# Enphase inverter PV systems



## SolarGary (Sep 8, 2005)

Hi,
Finally getting serious about doing a PV system.

I've been looking at the possibilities, and am kind of liking the Enphase microinverter system.
This system uses one small grid-tie inverter mounted behind each PV panel, so basically the output from the PV panel inverter combo is 240VAC. The 240VAC lines get strung from from one microinverter to the next up to about 15 of them. Then the 240 VAC line from the string of microinverters goes to an AC disconnect and to a 240VAC breaker in your CB panel. The disconnect may not even be required in some areas, since the breaker it feeds into on the CB box is basically a disconnect.
These microinverters are full fledged grid-tie inverters that meet the UL1741 standard that utilities require.

The things that appeal to me are:
- Can start fairly small and expand over time. You don't even have to use the same PV modules.
- Each panel gets its own MPPT controller.
- Easier wiring.

Maybe not so good:
- The normal mode for monitoring the system uses their Envoy box at your site to send data up to their website, where they then rehash it and report to you on a webpage. The reporting looks very through (panel by panel), but it seems complex, and you have to pay $2 per inverter per year.
They do offer some local reporting capability by hooking your PC directly to the Envoy box via an eithernet cable.
- Not an old company, so you have to wonder if the inverters and the company are going to have a good long life.

Enphase site:
http://www.enphaseenergy.com/products/products/micro-inverter.cfm

Guy Marsden is building one of these systems and reporting it on his website:
http://www.arttec.net/SolarPower/index.htm

So, just wondering if anyone has any thoughts on this -- particularly any bad features?

Gary


This kind of indicates how small you can start with this system:
This is a 1 panel Enphase kit that Affordable Solar sells.
http://www.affordable-solar.com/ASGP-solar-starter-kit.htm
While it would not be legal, it seems like the output from this kind of small system could be plugged into and available breaker, or into a 240VAC outlet. It seems like it would be as safe as any grid-tie system?


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## Ken Scharabok (May 11, 2002)

There is an article in the Sept/Oct 09 issue of _Countryside and Small Stock Journal_ on these. By the co-author of _Got Sun - Go Solar_.

As I see it, it makes the installation/use much easier. The only DC wiring required is from the panel to the inverter. From the inverter to the structure it is AC. Within the structure you appear to have the option of 12V DC or 110v AC. At 240v, same as the electricity coming in off the grid. Standard battery chargers could be used.

Would seem to work well with a utility buy-back. When your solar exceeds your needs the excess is fed into the local utility grid. When it doesn't, the grid makes up the difference. Say your weekday demand is highest between 6-8AM and 5-9PM. Between 8AM and 5PM you may be a net producer.

However, on the utility buy-back, where they have a separate meter rather than running one meter in reverse, they are only required to pay their cost of production, not their retail rate. We have a local electrical co-op who obtains their power from TVA. If the retail rate is $.12 kwh, their supply cost (TVA) may be $.06 kwh.


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## wy_white_wolf (Oct 14, 2004)

Ken

All that depends on the net metering law for your state. Dsire has links to the laws for your state.


I have mixed feelings about the Enphase system. I doo see it making the install easier, but the higher equipment costs of the system easily offset any savings. I also don't like that they have no compatability to a backup battery bank. Grid goes down, so does your system.


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## Ken Scharabok (May 11, 2002)

Why can't the 110v be used to charge the batteries, which then feed into a 12v system?


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## TnAndy (Sep 15, 2005)

Ken Scharabok said:


> However, on the utility buy-back, where they have a separate meter rather than running one meter in reverse, they are only required to pay their cost of production, not their retail rate. We have a local electrical co-op who obtains their power from TVA. If the retail rate is $.12 kwh, their supply cost (TVA) may be $.06 kwh.



TVA has a good solar buyback program going.....Green Partners. They now pay 12 cents per kwhr OVER whatever your local retail rate is for any power produced by solar......so if your retail is 12 cents, you would get 24 cents for your solar production.....and give a 10 year contract to purchase at that rate.

Your local retailer must agree to participate, and so far only about 10% of the TVA retailers are.....but likely because nobody has asked....that's the way it was with ours until I did.


There IS a separate meter ( and disconnect ) required for the solar production.....and the buy meter is also bi-direcitonal....so if you produce more than you consume, it runs in reverse....and you get the full 24 cents ( as above ).....otherwise, you get the 24 cents less what you consumed at the retail rate.....but still, 12 cents is 12 cents.

For example:

Use 900kwhr/month Our local rate is 9 cents. .09x900= $81 + $8 flat customer charge = $89 power bill

Produce 350kwhr/month ( about what my 3kw system does typically ): 350 x.21 = $73.50

89 - 73.50 = $15.50 power bill.



First megawatt/hr on our system April, 2009


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## TnAndy (Sep 15, 2005)

wy_white_wolf said:


> Ken
> 
> I have mixed feelings about the Enphase system. I doo see it making the install easier, but the higher equipment costs of the system easily offset any savings. I also don't like that they have no compatability to a backup battery bank. Grid goes down, so does your system.


I don't think the equipment is that much higher.....the Enphase inverters run about $200/ea ( depends on your panel brand....they are matched to a specific panel ), so for a 200w panel, you'd spend another 200 for the inverter.

