Solar Energy

Instapark 10 watt solar panel charging a 5200 milliamp-hour lithium-ion battery pack

This setup costs about $60 and it will charge iPhones in about an hour on a sunny day. It'll also charge an iPad Air, with its stunningly high capacity (32400 mAh) internal battery, but if the battery is real low, it'll take all day. Maybe two or three. And those had better be sunny days. 

Daffodil Desk Lamp - 1.25 watts (250 mAh)

The 10 watt solar panel will also charge a battery pack that can power USB devices (such as our little desk lamp, above) and to recharge phones at night. The off-grid alternative is to use a vehicle's 12v cigarette lighter plug, but you have to do it prudently or risk damaging the battery and being unable to start your car - especially in subzero weather. Running the engine for an hour just to charge batteries is environmentally sociopathic. 

Solar power is addictive, for individuals and countries. Once you see how easy, inexpensive and liberating it is to generate your own power you'll get hooked. The same phenomenon occurs in countries - last year natural gas-fired units led the new generating installations in the USA but solar energy was second. By 2016, solar will be first. 

If you do get hooked and want to power more electrical appliances off grid, you'll need to know a bit about electricity. We are conditioned to unconsciously plug in an appliance and turn it on. Many people auto-pay the electric bill, gripe about the withdrawal from checking every month. That's about the extent of their electrophysics experience. If appliances don't work when switched on, and there's zero mechanical aptitude within hailing range (more common today because fewer kids have the time or motivation to learn how to fix things) then we complain, call customer service, or discard it and buy another one. Often, all three are done. Society has learned to plug, play, and pay the electric bill like good, obedient consumers. If the power goes down then it's an easy descent into victim-hood and FEMA-blaming.

It doesn't have to be that way, a little knowledge of electrophysics combined with some curiosity and common sense can get you through any power outage, even a perpetual one such as here in off-gridistan.

Even immortals cannot escape the grasp of the NTA

The subject of electricity often invokes fear and boredom in the plug-and-play, victim-and-blame world. We occasionally run into sensational signs like this but you won't be generating anywhere near the energy required to run a tram. Electrocution is certainly a hazard, but you are 100 times more likely to die of an infection, so it's important to keep risks in perspective. 

Electricity is the management of electrical charges: storing, transporting, and converting the charges to a useful (and often, useless) product such as light, heat, an MP3 or (ahem) a blog post. Electricity flow is similar to water flow (this is known as the hydraulic analogy). All you need to know are two basic concepts: volts and amps and we'll derive a few others from those. The hydraulic analogy involves considering the charges the same as water molecules. Volts, for instance, are similar to water velocity - the swiftness of a river, for instance. A fast river, like the AuSable after it rains, is similar to high voltage. When it doesn't rain for awhile the AuSable has a slower flow - lower voltage. 

Volts are named for the Italian dude who invented the battery, Alessandro Volta, about 200 years ago. He noticed he could make frog legs twitch by applying electrical charges to them. Most electrical physicists and engineers are a bit eccentric, tortuing frogs is normal behavior for them.  

 

Volta immortalized on a 10000 lira note, worth about $6 in pre-Euro days.

Volts are like water pressure - when you stick your hand in the river you feel the force of the flow. A cell phone is a 5 volt device. A blow dryer runs on 117 (nominally, 125) volts...in the US. An electric stove or air conditioner nominally requires 220 volts.  If you put your thumb over a squirt gun nozzle, you can easily stop the flow. Low pressure...low voltage. If you put your thumb over the nozzle of a high pressure washer, you can't stop the flow and you'll injure your thumb. (I know this firsthand...literally.) That's similar to high voltage. So the first hydraulic analogy takeaway is that high voltage can injure you but low voltage can't.

Testing, not tasting, a 9 volt battery.

This is why you can touch the battery contacts on a flashlight battery and not even feel it. It's only 1.5 volts (12,000 milliamp-hours, mAh). You can touch your tongue to a 9 volt (500 mAh) battery and feel a slight tingle (the tongue being more sensitive than a finger). We actually used to do stuff like that in grade school science class. If that were attempted today one of the students would tweet it to a parent, who would tip off CNN and they would helicopter a news crew to the scene. EMS would be activated, the school would go into full lockdown, the resulting lawsuits would take out the insurance sector and crash the stock market. 

