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#19661 - 09/29/03 11:01 PM Solar / Wind 12v Battery Charge?
Casual_Hero Offline
new member

Registered: 11/19/02
Posts: 134
Loc: England & Saudi Arabia
Seems that whole country power cuts are the rage at the moment. If I wanted to charge my inverter 12v batteries via solar / wind how viable is this? Can you sensibly generate enough power to run the batteries continuously, or would you have to stop the load whilst charging? Any help gratefully received. <img src="images/graemlins/smile.gif" alt="" />
In the end, all you have left is style...

#19662 - 09/30/03 02:20 AM Re: Solar / Wind 12v Battery Charge?
RayW Offline

Registered: 12/06/01
Posts: 563
Loc: Orlando, FL
Scott, sure it's easy and it's expensive. If you are looking just to run a few small things and keep your batteries charged a few hundred $US might do it. Solar power starts at about $5US a watt. Plus the cost of batteries and inverters. Wind power gets cheaper per watt as the size of the generator gets bigger, but you need to be where the wind blows. Now i know that seems obvious, the winds need to blow around 10mph constantly for wind power to be feasible. Here are a couple of sites with FAQ's if you want to read more about it.



#19663 - 09/30/03 02:26 AM Re: Solar / Wind 12v Battery Charge?
AyersTG Offline

Registered: 12/10/01
Posts: 1272
Loc: Upper Mississippi River Valley...
Eh, that's a bit difficult to answer... if your power generation exceeds your power consumption, yes, of course - assuming that you have proper load management/charging controls and so forth. Go from the other direction: What do you need power for? How many kw-hrs/day? What does it take at the low voltage DC side for your inverter to meet those demands? And so forth.

Not economical to cobble up photovoltaic on your own and any significant amount of power from them is not going to be inexpensive. Then there's nighttime, your latitude, and your maritime climate to factor in... I'm guessing that PV costs would be frightening and battery storage requirements significantly larger than a sunnier clime.

But you should have plenty of wind and to a certain extent it is feasible to DIY some or possibly all of a wind generating system - proper controls would be simpler to purchase, but the generation can be handled on a "Junkyard Wars" approach up to about 360w to ~ 1.5kw at max output, depending on your alternator - be forewarned; the size of the mechanical parts that the wind operates on are probably much larger than you think.

I'm not at all opposed to the idea; good for you. Just trying to introduce a little reality. Converting lowgrade energy (sunlight or wind) into high grade energy takes up a bit of space and initial cash outlay.

You could tinker a bit with a surplus automobile alternator, a surplus 1 lung gasoline engine (over here we would think of something like a used 5hp lawnmower engine), appropriate pulleys and belt, and whatever automotive gizzards you need to rectify (if you're using an old externally rectified alternator) and regulate the voltage. Usually you'll find internal rectification, but I'm not sure anymore about voltage regulators - I know what had them and what they look like, but nowadays... you'll have to ask.

You'll need your battery to provide field current for the alternator (there are a FEW that are self-exciting, but not many). Just hook it all up electrically as if it was in the vehicle. A careful and clever person could easily use the lawnmower deck to mount the alternator and battery and inverter along with the engine... I imagine the alternator bearings might not like the vertical mounting forever, but who knows <shrug>

While you're gathering experience and data from that, you could do a bit of reading on extracting power from the wind - the mechanical part. Then decide if you want to go ahead. All in all, I think it would be a fascinating opportunity for you to learn about how all those bits go together and at worst case you'll have a junkyard wars sort of portable generator that has a battery reservoir - drive the neighbors mad wondering what you'll cook up next, hehehe...

I've done the alternator-engine-vr thing many years ago - it works. TANSTAAFL. Do the math on the DC side and you'll see: Suppose a 55 amp alternator @ nominal 12v - that's 660watts. Is that enough? Bigger ampacity alternator... hmmm, let's say 135 amp (less common in what you're looking for, but available). Now you've theoretically got 1620 watts. And I'll predict that a 5hp nominal engine will have all it wants cranking that many amps out of an alternator, even though in theory it is capable of more. You'll want some airflow thru the alternator and over the engine if you're running either at close to max - but these are all fun things to figure out, so I'll demure. Watch your wire sizes on the low voltage side - those are big currents and require big wires - especially if your paradigm is at over 200v AC.

It's possible to make the whole thing amazing quiet, FWIW, although forced (and baffled for noise control) air for cooling becomes essential then, as well as re-locating the fuel tank.

Heck, I've just talked myself into a "Science Dad" project with the boys! Last time I did this sort of thing, they hadn't been born yet...

Hope you take a crack at it and have fun learning the answers to your questions.



#19664 - 09/30/03 07:58 AM Re: Solar / Wind 12v Battery Charge?
joblot Offline

Registered: 02/21/03
Posts: 258
Loc: Scotland
I recently looked into this my self, and wrote and asked a few companies. My idea was to buy two batteries, one on, one charging. The set up below should power( I haven't bought it yet) a varierty of 12v appliances. Televisions and fan heaters are out though - too much start up power needed. Cost around 250.