Say you had 12 panels ( 2.4kw system ) and 12 Enphase inverters @ $200 each.....that would be $2400.....not too much more than a single 2500w grid tie inverter. Plus, you can run smaller wire by stepping the voltage up AT the panel, and eliminate a DC disconnect, etc.

The biggest advantage of the Enphase I can see is the ability to add on to the system fairly easily, AND if you lose one inverter, your whole production doesn't go down, whereas with a single large inverter, it does.

Ken:

You COULD use a 120v battery charger to charge batteries, but then you have to buy the charger ( built into most grid tie/battery backup inverters or off grid inverters ) for several hundred bucks..it takes a SMART charger like an Iota brand, not a cheapy automotive charger with a just a timer.......AND you have to have another, separate inverter + transfer switch to invert the power back to 12v AC if that's the way you want to use it while off grid......whereas you could get all of that in a package like the Outback GTFX series inverters.....grid tie when the grid is up, off grid use when the grid is down ( with a transfer switch to isolate out the circuits you select for your house...like whole house generator )......and going from 120v to DC and back again would mean probably 25% loss of power.

No, Enphase is really ONLY for grid tie uses....


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## wy_white_wolf (Oct 14, 2004)

"the Enphase inverters run about $200/ea"

If they've came down that much than maybe. Last year when I was checking them out the inverters where selling between $450 to $500 each. I did work out then that the materials to do a 1KW system ran $12 a watt using them. A 1KW system using a traditional style inverter could be done for about $7 a watt then.


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## TnAndy (Sep 15, 2005)

$182 to $225, depending on the model required by the panel you're using....

http://www.wholesalesolar.com/inverters.html#enphase

You'd also need 1 branch connector kit for 60-70 bucks.....and I'm not sure how many inverters can connect to that one kit....PDF instructions say "do not exceed 15amp limit"....so I'm gonna guess it's quite a few, since that's on the 220v AC side...

Their extension cables are WAY overpriced if you need them, but the way the inverter is designed to fit on the back of the solar panel, you really SHOULDN'T need them.


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## SolarGary (Sep 8, 2005)

wy_white_wolf said:


> "the Enphase inverters run about $200/ea"
> 
> If they've came down that much than maybe. Last year when I was checking them out the inverters where selling between $450 to $500 each. I did work out then that the materials to do a 1KW system ran $12 a watt using them. A 1KW system using a traditional style inverter could be done for about $7 a watt then.



[FONT=&quot]Most of the places sell the microinverters for about $190 ish each now, but you also more or less have to buy the box that monitors all of the inverters, and it cost $340 (only need one for the whole system). So, for a 2KW system, the total inverter cost would be (10)($192) + $340 = $2260 or $1.13 per watt -- this is with 200 watt PV panels. You can get a Fronius 2KW inverter for $1812, and a 3KW for $2052 (which would have some room for growth).

I guess one thing in the back of my mind is that basically the system is almost all regular AC wiring, and I am pretty comfortable with that, and know most of the rules. Also, the best place for a regular inverter in my setup would be outside on the house wall. There would be occasional cold mornings when the inverter would be exposed to temps colder than its spec range -- at least until it warmed up while working. [/FONT][FONT=&quot] I was told by one very experienced WI installer that this is not really an issue, but still seems a bit doubtful.[/FONT][FONT=&quot] 
The Enphase inverters are made for the full outdoor range of temps. 

Gary

[/FONT]


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## SolarGary (Sep 8, 2005)

TnAndy said:


> $182 to $225, depending on the model required by the panel you're using....
> 
> http://www.wholesalesolar.com/inverters.html#enphase
> 
> ...


I noticed the extension cord price also. I think that I would not need one, as my PV panels would extend in on straight line with no double back, so the inverter on the last module could go right to the junction box (I think).

Interesting thing if you read Guy Marsden's story so far, he did not realize that he would need the extension cords until the parts arrived -- when he called Enphase support they sent in 3 of them for free -- the reward for not planning ahead I guess 

Have you gotten any reading on whether you will need to install a separate AC disconnect, or if the new breaker that ties the PV into the system can serve that purpose?

Gary


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## TnAndy (Sep 15, 2005)

I think the disconnect issue would be on a case by case basis depending on what your local utility requires. I believe the breaker would meet the code requirement, but you would have to mark the breaker with that red warning label you see part of on my disconnect....that IS a code requirement. IF you have a separate meter for the solar like we do, I think the disconnect would be required by the utility for the meter servicing.....that's the deal here.

Anyway, it's a pretty nickle and dime cost......I used a non-fused, simple knife type double pole switch, NEMA 3 ( outdoor ) rated. It was 12-15 bucks.....almost nothing in the scope of the whole install.


The junction box "kit" that is sold to go with the Enphase units is just a waterproof single gang type box with a blank cover....but I've seen pictures of it using a heavy duty double pole flip type switch ( like a regular house light switch, only both hot legs of the 220 connect to the terminals on the switch...about a 10 buck switch ) with one of those weatherproof 'flip switch' covers to go over it, so you have a disconnecting means up at the panels.


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## greg273 (Aug 5, 2003)

Sounds pretty cool. Grid-tied inverters and photovoltaics could power a large portion of our domestic electricity needs in this nation. Think of the contribution to the national electrical grid that a few tens of millions of grid-tied PV systems could produce. The reduction in pollution would be huge. Not to mention it might save a few mountain tops from having to be torn down to get at the filthy fossil fuels buried beneath.


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