I definitely wouldn't advise it but if you touched higher voltage, say, 115 volts from the household outlet, then you will get a heck of a shock, as some of us kids of the 60's could attest. Back then the electrical code didn't require grounded outlets or even polarized plugs. The code has been changed, products are better insulated and many circuits have ground fault devices, so electrical shocks are now rare. That's a bit of a pity as kids can grow up without ever getting zapped, a teachable moment for the survivors. 

Now you know that you're not going to even feel 12 volts on a car battery (40,000 mAh) unless you have a really long tongue because the terminals on those batteries are far apart. So, provided our wires are small in diameter, we can safely fool around with 12 volts or less. That's the typical voltage for off-gridders, but I think 5 volts (for those USB gadgets) is also handy. 

Only a stamp. Alas, no French currency
immortalizes the man who discovered current.

The wire diameter is important because of the next important concept, amperes, generally shortened to simply 'amps'. While Volta was zapping frogs, André-Marie Ampère was experimenting with electrical charges. Back then, science was the domain of the idle rich, as most commoners 200 years ago had to work day and night just to survive. Ampère had all the time in the world to fool with wires and electricity. He discovered that the two wires carrying current repelled or attracted each other and the force was related to the direction and strength of the current. Ampère's wife, Julie provided a timeless assessment of engineers as well as her husband: "He has no manners; he is awkward, shy and presents himself poorly". 

Back to the hydraulic analogy. Recall that volts are analogous to water pressure. Amps are similar to the diameter of the pipe or the width of the river. Big pipe or wide river means lots of amps. 

Long Beach Freeway - example of high, albeit slow, flow

Another way to think of it is to consider a small country road and a giant freeway. Our road has a speed limit of 10 MPH because Irene washed out half a bridge three years ago. It's an example of low capacity, or low flow. Compare that to the Long Beach freeway, a multilane monstrosity in LA. The capacity is much higher than our little bridge.

One lane bridge - example of low (also slow!) flow

Using a highway analogy, volts would correspond to the vehicle speed and amps would correspond to the number of vehicles. The vehicles are similar to electrical charges. So the freeway can move a tremendous number of cars (charges) per minute - even at a crawl. Our one lane bridge-constricted road can move only a few per minute. The capacity of the road (cars per minute) is analogous to amps. 

Armed with a basic understanding of amps and volts we can now discuss the art of the possible when living off grid. With an unlimited budget you can do anything, but our goal is to conserve resources and live simply. The first step is to identify essential electrical devices and determine their energy requirements. Energy is measured in Watts, which are simply volts multiplied by amps. 

Watt, on the right (shown with another inventor, Bolton) on a 50£ note

James Watt wasn't rich or eccentric, but he wasn't into electricity, either. He perfected the steam engine, which ushered in the Industrial Age. Watt invented a well known unit of energy, horsepower, and patented the first copying machine. The modern unit of energy, the Watt (which ironically replaces horsepower), is named for him. 

Many electrical appliances indicate the wattage or amperage. 

Most appliances have a label indicating the wattage or amperage. This is the key to determining if it can be used in your off-grid abode. This typical blow-dryer, for instance, uses 1875 watts. Divide that by its rated voltage, 125, and you see that it'll require 15 amps. If you run it for an hour, you'll need an 15 amp-hour, 125 volt, battery. If you run it for five minutes then you'll need five-sixtieths of that or 1.25 amp-hours at 125 volts. 

Don't bother shopping for a 125 V, 1.25 Ah battery. First off, they don't exist (you could make one, but that's for another post). Secondly, note where the yellow arrow is pointing - you need alternating current, AC. We'll get to that in a moment. Thirdly, you shouldn't discharge batteries all the way - that'll greatly shorten their lives. There are exceptions, but off-gridders typically use lead-acid batteries, the usual ones found in cars, except designed for deeper discharge. What that means is that your battery load shouldn't exceed 10% of its rated capacity. Stated another way, multiply your power requirement by 10. So now you need a 12.5 Ah battery. Here's one (14 Ah, but close enough) on Amazon for about $65, with shipping (they are heavy). 

Now we have to bring in one more character, but we're saving the best for last - Nikola Tesla. 

Tesla on the (former) Yugoslavian 100 Dinar note
 featuring an actual equation and a motor schematic. 

Tesla was the exponent of electrophysical eccentricity but he wasn't born into wealth. He was a brilliant scientist and inventor and somehow figured out that alternating current was a more efficient method of transmitting electricity. This concept is so counterintuitive that it took a mind like Tesla's to think of it.  

