How do you go off grid without UPS or generator - daytime only power?

bpulvbpulv Registered Users Posts: 1
In an emergency, is there a way to go off grid and have daytime power without a supplemental system such as UPS/battery, generator, etc.?
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  • jonrjonr Solar Expert Posts: 1,384 ✭✭✭✭
    A similar and probably better approach is to build a system with very minimal battery capacity.    Then work on ways to shift loads to the daytime.

    I am available for custom hardware/firmware development

  • PhotowhitPhotowhit Solar Expert Posts: 5,543 ✭✭✭✭✭
    You can run some thing directly off DC solar electric, I've even seen small inverters run directly off Solar, with a voltage regulator between the solar array and inverter so too high a voltage isn't reach and the inverter shutting down on it's own. But it's difficult to run many items with high starting loads, like motors. There are some specifically designed system that will run without batteries.

    What are your needs?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • BB.BB. Super Moderators, Administrators Posts: 31,433 admin
    Welcome to the forum bpulv.

    There are lots of ways of doing things. Need to make sure to understand your loads, your needs, and pricing/other issues (no battery, no genset, where are you located--lots of sun, or marine layer that kills sun, etc.).

    If your loads have batteries (laptop, cell phone/internet hot spot, LED lighting with batteries/USB battery brick, etc.) or are you looking for "more power"... Such as a refrigerator/freezer which needs (typically) around 1,200 Watts minimum to start, and ~120 to 600+ Watts to run (compressor running/defrost heaters).

    And, "how reliable" does your backup power need to be? A laptop, you can flip AC on and off all day long. Running your desktop without a UPS--Killing AC power means loss of work. A refrigerator does not "like" power interruptions--But can be OK in the long term (of course, there are refrigerators with "one bit" computer (thermostat) and refrigerators with linear compressors/inverter compressors, and even Internet connectivity--Something that may not like power hits).

    One way that can make economic sense... For example, GT Inverter companies are starting to offer "secure power TM" options. Basically they operate like GT inverters in normal times (feed power back to the grid, turn your meter "backwards", etc.--Assuming it is legal with your power company):

    https://www.solar-electric.com/sma-sunny-boy-7-0-1sp-us-41-grid-tie-inverter.html
    https://www.solar-electric.com/lib/wind-sun/SMA-SBxx-1SP-US-41_User_Manual.pdf (see page #34)

    I think you have to manual start secure power--If you are not home, you cannot use (at least the standard setup--I am no expert here).

    Of course, if you have cloudy weather/storm coming through, not much sun during the day/winter, Secure Power is going to have issues with stability... Again, depends on your loads/needs.

    There is/was a Chinese company that offered Off Grid inverters that could run directly from solar panels/no battery bank. I could not find the inverter(s) at this moment... Perhaps you can go through all their models and see if any still spec'ed to run without batteries:

    www.mustsolar.com/

    And--First of all, make sure your loads are very energy efficient. It is almost always cheaper to conserve energy than to generate it.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,247 ✭✭✭✭✭
    And your weather MUST be cooperative with your needs, how many days can you go if it's cloudy, if you dont have a generator


    Powerfab top of pole PV mount | 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 ,

  • RCinFLARCinFLA Solar Expert Posts: 1,351 ✭✭✭
    edited August 2020 #6
    Solar panels are voltage clamped illumination based current sources.  Voltage clamp is about 0.6v times number of cells in panel.

    Probably best arrangement is balanced stack of supercaps followed by a buck switching regulator.  Enough supercaps to at least ride you through the time of a small passing cloud.

    For 5 amp load at 12.5v, with 180 watt 9.5amp Isc panel with 36 cells.  Having ten 3000 Farad Ultracaps in series will get you over 10 minutes of zero panel output time. Time is longer if panel output just reduced in level or output load is less.

    Ten 3000 Farad Ultracaps are not cheap.
  • mike95490mike95490 Solar Expert Posts: 9,247 ✭✭✭✭✭
    RCinFLA said:
    ......  Having ten 3000 Farad Ultracaps in series will get you over 10 minutes of zero panel output time. .......
    Is that holding above 10.5V, to keep an inverter running or is that 10 minutes to total exhaustion ?
    Powerfab top of pole PV mount | 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 ,

  • RCinFLARCinFLA Solar Expert Posts: 1,351 ✭✭✭
    edited September 2020 #8
    10 minutes is time until Ultracaps drops to 13.3v from between panel Vmp to Voc starting voltage which is minimum input voltage I put in for buck switcher overhead to maintain 12.5v output voltage.  

    Actually it holds up a bit longer but I trimmed it down to 10 minutes as a SWAG for panel leakage.  Probably should put a blocking diode or MOSFET switch between supercap and panel to stop panel back leakage current from supercap.  Diode drop from panel is not very critical in this application. The higher the fractional sun intensity the longer the holdup time.

    Could probably get a higher percentage panel power utilization with an MPPT converter from a higher voltage panel down to 24v supercap followed by 12.5v switching regulator from 24v supercap as before..  Would give higher power output and faster supercap recovery time after a panel dropout.

    Still think I would spend my money on LFP batteries instead of Ultracaps but I got to admit the small package with no maintenance is intriging.  Scale it up to run a refrig at a reasonable cost and you might have a real product.  Lunch box sized device with three or four lightweight flexible fold out panels. Call Elon, he now owns Maxwell Ultracap company.
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