solar power question

[rgs80074]

Hello Everyone,


A while ago I posted a question about solar power and got all sorts of replies most basically stating it could not be done. I read links and information given but I am still at a lose. when it comes to power and electricity I get lost/confused easily. I know the less you use the better off you are.

I am not a van dweller per say but there are times when I got on errands from work and have a few hours to kill and at that time virtually nothing is open so I like to lay down. Now that my van repairs are getting done to where I can drive and things are falling into place I am looking into this again but I have some questions.


I don't understand the battery usage and such. I see some battery's are rated in amp hours. I don't understand how to figure out how much a battery can power and how much solar panels are needed to power them.

I don't have a lot I want to do with it so I'll just lead with an example of what I would like to power and most of the time these would be for only a few hours at a time and depending on what I am doing depends on what I'd be using.

Its all like computer programming to me I just can't seem to understand it. I am not stupid and probably just missing some key basic information that would make everything make sense but I've just not figured out what I am missing.

Ok from the prior thread i know running an ac would not work without an big expensive setup and other than a window unit you run into other issues as well.

One other thing I don't understand is the gassing of batteries. if they are inside the van how do you get around that even if enclosed I don't see how the gas wouldn't escape the enclosure unless its airtight which would be hard with wires running into it.

Ok I'd like to limit myself to one or two batteries total here's what I am looking at running.

looking at a small fridge (to mainly keep drinks/ice cold and ready for usage whenever). this would be used constantly the only thing always running. I know they are pretty efficient to run and don't use tons of power but is this feasible? What kinds of fridges do people use the most here?

other things:

one or two fans for when I am trying to sleep somewhere while I wait for them to open up.

a few led lights for when there is a need to see at night (probably not often) I have just bought some for the house rated as a 60watt replacement and they use 8.5watts, for a van one of those would be enough and might be over kill but I'll use that as a base.

again depending on what i am doing powering/charging a laptop and/or cell phones.

perhaps if i can get one installed i hear a exhaust air vent/van makes huge differences in the comfort level in the vans.

the thing to remember here is except for the fridge most of this other stuff is for small amounts of time at once, maybe a few hours total some of which would likely be before the sun is out to charge/run anything. my only concern would be the fridge running at night for various reasons but if i can't use it to keep the items cold at all times it don't work for me.

what would I be looking at here?

would a 200watt panel kit work? I have a rack on the top of the van but nothing installed on it or anything like that.

any advice would be greatly appreciated

any easy to understand information on how to figure stuff out myself would also be appreciated.

the only other piece of information would be I live in central florida

thanks

Ryan

 

[K1ngN0thing]

cheaprvliving.com/electrical/electricity

watts/volts = amps
amps x volts = watts
watts/amps = volts.

It's easier to think of things in terms of watt hours. 1 amp hour in a 12v battery bank is equal to 12 watt hours. 10 amp hours is 120 watt hours. You could run a 1w thing for 120 hours or a 120w thing for one hour. Figure out what your energy needs are and build from there. It's said you should stay away from your typical dorm fridges as they're not built to withstand constant agitation from travel. You'll probably have to fork over at least a few hundred for one that's meant for it. A lot of RVs come with Dometics, for example. To run your fridge overnight, you'll have to calculate how many watts it uses, and make sure it doesn't exceed 50% of your battery bank's capacity. Should probably make it 75% to be on the safe side. My 125ah battery give me 62.5 amp hours, or 750w hours. My 300w or so Dometic would eat that in 2 hours.

Battery gassing: if i understand it correctly, the gasses can cause corrosion if not vented. You also don't want that pressure building up. If you can afford it, go with AGM. No venting required, and can be stored in any orientation.

 

[Optimistic Paranoid]

any easy to understand information on how to figure stuff out myself would also be appreciated.

Lets go over some fundamentals, kept as simple as possible.

Voltage is pressure.  It's what forces electrons to flow through a circuit.  If we were talking air instead of electrons, you know that if you have a tire with 20 lbs. of air pressure, and you hook an air tank  holding 50 lbs of pressure up to it, air will flow from the air tank into the tire.  If the tire and the air tank both held the same pressure, no air would flow in either direction. 

