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  • Advice for installing storage system

    I'm in California and it appears I qualify for a substantial rebate for installing a storage system since I'm in a high wildfire risk area with safety shutdowns and am on a well. I'm working with my solar installer for a bid (as well as another competitor) but my system is complicated so I thought I'd get some advice for my options. I want to have battery back-up with the ability to keep the solar going when the grid goes down. A bonus would be the ability to recharge the batteries using a generator when the grid goes down during the winter.

    I have 2 separate solar systems installed on an outbuilding. One is an older 4KW string system. The other is a recently installed (last year) 6KW Enphase/Panasonic system with IQ7 microinverters.

    My 400 amp combination service entrance panel/load center is mounted on the outbuilding. It has 2 branches. One branch goes through a 200 amp breaker (no load center) to feed my subpanel at my residence (about 250' away). The other branch goes through a 150 amp breaker to feed the integrated load center for the outbuilding. My solar systems are tied into this load center.

    My solar installer is leaning towards an Enphase Ensemble system. An advantage of this system is the new transfer switch coming out has the ability to accept generator output. A problem with this is I would need to replace my string inverter with Enphase microinverters (as far as I can tell) for the 20 200W panels on my old system.
    I'm also getting a bid for a Powerwall 2 system.

    As far as I can tell, the storage system will need to be installed at the outbuilding and tap into the branch feeding my residence down there.

    One concern I have is what happens when the grid goes down and the system automatically switches over to backup while the demand (A/C, spa, oven, well, etc. is running) exceeds the system capability? I'm assuming it does some kind of shutdown. Do I risk damage to my system or appliances in my house?

    How would I know when the system is switched over? I'd like to shut down unnecessary items to conserve storage.

    Normally you'd put in a separate subpanel for critical items but it isn't practical because of the distance between the outbuilding and my residence.

    Are there other systems that would have an advantage in my situation?

    Thanks

  • #2
    I would make an assessment of your critical loads and get a second opinion about whether a critical loads panel can be installed. I have seen a number of installs where sub panels were cascaded off other sub panels. If you are planning on powering your entire house you will need at least two Powerwalls anyway. That is over 20 kWhrs of storage and 14kW of peak power. I would compare that extra expense with the cost of 250 feet of conduit if that is the only way to separate the loads. The existing conduit may be capable of carrying two smaller sets of wires. I don't know how the rebate covers infrastructure upgrades but I recall it is based on kWhrs of capacity. The Federal tax credit is calculated on the total cost so there may be som support there.

    Outback and others have generator support and can use batteries that can scale up. Enphase Ensemble is a great system that starts small but I am not sure it scales up cost effectively.

    The only reason your old inverter would need to be replaced is that it would not be capable of AC coupling with a hybrid inverter effectively. In other words depending on your loads it would toggle between on or off. The Enphase IQ7s can modulate power. They AC couple with most hybridvinverters which are compatible with CA Rule 21. BTW most string inverters last 7 years so if your older inverter is that old it may be worth replacing it with a hybrid inverter..
    9 kW solar. Driving EVs since 2012

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    • #3
      Running another conduit at this point would be ugly. I'd have to go through landscaping, lawn, concrete patio or have a long circuitous route.
      One thing I forgot to mention is I have Ethernet (and a spare Cat-5 cable) between my house and the outbuilding. And the outbuilding has wifi.
      I saw some smart breakers online but I have no idea how they work.

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      • #4
        Your high power, optional loads (spa, oven, electric heaters) need to be on a separate panel that will not be energized by your battery backup. No smart breaker and computer will be fast enough to cut the heavy loads before the inverter shuts down.

        What is the vaporware transfer switch capacity ? 60A 150A 250A ?? (until they ship yours, they are vaporware. Learned that long ago)

        Your well pump is a critical load, and you should have some water storage (3k - 9k gallons) too.

        Batteries- only reason to use Li batteries (powerwall) is if your power co will allow load shifting/selling and you can save bunches of $$ (to pay for the $$ Li battery)

        Otherwise, go for a smallish lead acid battery that is on float most of the time, and when the power cuts off, the system switches over and after 2 minutes, the generator starts up.
        Or size the battery for overnight power so you don't have to listen/worry about the generator when sleeping.

