Two Meters- Your Thoughts

Please see attached PDF for reference.
I am getting ready to install a 10 Kw solar system for a customer. I would like to backfeed a panel the customer has that is 250 feet from the array. It is a 200 amp panel in the garage area. All of the loads on the system are over at the home panel which is about 325 feet and not too easy to get to. Is it ok to backfeed at the garage in this situation? This state has a 10 kw (rated at the inverer) limit. So bottom line- Im not going to "slow down" the meter at the house and I am going to net-meter ALL of my Kw back onto the grid. Does it make any sense to do that?? My gut tells me no. What are your thoughts?


  • BB.BB. Super Moderators, Administrators Posts: 33,082 admin
    Re: Two Meters- Your Thoughts

    Two points... The first, for most installations, understanding the billing/net metering/payment from the utility can make a huge difference in what the payback is on the system.

    At least in California, the regulations were setup to favor offsetting existing use and zero incentives for anyone that produced more power than they generated... Now, they are talking about paying $0.06 per kWH for > 1 year banked accounts--But, given that the price of power runs between $0.09 and $0.45+ per kWH for Time Of Use / Seasonal panels in my area--the $0.06 / kWH is pretty much still a whole bunch of not much.

    There are allowances in the regulations to allow a communally owned GT system to share the "revenues" across multiple meters (say as in a condo project with one communal GT system)--So, perhaps that will allow you to be "within the intent" of the PUC's regulations.

    Second--I worry about voltage rise (your system pumping 10kW back towards the utility). I see you have a long run of wiring as DC (Varray)--So, that part, from my humble point of view, for either option is a good choice.

    However, what is the Nominal/High/Low voltage at the panels (home/garage) and what will be the effective resistance back to the transformer (or to main distribution).
    • 10,000 w / 240 vac = 42 amps
    • Say High line is 250 VAC and Inverter shuts down ~260 VAC
    • R=V/I= 10 volt delta / 42 amps = 0.24 ohms
    I would expect a 200 amp service would have pretty low resistance back to the Grid--But I have seen and read about some pretty iffy setups by utilities for customers that are at the "end of the line" (very high line voltage, for example).

    In the end--What are the advantages and disadvantages to having the customer on two vs one meter--and would one meter/panel at/near the transformer and you dropping the inverter there be a possiblitiy (address several issues at once)?

    I guess you are around Indiana--So your PUC requirements are probably light years from what is currently being done in California.

    So, your concern (appears to be) is about the two billing meters rather than the engineering issues of the long DC and AC wiring runs?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Two Meters- Your Thoughts

    The diagram shows the house meter as "residential" and the carriage house meter as "non-residential". What does "non-residential mean"? Commercial?

    There might be a different rate plan if that is the case. It might also affect the rebates or tax credits.
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