Frequently Asked Questions

(about the $300 Solar Power Generator)

1. "How many appliances can I run off your system?"
"How many" refers to the total number of watts required.

Different appliances use different amounts of watts. You don't need to know what a watt is; you only need to count up how many total watts your appliances require. Your television, your laptop, even your hair dryer will have a little nameplate somewhere listing how many watts, volts, and amps it takes. Sometimes it only lists the volts and amps. To figure out the wattage, multiply the volts times the amps.

Here's the formula: Volts X Amps = Watts.

That will give you the watt hour load. For example, add up all the wattage on all the light bulbs you will be running off it. Two sixty watt light bulbs means 120 watts. Add an inkjet printer (35 watts), computer (55 watts), 17" LCD flatscreen monitor (45 watts), and a cellphone (5 watts) and your office is fully running at 260 watts. Get an inverter of at least 300 watts.

You will quickly learn how inefficient many of our everyday items are. For example:

Microwave 900-1500
Coffemaker 1200
Toaster 1200
Food dehyrater 600
Dishwasher 1450
Hairdryer 1500
Electric iron 1200

A sun oven could replace all of them for free. (Well, maybe not the hairdryer--I don't recommend sticking your head in a sun oven.)

Other equipment:

10" table saw 1800
1/2" Hand drill 600
Vacuum cleaner 900
Laser printer 900

So the best thing to do is figure out your minimum needs, and then buy an inverter that at least covers that, or better still, buy the biggest inverter you can afford. Then you can add on to it.

2. "How long can I run them?"
"How long" refers to the total number of amps required.

Again, you do not need to know what an amp is other than it is the unit for measuring how long your set up can help you out. An amp hour (AH) is how many amps required to run it for an hour. A kilowatt hour (KWH) is how many kilowatts are needed in an hour.
How many Watt-Hours in a battery?: Watts are pretty simple - it is just battery voltage times amp-hours. A 12 volt 105 AH battery can supply (under perfect conditions and to 100% discharge) 12 x 105, or 1260 Watt-hours (1.26KWH).

Here's the formula: Amps = Watts/Volts

The amps listed on your appliance are probably listed in milliamps (mA) or thousanths of an amp. An alarm clock takes about one. A refrigerator will need a few amps. A toaster will take more amps than a refrigerator, but runs for only a few minutes.

BUT, deep-cycle batteries can only be discharged to about 50% of their capacity without damage. In other words, you can expect a 100 amp-hour battery to supply around 50 amp-hours of power between charge cycles without suffering damaging.
THEREFORE: get a battery with twice the amps you think you'll need.
Then test your battery with a meter.It should always be in the 80-90% range. If you use a charger, then you need to take a reading ONE HOUR after any charging cycle. It is important to wait this hour because all batteries hold a surface charge that will give you a false reading after charging.
All deep cycle batteries are rated in amp-hours. An amp-hour is one amp for one hour. It is amps x hours. If you have something that pulls 20 amps, and you use it for 20 minutes, then the amp-hours used would be 20 (amps) x .333 (hours), or 6.67 AH. The accepted AH rating time period for batteries used in solar electric and backup power systems (and for nearly all deep cycle batteries) is the "20 hour rate". This means that it is discharged down to 10.5 volts over a 20 hour period while the total actual amp-hours it supplies is measured.

3. "Can I run my refrigerator off your system?" (No.)

Your refrigerator is too inefficient. As much as 20% of an average home's energy usage is for the frige. Even small dorm-sized models draw too much for a practical solar system.

But you can invest in a 12-volt DC powered refrigerator. The best ones use zero maintenance, brushless, thermostatically controlled DC compressors. They cost about half as much as propane refrigerators. You will also need a bigger panel, a 150-300 AH battery, and an amp controller to keep from overcharging your battery my basic $300 system does not need one.).
Unless you live in the very cold northern latitudes having short days and low sun angles, most parts of the United States will average 4 to 4.5 hours of direct sun per day during the winter months and 5 to 6 hours per day during the summer months. Of course, some milder geographic locations may also have lots of rainfall and cloud cover, which reduce these average hourly values. As an example, if you select a refrigerator or freezer that requires 40 amp-hours per day to operate, this means you will need a solar array that can provide at least 10 amps output (40 amp-hour/4 hours) during the winter, and 6.6 amps output (40 amp-hour/6 hours) during the summer. If your solar system will be used year-round, then you may want to use the smaller sun-hour value. Since the ambient air temperatures are cooler in the winter than summer, all refrigerators and freezers will require less energy to operate during colder months, so a more accurate winter calculation would use the amp-hour load given for lower ambient temperatures.