A 12 volt battery consists of 6 cells, each of which are actually 2.1 volts, wired in series, so a it is actually a 12.6 volt battery.  (6 volt batteries each have 3 2.1 volt cells, so when you wire two of them together in series, you have a 12 volt battery).

To recharge a 12 volt battery, you have to force electrons into it, which means your charging source must have more pressure.  That's why 12 volt charging sources have to be 13 to 15 volts.  The higher the voltage, the more electrons are forced into the battery.  Of course, there is a limit to how much electrical pressure you can put on a battery without damaging it.

Amps is a measure of how many electrons are actually flowing through the wire.  Since electrons are incredibly small, it turns out that the number of electrons necessary to equal one amps worth is stupidly big, literally gazillions of electrons.

Power is measured in Watts, and it's figured by multiplying the amps by the volts.  A 100 watt light bulb, powered by 120 volts would use .833 amps.  If you powered a 100 watt light bulb with 12 volts, it would require 8.33 amps.

An amp hour is the amount of electrons that would flow in one hour.  So if you had a 100 watt bulb powered by a 12 volt battery, it would use 8.33 amp hours every hour you left it on.  If you left it on for 3 hours, it would use 25 amp hours.

Engine starting batteries are designed to put out a large amount of power for a very short period of time.  They are rated in Cold Cranking Amps (CCA) and that is a measure of how many amps they can supply to the starter motor at 0 degrees Fahrenheit.

Deep cycle batteries are rated in amp hours.  A battery with 100 amp hour could THEORETICALLY power one amp for 100 hours, or 2 amps for 50 hours, or 100 amps for 1 hour.  We are keeping it simple here.

In the real world, it doesn't quite work that way.  Batteries are not simply tanks that hold electrons.  They are actually chemically powered generators.  They use stored chemical energy to produce electrons, and when you recharge them, they convert electrical energy back into chemical energy and store IT, not the electrons themselves.  Also, in the real world, resistance becomes a factor.

Which means that while you could pull one amp out for 100 hours, if you try to pull 100 amps out of a 100 amp hour battery, it won't keep it up for a full hour, the chemical reactions can't keep up.

It also explains why you can't discharge a battery past 50% without SERIOUSLY reducing it's lifespan.  A 100 amp hour battery really only has a real world working capacity of 50 amp hours.

It also means that you need to put slightly more energy back into a battery when you recharge it than you took out.  On average, roughly 10 percent more.  If you took 40 amp hours out of a battery, you'd have to put 44 amp hours back in to fully charge it.

I don't know what the exact specs are for your 200 watt solar panel.  I've got some Kyocera 140 watt panels, and the specs for them are 17.7volts at max power, and 7.91 amps at max power.  (BTW, 17.7 volts would damage a 12 volt battery, which is why a Solar Charge Controller goes between the solar panel and the battery.)

That means that under ideal conditions, bright sun, no clouds, a cool day, etc.  it will produce 7.91 amp hours for every hour it is in the sun.

Unfortunately, solar cells heat up when exposed to the sun, and as they get hot, their efficiency decreases.  Rule of thumb is to assume 80% output most of the day, so now we are talking 6.4 amp hours every hour.

Finally to use one example relevant to you, the 12 volt Endless Breeze Fan, which has 3 speeds, will use between 1.2 and 2.6 amps, so on high speed, it will use 2.6 amp hours for every hour you run it.

Hope these over-simplified explanations make some of this clearer to you.

Regards
John

PS:  Remember:

Watts equals Volts times Amps
Amps time Hours equal Amp Hours
Watts divided by Volts equals Amps
Watts divided by Amps equals Volts

 

[jimindenver]

I'd like to read the other thread. Please link to it.

A few things. Battery gassing is not only corrosive, it can be explosive if it builds up. That's why flooded batteries have to be vented.

AGM are sealed but under the right situation can vent gas too in a spectacular fashion. That is uncommon but there is still a need to vent them because they can get hot while charging.

AGM's can have unique charging requirements.

