV combiner box is supposed to be near the array. There are combiners that are roof mounted (with the array) that have disconnect switches at ground level.

Either method is just as safe for families and emergency personnel.
I completely disagree that one is just as safe as the other. Sure I consider both to be safe but with microinverters the fire department can pull your meter and now there is no high voltage in your house. With strings of PVs there is no way to disable the high voltage DC being created by the sun.
Sorry, I have to disagree here. Look at the video again - the 'bird house' is a remote switch that's placed near the service entrance. It disconnects the breakers in the combiner box on the roof. It'll take much longer to pull the meter than to hit the switch and restrict the DC to the panels. There's no DC in the house with that system either.
QueenBee wrote:From a self install point of view the idea of not having to deal with high voltage DC was huge. Enphase makes the install very much plug and play with simple standard AC wiring from the panel to the roof.

For people that know what they are doing I imagine figuring out DC wiring size, string size, inverter size, etc. is a no brainer but trying to learn that stuff is not fun.
My system is off grid and the array will be 90V max. The disconnect is about 3' from the panels. All the DC wiring from the panels to the combiner box is done with MC4 connectors - it's like working with Legos. It took time to learn enough to design the system, but the payoff is the adventure and the money savings.

The beauty is that the solar industry continues to expand to include more possibilities and more professional providers and installers. That's good all the way around!
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QueenBee
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Re: Is this Solar Deal good??

Thu Nov 15, 2012 8:53 am

AndyH wrote: Sorry, I have to disagree here. Look at the video again - the 'bird house' is a remote switch that's placed near the service entrance. It disconnects the breakers in the combiner box on the roof. It'll take much longer to pull the meter than to hit the switch and restrict the DC to the panels. There's no DC in the house with that system either.
QueenBee wrote:From a self install point of view the idea of not having to deal with high voltage DC was huge. Enphase makes the install very much plug and play with simple standard AC wiring from the panel to the roof.

For people that know what they are doing I imagine figuring out DC wiring size, string size, inverter size, etc. is a no brainer but trying to learn that stuff is not fun.
My system is off grid and the array will be 90V max. The disconnect is about 3' from the panels. All the DC wiring from the panels to the combiner box is done with MC4 connectors - it's like working with Legos. It took time to learn enough to design the system, but the payoff is the adventure and the money savings.

The beauty is that the solar industry continues to expand to include more possibilities and more professional providers and installers. That's good all the way around!
Actually that product kinda proves the point that central inverter systems are either less safe or at least perceived to be less safe or else they never would have came up with the idea. Is it actually out yet? If not looks like any time now. I'm guessing having that added to a system would add another $1,000 to a project.

Being off the grid you didn't have much of a choice though.

So 90 volts, what do you have strings of 3 or 4 panels?

AndyH
Posts: 6388
Joined: Fri Apr 23, 2010 3:43 pm
Location: San Antonio

Re: Is this Solar Deal good??

Thu Nov 15, 2012 2:00 pm

QueenBee wrote: Actually that product kinda proves the point that central inverter systems are either less safe or at least perceived to be less safe or else they never would have came up with the idea. Is it actually out yet? If not looks like any time now. I'm guessing having that added to a system would add another $1,000 to a project.

Being off the grid you didn't have much of a choice though.

So 90 volts, what do you have strings of 3 or 4 panels?
I think this remote disconnect is on the streets now (this one from Midnite solar). It's designed in advance of an impending code requirement for an easily-reachable disconnect (I assume, haven't read the code requirement).

Off grid gives me all the choices everyone else has - including the first one to go off grid. :)

I could use microinverters and use an AC battery charger. But since I only need 10 panels and they're all on a single plane with dawn/dusk exposure, there's no benefit.

The system I'm building is for a passive solar Earthship so the electricity loads are small - no HVAC, for example. The refrigerator and home office are the largest (and only significant) loads. The array is 5 strings of 2x36Voc panels - they only approach 90VDC during a record cold...not too likely as climate change continues to make solar systems 'safer'... :(

As for the price of the disconnect, I'd have to evaluate a grid-tied system and compare/contrast string- VS micro-inverters. I suspect there's enough of a difference between inverter types to pay for the required disconnects, but I may be wrong - I haven't done the math for a large grid-tied system.

Edit... PS - panel-level MPPT/tracking/isolation/etc. is available without using micro-inverters.
http://www.ecodirect.com/Solar-Power-Op ... -s/277.htm
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