        Lots of choices to think through. Propane or diesel for the generator ?
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

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        • #5
          Does the SGIP program recognize Lead Acid systems? I think there is some requirement for manufacturers warranty period to qualify for that incentive. LG Chem, BYD, Enphase Ensemble and SimpliPhi are a few in addition to Tesla Powerwall. I don't know the details of how SGIP certifies capacity but one constraint may be finding an installer who is familiar with Lead Acid systems and willing to to the paperwork for the rebate. Most of the installers I talked with were electricians that had rebranded themselves to capture the business of installing systems and processing the SGIP paperwork. They had no experience with Lead Acid. At this point in the evolution, Lead Acid has become a niche relegated mostly to off grid installations.
          Last edited by Ampster; 04-10-2020, 12:30 PM.
          9 kW solar. Driving EVs since 2012

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          • #6
            Originally posted by Ampster View Post
            Does the SGIP program recognize Lead Acid systems? I think there is some requirement for manufacturers warranty period to qualify for that incentive. LG Chem, BYD, Enphase Ensemble are a few in addition to Tesla Powerwall.
            I couldn't find any details on how to calculate the SGIP rebate or the maximum amount allowed in my case. Does anyone know? What I do know is that I was told I could get a $26,400 rebate on a $27,900 2 Powerwall 2 system.

            I don't mind manual load management. That is what I do now. I have a generator input on my house subpanel (with interlock) and choose what loads to run when. This allows me to run loads that I wouldn't be able to run if I only had a critical loads subpanel. My main concern would be if the system automatically switched to backup and it couldn't handle the existing load. If everything shutdown without damage I'd be OK with that.

            Depending on how the rebate is structured, "oversizing" the storage system may be the cheapest alternative.

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            • #7
              Originally posted by Ampster View Post
              The only reason your old inverter would need to be replaced is that it would not be capable of AC coupling with a hybrid inverter effectively. In other words depending on your loads it would toggle between on or off. The Enphase IQ7s can modulate power. They AC couple with most hybridvinverters which are compatible with CA Rule 21. BTW most string inverters last 7 years so if your older inverter is that old it may be worth replacing it with a hybrid inverter..
              My string inverter is over 7 years old and is not CA Rule 21 compliant (as far as I know). It looks like I should consider replacing the old inverter also.
              But it does currently play nice with my new Enphase system.
              Last edited by RKCRLR; 04-10-2020, 11:30 AM.

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              • #8
                Originally posted by RKCRLR View Post
                My string inverter is over 7 years old and is not CA Rule 21 compliant (as far as I know). It looks like I should consider replacing the old inverter also.
                But it does currently play nice with my new Enphase system.
                Replacing an inverter is a piece of cake compared to mounting panels and racking on a roof. Replacing a string inverter with a hybrid inverter is a little more complicated because the hybrid inverter also has a transfer switch and the hybrid inverter needs to be matched with a critical loads panel that should not exceed the kW capacity of the hybrid inverter. Some of them have generator inputs and you may be able to use some of the infrastructure of your existing Generator transfer switch. Depending on how the panels on the roof are configured you may be able to use them as is. My hybrid inverter can handle a wide range of string voltage.
                I am not sure what you mean when you say your old inverter plays nice with your Enphase system? That is not rocket science when the grid is up. The challenge is when the grid is down and you want to leverage existing grid tie solar with AC coupling. The advantage of some hybrid inverters is they can DC couple to an existing string and AC couple to a system like your Enphase micros.
                9 kW solar. Driving EVs since 2012

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                • #9
                  Originally posted by RKCRLR View Post
                  I couldn't find any details on how to calculate the SGIP rebate or the maximum amount allowed in my case. Does anyone know? What I do know is that I was told I could get a $26,400 rebate on a $27,900 2 Powerwall 2 system.
                  I live in Sonoma and briefly thought I could get some of those rebates. I did some investigation and found I was just outside of the critical area even though I had public power shutoffs. What I also discovered was the big incentives had income limitations and that would have reduced my compensation or eliminated my participation. The foregoing may not apply to you, but I am offering it as advice to guide you through your investigation of the details. My best advice when evaluating investments like this, is to check and recheck your assumptions. That is especially true in a situation where you may commit to something an installer tells you about a very large rebate.

