Enphase Mico Inverter

[rick1]

When I was designing my solar grid tied system, I was attracted to the Micro Inverters. But I hit a roadblock when I did the voltage drop calculations because my array was situated 260 feet from the house. This is a very critical calculation since Micro Inverters output at 240 volts AC. As most of you know, lower voltage creates higher voltage losses over long distances and thus large power losses. But the real problem is if the AC voltage drop is out of range for the Micro Inverter, it will shut down.

I was able to over come the distance (ie voltage drop) problem by designing a higher voltage DC home run to a single inverter mounted on the house without using huge copper lines.

This factor alone precluded me from using Micro Inverters. I seldom, if ever, see this discussed in the pros and cons of Micro Inverter discussions.

Micro inverters are the way to go as they have a 25 yr. warrentee, are better in shading, do not have a single point of inverter failure, and are a little more efficient. Most string inverters are warrenteed for 10 years and fail between 10 to 15 years so you get to purchase another one for about $1.00 to 75 cents a watt.

I HAVE 46 ENPHASE M215 MICROINVERTERS 300 FT FROM MY HOUSE USING 1/0 COPPER WIRE. On PVoutput.org my system is labeled as "R & C Hannah Array1 Urbana IL". It works just fine with more efficiency than most systems in its 10 kw size.

[bwillng]

I suggest you read up on the topic of high voltage power transmission a bit - your 'facts' are wrong.

About your wind turbine- no dump load or other protection?

Wind turbine is a skystream. It has a self contained inverter and auto disconnect for power company power failures. Protected by standard circuit breaker at main panel and knife switch disconnect at base of tower. Wind was connissioned by power company in 2009.

[billvon]

I am no genius by any means, but what type of power do you have coming into your home or commercial establishment. Why did Tesla beat out Edison for power distribution, because as I understand it AC is easier to transmit over longer distances?

DC is more efficient over long distances, which is why all the really high voltage transmission lines use DC.

However, AC was easier to step up and down in Tesla's day - a simple transformer did it. You need all sorts of complex hardware to do the same for DC. So in many ways AC is just plain easier to step up and down, and thus in Tesla's time AC won handily over DC. Now that DC/DC converters are easy to design and use, DC is starting to reappear in applications where efficiency matters - long distance transmission, building distribution wiring, photovoltaic array connection etc.

Do any of you have DC from the power company? I guess this is why I chose Enphase inverters because I thought AC would be best transmitted over greater distances.

Higher voltage is always better for distance. With AC you can't go as high in average voltage because the peaks are what cause breakdown. So if your wire insulation is rated for an absolute max of 600 volts you can send 600 volts DC or 424 volts AC - and thus the same wire can send DC more efficiently than AC power.

[quote]so I guess according to the discussion I should expect subpar performance from my micros? How much degradation should I expect for the 125

[inetdog]

But the real problem is if the AC voltage drop is out of range for the Micro Inverter, it will shut down.

This factor alone precluded me from using Micro Inverters. I seldom, if ever, see this discussed in the pros and cons of Micro Inverter discussions.

Is the problem really the voltage drop, as in the voltage goes too low, or is it just that the Micro Inverter is testing for presence of grid (rather than any other source of AC voltage) by sending a high current pulse and expecting the low impedance of the grid to absorb it?
In any case, throwing some money into large gauge aluminum wires should fix that problem and may not be much more expensive than the minimum required for the AC load.

[bwillng]

DC is more efficient over long distances, which is why all the really high voltage transmission lines use DC.

However, AC was easier to step up and down in Tesla's day - a simple transformer did it. You need all sorts of complex hardware to do the same for DC. So in many ways AC is just plain easier to step up and down, and thus in Tesla's time AC won handily over DC. Now that DC/DC converters are easy to design and use, DC is starting to reappear in applications where efficiency matters - long distance transmission, building distribution wiring, photovoltaic array connection etc.



Higher voltage is always better for distance. With AC you can't go as high in average voltage because the peaks are what cause breakdown. So if your wire insulation is rated for an absolute max of 600 volts you can send 600 volts DC or 424 volts AC - and thus the same wire can send DC more efficiently than AC power.



Your losses will be I^2R. So if you have 20 amps coming through and a total resistance of .5 ohms you will lose 200 watts. Double the voltage and you'll have 10 amps at .5 ohms, for a total loss of 50 watts.

I am using #6 AWG copper and it's resistance is only 0.4028 ohms / 1000ft. My run is 125' for the resistance is .000465/ft * 125 = .058 ohms. At 20 amps the loss is 23 watts. I also found this site which is helpful. http://www.sengpielaudio.com/calculator-ohm.htm I used .000465 rather than .0004028 because different sites and tables do not agree so I used the higher of the sites found for a safety factor.

The electric company was commissioning my site today and my line voltage where I am at is on the high side at 252 V & 126V to ground. Our voltage has always been on the high side. They made me initially (in 2002) put a transformer on my property which is only 20' from my entrance cable to my main panel. The utility easement and transformer is 300 feet from the original building.

When the (WE Energies of Wisconsin) electric company was at my site they complain about labeling and want more permanent compliance labels that do not fade with the sun. Any ideas on what every one else is using to over come this issue?

[billvon]

I am using #6 AWG copper and it's resistance is only 0.4028 ohms / 1000ft. My run is 125' for the resistance is .000465/ft * 125 = .058 ohms.

If your total distance is 125' then you have 250' of losses to deal with (2 wires.)

