I need help with a back up power idea.



HI there...

OK so here's my deal. I have an idea but, since I lack the knowledge to apply my idea I'm a bit confused with all the information I've found. As of right now I feel a bit inundated and since what I know about solar would rattle in a match box I figured it's best to stop and ask.
First thing is my idea. I live in southwest FL.I've been through several hurricanes and I would like an alternative to my generator. I would like something a bit more renewable and quieter. A little more lower profile.
So I'm basically looking for a backup system. I'm looking for some very basic "work" lighting and one or two fans to move air. I want this to be some what portable in case I have to leave one day and I need some sort of power source.
With my limited knowledge I believe I need a fairly rugged panel or panels, a charge controller, inverter, and a battery. What size, how many amps, watts, etc. That's where I draw a blank. What's a good source for material? What sort of ball park figure am I looking at? What am I missing? What should I be looking for?
Any advice and guidance would be greatly appreciated. Thanks again.

J

Comments

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: I need help with a back up power idea.

    well to start you need to know the wattage of your loads and how long you need to use them for over a 24hr period. a possible rough indicator may be the present generator size in kw and how long you run it for. a killawatt meter can help you in that area as it will show watthours accumulated. the fact that you want fans may indicate the inverter should be sine wave for if were just the lights (cfls i trust) then a cheaper modsine would work. of course if these fans are to run off dc then problem solved on needing the more expensive sine wave inverter. the batteries need to supply all of your power needs without going beyond 50% dod or halfway in layman's terms. some may advise to have enough battery capacity to last at least 3 days, but keep in mind you need to charge these batteries with at least a 5% charge rate and preferably around a 10% rate to give a faster turnaround on the batteries state of charge. some inverters have this charger built into it and care needs to be given on the current such an inverter charges at that it would fall within the 5-13% charge rate specifications unless you opt for agm batteries that can take a higher charge rate. when relying on pvs as the charge source then these must supply the same current levels i have indicated. a charge controller would also be needed for the pvs.
    as for portability, don't count on moving this stuff very far if at all.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: I need help with a back up power idea.

    Make a list of everything you feel you'll need to run off the inverter. Buy a Kill-A-Watt meter and measure each item's actual power consumption over a few days 'typical' use. Then you have some idea of what kind of load you'll need to supply.

    The total cumulative load is the key to sizing the inverter: whatever maximum Watts you come up with you have to be able to supply. For how long, your Watt/hours, will give you a clue to the battery bank size. If you have to supply 1200 Watt/hrs you need 100 Amp/hrs @ 12 Volts (basically). This is always times at least two to get battery size, because you don't want to draw the batteries below 50%.

    Now, about those panels. You need enough to recharge the batteries @ 5%-13% of their Amp/hr rating. I usually shoot for 10%.

    But you know solar panels are made of glass. In a hurricane you may have zero charging power as a result. I suggest you plan on recharging with a small, fuel-efficient generator instead. Then you can have "quiet power" all night and run the gen during the day to recharge. It would also be cheaper than buying all the necessary panels. Especially if they end up as shards of broken glass blowin' in the wind.

    But get a handle on the potential loads first.
  • porkfarmporkfarm Registered Users Posts: 19
    Re: I need help with a back up power idea.
    Rosco79 wrote: »


    HI there...

    OK so here's my deal. I have an idea but, since I lack the knowledge to apply my idea I'm a bit confused with all the information I've found. As of right now I feel a bit inundated and since what I know about solar would rattle in a match box I figured it's best to stop and ask.
    First thing is my idea. I live in southwest FL.I've been through several hurricanes and I would like an alternative to my generator. I would like something a bit more renewable and quieter. A little more lower profile.
    So I'm basically looking for a backup system. I'm looking for some very basic "work" lighting and one or two fans to move air. I want this to be some what portable in case I have to leave one day and I need some sort of power source.
    With my limited knowledge I believe I need a fairly rugged panel or panels, a charge controller, inverter, and a battery. What size, how many amps, watts, etc. That's where I draw a blank. What's a good source for material? What sort of ball park figure am I looking at? What am I missing? What should I be looking for?
    Any advice and guidance would be greatly appreciated. Thanks again.

    J


    Are you thinking something like the portable Xantrex XPower 1500 ? I was thinking about making my own version. Maybe bigger...
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: I need help with a back up power idea.

    While a small solar system is a fine idea for back up power, if that is what you really plan on using it for, you will find it to be wildly expensive compared to simple generator power.

    For example, a Honda EU 1000 generator, which burns ~one quart of fuel every four hours to produce ~800 watts, costs ~$700 and costs say $1/hour to run. 800*24= ~19 kwh/day

    Stair step up from there for larger capacity.

    An PV system that yield 800 peak watts might be ~ 1kw, costing say $8/watt installed including inverter and batteries or $8000. This system might yield (out the inverter) 2.5 kwh/day. Calculate in batter replacement every 5-10 years and you will see how expensive it really is. Scale this up or down as needed to cover your essential loads, but the numbers will stay fairly consistent.

    Even if you could do the PV for 1/2 as much per watt, it still is ~4-5 times as expensive per watt, and 40-50 times as expensive per useable watt hour.

    Just to be clear.

    The numbers get somewhat better if you have use for the power other times, or if you wish to quantify how valuable lack of noise is etc.
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