                  Speaking of PowerWalls, Tesla has the best prices but they have reached their quota on SGIP rebates. As a result, third party installers have jumped into the market but marked up the prices to the point that the difference between their price and Tesla's is the rebate. Also do not confuse the Federal Tax incentive with the SGIP rebate. They are entirely different and you still get the Federal Tax credit with a Tesla system. I once had a deposit on a PowerWall with a third party but cancelled that to install a hybrid system. I can go into details if you are interested.
                  I don't mind manual load management. That is what I do now. I have a generator input on my house subpanel (with interlock) and choose what loads to run when. This allows me to run loads that wouldn't be able to run if I only had a critical loads subpanel. My main concern would be if the system automatically switched to backup and it couldn't handle the existing load. If everything shutdown without damage I'd be OK with that.
                  That may save you some money. Your system is complicated and you are almost at the point that it might be worth the cost to get a basic electrical system design. Some of that cost may qualify for Federal Tax credit depending how it is structured. This is not tax advice but another assumption to check with your tax professional.
                  Depending on how the rebate is structured, "oversizing" the storage system may be the cheapest alternative.
                  All I can say is that one aspect of the rebate is based on kWhs of storage. That was one consideration when I cancelled the PowerWall. This is where distinguishing between kW of power capacity and kWhs of storage (energy) capacity is important. The short answer was that I did not need the power of two PowerWalls but I wanted the ability to last through a long power outage with lots of kWhs of battery capacity. I figured I could self install a hybrid system with the Power of one PowerWall and the battery capacity of two PowerWalls for a lot less than the inflated cost of two third party installed PowerWalls.

                  NOTE: I subsequently found a SGIP website and the two largest rebates were $0.85 to $1.00 per Watt so that is in the ballpark of what you were told for twomPowerWalls, each of which has 13.5 kWhs of useable capacity. Both those programs had "Eguity" in the description which I assume may be the programs for disadvantaged communities or incomes below a threshold. That is an assumption that needs to be checked and verified.
                  Last edited by Ampster; 04-10-2020, 06:54 PM. Reason: Update Rebate info
                  9 kW solar. Driving EVs since 2012

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                  • #10
                    ^^^^
                    I'm in a Tier 2 moderate wildfire risk area and have PSPS shutdowns (way too many). I had looked into the SGIP rebates earlier but, like you, I determined I didn't meet the income eligibility requirements. But I guess a recent rule has been put in place that if you are on a well that relies on power from the grid then you don't need to meet the income eligibility requirements. I've been told this by two storage installers now.
                    My solar installer got back to me about how the rebate works. He said "it is $1,000 per kWh of storage. It is based on the amount of hours it takes to discharge. 2-4 hours gets 100%. 4-6 hours 50% and greater than 6 hours is 0%." I don't quite understand the discharge rate thing, it seems I'd be able to discharge any of the batteries in 4 hours.

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                    • #11
                      The big unknown left to solve is the possible need for a sub panel and how to feed it, if it needs to be in the main house and on a separate separate feed from the battery backed inverter.
                      Do you know if the 200 Amp panel is fed through conduit or direct burial cable? If in conduit, what size is the conduit and conductors?
                      9 kW solar. Driving EVs since 2012

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                      • #12
                        Originally posted by Ampster View Post
                        The big unknown left to solve is the possible need for a sub panel and how to feed it, if it needs to be in the main house and on a separate separate feed from the battery backed inverter.
                        Do you know if the 200 Amp panel is fed through conduit or direct burial cable? If in conduit, what size is the conduit and conductors?
                        The PVC conduit is 2 1/2" OD. I don't know the size of the conductors but they are big. I don't feel like shutting the power down to measure and I don't like poking around in a live panel but I've included a picture (before the last solar install).