A small fridge can be done if set up right. Residential units can be found fairly energy efficient but nothing like the 12v compressor fridges . Neither runs all the time and adding insulation to them helps. The 12v versions cost considerably more so it is a balance of budget and power. In my case I have more power than money so I'll get a residential unit.

200w of solar should cover 200 Ah of battery. The question is will 200 Ah of battery run your fridge. I know 250 Ah of battery could not start my little air conditioner on its own due to the start up surge. The longer it runs the less charge would be in there to handle a start up surge when the compressor cycled so things would get worse as they go along.

I may be easier to find another solution to the fridge.

 

[rgs80074]

thinking of something like this for a fridge

http://www.amazon.com/Danby-Designe...tor&refinements=p_n_srvg_3000479011:598341011

the idea of the refridgerator is so I can always have drinks in it and whenever i need one they will be cold. storing of other food more short term but could be used for meats and such so I can make a sandwich or something when at work instead of running to a store to buying stuff.

 

[rgs80074]

think to other thread. I guess I had really high expectations for solar power and as much as i've searched I've found no zpm's i can use.

https://vanlivingforum.com/Thread-not-a-van-dweller-but-have-a-few-questions

 

[jimindenver]

Solar can do a lot, as long as you have a lot of solar. I'm the guy that runs a 5000 BTU airconditioner while out in the boonies. They were right on the other thread when they said you would have to spend thousands to do it. Just my batteries alone would cost a few grand to buy new, they weigh a quarter ton.

I have been researching small fridges just like the Danby. Some smaller, some bigger too. I need expanded capacity for when we are on longer trips. It use to be I could find the draw on most anything, anymore it's like pulling teeth. From what I have been able to gather the mini fridges use between .8 and 1.3 amps running at 120Vac or 8-13 amps plus losses at 12Vdc. So it may be easier to run than our air conditioner that pulls up to 39 amps at 12Vdc. Maybe there is a smaller cube that would use less.

Fridges don't have a 100% duty cycle and pop only really needs to be cool to be enjoyed. I bet if you really cooled it down by plugging it in at home overnight and the turned the thermostat back up before you left, that the compressor wouldn't come on for quite a while. They are well insulated.

Now comes the hard part. 200 Ah of battery and 200w of solar may actually run the fridge, and we are just talking he fridge here. The problem is you would have to be in a really sunny climate all the time for it to keep up with it. you will be using roughly 1-200 Ah with a 50% run cycle and not only will the solar have to replace last nights uses, it will have to provide the power to run it through out the day too. One cloudy day and you are hopelessly behind unless you can plug in or recharge by another means. In your case spending the money on expensive 12v fridge will make it much more possible than buying the solar and batteries to run the residential style.

You said you run errands correct? There are ways to use the alternator to charge your batteries. That would take a huge load off of the solar if not be able to take care of the issues it self. I would explore all of your options and really get settled on what you can do before you move forward.

I will also let the van guys tell you about the alternator.

 

[K1ngN0thing]

http://smile.amazon.com/Koolatron-P...TF8&qid=1441143385&sr=8-4&keywords=12v+cooler may also be a consideration for cooling. Keeps your food up to 40 degrees cooler than the ambient temperature, so if you've got decent ventilation, that may be a more energy efficient way of indirectly cooling your food (this one is 4.5 amps, I'm not sure how that compares to residential style or other coolers of this type).

 

[LoupGarou]

In the simplest terms, solar panels are just battery chargers. People say their running off solar, but it's the battery bank that does all the work.

 

[Optimistic Paranoid]

http://smile.amazon.com/Koolatron-P...TF8&qid=1441143385&sr=8-4&keywords=12v+cooler may also be a consideration for cooling. Keeps your food up to 40 degrees cooler than the ambient temperature, so if you've got decent ventilation, that may be a more energy efficient way of indirectly cooling your food (this one is 4.5 amps, I'm not sure how that compares to residential style or other coolers of this type).

Since you said it was primarily for keeping drinks cool, K1ngN0thing may be on to something here.  Coolers like this should NOT be trusted to keep food safe, if it's 90 degrees in your van, the cooler will be holding at 50 degrees.  But it will keep cool drinks cool, just not cold.

