Thanks to someone earlier (forget who, sorry) posting the URL to Sun-Mate Corp., I'm interrested in buying one of those portable solar panels, specifically this one, item #500

My husband says 17 V. or 8.5 watts isn't worth anything and wouldn't even power the fan for the high efficiency fireplace insert. But the specs on it says it powers water pumps, recreational vehicles, portable t.v.s etc. Who's right? The price at $79 seems a resonable investment to me if it is strong enough to power what it says it can on the spec sheet. (Heck, I've spent a lot more now on Duracell batteries! That to me is a waste if I can instead get unlimited recharges from the sun for what those batteries cost for a few hours.)

Thanks for any input. (My husband still isn't very cooperative with preparations and tries to discourage me from a lot of things I believe essential for even a one week power outage.)

-- Chris (catsy@pond.com), October 19, 1998

Answers

Hi Chris, How's this for diplomacy...you're both right! Yes, the smaller modules (8, 10, 20 watts) will power RV booster pumps, fans, lights, TV, etc. BUT...only if used as part of a battery charging system. Let's say you want to run a 3 amp @ 12 volt RV water pump...that would be 36 watts if you ran it for an hour. But 1/4 hour would be a more realistic amount of time per day...giving you app. 60 gallons of water. That would = 9 watts. And lets say you ran a 12 volt TV for 1 hour @ 25 watts and that fireplace fan for 2 hours @ 20 watts (40 watts total). The grand total per day would be 9 + 25 + 40 = 74 watts. We'll use a figure of 4 hours of full sun per day, so...74/4= 19 (rounded). So with a 20 watt or larger module you would put app. 80 watt hours of power into a battery during the day and have it available for use 24 hours per day. And you can add modules as you go, increasing your power production and running more appliances.

-- Roy @ Four Winds (4windpwr@infoblvd.net), October 20, 1998.

Hi Chris, How's this for diplomacy...you're both right! Yes, the smaller modules (8, 10, 20 watts) will power RV booster pumps, fans, lights, TV, etc. BUT...only if used as part of a battery charging system. Let's say you want to run a 3 amp @ 12 volt RV water pump...that would be 36 watts if you ran it for an hour. But 1/4 hour would be a more realistic amount of time per day...giving you app. 60 gallons of water. That would = 9 watts. And lets say you ran a 12 volt TV for 1 hour @ 25 watts and that fireplace fan for 2 hours @ 20 watts (40 watts total). The grand total per day would be 9 + 25 + 40 = 74 watts. We'll use a figure of 4 hours of full sun per day, so...74/4= 19 (rounded). So with a 20 watt or larger module you would put app. 80 watt hours of power into a battery during the day and have it available for use 24 hours per day. And you can add modules as you go, increasing your power production and running more appliances. BTW...the small modules are neat, but usually the larger modules are a better value...less $ per watt. Your $79 module (8.5 watts) = $9.30 per watt. You can get a UniSolar 21 watt module for $167 which is $7.95 per watt...a Kyocera KC35 watt module for $244- $6.97 per watt...UniSolar US32 watt module for $205- $6.41 per watt...etc. Not trying to push you on spending more $, but rather showing you that the larger modules will give you more bang for your buck and let you run more things. Also...with the larger modules you need a charge controller to prevent the module from overcharging the battery...the KC35 is "self-regulating" and in most cases soes not need this controller. Hope this helps to answer some of your questions...tell your husband that solar makes sense for many reasons...including economics and environment...not just for emergency prep! Roy @ Four Winds www.infoblvd.net/4windpwr

-- Roy @ Four Winds (4windpwr@infoblvd.net), October 20, 1998.

Chris,

The short answer to "My husband says 17 V. or 8.5 watts isn't worth anything and wouldn't even power the fan for the high efficiency fireplace insert. But the specs on it says it powers water pumps, recreational vehicles, portable t.v.s etc. Who's right?" is: Both are sort of right but incomplete, but your husband's answer may be the more practical one, overall, for your situation.

The long answer is:

8.5 watts is the maximum rate of power that panel will provide.

But 8.5 watts is not enough to _directly_ power practically any household electrical item. (My electric typewriter needs four times that much power!) You'd need seven or eight of those panels to directly light a 60-watt bulb to its usual intensity.

So the way you'd probably need to use that solar panel would be to recharge batteries (large-capacity deep-discharge batteries, not little rechargeable D cells) all day, then separately run your electrical items from those storage batteries through a DC-to-AC inverter for short periods of time.

In order to figure out how much power that 17-volt, 8.5-watt solar panel will provide for you, compared to what you need, lets go through some basic calculations.

In order to get that maximum 8.5 watts from that solar panel, it must be "pointed" fairly straight at the sun to provide that rate, which means that during the course of a day you'd have to reposition it every couple of hours for maximum sun reception. (And of course that 8.5 would be on a clear day. A cloud over the sun will cut way down on the power produced.) Let's suppose you do keep the panel pointed close enough to the sun for an average of 8 watts during the day.

Since I don't know where you live, I'll use my location, mid-northern US. On a winter day (2000/1/1 is in the northern winter, remember) here there are about 8-9 hours of useful daylight (if you don't have a lot of trees to the east, south, and west). Multiplying by the power rate of 8 watts, that gives about 70 watt-hours of electricity produced by the panel in one _clear_ winter day, with the sun unblocked by any trees, and the panel diligently turned to face the sun throughout the day.

But about two-thirds of the winter days here are cloudy. Suppose the panel can produce 10 watt-hours on a cloudy day. Then on average every three days the panel produces 70+10+10 = 90 watt-hours, or 30 watt-hours per day. (And you _are_ keeping the snow off the panel, aren't you?)