                        Having said that, both installers are proposing a "whole house" backup solution. I put "whole house" in quotes because the batteries won't actually be able to power everything in the house. Both have said that the systems will just shut down (like a power outage) if they detect an overload condition (and my research supports that), and I'm OK with that. I don't mind managing the loads manually.
                        20190607_113724.jpg

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                        • #13
                          Okay then, I won't put any effort into figuring out a different solution. Where I was going with that is the possibility of derating your main house panel and pulling new conductors plus another set for a sub panel. I am not sure 2 1/2 conduit would have given you much flexibility anyway. The labor cost plus over 1,000 feet of wire was going to be expensive. That is a moot point now that you are comfortable manually controlling the loads. You could use the extra Cat 5 cable to send a control signal to some kind of bell or flashing light that would alert you when the grid drops so you can shut down any loads or at least be notified when the grid drops.

                          With regard to any Tesla Powerwall proposals, one caveat that I have heard through the grapevine is that Tesla Powerwalls are limited to 30 Amps each. That may mean that you might require 3 or 4 depending how they calculate that. However if you are going to be get a rebate at $1,000 per kWh of storage that extra storage might not cost you anything anyhow. I have pondered the 4 hour discharge test and I can understand how that might be a constraint but that would depend on all your loads running at once and might be worth verifying. There are probably some workarounds and it would be worth finding out which vendors are most familiar with those details. Interestingly, if you are in Sonoma or Mendocino counties, there may be a way to reduce the rebate risk if your vendors are not willing to guaranty the rebate. Let me know, and I can provide details. It is a non profit entity that provides gap financing.

                          Keep us informed as you progress through your decision process since this will be a good example for future readers to benefit from. This is especially true for readers in California because I think the state will continue to fund more SGIP rebates.
                          Last edited by Ampster; 04-11-2020, 05:01 PM.
                          9 kW solar. Driving EVs since 2012

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                          • #14
                            ^^^^
                            I live in El Dorado county but thanks for the offer.
                            The Powerwall app has an option to send send you an alert when the grid goes down. I suspect Enphase will have something similar.
                            I think the limiting factor on how much rebate I can get will be based on the discharge rate. I get the feeling 2 Powerwalls (or equivalent) will be the sweet spot from the conversations I've had so far.
                            I think the 2 Powerwalls will be the cheapest initial solution since they will work with both the Enphase microinverters and my old string inverter (although not efficiently since it will be operating in bang-bang mode). But it would probably still be the cheapest even if I factor in a new string inverter.
                            The Enphase Encharge batteries don't appear to support anything other than Enphase IQ6/IQ7 inverters so I would need to upgrade my old system to IQ7 microinverters, but my old string inverter is probably on borrowed time anyway. The nice thing about the Enphase Ensemble system is how well integrated it is. And the Enpower smart switch has generator input if they release the planned firmware (vaporware?) update. But it isn't clear to me if the generator input would recharge the batteries unless a "special" generator is used.
                            Enphase seems big on powerline communication. I wouldn't be surprised if they introduced a smart transfer switch some time in the future that can be controlled by the Ensemble system.

                            Edit: I've found conflicting information that the residential “Equity Resiliency” storage rebate is limited to storage sizes of 10 kW or 10 kWh. I emailed PG&E for clarification (even their website doesn't state any size limit).

                            https://www.pge.com/en_US/residentia...r-process.page
                            Last edited by RKCRLR; 04-12-2020, 04:53 PM.

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                            • #15
                              It sounds like the incentives are the critical factor for your Powerwall decision to deal with PG&E PSP (i.e. mainly backup power during outages) so you should investigate and understand all the restrictions of Powerwall with various incentives. Depending on the incentives you utilize you may not be able to use Powerwall like a regular battery/inverter system in many ways (e.g. charging from grid/generator as needed, etc.) that are important for backup power usage during outages especially extended ones.

                              I have found the experience of this owner of 6 Powerwalls very informative. It's way more complex than I had expected and seems more like a science project.
                              https://www.youtube.com/watch?v=2hYONZqkZcg

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