The Battery

The solar panel

the Inverter

I hope this gives you a few ideas. The company replied to my email promptly if you have any questions.
It would be interesting to find out what you decide on.

#19665 - 09/30/03 11:45 AM Re: Solar / Wind 12v Battery Charge?
NeighborBill Offline

Registered: 03/02/03
Posts: 385
Loc: Oklahoma City
Home Power Magazine has a setup designed for a small "retreat" type cabin


Check under "Education" and select "RE Components"
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#19666 - 09/30/03 12:51 PM Re: Solar / Wind 12v Battery Charge?


The family once owned an island cottage. Electrical power was not available, and we ran most things off propane or 12v DC deep cycle batteries. Humping batteries back home to charge was not particularly fun.

I looked into a variety of options. I considered both solar and wind generating systems. There is a lot of decent information available on the internet (and a lot of bogus bull too).

I ruled out solar as a viable option for my area. We simply do not have sufficient sunshine to make the solar systems particularly viable here. A websearch and a little time online shouls provide you with some basic information regarding expected number of days of sunshine in your area. If you are one of those lucky few in Arizona or some such place, have at it!

Wind was a more realistic option for me. Although I live in a margin area for wind generation (average wind speed of about 8.5 miles per hour), the cottage was located on teh windward side of an exposed island. It was ALWAYS blowing there. I never actually installed a system, since I tired of the continual maintenance demands of the cottage and gave it to my brother. Now HE mows and paints, and I show up on Sundays to drink HIS beer.....

In any case, your very specific geographic location will likely determine the wind turbine effectiveness. Are you on a hill top? Down in a valley, surrounded by trees?

The information I found indicated that wind systems generate ever increasing amounts of power as windspeeds increase. I could be wrong about this , but around here the line power usually kicks out during storms. Storms are accompanied by wind, so I'd assume the wind sets would be doing quite nicely.

Search for an AIR 403. I know Lehmans has the,, but they are about 30% more expensive than the same unit elsewhere. I have no experience with these, but they looked appropriate for your intended use.

Don't forget: In addition to a $500+ turbine, you need a tower.


#19667 - 09/30/03 07:53 PM Re: Solar / Wind 12v Battery Charge?
joblot Offline

Registered: 02/21/03
Posts: 258
Loc: Scotland
I suppose at the end of the day the eqipment you buy has to be in relation to your needs and wants. Billy Guttery link is very informative but for me not realistic (or with my talent possible!). If I can russle up some light, keep my food cold and maybe some heat during a black out I'll be happy.

#19668 - 09/30/03 08:30 PM Re: Solar / Wind 12v Battery Charge?

Another approach to this it to examine your usage and look for ways to cut that back along with the addition of small generation capacity and battery storage capacity.

It is very difficult to concieve of replacing my 7 KWh I use with solar or wind. OTOH, If I can reduce that to 4 then it might be much more possible. Switching lighting to florescent is a major savings of wattage. Switching from flourescent to LED would be even greater savings. These cost something but you can get fixtures that "plug-n-play" with your current house wiring. Making sure that you have the most energy efficient appliances is important. The newer "energy-star" rated fridges are comparable to the super efficient stirling cycle 12 volt fridges of the '70s and are commercially available for a decent price. Getting a stand-alone freezer is more efficient. Downsizing your refridgeration needs to only dairy and cheese and using your vegies fresh, dehydrated or canned will save bunches. I have never understood why people buy items like carrots from an unrefridgerated shelf at the super and bring them home and refridgerate them. Everyone does but why? If you buy so much that you need to worry about spoilage then you can can it or dehydrate it. Both of these options last longer and don't require storage energy just processing energy. Also look into your heating and cooling needs and determine if there are ways to make the house more efficient. AC is an electricity pig! If you have a cellar then you have a ready made heat-sink that, with the proper application of ventilation, can cool quite a bit of air. Ventilation is cheaper than AC.

Once you have downsized you energy diet then take the new smaller wattage requirements and see if you can satisfy that appetite with some kind of co-generation local options like solar, wind, biomass, hydro etc. If you are on a stream, river, or even some sea shore locations, there may be decent small scale hydro options available. All of this starts to work better if the demand has been downsized first.

BTW, downsizing the demand from your household will lighten the load on the grid thereby reducing by some small percentage the likelyhood of a grid failure in the first place.

#19669 - 10/01/03 09:36 AM Re: Solar / Wind 12v Battery Charge - Update
Casual_Hero Offline
new member

Registered: 11/19/02
Posts: 134
Loc: England & Saudi Arabia
Thanks for your posts everyone.
I've found a cracking website thats chock full of info. It even includes downloadable power estimators.

Well worth a vist at:


In the end, all you have left is style...


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