For reference, your electric utility bill probably shows units of kilowatt-hours (kWh). On my bill, the cost is $0.07 per kWh. 30 watt-hours is 30/1000 of a kilowatt-hour. So 30 watt-hours coming to me through the utility lines costs me (30/1000) x $0.07 = $0.0021, about one-fifth of a cent.

Some of your household appliances and other electrical items will have a power rating in watts: 60-watt bulb, 900-watt microwave oven. For others, there will be an amperage (current) rating -- for these, you'll have to multiply the amps (current) by 110 volts to get the wattage (power).

Example: my electric typewriter says 0.31 amps, so its power rate is 0.31 x 110 = 34 watts. 30 watt-hours from the solar panel, stored in the batteries, will power my typewriter for a little more than 50 minutes.

Example: 60-watt bulb. 30 watt-hours will light it for 30 minutes.

Example: 900-watt microwave oven. 30 watt-hours will power it for two minutes. Yes, just 2 minutes. However, on a clear day the panel can produce 70 watt-hours, which will run the microwave for 280 seconds = 4 2/3 minutes, enough for a baked potato, perhaps.

So it's not just a matter of _whether_ the solar panel can provide enough power for an electrical item. You have to consider how long you want to run it, and you have to add in the cost of the storage batteries and the DC-to-AC inverter.

-- No Spam Please (anon@ymous.com), October 20, 1998.

Wow Mr. Roy and Mr. NoSpam, thanks a great bunch for the crash course! I love this forum :)

Ok, now I understand perfectly with those calculations and examples. I've printed this thread too for later reference. I'll sit down and figure out what I need and what I can afford and what is feasable to use in our location/situation.

(Dammit Jim, I'm a nurse, not an electrician!)

-- Chris (catsy@pond.com), October 20, 1998.

Chris/Bones: Careful...Jim must believe you're a miracle worker at all times..."I want answers, Mister!!!!"

LOL

-- Donna Barthuley (moment@pacbell.net), October 20, 1998.

So, what you electrically saavy folks are saying is this type of PV unit plus however many deep storage batteries will give me some livable electric power,...am I understanding this correctly? What about an inverter? Mind you I've read some, but have been thinking all the PV stuff way out of my league cos I'm poor as a church mouse. What about rotating regular car type batteries...keeping them used and recharged?

Would be nice to have just a bit of electricity, especially since I've been thinking I could afford none.

"Damnit Jim, I'm a survival-minded pianist, not a miracle worker"

Thanks everyone...great information.

-- Donna Barthuley (moment@pacbell.net), October 20, 1998.

Donna,

DB>So, what you electrically saavy folks are saying is this type of DB>PV unit

For the lurkers: "PV" = photovoltaic, meaning it converts light ("photo") to electricity ("volt"); i.e., Donna's referring to the solar panel.

DB>plus however many deep storage batteries will give me some DB>livable electric power,...am I understanding this correctly?

It's important to remember that the best type of battery for use in storing electricity produced by solar panels is the "deep discharge" or "deep-cycle" type. This type is designed to be _routinely_ drawn down to a low level without damage.

Wny? From the battery's point of view, it gets slowly charged from the solar panel over long periods of time, then rapidly discharged to run electrical stuff for short periods of time. The discharges will often drawn its stored electrical energy down all the way to the bottom. This is a "deep" discharge.

Automobile batteries are _not_ deep-cycle batteries (usually). They are _not_ designed to be _routinely_ drawn down to their lowest levels. Typical automobile use of a battery draws it down only a modest amount when starting the car. When one has trouble starting, and runs the starter for multiple minutes (a long time, in this context), one draws down a car battery deeply, but this is not the routine use.

Car batteries are designed to give maximum performance and longevity when used in the usual, modest-drawdown at starting-time, fashion. Whenever a car battery is deeply discharged, its longevity and ultimate capacity are reduced sowewhat. A car battery that is deeply discharged between each recharge will not last nearly as long as it would in routine automobile use.

When you're shopping for deep-cycle/deep-discharge batteries, look for _marine_ batteries. These are used on boats, where they will often be used to power stuff for long periods while not being recharged, thus undergoing deep discharges.

But the important point is to insist on deep-cycle or deep-discharge batteries, no matter what their usual application.

DB>What about an inverter?

Yes, you'll need an inverter to change direct (DC) current from the storage batteries into alternating (AC) current because most household electrical items use AC. Anything you've plugged into wall sockets is run on AC. These are the items that won't run if "the power is out".

DB>Mind you I've read some, but have been thinking all the PV stuff DB>way out of my league cos I'm poor as a church mouse.

Better add up the costs of all the items, including however many multiple batteries you think you'll need, before starting to buy any of them. You may very well find that you cannot justify the costs in your particular situation.

Perhaps neighbors and you can make plans for sharing equipment and resources in an emergency.

DB>What about rotating regular car type batteries...keeping them used DB>and recharged?

As pointed out above, though you _can_ use car batteries, they won't last as long as they do in your car. But this is relative, and I don't have any figures on it. I expect that a car battery that's originally in good condition can be used in several or many deep-discharge cycles, but I don't know whether "several or many" is closer to 10 than to 100.

Of course, the car batteries that are advertised like "DieHard" as being able to power headlights all of a winter night, then start the car the next morning, will last longer in deep-cycle use than cheaper batteries, but still they're not designed to be _routinely_ used that way.

-- No Spam Please (anon@ymous.com), October 22, 1998.

Gee, I keep forgetting that the forum-posting software removes my CR/LFs and there goes my formatting work...

-- No Spam Please (anon@ymous.com), October 22, 1998.