Gird tie metering plans

icarusicarus Solar Expert Posts: 5,314 ✭✭✭✭
So, I’m designing a number of systems for a client that continues to present challenges.  Not having too much experience with unusual grid tie schemes I have a couple of questions.  

Conventionally, residential grid tie will tie into the grid either on the main panel or a sub panel, all with proper ratings etc.  This particular installation has 3 phase underground grid, that transforms on the site (on a pole) to return underground,  to 3 phase metering and service.  The service goes to a myriad of buildings each with it’s own sub panels .  My question is...is there a way to do a ground mount PV, (the ground mount locations are not near any buildings, but are near the service entrance power pole).  With an inverter tied to the grid, not at a sub panel, but directly to the service conductors near the service entrance, is this possible, and what would the typical wiring/meter scheme be?

Tony

If you have been following this, I started with the issue of melting snow off the PV.  I have decided on adjustable pole mounts that allow proper orientation in spring, summer and fall, and then vertical or near vertical orientation during the snow season.  It also turns out that non of the roof structures are very well oriented for PV, but there are a number of large, open ground spaces perfect for pole mount PV.

T

Comments

  • mcgivormcgivor Solar Expert Posts: 3,126 ✭✭✭✭✭
    edited October 11 #2
    The tie in must be on the consumer side of the demarcation, the main disconnect, the metering is on the utility side. The only way to get around the problem would be to relocate the demarcation closer to the service pole, there would need the metering along with fused disconnect mounted in a kiosk, this will involve both the utility as well as the AHJ and would be expensive. 

    This is something I've had to do in the past to get around the utility rule of a maximum of 270° inclusive bends allowable, I was upgrading the service to 3 phase in an old commercial building which had the main distribution/disconnect in the center of the structure. The amountof bends needed was 360°, acceptable to CSA code rules but not utility (BC Hydro) rules.

    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • icarusicarus Solar Expert Posts: 5,314 ✭✭✭✭
    So how does utility scale solar metering work, since there is no “service” per se?   T
  • mcgivormcgivor Solar Expert Posts: 3,126 ✭✭✭✭✭
    edited October 11 #4
    There will still be a demarcation, a main disconnect switch even with a large scale installation, there has to be a means of physical isolation. My comments are strictly based on logic, not nesesarally direct experience with grid tied solar, other than a demonstration array, the utility BC Hydro (British Columbia Canada ) didn't allow feeding into the grid at the time,  though that may have changed, the installation was strictly self consumption.

    There are basic rules which are explained in paragraphs in both the electrical code and utility codes, which may differ from one another, I would highly recommend checking with both before proceeding. The best resource if in BC is a gentleman named Wayne Cousins, he will provide all relevant information, if I'm correct that you are in BC.


    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • icarusicarus Solar Expert Posts: 5,314 ✭✭✭✭
    Mcgivor,

    thanks for the response.  I certainly understand the need for proper disconnects and fussing.  My question revolves around where and how one might be able to tie in, but not in a conventional service panel.  I am not in BC.  This installation will be (if it ever happens) in remote Northern Minnesota.  I am awaiting a conference call with the electrical utility co-op to find out what their rules are etc.

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 29,644 admin
    edited October 11 #6
    And in the USA, there is a big difference between Residential and Commercial rate plans.

    Your utility can either take readings from different meters (load meter, GT solar meter) and come up with the appropriate billing (if they want too). Or they can treat the GT Solar simply as a Solar Generator and pay according to that plan(s).

    What "killed" commercial installers initially in the USA, was that (roughly) 1/2 the bill was $/kWH charges & credits, and the other 1/2 of the bill was "Demand Charges".

    For example, this "killed" schools with GT Solar... As you know, the GT Solar is usually designed to have greater average output power than the average loads--So that you "harvest" energy in ~6 hours of sun and make up for 24 hours of load.

    With schools, they have very low loads in summer (no classes), and lots of GT solar... The "demand charges" did not "care" which direction the energy flowed (loads or generation), they were just "charges".

    So, what happened is the schools got GT Solar credits on their bill, but got hit with very high (say 4x normal) for the demand charges, which in the end in some cases, the GT Solar increased their overall electric bill.

    None of this is "obvious", and the various different plans between residential/schools/commercial/agricultural/etc. -- It took very detailed reviews of which plan(s) would be optimum for a specific customer. Add Time of Use charges--And unknown load/charging profiles (prior to actual installation)--There could be surprises down the road. And each state PUC/utility company/etc. has their own mix of rate plans (and which rate plans GT solar may be allowed to use).

    Not saying that any of this applies to your installations--But things that need to be researched before spending money. For a larger system, you may need to hire a power engineer with experience in GT Solar... And the utility will probably assign an engineer/engineering review of their local (to the GT installation) distribution system on their side too. And they may take months to get back to you (or as in Ontario's case some years ago, they "changed their mind" between permit and actual final inspection/connection OK when they had more solar than they could manage/wanted in some areas).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,314 ✭✭✭✭
    Thanks for that Bill.  As I said, this will be in Minnesota. 

    The client has commercial power rate of ~.$.11 vs .13 for residential.  This is all made more complicated by the fact that it is a non profit agency, and there are three distinct properties one of which is an island locations.  Also, virtually all the loads occur between May 15-Sept 1.  I am assuming I will have to hire a local GT engineer to work with the utility.  What I am trying to do at this point is come up with a ball park solution to draft a proposal to send to principals to see if they wish to proceed.  I can’t find many info on line as to the feed in, or net metering tariffs the utility uses, hence waiting on a return call from the utility.  I’m guessing that virtually no one has done a grid tied system in their service area.

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 29,644 admin
    Yea, Grid Tied Tariffs are highly political/utility dependent... Have to find the right guy (or other gendered person) to give you, in writing, what rate plan/schedules they will use for that site. But they will also need to engineer their distribution/transmission capabilities in the area to make sure the solar does not supply more energy than they can handle in the region.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Solar Expert Posts: 3,126 ✭✭✭✭✭
    Although perhaps not ideal, or possible for that matter having a second service drop dedicated to the solar, the problem is generally only a single service is allowed per site, but there are always exceptions to rules.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • icarusicarus Solar Expert Posts: 5,314 ✭✭✭✭
    I’ve gotten a bit more info from the site, and at least on case it looks easy.  The service comes up from underground (actually under water as this is an island property) climbs a pole to a transformer, and then comes down the meter at 208 3 phase to a meter base and a serviced disconnect with breaker.  A simple matter to do the tie on that service there.  

    The other two sites either have handier buildings with sub panels, or a similar main entrance.  At this point, I don’t know (yet) where the pole(s) are relative to a good solar site.

    Tony
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