Inverter choice

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stoichiometry
stoichiometry Solar Expert Posts: 27 ✭
in Solar Product Reviews & Opinions #1
Hello,

Alright - I'm getting closer to having full time power at the cabin. I appreciate the help with the QO panel/combiner. My next question is about inverters [which, I'm told is a hot button issue ....]. What should I get for an inverter? MSW vs. PSW? Bigger for planned expansion? or sized exactly?

Currently my most important need is refrigeration. Here goes:

My loads include
a GE 16.5 refrigerator ... <12 Amps on startup and < 0.85 kwh per day,
a morning cup of coffee (700 Watts for <15 mins)
an occasional slice of toast,
lights (7 cfls at night for <2 hrs),
a laptop (haven't plugged into KILL-A-WATT).

PLanned expansion includes 110 V water pump, circ pump for heating, more lights, curling iron/blowdryer for wife, etc.

Kindly,
M
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Inverter choice

    Hoo-boy.

    Refrigerator = big load (nasty start-up surge; running Watts are quite reasonable).
    Electric coffee pot - ever heard of propane? :p
    Electric toaster - ever heard of propane? :p
    Curling iron/blow dryer - ever heard of pro ... oh, maybe not. :p

    Problems with electric heating things: big draws, even if for a "short" period of time. Needs hefty inverter (but can be MSW because resistive elements don't care) and a sizable battery to "take the hit" (need to supply a lot of Amps quickly).

    Your seven CFL' will run around 200 Watt hours. That's a lot of lights, btw. Will they really all be on at once, or can you teach family members that switches also have an "OFF" position? :p

    Water pump & circulating pump. Two more big surge heavy power users.

    Normally you size an inverter to handle the maximum Watts it will have to supply at any given time. With a bit of load-shifting this can be minimized. If that isn't possible, make sure it's easily accessible so you can reset it when it faults from being overloaded.

    The motors, including refrigerator and pumps, will be much happier on true sine rather than MSW. They'll start easier, last longer, and not draw as much power.

    Another factor: battery bank size. This would be determined by how many Watt hours you need to supply: Watt hours / nominal system Voltage *2 (for 50% DOD) is a minimum. Depending on what that number is you'll want to pick from 12, 24, or 48 to keep the Amperage draws down and simplify wiring and even out current flow among the batteries.

    Can't really be any more specific without some more specific numbers on the loads.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
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    Re: Inverter choice

    psw for any inductive loads like fan motors, compressors, etc.

    i'm assuming this is off grid and i'll give mostly general speak.
    you could possibly get away with a 2kw inverter if you watch what loads go on at any one time and when for the overlap of the big draw items could easily exceed that 2kw and we aren't even including surges from some of those at start up. you could go bigger if you like for everybody knows loads wind up expanding, but the smaller inverter may also teach you about managing and conserving power some. of course anything that draws allot of power needs a source of allot of power and batteries to store allot meaning it'll all cost allot. too much with the allots here.;):p
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  • SCharles
    SCharles Solar Expert Posts: 123 ✭✭
    #4
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    Re: Inverter choice

    Bare minimum, if you can keep the heating element stuff off during well pump usage, is the well-pump plus the fridge kicking in with a surge. Plus a little for some lights. If the well pump is manually turned on, however, and not on a demand/pressure switch, ignore what I said above as you can time pump usage to avoid any other usage.

    Personally, though, I would want a larger inverter than the bare minimum. Over the past few years, too, sine wave inverters have come down in price compared to what they used to be, like twenty yr. ago, and relative to modified sine waves. If you are gonna "expand" usage [of electricity], or think you might, and you can afford it, I'd go for a pure sine wave and not have to buy another brand new inverter a bit down the line when your needs change.

    Fact: you will want to use more electricity as time goes on. And you will eventually have something that will prefer a sine wave inverter. Unless you are running a very basic little cabin only used as an occasional getaway.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
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    Re: Inverter choice
    SCharles wrote: »
    Bare minimum, if you can keep the heating element stuff off during well pump usage, is the well-pump plus the fridge kicking in with a surge. Plus a little for some lights. If the well pump is manually turned on, however, and not on a demand/pressure switch, ignore what I said above as you can time pump usage to avoid any other usage.

    Actually I have both a pressure switch and a manual switch on mine: the pressure switch shuts the pump off once the (large) tank is full, and the manual switch prevents it coming on if there's not enough power available. If I weren't so lazy I'd rig the MX60's AUX control to activate the pump automatically once Float is reached, with the pressure switch still turning it off when full.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #6
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    Re: Inverter choice

    Wow! You're looking at a big hefty system. Nothing like starting big! :D
    Did anyone happen to mention the #1 item of importance with a solar system? It's "Conserve, Conserve, Conserve"! Just an idea to chew on - - bigger inverters tend to have bigger idle consumption, and with that in mind, I run a Morningstar PSW 300 watt 24/7 for lights and other smaller items that could need power all the time, or anytime. For big loads, I have a Xantrex pure sine 1800 watt unit in power save mode, so it only runs when necessary. This works great for me. Started out with MSW inverters, and actually still have them ready to go if one of the PS units fail, but definitely find the pure sine inverters work better, even though they do tend to have a somewhat higher idle draw than some MSW inverters. Having used both kinds for some time, I'd now only use MSW as a last resort. With psw there are no worries of items connected to it putting out smoke signals like sometimes happens with MSW. Pure Sine is worry free. It's very easy to forget that for all intents and purposes, I'm living off grid. Loving it :)
    PS: Like Cariboocoot, I also have two switches on my pump. The normal automatic pressure switch (it's the standard, normal, pressurized water system) and a second switch that cuts power to the pump in case of a failure or water line break when I'm away. Fear of flooding the house isn't the main reason for the kill switch, it's the fear of having the pump run continuously while I'm away and killing $3000 worth of batteries!
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
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    Re: Inverter choice
    waynefromnscanada wrote: »
    Wow! You're looking at a big hefty system. Nothing like starting big! :D
    Did anyone happen to mention the #1 item of importance with a solar system? It's "Conserve, Conserve, Conserve"! Just an idea to chew on - - bigger inverters tend to have bigger idle consumption, and with that in mind, I run a Morningstar PSW 300 watt 24/7 for lights and other smaller items that could need power all the time, or anytime. For big loads, I have a Xantrex pure sine 1800 watt unit in power save mode, so it only runs when necessary. This works great for me. Started out with MSW inverters, and actually still have them ready to go if one of the PS units fail, but definitely find the pure sine inverters work better, even though they do tend to have a somewhat higher idle draw than some MSW inverters. Having used both kinds for some time, I'd now only use MSW as a last resort. With psw there are no worries of items connected to it putting out smoke signals like sometimes happens with MSW. Pure Sine is worry free. It's very easy to forget that for all intents and purposes, I'm living off grid. Loving it :)
    PS: Like Cariboocoot, I also have two switches on my pump. The normal automatic pressure switch (it's the standard, normal, pressurized water system) and a second switch that cuts power to the pump in case of a failure or water line break when I'm away. Fear of flooding the house isn't the main reason for the kill switch, it's the fear of having the pump run continuously while I'm away and killing $3000 worth of batteries!

    from me,
    "the smaller inverter may also teach you about managing and conserving power some"

    i said that because he would have no choice then, but to watch and conserve on his loads.
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