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PNM says either upgrade the transformer or downsize my expansion proposal.

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  • PNM says either upgrade the transformer or downsize my expansion proposal.

    Hi, this is my first post here. I've had a 3.6 KW grid tied system since 2010. Here in southern New Mexico, it's performed very well, and the REC's have been good. A couple things have been pushing me to expanding my system. Even though I've had a 0 bill for ten years, that will soon change. In November I had a Rheem 20 SEER heat pump installed to cut down on my propane usage. I took out my propane hot water heater, and installed a heat pump heater. This time of year I'm usually banking KW's for the summer cooling season. Not this year. I'm running a deficit with most of my heating coming from electricity. The heat pump heats down to 30 degrees, ( and I can adjust it lower). With my plans on getting a EV in a couple years, and wanting take advantage of the current Fed and State tax credits, I signed a contract with Sunspot Solar to expand my system from 3.6 to 12.4 KW DC, or 10KW AC. It passed PNM's first examination, but failed their technical one.
    From PNM yesterday:
    "You have several options: Downsize your system to meet PNM requirements
    Request that the transformer that supplies electricity to you be upgraded
    Request a Customer Options Meeting on Supplemental Review. We will be happy to discuss your options in detail during this meeting.

    To note, my neighbors across the street have at least a 10KW system they put in last year. I'm thinking that may have used up all the spare capacity on the transformer.?
    Has anyone dealt with this issue before?

    I'm considering asking my contractor if I can have a hybrid system with a battery back up. I sent an e-mail to PNM asking what the maximum size I can have, and am waiting for their response.
    I know PNM is looking at my 0 bill and wondering why I want such a large system. Well, I want enough power for any future upgrades including an EV which will use a lot, while taking advantage of the tax credits. After my contract with them runs out in 2023, they won't have to pay me any more REC's to speak of. It'll go from 13 cents to 1/4 of 1 cent.
    Thanks for taking the time to read this.
    Last edited by NMDan; 02-24-2021, 12:32 PM.

  • #2
    If the response from PNM is some reasonable figure then a hybrid that could limit your ecport would be the easist. It is a challenging situation if they do not allow more. I have two EVs and a hybrid system with 40 kWh of batteries but I would not use my stationary batteries to charge my EVs. I have tried using my excess solar capacity to charge my EVs with limited success.
    You would have to look at your agreement with PNM to see if the following is viable. A lot may depend on your building authority as well. The concept is to leave your existing GT system intact but send as much power as permited by your agreement with PNM. An additional hybrid or GT inverter would generate power and only use it behind your meter with no export. One of the advantages of some of the hybrid systems is they can be programmed for no export or limited export. Even less expensive are grid tie systems that can be export limited. In my case I limit the export of my hybrid system which allows my GT system to export all that it produces. My house loads are covered by the hybrid system and the batteries. The GT system is the only part of my system that is directly connected and permitted by my power company. I have a building permit for my hybrid system but it exists solely behind the meter.

    With an EV it is a juggling act because there are only a limited number of EVSEs (EV charging stations) that can modulate power based on solar production. I have heard that certain models of the Solaredge Inverters can be configured with an EVSE so that the EV can be charged from solar. I do not know if they can be simultaneously configured for no export. In my case it is more a hobby because it was difficult to model and control all the elements. I do not know if an installer would even be interested in the complexity of such a system. I only know one installer in Southern California that has even tried to come close to doing something like this.
    if the response from PNM is not enough capacity, I would also go the route of a meeting to discuss the options.
    Last edited by Ampster; 02-24-2021, 11:52 AM. Reason: Add sizing duscussion with PNM.
    9 kW solar. Driving EVs since 2012