Nova Kool and Sundanzer both make 12- and 24-volt DC powered refrigerators. Some are AC/DC. (That would be perfect for rolling blackout areas--most of the Third World. They live on AC and then automatically switch over to the DC battery when the power goes out.) You can view the whole line here. But let me break down what else you will need.

This small 1.8 cubic foot capacity model REFRIGERATOR will require a 45 watt solar panel, a 60AH battery, and a 15 amp charge controller.

This FREEZER is also 1.8 cubic ft. but requires a 110 watt solar panal, a 150 AH battery, and a 15 amp charge controller.

This 8.1 cubic ft. capacity freezer gives you over four times the capacity at less than twice the price but will require a 215 watt solar panel, a 300 AH battery, and a 15 amp charge contoller.

4. "Does it matter how thick my wires are? I put my solar panel on the roof and it doesn't deliver as much power to my battery as before, when it got less sunlight. Um...what's an ohm?"

These are all the same question. Electricity flowing through a wire must overcome resistance to get from one end to the other. A thicker wire has LESS resistance than a thinner one. A wire twice as thick has half the resistance. A longer wire has more resistance than a shorter one. The amount of resistance is measured in ohms. When one volt causes one ampere of current flow, the resistance is one ohm. You can buy an ohmmeter to measure your ohms, but electricians mainly use them to find defective connections.
DC electricity is more vulnerable to resistance than AC. That's why the battery in your car has short, thick cables.
So, use wires as thick as practical. The wires from the panel to the battery should be as short as possible. Carry the battery up to the roof if you have to. Then a short connection to the inverter. And then a long line can go from the inverter to you (because it is AC).

This digital multimeter will test ohms as well as voltage, current and other useful stuff:

5. "In your instructions you say to buy a DC meter. What's it for?"

The DC meter lets you know how much of a charge you have in the battery. Remember, you don't want it to discharge more than 50%. And you don't want to damage it by overcharging. The DC meter (one of the settings on a multimeter) will allow you to monitor the state of your battery.

6. "Can your system pasteurize water and milk?" (Yes)

The original question was "Can your system boil water long enough to make it safe to drink?"

Yes, it can. But it is a myth that drinking water has to be boiled for ten minutes. Pasteurization is achieved at a lower temperature for a shorter period. For both water and milk (or anything) all the necessary germs (including E. Coli, Rotaviruses, Giardia, the Hepatitis A virus, and Colera) are dead after having been raised to a temperature of 160 degrees F (72 degrees C) for one minute.
Therefore do not waste the precious stored energy of the battery by bringing the temperature up higher than you need to. Heating water is probably the most inefficient use of this system. A sun oven would do the job more efficiently with the sun rays--assuming it was in the daytime, sunny, and safe to go outdoors.
A typical commercial sun oven. They work really good and are a lot of fun. But they cost about $240 each. They reach 300 degrees F and higher.

BUT, if all you want to do is pasteurize, a homemade sun oven made out of cardboard and tin foil should be able to get you in the right temperature range. Use a thermometer to be sure.

Health care providers will want to test their results. One way this can be done is with a nifty little device called a "pasteurization indicator."

[IMAGE] You can get one for about nine bucks from my friends at Solar Sphere.

"So with a few thousand cardboard boxes, a few hundred rolls of aluminum foil, and the proper guidance the Cholera epidemic in Haiti could have been prevented and 1,751 lives (as of Nov. 30, 2010) could have been saved?"

Yes. This is no joke.

BUT, if all you have is the solar power generator pasteurize with, here is the smartest way to do it:

First of all, don't use an inverter to power a microwave or electric range. This will suck your battery dry very quickly. Instead, use direct connections with the battery. There are a variety of devices that plug directly into cigarette lighter ports. These range from little dip-in infusers to 20-oz. coffee pots. And still the best way would be to monitor what you are doing and only raise the temperature for as high as you have to for as long as you have to. These little beasts take about 20 amps each.


I have to warn you that these immersion heaters are dangerous (the dip-in model can brand you) and the other two will permanently self-destruct if you keep them plugged in without any liquid in them just once. Just be careful. I personally hve never had these problems.

Back to "How to Make a Solar Power Generator for Less Than $300."

Copyright 2010. SolarLight Productions.