1. Welcome Hearth.com Guests and Visitors - Please enjoy our forums!
    Hearth.com GOLD Sponsors who help bring the site content to you:
    Hearthstone Soapstone and Cast-Iron stoves( Wood, Gas or Pellet Stoves and Inserts)
    Caluwe - Passion for Fire and Water ( Pellet and Wood Hydronic and Space Heating)

PV Planning & Design

Post in 'The Green Room' started by kmachn, May 16, 2012.

  1. kmachn

    kmachn Member

    Joined:
    Oct 27, 2010
    Messages:
    57
    Loc:
    St. Louis, MO
    Just getting rolling on the planning/design of a DIY PV install, grid-tied using Enphase M215s. I have a whole variety of questions to ask some of the solar-electric experts here, but thought I would start with a relatively simple one for anyone who may have done this or is working on it.

    I am working on the electric schematics (for the permit & utility company) and have a question about the disconnect. I know I will need to install an AC disconnect to disconnect the PV array from the utility (for worker safety during a power outage) but I'm not sure where in the schematics to place it. This layout seems like it would provide the safety for the utility workers and be appropriate...
    PV Array>AC Subpanel>Main Service Panel>AC Disconnect>Electric Meter>to Grid.

    A couple of other installations I have seen (like Gary's PV Array on BIS) have it either immediately after the array or between the AC Subpanel and Main Service Panel (which would not work on mine, unless I also installed another subpanel.)

    Does anyone see issues with installing the AC Disconnect where I have it planned? BTW, I am meeting with an electrician to review all of these things with me, but it is his first solar project so he may not be able to consider any factors unique to the solar/grid-tie arrangement. Also, I have checked the Enphase wiring diagrams and they do not even show the AC Disconnect. I think it is because the inverters shut down themselves when disconnected from the grid for this very reason, but I'm sure the utility will want to have this fail-safe in place. Thanks in advance

    Helpful Sponsor Ads!





  2. GaryGary

    GaryGary Feeling the Heat

    Joined:
    Jul 12, 2010
    Messages:
    286
    Loc:
    SW Montana
    Hi,
    I suspect (but not sure) that Enphase takes the position that the AC breakers that connect the group of micro inverters to the breaker box are the AC disconnect. You could call and ask them -- they have good customer support.
    http://enphase.com/downloads/Enphase_Wiring_Diagram_1_240_Single_Phase.pdf

    Maybe I'm missing something, but with the arrangement you propose, it seems like the AC Disconnect will cut off all power to the house? This seems like a bad way to go in that its nice to have a way to disconnect the PV array from the grid and house.

    Did you look at the way Doug did his?
    http://www.builditsolar.com/Projects/PV/DougEnphase/DougEnphase.htm
    He has a box that combines the two Enphase arrays out where the arrays are, and then runs a single set of 240VAC wires to the house where the AC disconnect is located next to his meter.

    Gary
  3. kmachn

    kmachn Member

    Joined:
    Oct 27, 2010
    Messages:
    57
    Loc:
    St. Louis, MO
    Thanks Gary, you nailed it, it would disconnect me from the grid. But I wonder how big of an issue this is. After all, the disconnect would only need to be shutoff if the utility was working on the lines, in which case disconnecting me from the grid would not be an issue. Nonetheless, having the disconnect between the array and my main service panel would probably be a good idea in case I needed to disconnect it for maintenance or some reason. Although as you mentioned, in that case I could use the breakers in the subpanel. You may be right in that the AC breakers in the breaker box as long as the breakers are lock-capable and are accessible from the exterior.

    If you don't mind, another issue I am trying to figure out. Our utility is offering rebates of $2.00/DC-rated watt and the package I am looking at is about $2.70/rated watt.

    http://www.solarpanelstore.com/sola...nphase-grid-tie-packages.gte_7200.info.1.html

    Do you know if the federal tax credit (30%) apply towards the total cost of the system, or just after the rebate? http://www.dsireusa.org/incentives/incentive.cfm?Incentive_Code=US37F seems to indicate that it is the cost of the system "at installation". Since I would receive the rebate a few weeks following the completion of the installation, then the entire system should be eligible for the credit, correct? That would put the cost of the system (as a DIY project) next to nothing.

    Also, a 2-3 of the 30 panels may have a little shading in the afternoon in the winter time. I used the Solar Survey from your site, should have little effect on the total output annually given the benefits of the Enphase technology. At any rate, I am thinking that given the final cost of the system I shouldn't be concerned about that small hit. After all, the only other way to avoid shading is to use a smaller system (not really a good place to relocate), but with the utility rebate and tax credit it seems to me that it is probably worth going with the bigger system. Thoughts?
  4. begreen

    begreen Mooderator Staff Member

    Joined:
    Nov 18, 2005
    Messages:
    44,544
    Loc:
    South Puget Sound, WA
    You want to also be able to isolate the system from the main electric panel. I would expect a disconnect or at least a breaker(s) for each array before connecting to the main house panel.
  5. GaryGary

    GaryGary Feeling the Heat

    Joined:
    Jul 12, 2010
    Messages:
    286
    Loc:
    SW Montana
    I'm not at all an expert on wiring, but I think that one consequence of putting the disconnect where you propose is that it would have to be rated to take the full main panel current? That is, it would have to be something like a 200 amp rated disconnect vs just enough to handle your PV array output?
    Other than that, I'd just feel uncomfortable with switching the whole house off, but, as you say, I can't point to any particular circumstance where it would be a problem.

    That looks like a good package at a good price -- nice that they include the mount rails as some of the packages don't these days.
    You will, of course, have some other expenses, but the package appears to cover a lot of it.
    One thing to be careful of is that they know how you plan to arrange the panels (portrait or landscape and how many rows) -- the new Enphase scheme with the cable that goes along the row of panels and connects the inverters is nice, but it has to be one with the right spacing.
    I'd like to hear how you like the new cabling arrangement when you get there.

    I've always assumed that the 30% tax credit only applies to your actual out of pocket expenses (after other rebates), but I've never actually checked on it. It would be nice if it turns out to be the other way :)

    Gary
  6. kmachn

    kmachn Member

    Joined:
    Oct 27, 2010
    Messages:
    57
    Loc:
    St. Louis, MO
    You have excellent points Gary, that is why I wanted to ask. I knew I would learn something from someone else that I had not considered. I will just make sure to install it between the PV array and the main service panel, finding and purchasing a 200 amp disconnect (which is the size of my service panel) would be grossly unnecessary.

    I have thought about the fact that my layout will be somewhat different, and therefore a few more rails, probably splices, etc will need to be purchased with the kit. I haven't gotten to the point of figuring it all out yet, but I know I will need to dot "I's" and cross "T's" before I place my order. I will definitely let you know how the installation goes and the cabling arrangements. I am hoping to log/photograph the process as another resource for others.

    I just did a few quick searches on the credit only to find very conflicting information. Below are two sources I found (although unofficial, technically) that states it can be taken before the rebates (initial cost) BUT only if the "rebates" are considered taxable income. I'll need to do the math to determine how it will work out, but I know the rebate application with my utility company requires me to fill out a tax form, so I assume should plan on it being part of my taxable income. I suppose I will need to speak to a tax advisor to be sure, although even then I may get conflicting information.

    http://www.azcentral.com/arizonarep...00705arizona-solar-tax-credit-irs-letter.html
    http://calseia.org/tax-credits.html (under "Solar Scam Alert: Tax Fraud", 2nd paragraph)

Share This Page