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    • #3
      That's what I have been thinking about. Staying with the same size as originally planned, yet splitting it between what PNM allows, and using the rest with a battery behind the meter with no export. I have maybe a unique situation where my utility power runs from the road underground to my well house, where both meters are. From there it runs underground to my garage where the breaker panel is. The well pump circuit is at the well house. I definitely would want the pump supplied in the event of a grid loss.
      My system currently uses 16 Enphase M-190 micro inverters. The expansion part would use the newer IQ-7 plus, I agreed to the Enphase swap out program offer, and just received 16 IQ-7 PD, and an Envoy monitoring system, with a couple CT's and the necessary wiring.
      I've been looking at the Fortress 18.5 KW LFP battery. It seems reasonably priced, does anyone have any experience with them..? Any AC coupled inverter recommendations.? If I go the battery route, I may want to add another battery at some point. Is it true you need to size your AC coupled inverter to match your battery size.? Would that mean to add another battery (in my case), I would also need to add another inverter.? Sorry for so many questions, I'm trying to get as much information as possible before making this leap.

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      • #4
        I'm guessing that you have a flat roof. If you have a sloped roof, perhaps you can put one set of panels on the East roof face so you get morning power, and another set on the West face to get evening power. That way, you get low power but more hours, better utilizing the transformer.

        That aside, it would be great to learn more from the power company about their limits. Can you add 2kW, 4kW, or 6kW with the current transformer? Will they make you pay for the new transformer? If so, how much?

        I'm not a fan of batteries, especially in a hot climate. They wear out too soon and the cost is rarely justified by the return.

        I like Ampster's idea of upgrading your system, but setting it up so that the output to the grid is limited. When the sun is shining, you can air condition the house free and send any small excess back to the grid. When the AC turns off, the system puts out less. But common inverters are not that sophisticated. Ampster's idea is simpler: use the existing half of the system for grid export and limit the expansion for zero export. That might be a clean compromise, if you can get two inverters to play well together in this fashion.
        7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

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        • #5
          Originally posted by bob-n View Post
          I'm guessing that you have a flat roof. If you have a sloped roof, perhaps you can put one set of panels on the East roof face so you get morning power, and another set on the West face to get evening power. That way, you get low power but more hours, better utilizing the transformer.

          That aside, it would be great to learn more from the power company about their limits. Can you add 2kW, 4kW, or 6kW with the current transformer? Will they make you pay for the new transformer? If so, how much?

          I'm not a fan of batteries, especially in a hot climate. They wear out too soon and the cost is rarely justified by the return.

          I like Ampster's idea of upgrading your system, but setting it up so that the output to the grid is limited. When the sun is shining, you can air condition the house free and send any small excess back to the grid. When the AC turns off, the system puts out less. But common inverters are not that sophisticated. Ampster's idea is simpler: use the existing half of the system for grid export and limit the expansion for zero export. That might be a clean compromise, if you can get two inverters to play well together in this fashion.
          My solar system is ground mounted, and the expansion would also be ground mounted nearby. I'm still waiting for PNM to get back with me on what they will allow me with the current transformer, but I'm pretty sure I'd have to pay for a transformer upgrade. From what I can find out, in some states you would just pay for the labor. But that would run $1000 to $3000 or more. Plus it would probably piss off my neighbors to have their power cut for maybe a day or two.

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          • #6
            Originally posted by NMDan View Post

            My solar system is ground mounted, and the expansion would also be ground mounted nearby. .....
            Take a look at the thread of @bcroe who has a number of ground mount arrays at different azimuths (orientations). Ground mount gives you additional flexibility. I suspect PNM is only concerned with peak output in kWs, not total kWhrs, especially if spread out more evenly during the day. Over driving your existing inverter within the manufacturers specs may also be an option to look at for starters. That would result in clipping but the increased production in the morning and afternoon might be worth it in your unique circumstances.
            Last edited by Ampster; 02-24-2021, 03:25 PM.
            9 kW solar. Driving EVs since 2012

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            • #7
              Finally heard back from PNM:

              Hi xxxxxx,
              The transformer connected to your home has no available capacity left and needs to be upgraded. Typical costs are around $2,000-$4,000. You or your contractor can apply for this upgrade to find out what the actual cost will be at https://erequest.pnm.com/

              Best,
              -Aaron

              If I went that route, the REC's I would receive for the remainder of my contract would probably cover that. Kind of ticks me off though......




















