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  • Substantial Import/Export Mismatch

    I have a home in Hawaii, where net metering was ended in 10/2015. I have 60x330w = 19.8 kWdc connected to 2 Solaredge HD Wave inverters (10k, 7.6k). Six months per yr I live there and use 2 EVs. Six months/yr it is a vacation home on the Sunniest but hottest part of the island where renters run my AC 24/7 as low as I will permit them (72F). During both periods my production is usually close to but some times 10-20 kWh below my consumption. However, I usually export & import about 35-50 kWh during the 6 months that guests use it due to high AC use. My utility credits me $0.1 & I pay $0.32kWh for export/import amounting to $350-450/month when guests are present. My AC comes from an Icebear 20, which I have programed to make 'ice' from 9a-5p. The IB20 uses the 'ice' to chill the coolant after 5 pm til it isn't cool enough to help. When I am there, it can keep my master BR ~76F til 2-3 am. When renters are there, the 20 tons of cooling from the ice last 2-3 hr.

    I self consume as much power as I can by running my pool pump & heater, making 'ice, super heating my HPHW tanks to 140F and charging my EVs from 8:30a-4:30p.

    One solution is to add batteries but they are very expensive on the Big Island. There is no Tesla Direct solar here and local installers charge about $12-14k per PW2. I would prefer LG Chem 16 kWh (~$8k each) batteries because they can be connected DC-DC, which not only provides slight increased efficiency but would allow me to oversize my inverters without clipping. My HD Wave inverters can not be linked DC-DC to batteries. I could replace my 7.6 kW inverter with a 7.6 energy hub inverter & connect that to two 16 kWh LG Chem batteries. A new inverter plus the back up unit would be about $5k. I can use the original 7.6 inverter at my other house.

    Another step might be to change my AC system to decrease my AC power consumption. The IB20 has a SEER of 14 but newer AC units have SEERs of 22 or higher. I could add a higher efficiency AC unit and switch the IB20 to just making ice from 8:30a-4:30p and using the 'ice' after 5 pm. Does anyone know how much less power a 22 SEER AC would consume vs the 14 SEER? That would probably cost less than $10k.

    Any thoughts or suggestions?
    20210911_035308.jpgimage_14755.jpg 20210911_035308.jpg
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    Last edited by Steeler.Fan; 09-11-2021, 04:03 PM.

  • #2
    One thing that could help, is changing your air conditioning units. Some of the latest
    mini splits have a SEER in the high 30s, cheaper to run at night, and leaving more of
    your generated energy for other things in the day. Here, these have have been found
    to have a list of other advantages as well. Some units are available capable of operating
    directly from solar panels, but may have a lower SEER that cancels the advantage at
    night when they change over to line power.

    Do look into pool pump options as well, including 2 speed and direct solar operation.
    I avoid batteries at a desperate and extremely limited last resort. Bruce Roe

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    • #3
      Originally posted by Steeler.Fan View Post
      .........

      Any thoughts or suggestions?
      I think you have summarized the options. Unfortunatly we are at a time when the two most viable options are constrained. LG Chem supply is constrained by battery recall issues and Tesla Powerwalls are constrained by production capacity. The high cost of energy in California and Hawaii make batteries a viable economic alternative where they are not viable economically in other parts of the Country. In Hawaii the lack of NEM makes batteries a perfect combination with solar to avoid high utility rates.

      My brother has a couple of homes on Mauai that are also used as vacation rentals. He bit the bullit and installed Powerwalls when they were more available but he still paid high prices compared to the Mainland. I do agree with bcroe that conservation measures have a great payback. My brother did install additional insulation and heat pump water heaters while he was waiting for his turn to come on his Solar and Powerwall installations.
      9 kW solar, 42kWh LFP storage. EV owner since 2012

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      • #4
        I want to add 2 LG Chem 16 kWh batteries to my system. I hoped to replace my 7.6 KW HD Wave inverter with a 7.6 KW energy hub and add the backup interface to connect the 2 batteries. However, I have a CGS+ plan and need to connect both to a CGS+ meter. SE support tells me that at this time, I cannot connect both of these inverters to their BU interface. The largest size 2nd breaker that I can install in their BU interface is 63 amp, which isn't large enough for me.
        Does anyone know if I buy a 7.6 StoreEdge inverter, can it connect to 2 LG Chem RESU 16 kWh batteries?

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        • #5
          Resu 16 is one per inverter so I think you would either need two 10's or two inverters for two 16's. Some info about SE's own energy bank 10kwh batteries has come out recently which says you can put 3x 10kw on one inverter so it might be worth waiting to see how the pricing is on them if you want ~30kwh on one inverter. NIB energyhub inverters pop up on ebay pretty frequently for sharp discounts, I picked up a 3800 energy hub for $600 last month to swap with my regular 3800h, I got a installed but never used resu 10 for $2500 so might also look for deals on the older models if you are installing or have a installer willing to let you source the hardware.
          Last edited by hayhayday; 10-15-2021, 06:08 PM.

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