Permitting and System Size, Inverter or Panel Output?

mstgkillr Registered Users, Users Awaiting Email Confirmation Posts: 9 ✭✭
I'm considering a DIY grid-connected PV install and I have been doing some research. It appears there are two tiers based on the size of the PV system, Tier One (0kW-10kW) and Tier Two (>10kW-100kW). The problem with a Tier Two system is the additional interconnect fees, paperwork, and the requirement of carrying $1,000,000 of personal injury and property damage liability insurance. After calculating my PV requirements, I could go with either tier. I'm not sure how much the additional insurance would cost but I assume it would be better to stay with a maxed out Tier One system.

Now, I know a Tier One system is rated between (0kW-10kW) but I was told that I could go with up to an 11.76kW system assuming 85% efficiency, which would bring the actual system output to 10kW.

I am strongly considering Enphase microinverters due ease of installation, unless someone suggests otherwise. My question is, how do I calculate the actual output of the system for permitting? Let's say that I'm considering 37 LG panels at 315w each and 37 S280 Enphase microinverters at 280w each... since the microinverters max out at 280w, do I base the system size on the microinverters (288w X 37 = 10,360kW) or on the panel size (315w X 37 = 11.66kW)? And can I sill use the 85% efficiency to keep the system under 10kW?    


  • mstgkillr
    mstgkillr Registered Users, Users Awaiting Email Confirmation Posts: 9 ✭✭
    How do you interprit this with respect to microinverters? 

    1. "Gross power rating" (“GPR”) means the manufacturer's AC nameplate generating capacity of the RGS that will be interconnected to and operate in parallel with LCEC’s distribution facilities. For inverter-based systems, the GPR shall be calculated by multiplying the total installed DC kW nameplate generating capacity by 0.85 in order to account for losses during the conversion from DC to AC. The Customer shall notify LCEC of any modifications or additions to the RGS that increase the GPR so that it exceeds ten (10) kW AC by submitting a new application for interconnection specifying the modifications at least thirty (30) days prior to making the modifications. If such modifications are approved by LCEC, a new Interconnection Agreement shall be executed by the Parties and the Customer recognizes and agrees that an increase in GPR in excess of ten (10) kW AC may impose additional requirements on the Customer. 

  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    I would say your interpretation is correct at a max of 11.76Kw system.  Why not ask the AHJ if you met the requirements at that installed size?  
  • BB.
    BB. Super Moderators, Administrators Posts: 33,522 admin
    A $1 million "umbrella policy" which takes your basic liability insurance and raises the limits to $1M may cost $100 to $200 per year (guesstimate).

    All code questions are "local". You need to talk to your building department and utility to get the details.

    Have you done as much conservation as possible?

    In the longer term, in my opinion, Grid Tied systems are going to lose their subsidies and become much less "interesting" to install. A few states have already pretty much put GT installers out of business (Hawaii, Nevada). And states like California are gradually changing the rules to make it more costly to connect GT systems (higher minimum monthly bills, changing rate plans to be less solar "friendly", and such). And some smaller utilities have never allowed GT solar.

    At least with conservation, they cannot make your changes "useless" with some chances in policies and politics. Also, many times conservation can make the home more livable (quieter, less air infiltration, less heat from appliances, etc.).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset