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Need some with a solar battery charger. Is a 5 watt panel with a 15 volt and 340mAmp peak enough to charge a battery that has been drained or is just to maintain the current charge.


-- James Jones (jamesjones@bbnp.com), December 17, 1998


It will do both .. but several things are at issue.
Here's a simple lesson: SolarEnergy-101
Imagination time. Think of the battery as the water tank on a toilet. If you trickle water into it, it will fill up .. eventually. Should you need to flush it only once a week (say you're there for a few moments just checking up on the cabin) .. then the trickle works just fine. On the other hand, if you need to use it on a regular basis, you'll need more than a trickle to fill/refill it in a timely manner. How long it takes to refill also depends on the size of the tank (battery).
  If you're recharging a set of AA fast-charge nicads (1.0 ampere-hour rating), the panel you reference will take them from dead to full charge in roughly 3 hours. C-size nicads will be fully recharged in approximately 8 hours (2.5 ampere-hour rating) .. and D-size cells (4.0 ampere-hour rating) will need about 12 hours with the panel in full sun. ("Full sun" is generally considered to be from 10 AM to 2 PM in the winter with the panel pointed directly to the sun. Anything less decreases the output from the panel and increases the charging time.)
  So .. it all comes down to:
   a) The size of the battery
   b) How deeply you discharge the battery
   c) The amount of sunlight available  
I hope this helps.
P.S. A 15 volt photovoltaic panel has barely enough extra voltage to fully top off a 12 volt lead-acid battery (need to get to 14.85 volts) .. and not quite enough to charge a 12 volt ni-cad battery (need to reach 16.5 volts). If you're working with a battery of less than 12 volts fully charged, you're ok. If not, look for a photovoltaic panel with at least 18 volts open circuit (not connected to anything). 20 volts open circuit would be even better, but may require a charge regulator depending on the battery capacity.
Expect to pay up to $8.00 in the smaller panels (less than 30 watts) and approximately $5.00 per watt in larger panel sizes (30+ watts). Prices vary a bit in the little panels depending on quality and construction.
Good luck.

-- Dan (DanTCC@Yahoo.com), December 17, 1998.

Where do you find solar panels at those prices?!

-- Nigel Arnot (nra@maxwell.ph.kcl.ac.uk), December 18, 1998.

How about $3.00 per watt. I purchased (8) 375 ah deep cycle batteries, (1)Trace 4048 inverter, (1) control center, (4) Solarex MSX 120 PV panels for $6611.00 installed. Millennium Power Systems is the cheapest yet helpful and knowlegeable outfit I found after investigating PV systems for three weeks. The PV modules will not sustain my battery bank though. Three hours of sun in southern Indiana times 120 volts times 4 modules = 1440 volts charging per day. The system I purchased from this company will handle enough future PV to run my entire 6000 square foot home off the grid. In the mean time the 6 KW Onan generator will charge the batteries in stand by. Not yet ready to commit a large solar array to my landscape yet. Their web site is www.offgrid.com. Their phone number is 410-686-6658. Ask for Paul and tell him Mike Kessler sent you, please.

-- flierdude (mkessler0101@sprynet.com), December 18, 1998.

So I'd only get a little more solar exposure down here near Atlanta right? Appears that it would be enough to charge NiCd's from, but not enough to "live" from or run a heater fan?

I'm forgetting my basic EE - what is impact of 12v dc on a nominal squirrel cage 120v AC motor? I seem to remember that if it is a brush armature motor - it will turn, but at a speed proprtional to voltage, not frequency? (Obviously - I'm assuming a "plug-in" power cord separately hooked up to one or more deep cycle (marine) batteries.)

-- Robert A. Cook, P.E. (Kennesaw GA) (cook.r@csaatl.com), December 18, 1998.