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              • #8
                Problem is a 10kW array needs more inverter than the 200amp service can handle thus the POCO's desire to upgrade.
                Answer is to just do a 7.7kW inverter which is the max for a 200a service and then split the array into two sections facing different directions so not to overload the inverter.
                BSEE, R11, NABCEP, Chevy BoltEV, >2500kW installed

                Comment


                • #9
                  Originally posted by solarix View Post
                  Problem is a 10kW array needs more inverter than the 200amp service can handle thus the POCO's desire to upgrade.
                  Answer is to just do a 7.7kW inverter which is the max for a 200a service and then split the array into two sections facing different directions so not to overload the inverter.
                  I will have Enphase IQ7 microinverters.

                  Comment


                  • #10
                    I went ahead and applied for the transformer upgrade. Does anyone know if that cost is claimable for the Federal tax credits..? I did a search and all I could find out is this:

                    "Eligible Expenses The ITC is calculated by multiplying the applicable tax credit percentage (10%–30%) by the “tax basis,” which is the amount invested in eligible property. Eligible property includes the following: • Solar PV panels, inverters, racking, balance-of-system equipment, and sales and use taxes on the equipment • Installation costs and indirect costs • Step-up transformers, circuit breakers, and surge arrestors • Energy storage devices (if charged by a renewable energy"

                    I'm not sure if this upgrade is a "step-up" transformer.

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                    • #11
                      Originally posted by NMDan View Post
                      I went ahead and applied for the transformer upgrade. Does anyone know if that cost is claimable for the Federal tax credits..? I did a search and all I could find out is this:

                      "Eligible Expenses The ITC is calculated by multiplying the applicable tax credit percentage (10%–30%) by the “tax basis,” which is the amount invested in eligible property. Eligible property includes the following: • Solar PV panels, inverters, racking, balance-of-system equipment, and sales and use taxes on the equipment • Installation costs and indirect costs • Step-up transformers, circuit breakers, and surge arrestors • Energy storage devices (if charged by a renewable energy"

                      I'm not sure if this upgrade is a "step-up" transformer.
                      Most transformers either drop or raise the voltage depending on how they are used. I think your POCO is just looking for a larger kVA rated transformer to handle more power being sent to the grid so it could be considered a "step-up" transformer for power going to the grid.

                      I would contact your CPA to find out if you can claim the cost of the new transformer as part of the solar pv system but remember the credit may be based on what you don't use from the grid as opposed to what you can send back onto the grid.

                      Comment


                      • #12
                        Originally posted by SunEagle View Post

                        Most transformers either drop or raise the voltage depending on how they are used. I think your POCO is just looking for a larger kVA rated transformer to handle more power being sent to the grid so it could be considered a "step-up" transformer for power going to the grid.

                        I would contact your CPA to find out if you can claim the cost of the new transformer as part of the solar pv system but remember the credit may be based on what you don't use from the grid as opposed to what you can send back onto the grid.
                        Yes, I'm sure it's for a larger kva transformer they're talking about. The PNM person that contacted me said the job would be completed in a few hours.

                        Comment


                        • #13
                          Originally posted by NMDan View Post
                          ......"

                          I'm not sure if this upgrade is a "step-up" transformer.
                          Since most transformers are capable of being bidirectional and since this is a requirement of installing solar I would certainly characterize that expenditure as part of the solar upgrade if it were my tax return.
                          9 kW solar. Driving EVs since 2012

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                          • #14
                            Originally posted by solarix View Post
                            Problem is a 10kW array needs more inverter than the 200amp service can handle thus the POCO's desire to upgrade.
                            Answer is to just do a 7.7kW inverter which is the max for a 200a service and then split the array into two sections facing different directions so not to overload the inverter.
                            That's only true with a backfed breaker and a 200A BussBar panel. We routinely backfeed system up to 38.4 kW AC on 200A 240V single phase services via a line side tap.

                            Andy

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                            • #15
                              my electric co-op made me add batteries and solar to the back feed request (56x295+8x5000=56,520w or 235 amps). they had me sign a agreement that i will not backfeed more then 200 amps, reasonable!

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