A question about solar panels

[MarkP]

I stopped in to the little solar shop next door to J. Hara's a while back. The guy there was helpful and pleasant except for one thing. The 12 volt dc chest freezers were labeled with how many watts per day they used. I asked him about this and we went back and forth a bit before he condescendingly suggested that, since he had been doing this for a while, I should do more research before bothering him further. Didn't know what to say at that point.

[Bullwinkle]

when figuring out how much juice one will need - add up all you usage during a 24 hr period to determine a total kw per day load

add up all the panels - rated in watts per hour at peak efficiency - I take about half that number - reflects real world

multiply your panel output by hours of peak sun - I figure about 6 hrs a day - to determine total daily output - compare that to use.....

Losses will be another 30% of so charging and discharging batteries ... as voltage drops - so will the battery effectiveness - if one needs 10k watt of reserves - a 20kw battery bank a wise choice for example

[MarkP]

Kw is the instantaneous rate of power use. One kw equals 1,000 watts. Kwh (kilowatt-hours) are what gets totaled up over the course of the day, as in .5 kw for 4 hours works out to 2.0 kwh. There is no such thing as kw per day or watts per day.

Usually this is just a spelling error where someone leaves off the h in kwh but the guy at the solar shop really dug in his heals and insisted I was wrong. I often am, but not that time. Not sure what is more shocking, that he would make such a newbie error or that his survival instincts would be so atrophied that he would continue full speed ahead despite signs that he should slow down and check his facts, which would have cost him little. He could have humored me and not given a bad impression, or better yet he could have taken the advice of a licensed professional engineer who has worked as an energy engineer and has built his own PV system and double checked his facts.

[Bullwinkle]

watts = amps x volts A kilowatt short hand for 1000 watts - a 10kw battery bank or a 10kw generator mean completely different things

you are correct kwh is 1000 watts for one hour - a electrical utility measurement - like a cubic foot of gas is measured in therms.

as to a 12 volt top loader rated in daily watts :

In my day 10 amps for 1/2 of the hour so, for a total of 60 watts an hour / 1.5 kwh a day was the best I could do - I used a lot of the expandable foam as insulator for built ins.

it pains me to see dew forming on the surfaces of domestic refrigerators in my current set up ..... poor insulation being the #1 energy hog

Im a hair trigger away from ditching the fridge for a small top loader freezer and a dorm style mini fridge ....

[MarkP]

10 amps at 12 volts is 120 watts x .5 hours is 60 watt-hrs each hour, not 60watts each hour. Everyone casually forgets the h in kwh.

I got a small half height reefer, the smallest that had a separate freezer, rated at 235 kwh per year. It gets condensation on top. I put a 1/2" piece of styrofoam (part of the packaging it came in) on top. Even so I think it is a better decision than a propane fridge. $150 vs $1, 500 initial cosg will buy a lot of extra solar panels.

[Delta9r]

I got my regular AC refrigerator from Home Depot for about $250. It's rated at 1.5 amps and is the lowest draw full size refrigerator/freezer I could find in Hilo. Not sure about all the math regarding Kwh etc, but I do know that it works great with my present setup and is always powered on. A friend has a smaller fridge/freezer from Home Depot, and I think that one is rated at 1.4 amps, but it's a bit small for my needs.

I got my small chest freezer from Wal Mart, also about $250, and I only run the freezer during the day in order to conserve battery power, but I could probably leave it powered on all the time. So far it's been working well for me, and they're so much better than any of the propane refrigerators I've had in the past.

"Life is labor, and all that is good in life comes from that labor..."

[MarkP]

If you go below a certain size of fridge, such that it would only be purchased by students to use in a dorm room, then efficiency goes out the door. Someone gave me a tiny solid state cube fridge that used almost 3 kwh a day, way more than a full sized 18 cf fridge. I had to get rid of it as it was worse than useless to me. Point being that small doesn't always equate to either efficient or low power use

[Guest]

This is all kind of confusing. I am guessing since I run a lot of electrics (computer, surround system, speakers, flat screen...) that it isnt looking so feasible.

[PaulW]

Easy: connect to the grid but buy solar panels to keep the cost down.

[kalakoa]

quote:

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This is all kind of confusing. I am guessing since I run a lot of electrics (computer, surround system, speakers, flat screen...) that it isnt looking so feasible.

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Water pump and fridge (and washer/dryer/dishwasher/garbage disposal) use the most power and require the most surge capacity; everything else, not so much -- a couple of batteries and a few hundred watts of PV will power lots of computer/TV/cell phone charger/etc.