Check my configuration

Hello everybody.

First at all, I'm apology for my English, It is not my primary language.

I already have a 120 w PV with a Morningstar Prostar 15 amps Controller for a 45 Qt Enegl Freezer and Coleman 300w Inverter for a Five 9 W 110v Bulbs. The Freezer is conected 24 hrs a day around 85 F, and the inverter only works around 5 hrs a day (night time) On a Optima Blue top D31M, Reserve capacity @25 amps 155 min. On a Toyota Land Cruiser 80 Serie.
Usually the sun shows around 5:30am up to 6:00pm fully bright.

I use this truck for a 4X4 trips, for about 4 days average.

My question is.

Should I do any upgrade (like change the controller ) in order to extend the usefull time about 10 days, with out a engine generator ?

Thanks for your Help


  • BB.BB. Super Moderators, Administrators Posts: 29,883 admin
    Re: Check my configuration

    Your English is fine--Want to see my Google Translate Spanish? ;)

    For your needs--You need to measure your loads and look at conservation first.

    It does not sound like you are wasting energy--but changing to 1-4 watt 12 VDC LEDs (expensive) but if they provide focused light (for reading) vs the 9 watt 110 VAC bulbs (are these filament, florescent/CFL, or LED?).

    If you can use efficient DC lights/loads (there are 12 VDC LED lamps and even 12 volt CFL--compact florescent/twisty bulbs--but they may be cost prohibitive for your usage), that may save running the inverter (~5-10 watts losses for a smaller inverter).

    The PWM controller you have is fine for the current solar panel. And a new MPPT charge controller is 2-3x the cost and may get you 10% more power (a bit more if very cold winter days).

    If you need more power, another solar panel (and a second or larger charge controller) would be more helpful.

    It may be too expensive to justify for your smaller system--But knowing your battery usage by installing a Battery Monitor (the Trimetric is a good cost effective starting point) would be really nice. Having one is almost like adding a gas gauge to your fuel tank vs not having a fuel gauge for your truck.

    Assuming you have ~5+ hours of "Full Sun" Equivalent per day... Measuring your loads would give us something like this...
    • From this thread, your cooler may use around 300-660 Watt*Hours per day.
    • 5x 9 watt bulbs and a 85% efficient inverter (guessing) + 6 watt switching losses = (6w+5x9w)*5hours*1/0.85=300watt*hours/day
    So the battery sizing assuming 1 day of energy and 50% maximum discharge (for longer life) and assuming 440 Watt*Hours per day for the cooler:
    • (440wh+300wh) * 1/12 volt battery = 62 AH per day
    • Battery capacity = 62 AH * 1 day storage * 1/0.50 max discharge = 124 AH battery
    For solar panels--Assuming 0.52 system efficiency, 5+ hours of full sun per day:
    • (440+300)WH * 1/0.52 system eff * 1/5 hours of sun per day = 285 watts of solar panels
    So, 285 watts of solar panels would be about your "break even point" for power.

    I have made lots of guesses--but I did "show my work" so you can use your real numbers to better refine the results.

    A couple suggestions... If you need to charge your batteries, a small fuel efficient generator and battery charger (like a Honda eu1000i -- if available for a reasonable price in your area) is usually more fuel efficient than running the truck engine.

    Also, since these are relatively short trips--Do you have a ~10kg bottle of propane (LPG--liquefied petroleum gas) gas? A small RV propane refrigerator may be a better solution for your setup... They probably use less than 1kg of gas per day (depending on your usage--pre-cooled food, vs adding specimens for freezing on a biological sampling trip).

    I hope this helps.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,399 ✭✭✭✭
    Re: Check my configuration

    Welcome to the forum.

    First do a real load calculation, adding up all their loads and how long they are on. It sounds like you have a substantial load. Then figure out what percentage of battery that load is. Then decide how many days you wish to go without external charging, and how far down you are willing to drain your batteries.

    My rule of thumb, (and it is actually worse in mobil installations) is the 50%* 4 rule.

    That is, take the name plate rating of the PV, divide that in half to account for all system loses, then multiply that number by four to a account for the number of hours of good sun you are likely to get (per day, on average over the course of a year). You can adjust the number of hours up or down to suit your particular situation, but be aware that for figuring, you not only have to average for daylight hours, you have to account for clouds, partial shading ect.

    So your 120 Watt PV might look like this. 120/2=60*4=250 watt/hours/day. So one might logically expect to harvest ~ 250 wh of power per day, on average.

    going back to my first suggestion, defining the loads,, your 9 watt bulbs times 5 is 54 watts. You could run these bulb (and only those bulbs!) for A bit less than 5 hours total. That alone would use up your potential harvest. With no allowance for freezers etc.

    Good luck and keep in touch,

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Check my configuration

    if this is the freezer,
    it could use up to 60ah per day at 12v for 720wh as it is rated 2.5a at 12vdc. i'm assuming the battery to be a group 31 and around 110ah and the frig alone will take over half of the battery capacity over the course of the day and it is never a good idea to take over half as it degrades the battery's useful lifespan.
    to eliminate the generator would need considerably more battery capacity and pv capacity.
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