Hands-off battery backup / self-consumption systems?

DanKegelDanKegel Registered Users Posts: 18 ✭✭
Hi all!

My SolarEdge 7600A system has been running well for about a year.
I picked that model because it was supposedly Powerwall compatible,
and figured I'd consider upgrading when costs came down.
(My neighborhood has power outages once every couple months.
They're mostly short, but annoying.  I'd put the fridge, the router,
and the two rooms we spend most time in on the backed up circuit.
Since I have net metering, and am in LADWP with fairly cheap power,
I don't think the battery would pay for itself; this is more of a thought experiment.
And I'm not into any battery that would require maintenance.)

Well, I ran into somebody last week who said he's adding a powerwall
to his solar house.  He said California's opening up its SGIP program, and
good battery subsidies are available, at least for now.  So I looked
into the upgrade.  SolarEdge tech support says they'll buy back your
SE7600A for $608 (about half credit?) if you buy a 7600USS (StorEdge)
system (ask them for details, there are hoops to jump through).
I think it's both Powerwall and LG compatible.

Has anybody done this yet?   Which battery did you use?  Got pictures?


  • BB.BB. Super Moderators, Administrators Posts: 32,800 admin
    At this point--Your best bet is probably to by a small UPS that supplies just enough power for your computer+router+model+a few LED lights (if needed).

    Any battery system is going to require maintenance (AGM, Li-Ion may not require monthly maintenance. And Power Wall systems probably are not maintainable by end users)--And is they don't require maintenance, they probably will need replacement (batteries) every 5-8 years, and electronics (inverters, charge controllers, other electronics) every 10+ years.

    It is just the nature of the beast (electronics, batteries, etc.).

    It very much leaves you with a cost/benefit ratio decision. How much is "UPS"+Off grid backup+solar worth to you.

    If you want to experiment... Get a Kill-a-Watt type meter and measure your AC loads. If you can live with a 1,000 WH per day system (1,000 WH / 24 hour per day = 41 Watt average load)... You can setup a small off grid system for not too much money and see how it works for you--And you learn the pieces of they system:
    • 1,000 WH per day
    • 1,000 WH per day * 1/0.85 inverter eff * 1/12 volt battery * 2 days storage * 1/0.50 max discharge = 392 AH @ 12 volt battery bank
    • 2x 6 volt @ 200 AH "golf cart" size batteries * 2 parallel strings = 400 AH @ 12 volts
    • 400 AH * 14.5 volts * 1/0.77 panel+controller deratings * 0.10 rate of charge = 753 Watt solar array nominal (full time off grid minimum)
    Solar power for Los Angles:

    Los Angeles
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 41° angle from vertical:
    (Optimal winter settings)
    Jan Feb Mar Apr May Jun
    Jul Aug Sep Oct Nov Dec
    Size of solar array to manage 12 months a year, 1,000 WH per day with 75% minimum available sun (minimum amount of generator/backup AC power usage):
    • 1,000 WH per day * 0.52 off grid system eff * 1/0.75 bad weather derate * 1/4.77 hours of average sun = 537 Watt array minimum for fixed loads 365 days per year
    • Looking above, 753 Watt array minimum (10% rare of charge minimum recommended for full time off grid power)
    Get a 300 Watt AC inverter:

    Plus an AC to DC battery charger for backup power during bad weather. Plus a genset for storm failures (Honda eu2000i ~$1,000 + siphon hose/5-10 gallons of backup gasoline+fuel stablizer, change 1x - 2x per year).

    The above system will supply about 3 hours * 300 Watts per day (3 hour blackout capabilities.

    The above is just a quick outline of what a capable 1,000 WH per day system can do. Start small, make plans, figure costs, then buy hardware--Do not buy the hardware first and figure out how to make a useful to you system.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,224 ✭✭✭✭✭

    I have a business contact taking orders for installing LG on grid power systems. It is a pretty amazing credit along with the Federal 30%.

    In the end the equipment is 1/2 the cost but the labor is still there. The sample below is with an XW+ 5548 not including labor.       . 5.5kW / 10kWh System
    Retail Price $10,800
    ITC = $3,240
    SGIP Rebate = $3,278
    Net Cost = $4,282

    Dive Insight:

    In March, Commissioner Cliff Rechtschaffen proposed a doubling of funding for the SGIP program.

    SGIP, created in 2001, provides funding for a variety of behind-the-meter technologies. In the past the program attracted controversy when fuel cell projects won many of the awards, even though the emission profiles of the projects were high compared with other technologies.

    The result of the controversy was a realignment of the program toward energy storage.

    “The important thing is to get the program up and running," Commissioner Rechtschaffen said at the CPUC meeting last week. "It has been on hold for a year, and there are many customers anxious to participate.”

    Rechtschaffen said the 85-15 split is based on estimates of where the interest is among would-be program participants.

    Last year, SGIP incentive rates ranged from $0.42/W to $1.49/W, depending on the type of system. Incentives are allocated through multiple rounds of bidding, with the incentive rate declining each round until all SGIP funds are doled out. 

    The first round of bidding for this year's SGIP funds is expected to open May 1, with rates starting at about $0.50/Wh for small storage and large storage without the investment tax credit (ITC), or $0.36/Wh for large storage with the ITC. 

    Recommended Reading:

    "we go where power lines don't" Sierra Nevada mountain area
    E-mail [email protected]

  • DanKegelDanKegel Registered Users Posts: 18 ✭✭
    Had another ten-second outage this week.  Every time that happens, I'm reminded of the idea of batteries.
    But getting a few UPS's for the computers and modem/router would be far cheaper.

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