When the (WE Energies of Wisconsin) electric company was at my site they complain about labeling and want more permanent compliance labels that do not fade with the sun. Any ideas on what every one else is using to over come this issue?

Engraved signs work well, since even if the plastic fades completely (very unlikely) you still have the label visible as a physical feature.

[Ian S]

Micro inverters are the way to go as they have a 25 yr. warrentee, are better in shading, do not have a single point of inverter failure, and are a little more efficient. Most string inverters are warrenteed for 10 years and fail between 10 to 15 years so you get to purchase another one for about $1.00 to 75 cents a watt.

A 7kW SMA Sunny Boy inverter can be purchased today for less than $3K.

[SoCalsolar]

Micro?

I have been reading these blogs for a while now and have finally made the jump to sign up. One point in the Micro vs String that is usually overlooked is replacement costs. I'm pretty sure changing out 20 or 30 micros will cost you more when they do go bad due to labor costs which typically go up over time while hardware costs typically drop. When you replace a string inverter you replace it all at once with micros you replace as they go bad or replace them all at once after the first one fails. Granted the Micros are warranted for 25 years the same warranty as most panels so replacement costs can work in favor of the micros if your time frame is less then 25 years. The benefits of micros in the shade has already been mentioned and I second that use of micros. Another situation where micros are good is when the array is on multiple roof surfaces with multiple orientations not being limited by string sizing. Higher prices for micros IMHO relegate them to niche applications like shading, small roof areas that can't accommodate strings and adding on to an existing systems. Feel free to not blow me up on my first post but call like you see it.

[bwillng]

I suggest you read up on the topic of high voltage power transmission a bit - your 'facts' are wrong.

About your wind turbine- no dump load or other protection?

I brought up this topic with the two engineers from the power company while the were commissioning my solar system and they do not agree with you and they said my facts were correct. Again I ask "now many of you actually receive DC from your power company?" I don't think many of your appliance would work on DC at least those that had transformers maybe a universal motor! I know shaded pole motors and induction motors rely on the cyclical field in AC. That means drill presses, saws, lathes, etc rely on AC.

[inetdog]

I brought up this topic with the two engineers from the power company while the were commissioning my solar system and they do not agree with you and they said my facts were correct. Again I ask "now many of you actually receive DC from your power company?" I don't think many of your appliance would work on DC at least those that had transformers maybe a universal motor! I know shaded pole motors and induction motors rely on the cyclical field in AC. That means drill presses, saws, lathes, etc rely on AC.

...high voltage power transmission... was the question, not what the utility delivers to you. As long as they do the conversion back to AC before putting it onto a local segment of the grid, your appliances will still work fine.
In the case of solar, the panel to inverter line can be the equivalent of long distance high voltage power transmission in the grid.

[bwillng]

...high voltage power transmission... was the question, not what the utility delivers to you. As long as they do the conversion back to AC before putting it onto a local segment of the grid, your appliances will still work fine.
In the case of solar, the panel to inverter line can be the equivalent of long distance high voltage power transmission in the grid.

Look at the 4th sentence of my original post!!

[bwillng]

...high voltage power transmission... was the question, not what the utility delivers to you. As long as they do the conversion back to AC before putting it onto a local segment of the grid, your appliances will still work fine.
In the case of solar, the panel to inverter line can be the equivalent of long distance high voltage power transmission in the grid.

Look at the 3rd sentence of my original post!!

[Naptown]

I brought up this topic with the two engineers from the power company while the were commissioning my solar system and they do not agree with you and they said my facts were correct. Again I ask "now many of you actually receive DC from your power company?" I don't think many of your appliance would work on DC at least those that had transformers maybe a universal motor! I know shaded pole motors and induction motors rely on the cyclical field in AC. That means drill presses, saws, lathes, etc rely on AC.

In the US no one. That's because Edison won over Tesla. This is the same reason we had low definition TV forever. The Europeans who adopted the technology later got higher resolution from waiting. Same thing with AC power 50 HZ is more efficient than 60 for motors etc. They also run everything on 220V instead of the 120 we use. Allowing for smaller wires and a more efficient install.
Just because something is the way it is doesn't make it the best.

And speaking of DC transmission there is a project goin forward near me where they are running high voltage AC to a large rectifier plant converting to DC going another 50 or so miles then inverting back to AC. The DC will be run under water for a good way.

[Naptown]

Wind turbine is a skystream. It has a self contained inverter and auto disconnect for power company power failures. Protected by standard circuit breaker at main panel and knife switch disconnect at base of tower. Wind was connissioned by power company in 2009.

What your wind generator is actually doing is producing AC power of variable frequency. This is rectified to DC then inverted back to AC.

[bwillng]

In the US no one. That's because Edison won over Tesla. This is the same reason we had low definition TV forever. The Europeans who adopted the technology later got higher resolution from waiting. Same thing with AC power 50 HZ is more efficient than 60 for motors etc. They also run everything on 220V instead of the 120 we use. Allowing for smaller wires and a more efficient install.
Just because something is the way it is doesn't make it the best.

And speaking of DC transmission there is a project goin forward near me where they are running high voltage AC to a large rectifier plant converting to DC going another 50 or so miles then inverting back to AC. The DC will be run under water for a good way.

I think the two power company engineers were eluding to something like that and I am not sure if it was between MI and WI or Canada but hey did say something about traversing water. they said there were problems but I did not press or ask about any more info.