Grid Connect Central Inverter

[Neil_D]

I had solar added to my home and there is an Enphase IQ Combiner that sends the power to the house and excess to the grid. I purchased some additional solar panels locally to set up a solar farm in a field on the back of my property. I could purchase another Enphase IQ Combiner which has 4 - 20 amp circuits ($650)but I was wondering if there was something less expensive that I could use as direct to grid. I am not interested in monitoring the output other than the power wire(s) from the solar farm will pass through the CT on the current combiner, but otherwise go straight to the grid. There will be two circuits (12 panels each)coming from the farm, 20 amps per circuit, about 2400 watts max. Any recommendations for a basic inverter that is moisture-resistant (mounted under the panels)? My future plans will be to add more solar in groups not to exceed 20 amps as I will be running conduit with extra 12 gauge wires for additional expansion.

[Ampster]

If you use Enphase micros the existing Enphase Envoy in the combiner should be able to pick up the powerline signals from both sets of inverters. Running the circuits through the CTs will measure the aggregate current but the panel level monitoring comes from the Envoy. You may need to upgrade the software so that you can get the Envoy to recognize the new inverters. The Enphase documentation is fairly good.
I am not clear how to interpret your statement "direct to grid"? Typically they are connected through a breaker panel and you should follow the code in terms of backfeeding a breaker panel. That revolve around the capacity of the bus bar of that panel. Do you know the bus bar capacity of that panel?

[J.P.M.]

I ask the OP's and membership's forbearance for a comment/2 not specifically related to your post: While it's a pretty safe bet that the area under an array is probably drier than the immediate surrounding not under the array, don't bet there will be no chance of things getting wet.

Besides the easy to visualize idea of a windy rain/snow event blowing moisture against the backside of a tilted array or under a roof mounted array, there is a situation I discovered in years of close monitoring my array that I've not seen or heard discussed.

On clear nights when the dew point is close to the dry bulb temp., and similar to the way dew collects on open ground under such conditions, moisture will collect (condense) on both sides of a panel/array in about equal amounts, front and back. The front side water will run/drain off the lowest edges of panels and onto the surface below, probably not getting in contact with the backside of the panels. The underside condensate will also tend to run "downhill" (DUH ?!?!) but while doing so may drip onto wiring or connections or other electronics. For the most part, that might not be a problem, but the underside of a lot of roof mounted panels can and do get wet. I've seen it up close and personal and had it drip on my head. As a matter of fact, I saw and felt it this morning about 45 minutes ago.

As an aside, and still off topic but perhaps useful, or FWIW, and contrary to what I once thought, the dew that collects on the frontside of a panel probably adds to array fouling. Reason: The dew that doesn't run off combines with the dust/dirt/fouling already there. The resulting soup has a higher viscosity than water and so tends to not "move" as much as "clean" dew. The result is that when the sun heats the panels and drives off the moisture, the mud turns to cake that's more difficult to remove. That the mud moves some may/probably be part of the reason why a lot of arrays show a "bathtub ring" at the lower 6" - 12" or so at the bottom of panels. The lower the tilt, the bigger (wider) the ring with horizontal panels turning into mud pans.

We now return to our regular scheduled programming.

[Neil_D]

Ampster That was my original idea. However at $160 a pop x 24 panels for the microinverters that is a high expense. Since the panels are extra and in a field, I do not care if a single panel is in shade, which would drive the power down until all are in full sun. Secondly, SunPro/ADT is the installer of the original system and combiner and they will not give me access to the EnPhase installer toolkit login credentials. So I can not add microinverters to the existing system without going through them and of course they charge 4k to add 2 panels to the system. I would like to kick them to the curb but that is another story for another time. All I am trying to do is sell enough additional power back to the electric company that my entire electric bill is paid and the loan on the original system is covered.

Direct to grid is basically me sending all the power from the inverter to the grid via my service panel without going to the house for use. I have a 400 amp service which is basically 2- 200 amp services. There is breaker capacity in the panel now for some additional breaker/circuits. Currently the power comes from the panels on my roof to the combiner, which has 4 -20 amp circuits, two are being used. Then the power goes to the service panel to a 60 amp breaker. If the house demands the electricity it gets it from the panel, otherwise the excess goes through the reverse meter back to the power company. My idea is to add my circuit to the subpanel through two additional 20 amp breakers and send any excess power to the power company. If I run the power wires through the existing CT that is monitoring the incoming power to the combiner I should be able to see it in the app as a higher output from the solar. Then run the wires to the breakers and so forth.

[bcroe]

I believe the additional panels would be set up with a simple string
inverter? Putting an outdoor inverter near the panels and running
the AC output to your plant works. The inverter(s) might serve
longer with less problems, if you ran panel DC to a shelter with the
inverter(s).

With a 12 panel string you are running like 400VDC, which would
have less loss, or require less copper, than running 240VAC from
the panel located inverter. Run the numbers. Bruce Roe

[Ampster]

Ampster That was my original idea. However at $160 a pop x 24 panels for the microinverters that is a high expense. Since the panels are extra and in a field, I do not care if a single panel is in shade, which would drive the power down until all are in full sun. .......

As bcroe . suggested the most cost effective solution would be a separate string inverter. Even though your existing PTO may limit how much you can export, my experience in California has been that the utilities do no monitor those installations that closely. I am not advising you to exceed your PTO capacity and I have heard reports of some people who have paired storage arrangements who have been monitored and charged back for excess sent to the grid. My own experience was that for whatever reason my breaker got turned on for the nine months that I was waiting for my PTO and my utility never called. I never got any credit but I did charge my EVs a lot from the available solar.