Replies to multiple postings:
Congrats on your system. Excellent gear all around. Good price on panels too. :)
A minor nit to pick first ... photovoltaic panels are most often rated in "watts". (You had "volts" as the accumulating unit of output). The MSX-120 must be a new product release from Solarex as it's not one I knew of until your posting. Since Solarex generally includes the panel output wattage in the model number (i.e. their model MSX-64 panels are rated for 64 peak watts out) I must presume that the MSX-120 are rated at 120 watts. Thus, 4 panels @ 120 watts each times 3 good sun-hours a day in the winter equals 1,440 watt/hours per day. In Indiana, you might even get closer to 4 good sun-hours a day in the winter, but it's best to play it on the conservative side as shown in your posting. Living electrically very frugally, you can actually get by on that. No, you won't be using an electric dryer or stove, but there's plenty there for lights (compact fluorescent), transistor radio, stereo, small water pumps, and other items .. for openers. In the summer, it will be even better with more daylight hours. A typical electricially efficient solar powered home gets by quite comfortably on 2,000-2,500 watts a day. The key here is using it carefully and wisely. Learn from experience and never be embarrassed to ask questions .. especially to prevent mistakes.
The panels you purchased are capable of sustaining the battery bank with careful use of your electricity. Change out incandescent lights (12-15% efficient) for compact fluorescent lights (85% efficient); make sure all non-critical "phantom loads" are turned off or disconnected. A phantom load is anything that uses a remote control; has an internal clock that stays on; "wall-cube" transformer devices such as answering machines, etc. Phantom loads are like a dripping faucet. You'd be surprised to learn how much electricity they use over the course of 24 hours .. even when turned off. Also, learn how to use the inverter and set its "sleep" mode at a level that's most appropriate for your usage. And one more item .. (please forgive the preaching) .. don't try to maintain your grid-connected lifestyle when living solar .. unless you have about 25-40 of the 120 watt panels installed. Even then there's still a finite limit to what your panels produce and the batteries store.
If the dealer didn't include "Hydrocaps" in the system, they are worth investigating. They capture the excess oxygen and hydrogen that's given off by the batteries during the charging process. These gasses are then reconverted back into water in the cap and returned to the cell. This dramatically reduces the amount of water loss thus reducing the amount of maintenance needed. It also results in cleaner cell tops. Win-win.
Also .. hopefully the dealer mentioned the need for a periodic "equalizing charge" for the batteries. The frequency of this process is determined by a variety of things .. but mostly how hard you use your system. Your dealer can tell you more about it. When solar, you are your own power company .. repleat with all the responsibilities for most efficient production and use.
Glad to see the Onan in the list too. Most gensets run at 3,600 RPM. The Onan loafs along at 1,800. With care, the Onan should perform well for you.  
You've got a great start on the system. Welcome to the world of living solar. Next .. a wind generator and a Sun Oven :)

Most AC motors won't run on DC. The exception to this is a "universal" motor, but they aren't very common. Even then, a universal 120 volt motor may not run at all on 12 volts DC. If it does, the useful output would be very limited. If you connect a 120 volt AC motor to 12 volts DC, at best it might get a bit warm -- and at worst -- you'd roast the windings.
Squirrel-cage motors are moderately voltage independent. While it's true that the speed will vary very slightly with a modest change in applied voltage, it will change a lot more with a change in frequency. A variation on the squirrel-cage motor is called the "hysterisis" motor. We find these critters in a variety of speed-sensitive applications such as record players and clocks.
Atlanta gets plenty of sun. I'm in the upper midwest .. 3-4 good sun hours a day in the winter .. if I'm lucky and if/when we see it. (It's pretty cloudy here in the winter). There are many people up here who live totally solar. Atlanta would be even better. Solar is VERY viable in your part of the world. :)
Hope this helps.

-- Dan (DanTCC@Yahoo.com), December 18, 1998.

Something I overlooked .. energy efficient appliances.
Conventional refrigerators and related items are usually not suitable for use in applications where maximum efficiency is paramount. Most commercial refrigerators (GE, Kenmore, etc) use between 5,000 and 7,000 watts every 24 hours (more or less depending on how it's used; how often it's opened, etc). SunFrost and LowKeep both make very efficient (albeit pricey) fridges in various sizes. To wit: 500-600 watt-hours per day - about 90% less than conventional 'fridges.
Learn all you can about your system and it will serve you well. I highly recommend Home Power Magazine as a starting point. Most articles are written by freelance contributors who are just ahead of you on the learning curve.

-- Dan (DanTCC@Yahoo.com), December 18, 1998.

Been looking into solar/PV power for my home. Just came across some info about California's Renewable Energy program for consumers. Seems that as of March, 1998, they'll reimburse a percentage of the costs of installing and maintaining a "renewable energy system", namely PV, solar/thermal, or wind.

Anyone here in the Golden State looked into this? Much as I'd be leery of getting too involved with the gummint, if they'll help with some cash, I'd be able to put in a system much more quickly and affordably.

-- Mac (sneak@lurk.com), December 18, 1998.

test2, please don't destroy these threads. We need the info.

-- Leska (allaha@earthlink.net), February 18, 1999.

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