Batteries produce direct current, DC. Back to the highway or river analogies, it's obvious that all the little water molecules are moving in the same direction, as are the cars on the freeway. Tesla somehow realized that electrical energy can flow rapidly back and forth, and by doing so it can be transmitted at high voltages and low current. As the electrical energy got closer to the user, it could be fairly efficiently converted into lower voltage and higher current. That's the system used for electrical grids around the world today.  

Now back to the blow dryer. It is designed for home use, therefore it runs on AC. If you plug an AC appliance into a DC circuit, it won't work and it may break. Fortunately, there's a device known as an inverter that will efficiently convert DC to AC.

This is a 2500W inverter, about $180. You connect it to your battery and there are outlets on the back to plug in household appliances. So now, for about $250, we have a battery and an inverter. All we need is a solar panel to recharge the battery.

Recall that all we're doing here is running one blowdryer for five minutes a day. We'd need more capacity to use other appliances, but the process is similar - find the energy consumption, estimate the daily use and add it up. Size your system for at least that, typically you'd triple your calculation to account for overcast days when solar panels aren't too effective. Solar panels come in many sizes but for our blowdryer application we'd need one that'll recharge the battery in a day. 

We've consumed 156 watts by running the blowdryer - that's 1.25 Amp-hours at 125 volts, as previously noted. Our little 10 watt solar panel would need nearly 15 hours of sunlight to recharge the battery. So that's out. But Instapark sells a 30 watt panel for $100, and 5 hours of sun is a more practical target. 

Now we're done with powering the blowdryer, total cost is $350 for the battery, panel and inverter. I don't see the business case in those economics, but a lot of people can't survive without a blowdryer, so perhaps its worth it. A more useful appliance, say a refrigerator, would involve a similar process. 

This is a Sundanzer DCR50, $650. It's quite small, about 2x2x3 feet, but it runs on 12v DC and only uses 9.6 Ah per day, 114 watts. That's less energy to run a refrigerator all day than using a blowdryer for just 5 minutes. The most important part of off-grid energy design is to research the energy requirements and buy the right appliances! You wouldn't need an inverter to run this, just a 100 Ah 12 v battery ($200) and the 30W solar panel mentioned above. The whole setup costs close to $1000, but you'll be completely independent of the power grid. 

Comparing the energy use of appliances gives an idea of how long they can be powered off of a battery. It's not an exact calculation because there are inefficiencies in any power distribution system, even a USB cable connecting a cell phone to a battery. But you can account for that. The lowest power consumer in this post is the desk lamp. It puts out a lot of light - equal to at least a 60 watt light bulb (back when those were legal). But it only draws 1.25 watts. Dividing that by its voltage (it's a USB device, so it runs on 5 volts DC), yields 0.25 amps. We'll use milliamps to eliminate the decimal, so multiply 0.25 times 1000 (milli) to obtain a handier value, 250 milliamps (mA). If you run the lamp for an hour, you'll consume 250 ma per hour, or 250 mAh. 

Anyhow, the battery pack way up at the top of this post has a capacity of 5200 mAh. So, it can power our lamp - theoretically - for 5200 mAh divided by 250 mA, or 20 hours and 48 minutes. In practice, the battery may be over-rated (companies are known to fudge the numbers for marketing purposes) and the lamp may draw more than 250 mA for the same reason. So you always knock down the value to be on the safe side, hence the classic engineering term 'safety factor'. I think the lamp would be good for at least 15 hours. That's rather impressive, by the way.

As for the iPhone, it consumes a variable amount of energy depending on the applications it is running, the type of cell network (phone calls and roaming increase power consumption) and screen brightness. The range is 0.7 to 2 watts, divide that by volts (it's a USB device, 5 volts) and you get between 140 and 400 ma. So our battery pack can power the phone for 13 to 37 hours, depending on usage. That's also rather impressive.

The same calculations can be done with the higher power devices. The refrigerator (9600 mAh) can't run off the Instapark battery because the battery only produces 5 volts. Also you'd be discharging the little battery so quickly that you may damage it. The 100 Ah battery referenced above will theoretically run the refrigerator for 10 hours but in practice you shouldn't do that as it'll wear out the battery. This is the reason people add solar panels and batteries to their systems, in addition to increasing capacity the systems last a lot longer.