panels with built in grid-tie inverters

[youmanskids]

hey all, I have a PV panel question for you all.  I've currently got a 10 foot dans wind trubine up and running now for 9 months  and am now ready to add some solar.   I live in Arkansas and have a friend in the RE buisness who is going to put in my solar system.  I plan a 4 kw grid tied system (our local municipal power distributor is setting up net metering this month) QUESTION:  he is recommending a new panel with a built in grid tie inverter, in each panel.  Has anyone see these or know if they are dependable/ good long term value. 
With these he says you can run AC power lines with standard romex.  the cost savings in DC high amp wire and cut off swithching etc.. apparenly out weighs the cost of the multiple small inverters.  He quotes $5 per watt installed. plugs right into my main power box for net metering.  total out of pocket cost to me after 30% fed tax rebate and $1.25 per watt "power production rebate" X 12 months from Arkansas, puts me at $1.50 per watt installed ( pay back in 7-10yrs depending on my mangement of power use) sounds to good to be true .  any input would be appreciated.  (I can get the company and model numbers if needed)  thanks in advance.  Roger

[youmanskids]

Enphase is the company and here is a link.  they shure look good.  anyone know of a problem with this type of set-up?
http://www.enphaseenergy.com/products/products/micro-inverter.cfm

[DamonHD]

I haven't heard anything bad about Enphase and the concept is one I agree with, eg to help minimise the problems with balancing strings especially if there is any chance of partial shading.  (They'd be good for my roof for example for that reason.)

Rgds

Damon

[B529]

If you don't have a partial shading issue,  would steer you towards a time tested single inverter.

Regarding cost, I disagree with your installer. Large gauge wire is usually not needed for a high voltage grid-tied system. SMA and other inverters come with a DC disconnect built.

What is the wire run from your array to the inverter? Keep in mind the inverter can be mounted outside.

[hydrosun]

Small enphase inverters have the advantage of being able to make the array any size you want without worrying about matching the inverter. So you can have a small system and grow as you can afford it.  But if you are designing from the start to maximizing the utility of the one large inverter I think that is the way to go. I did a 4KW grid intertie last year using 2 strings of 10 200 watt panels and a Xantrex 4 KW inverter. The panels all came with interconnect wire and then I used 10 gauge wire in conduit to run to the inverter at 300 volts dc.
 The one downside of the enphase inverter is the fee for the company to monitor the output of the system. There isn't any meters onsite with that system. You have to go to their website to get any info. And they charge you an annual fee for that service.  I think you also buy special interconnection wires. Only certain types of solar panels work with those inverters. They only work well on 72 cell panels. So you have less choice of sources for panels. The small inverters are outside under the panels in the heat. Time will tell how long they will work in that environment. The sells pitch is you can tell which ones fail by looking at their website. I'd rather not have a failure.
 I'd have your installer give you a full price breakdown on the two different system types.  I've done the math and on large systems the single inverter wins.
Chris

[ghurd]

They remind me of the old ones from Holland, Denmark, or the Netherlands?
I think Trace brought them in for a while with their sticker, but that did not last long.
They had issues with reliability.  And cost effectiveness (not surprising at $6/W just for the inverter, $300 for a 50W IIRC).

I am with Chris on using a larger inverter, out of the heat.
G-

[GaryGary]

Hi,
I have one of the Enphase systems.  I'm coming up on the one year anniversary -- no problems.

Its described in excruciating detail here:
http://www.builditsolar.com/Projects/PV/EnphasePV/Main.htm

Guy Marsden has a detailed description of his Enphase system here:
http://www.arttec.net/SolarPower/index.htm

I did all the work myself, and it was a very straight forward system to install.  Found the Enphase people to be very cooperative.

I agree with the comment that there should not be a lot of difference in wire size between a grid tie system with strings of PV panels hooked to the inverter vs the Enphase system -- the voltages are of the same order, so the wire sizes should be about the same.

Also agree with the ease of adding to an Enphase type system.  Its very easy.  You don't have to worry about getting a new big inverter, and the PV panels can be different.  WholesaleSolar.com actually has a demo Enphase system in which every panel is a different size and brand!

Also agree that you are more limited on the panels you can use with the Enphase system -- that said, their list of approved PV modules is huge.  One notable brand that does not make the list is Evergreen.

When you say you don't have any shading issues -- this is something to think about very carefully.  Shading can be very subtle.  A roof vent or a fence post you did not think about can cause some shading problems, and the Enphase inverters will handle this better.  I don't mean to make this a big deal, and its not that the big inverters fall apart with a little shading, but its something to carefully consider. 
http://www.builditsolar.com/Projects/PV/EnphasePV/Shading.htm

The online monitoring that Enphase offers is not required.  The EMU unit that goes with each Enphase system provides simple monitoring on its front panel.  Basically, it gives current power out, and the historic total output.  But, the EMU unit also generates some simple web page reports that you can easily look at from your local computer.  The local, EMU generated reports are free, and they do provide health reports and power out reports for each PV panel -- something not reported on big string inverters.
I ran my systems for several months with just the local reporting, and its OK.  In the end I signed up for the Enphase online reporting system.  This is my system:
http://www.builditsolar.com/Projects/PV/EnphasePV/RealTime.htm
I have to say that while they do charge a fee for it, its pretty nice to have. 
They keep track of any developing problems right down the the individual inverters, and send you an email if anything needs attention.  I'm the kind of lazy person where this kind of reminder is helpful


One piece of advise on the design of an Enphase system.  I would pick a PV panel that has a nameplate wattage that is somewhat over the inverter rating.  In my case, I'm using 215 watt panels on the 190 watt inverter.  I think this is close to the sweet spot.  If you go higher in wattage and have a good sun location and the panels are well ventilated, then there may be times when the inverter has to limit the PV panel to the inverter max output.  If you go with smaller PV panels, then you are paying for more inverter power than you need for the panel.  I guess this is a small point, but I tend to get carried away on these kinds of issues

Enphase just came out with a new dual panel micro inverter that controls a pair of panels rather than just one panel.  Don't know what the pricing is like.

Overall, I think that either type of system is fine -- especially if shading and later expansion are not issues for you.



Gary

[youmanskids]

Thanks for the input guys,  The shading will be a big issue for me. as for my rooftop, 1/2 faces southeast and the other 1/2 south west, with the hip lining up almost due south.  it is a 12/12 pitch and my latitude is 36 deg. N.   the plan is to have 1/3 of the panels on the SE face , and 2/3 on the SW face.  so i would have 2 different panel strings and would need 2 MPPT inverters at least. ( 23 panel system)  I am glad to hear the pros and cons.  I think I would like to see both system options laid out for cost comparisons as you suggest.  the main fear I have is with inverter failures.  they are rated for 190 yrs with 'expected time between failure' set at 390 yrs!  not sure how they arrive at that number but it is good to hear that Gary has at least 1 yr of good performance  .  I'll try to keep you posted.  thanks again for the advice,   Roger