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| DO YOUR HOMEWORK BEFORE WASTING YOUR TIME. |
A good friend of mine shared an article with me of a DIY wind turbine this morning, that I've actually seen several times before. I have to admit that I hadn't checked out the article before now, simply because by looking at the picture of this device it's easy to see that it has problems, and isn't really capable of supplying much energy for your homestead. Every once and a while there is a posting of some kind of an energy producing or home heating device that "Makes the rounds" here on the internet with wild claims about it's energy production or use and people seem to believe these claims because well "Everything you see on the internet is true." Right?
The thing that we have to remember is that the simple laws of physics apply to these things, and without using our knowledge of these constants, we're wasting our valuable time on the Homestead on building devices that can't work. Another of my perennial favorites, for example is the candle inside of two clay gardening pots. I could do an entire blog post describing how these devices may
make you "Feel" a little warmer because they can put off a little radiant heat to warm your body, but you can't heat a room with one..... End of story. I've done all the calculations and trust me it would take so many of these heaters to warm a room that there wouldn't be enough space left for you to walk around. A candle can produce less than 450 BTU's and that's it.
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| "Flower pot, candle heaters" won't heat a room!!! |
The wind generator made from a car alternator that you've been seeing on your "Facebook feed" has a number of problems, that I'll try to explain (Warning there's some math involved, but I won't go into it, in detail so that you don't have to burn up any brain cells. Otherwise if you haven't yet had your morning coffee, it could be fatal. :) ) The first glaring mistake with this wind generator is that the author uses an automotive "Fan Clutch" to connect the blades to the alternator. A fan clutch is designed to prevent the cooling fan on your vehicle from running and save on your fuel economy, when it's not needed, There are generally two types... One spins all the time, but at 30 to 60% of the speed of the water pump on the vehicle, and the other works on a thermostat. The thermostatic kind is disengaged until it's thermostat senses air coming off of the radiator at usually around 170 degrees Fahrenheit. Obviously unless you live in an oven, this won't work. The fan will spin, but not the alternator, or if the alternator is spinning, it's running pretty slowly.
The other glaring problem with this design is that they are using the radiator fan for the "Rotor" of the wind generator. Automotive engineers are a lot smarter than you and I are, and they spend a hell of a lot of time designing the parts of a vehicle. Radiator fans are designed to serve a very specific purpose.... Efficiently grab air, and suck it through the radiator to cool the engine. Sometimes they're even designed to imperceptibly flex at higher "RPM's in order to perform better at high speeds. Unfortunately, they aren't designed for the opposite, or catching wind to collect energy from it. In fact when you think about it... They're designed to live in a whole different little world than a wind generator. They have the horsepower of a powerful engine available to them, sometimes even a big
honking V8. They may be spinning at tremendous "RPM's". Even at idle, your car engine is running at 1100 RPM's, while a wind turbine might only ever reach a couple of hundred "Revs".
I said before that I wouldn't go into the math but if you wan't to have another cup of Java, and play with numbers here are some formulas. The "Swept area" of a wind turbine or the circle that you wouldn't want to stick your private parts into while it's spinning... Is calculated by using this formula... πr². The amount of energy you can get from a swept area at a given wind speed is calculated by using P= p x A x V³. (π is "Pi" or 3.1415, R is the radius of your blades, P is total watts available, p is density of the air which is about 1.225 kg/m³ at sea level, A is the swept area, and V is the velocity of the wind.) If you don't want to do all the math, here's an online calculator... http://www.ajdesigner.com/phpwindpower/wind_generator_power.php If you drink lot's of coffee, maybe have an energy drink, and suck down some espresso, spending a bunch of time with the math.... Some interesting stuff begins to show up! "Swept area" is important! If you increase the size of a wind turbine from say 9 feet in diameter by just one foot, the swept area increases by over 23%!!! What this means is that you just can't get much power from little blades (Typical radiator fans?) If you double the wind speed, you get a whopping 8 times more power! Here's a chart of the watts you could snag from different wind speeds, using different diameters that I captured from http://otherpower.com/ for you. Notice that with a 4 foot diameter blade (Big honking semi-truck radiator fan,) you would only get 60 watts from a 14 mile per hour wind. To make matters worse, there are lots of inefficiencies, so you can only expect about a third of the total energy available from the wind. Bottom line... The best you can get from a radiator fan on a fairly windy day, is about 20 watts!
The other glaring problem with this design is that they are using the radiator fan for the "Rotor" of the wind generator. Automotive engineers are a lot smarter than you and I are, and they spend a hell of a lot of time designing the parts of a vehicle. Radiator fans are designed to serve a very specific purpose.... Efficiently grab air, and suck it through the radiator to cool the engine. Sometimes they're even designed to imperceptibly flex at higher "RPM's in order to perform better at high speeds. Unfortunately, they aren't designed for the opposite, or catching wind to collect energy from it. In fact when you think about it... They're designed to live in a whole different little world than a wind generator. They have the horsepower of a powerful engine available to them, sometimes even a big
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| The "Swept area" of a wind turbine. |
I said before that I wouldn't go into the math but if you wan't to have another cup of Java, and play with numbers here are some formulas. The "Swept area" of a wind turbine or the circle that you wouldn't want to stick your private parts into while it's spinning... Is calculated by using this formula... πr². The amount of energy you can get from a swept area at a given wind speed is calculated by using P= p x A x V³. (π is "Pi" or 3.1415, R is the radius of your blades, P is total watts available, p is density of the air which is about 1.225 kg/m³ at sea level, A is the swept area, and V is the velocity of the wind.) If you don't want to do all the math, here's an online calculator... http://www.ajdesigner.com/phpwindpower/wind_generator_power.php If you drink lot's of coffee, maybe have an energy drink, and suck down some espresso, spending a bunch of time with the math.... Some interesting stuff begins to show up! "Swept area" is important! If you increase the size of a wind turbine from say 9 feet in diameter by just one foot, the swept area increases by over 23%!!! What this means is that you just can't get much power from little blades (Typical radiator fans?) If you double the wind speed, you get a whopping 8 times more power! Here's a chart of the watts you could snag from different wind speeds, using different diameters that I captured from http://otherpower.com/ for you. Notice that with a 4 foot diameter blade (Big honking semi-truck radiator fan,) you would only get 60 watts from a 14 mile per hour wind. To make matters worse, there are lots of inefficiencies, so you can only expect about a third of the total energy available from the wind. Bottom line... The best you can get from a radiator fan on a fairly windy day, is about 20 watts!
Another problem with our car alternator wind turbine is that alternators are designed to work at high RPM's. I built a little generator out of one connected to a lawn mower engine a couple of years ago, and one glaring thing that I found out is that the little lawn mower engine has to be going wide open in order for the alternator to produce much power. You can't get that much in terms of rpm's out of a wind turbine.
So there's a lot to consider when thinking about harnessing wind energy for your homestead! Begin by understanding that you have to have a pretty big 'Swept area" to get any useful power. Blades have to be designed to specifically "Capture" wind energy, not "Push" air at the end of a V8 engine. Don't be fooled by manufacturers claims of high wattage from small wind generators (They're telling you about hurricane force winds.) You have to have a large bladed wind turbine, on a high tower, with a generator designed for a wind turbine to get any useful energy on your homestead! If you want to build your own wind generator, a good place to "School yourself" is at the Otherpower web site ( http://otherpower.com/otherpower_wind.html) It's put up by a bunch of guys who've done a heck of a lot of experimenting with wind power..... I hope I've helped you here with your "Wind power efforts" on your homestead!!!
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