False economies

Cariboocoot
Cariboocoot Banned Posts: 17,615 ✭✭✭
in Off Grid Solar & Battery Systems #1
A tad anecdotal; bear with me.

My wife got the bright idea that we could save energy (immediately following a lecture about how much she was using) by taking the office equipment off the Outback and allowing it to run in search mode day and night. To do this she proposed installing a separate, small, 12 Volt system using the Morningstar 300 inverter which only draws about 6 Watts running. (See? Sometimes she pays attention.)

Here's how it would work: MS300 powers the office loads from 12 Volts, 12 Volts recharged from 24 Volt via MPPT. The Outback VFX3524 would run in search mode (6 Watts) not full-on to power the office (20 Watts). So instead of the inverter using 20 Watts, the two of them together would use 12. Save 8 Watts per hour! Since the office is "on" for about 12 hours a day, that's 96 Watt hours savings.

Here's how it all falls apart: 96 Watt hours on a 24 Volt system is about 4 Amp hours. There is no recharge savings (unless more equipment is added) because it charges from the 24 Volt system. The latter doesn't run at 6 Watts all day because the 'frige will operate about 1/3 of the time and the water pumps need to be powered, knocking the "savings" down to about 1 Amp hour per day.

Here's how it works out economically: the extra inverter, batteries, and charge controller plus installation equipment rings up around $1,000 +/-. For that money, we might as well just add more panels to the existing system (double the array size) and gain up to 2800 Watt hours per day.

That's a bit better than spending the same money to gain 24 Watt hours, eh?

The moral: always think the plan through.
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: False economies

    More panels on order yet?

    -Bill ;)
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: False economies
    BB. wrote: »
    More panels on order yet?

    -Bill ;)

    Not 'til I A). replace the roof and B). sell the other house.
    The way it's raining it's unlikely either will happen soon. :cry:
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #4
    Re: False economies

    Now...give us the goods if you were to run a similar 300w 24V inverter.
    Your SWMBO may be onto something there... At least she DID listen (once):cry::roll::p:-)
    I think she gotcha... Yes Dear (reverent humble tone) comes to mind...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: False economies

    You mean use a Samlex PST-30S-24A instead of the MS 300.
    Power draw: <10 Watts, so you'd only "save" about 10 Watts off the OB. Over-all power savings (12 hours, less the 1/3 running time of the OB) 80 Watt hours. Roughly 3 Amp hours on 24 VDC.
    Cost: $150, no need for second battery bank or MPPT charge controller.

    Or Exeltech XP-250-24 which uses only 6 Watts (total power savings 112 Watt hours, about 4.5 Amp hours) but costs $400.

    Samlex cost per Watt hour saved: $1.88
    Exeltech cost per Watt hour saved: $3.57
    Original proposed Morningstar cost per Watt hour saved: $40

    Some may argue the Samlex & Exeltech are not comparable to the Morningstar, but for this light duty application they would be.
    Of course that darn laser printer-scanner won't run off this, so it would still be sucking from the Outback.

    Like I said, always think it through.
    (But don't tell my wife.)

    Edit to add: if anyone is wondering about the above cost analysis, it is based on capital investment for Watt hours returned not operating costs. When you consider that a Watt hour off-grid can cost $0.00075 to $0.0015 (especially if you have to feed the generator) that 80 Watt hours is worth about $0.12 per day, making the payback time for the initial investment 1250 days (plus shipping and wiring). About six years in half-year staying time.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: False economies

    Watt*Hours or kWH?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: False economies

    Forgot to mention that most of the time this "savings" is completely unnecessary; it is an exercise to find some more power on those days when the rain blocks the sun and the generator is the source of charging. Every Watt hour really counts then. Normally we have surplus production.

    Good catch, Bill; I'll fix the math.
    The rain gets in to my brain.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #8
    Re: False economies

    I was thinking more about this model http://www.cotek.com.tw/product/56.html with 60 mA 1.44W no load 87% eff.

    Ya, rainy days....kind of like today...and yesterday...and Friday...and....

    yup it is all about 'shaving' loads/use.

    What about a different printer scanner combo or individual units when you next have to replace one of those ever-price-increasing cartridges?
    We got a new Laser printer for less than the cost of a cartridge for the previous one.
    Planned Obsolescence:grr comes into play and only 4 years old, to us...from new.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: False economies

    Used to use a Canon flatbed and Brother ink jet. Now she "has" to have this unit because ... uh ... because it self-feeds the documents.

    My policy of "turn it off when not in use" doesn't always play well. :roll:
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #10
    Re: False economies
    Cariboocoot wrote: »
    The rain gets in to my brain.
    Well known song by "Billy Vera and the Beaters" -Buckaroo Banzai's band?

    ...and we wonder on this Father's Day, if you wife didn't just out smart you, into thinking adding solar panels would be a good idea...lol.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: False economies
    Photowhit wrote: »
    Well known song by "Billy Vera and the Beaters" -Buckaroo Banzai's band?

    ...and we wonder on this Father's Day, if you wife didn't just out smart you, into thinking adding solar panels would be a good idea...lol.

    Well she's the one who pooh-poohed my solar expansion plan. Just because it would cost $3,000+ ...
    But it would eliminate that problem of the kids running the batteries dead every night when they're here on their own.
    I can manage on 1200 Watt hours a day easily (have done it).

    Maybe that's another rule: add a person, double the power consumption.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #12
    Re: False economies
    Cariboocoot wrote: »
    You mean use a Samlex PST-30S-24A instead of the MS 300.
    Power draw: <10 Watts, so you'd only "save" about 10 Watts off the OB. Over-all power savings (12 hours, less the 1/3 running time of the OB) 80 Watt hours. Roughly 3 Amp hours on 24 VDC.
    Cost: $150, no need for second battery bank or MPPT charge controller.

    Or Exeltech XP-250-24 which uses only 6 Watts (total power savings 112 Watt hours, about 4.5 Amp hours) but costs $400.

    Don't forget to consider Victron. Their 24 volt, 800 watt, pure sine wave inverter draws 5 watts no load and 2 watts in search mode. Unfortunately they are not inexpensive. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Lee Dodge
    Lee Dodge Solar Expert Posts: 112 ✭✭
    #13
    Re: False economies
    Cariboocoot wrote: »
    ...snip...

    The moral: always think the plan through.

    I think that the moral might be that you better go buy your wife some flowers for trying to come up with an idea to save energy!
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #14
    Re: False economies

    coot,
    i give her an A for effort. my other half couldn't tell you how many pvs we have let alone the wattage.
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