Regards
John

 

[jimindenver]

In the simplest terms, solar panels are just battery chargers. People say their running off solar, but it's the battery bank that does all the work.

In general this is the popular belief. Usually people don't have enough solar to do much more than charge a battery. However once you have more solar than the load you are trying to run, the solar has no issues running it. My 750w of panel runs my air conditioner pulling 450w while the battery sits in float.

 

[akrvbob]

200 watts feeding a pair of golf carts will easily do what you want.

I have a 190 watts on my trailer and run a 12 volt compressor fridge and lots of other thing very easily.

No problem at all.

However, the winter might be harder depending on your location. Washington or Oregon with their winter rain, probably not. I'm in the AZ desert and have no problem with the winter.
Bob

 

[highdesertranger]

you have gotten some good replies here, I hope it cleared up some of your question about 12v power.
imo you should search this forum for refrigeration. I am a huge believer in 12v compressor refers. I have tried ice chests, dorm refers, propane RV refers, and 12v coolers. nothing and I mean NOTHING works as good as a 12v refer. those small ones like you linked to I found use way more power then they lead you to believe. the 12v coolers are also huge energy consumers, for the power they take to run one for 2 hours you could run a 12v refer 24 hours.
basically you have to add up the usage of all your electrical needs. then get a battery that has a reserve at least twice that. then figure out how the best way to recharge your battery bank everyday. highdesertranger

 

[jimindenver]

Now then, the question is the expense of a 12v compressor fridge worth having cold soda.

 

[highdesertranger]

well I really don't drink soda so I really have no idea. highdesertranger

 

[akrvbob]

It goes without saying that cold beverages are the most important thing, but Most fridges will let you put other things in them! 

To me their main value is allowing me to cook up a larger amount and then put the leftovers in the fridge. that saves me time, energy and even money by allowing me to buy in larger sizes.
Bob

 

[highdesertranger]

x2 on what Bob posted that is how you cut your cost per meal down. highdesertranger

 

[VanLifeCrisis]

i tried the dorm fridge. i found a pretty efficient one as they go. I HAD 225 AH deep cycle battery and eventually 200ah solar. I could run that fridge, if i put it on a timer (forcing it off for long periods of time at night). But cloudy winter days and such put me at a deficit and as time went on it slowly killed the batteries. I have been using a dometic 12v compressor fridge with a cheapo marine battery from wally. The dometic is clearly more efficient, tho i think i would still recommend 200 ah of battery to run it. I run it on 90 ah (supposedly) but im riiight at the 50% mark by morning, and thats if i turn it down low at night (still pretty cold) and run nothing else.

so my suggestion is 200 watt solar kit (350 ish) and 200 ah battery (230 ish) and a small 12v fridge (350-400). This should give you a rainy day cushion and allow you to run other things. Consider a small generator too, to charge in case of long sunless periods.

gassing is only a prob during fast charging in my experiece, and i just open my vent. i have my batteries right near my bed, no problems.

 

[Spaceman Spiff]

Ok I'd like to limit myself to one or two batteries total here's what I am looking at running.

looking at a small fridge (to mainly keep drinks/ice cold and ready for usage whenever). 

other things:

one or two fans for when I am trying to sleep somewhere while I wait for them to open up.

a few led lights for when there is a need to see at night (probably not often) 

again depending on what i am doing powering/charging a laptop and/or cell phones.

perhaps if i can get one installed i hear a exhaust air vent/van makes huge differences in the comfort level in the vans.

what would I be looking at here?

I have 200W of solar panels (two 100W Renogy rigid panels) feeding 208 amp-hours battery (two 6 volt golf cart batteries).  This runs a 2.1 cu. ft compressor refrigerator (24 hours/day at 34°F), MaxxFan ceiling vent fan (10 hours/day), 12 volt LED lights (plenty of light to read by at night), charging my cell phone and laptop daily.  On all but the 90°+ days, my batteries are fully charged by noon.  Even parked in the shade or overcast skies, I can usually go 3 days before I need to find an alternate charging source.

-- Spiff