A Tinker's Handbook
A handbook of ideas, methods, conversion factors,
for the budding technomage.
Don't just think, Tink!
This is a work in progress, so far in no particular order.
Copyright by Fatcat the Tinker!
All technology has the potential for harm. Before you build or design something think about what the end results will be.
What will happen when a Dumb Ass gets their hands on something you have cleverly designed or built?
People are human, they will screw up.
Try hard not to make something that is
to cause harm sooner or later.
Put guards on rotating machinery.
Insulate and cover electrical connections.
Don't use materials that are dangerous if they get loose.
They will get loose.
Guard areas like the collector of a solar oven so potential harm to a child or adult is reduced.
Chose the way of doing something that is inherently safe.
Remember even you at times are a Dumb Ass.
Think before you Tink
The Sun, when its shining, provides us with all the power we need. The problem with solar power is that it doesn't always shine. So Remember that without a way to store heat or electricity, solar is a fair weather friend. And there is always that odd month when the temperature drops to -20 F and pretty much stays there and the sun is not to be seen. And every night it goes behind the planet.
Power is discussed in this book as watts, an electrical measure . Look on any electrical appliance to find its watt rating. I use Watts instead of BTU because I have a more intuitive grasp of watts than BTU. I know how hot a 100 watt light bulb is. Multiply BTU by .293 to get Watt hours. To convert watt hours to BTU multiply watts by 3.414
When thinking of solar heat it is useful to remember that out here in the Colorado countryside 10 cents buys 1000 watts for one hour, or 1 kilowatt hour of electrical energy.
A little one cubic foot electric space heater uses around 1000 watts, or one kilowatt of power and it will heat a well insulated bedroom fairly well. When it gets colder you will need to shutter the windows so the very high power loss through the glass doesn't suck heat faster than the little heater can dump it . When it's cold and the little heater has to run except for the 8 hours of bright sunlight when the windows heat the bedroom, that's $1.60 for a days worth of heat for the bedroom.
One square foot of collector receives about 65 watts of power when it faces the Sun. Since there will always be losses, figure that as 50 watts per square foot and you have a good place to start when figuring heat gain. So a large 3 foot by 7 foot glass door gathers about as much power as the little heater puts out.
For solar electrical, figure about 10 watts per square foot for the better solar electric panels. Use the numbers given by the panel manufacturer for closer calculations. It may be the specs are 10 percent higher than reality.
The potential for obtaining useful power at very low cost with an solar collector is amazing if you give it some thought. An acre has an area of 43,560 square feet, x 50 watts = 2.8 million watts. At .10 a Kilowatt hour that's $280 an hour, easily $2000 worth of power on a cloudless day, warming that acre. All you need is a cheap way of using that low grade heat to reap that harvest.
No one has figured out a good enough way to do it yet for commercial solar electrical power to really take off. There are commercial installations for providing heat and hot water for hotels and they exceed break even money wise, although they are not yet popular.
Near Colorado Springs a very well insulated, draft free house with no windows on the north wall and and normal sized expensive low heat loss windows will have very low heating costs. The solar heat gain through the windows does most of the work.
You can easily build a solar cooker to cook meals.
For heating or powering things you have a choice between:
An opportunistic collector
A flat plate collector
A concentrating collector
An opportunistic collector can be accidental. When I was living in a old school bus one summer I ran a 300 foot 1/2 inch dark coloured hose from the well to the bus. It turned out that my girlfriend and I could get a shower by squirting each other just enough to get wet, turn off the pump, soap up and then turn the pump back on and rinse off before the cold water from the well reached us. At worst the water temperature was air temperature and with any sun the temperature was perfect for a quick shower. Be careful, even this simple set-up could overheat. Check the temperature before you jump in your shower. A long enough supply hose to a campsite could give continuous very warm water when the sun was out.
Use the world for your collector. If water coming into your hot water tank is 55 degrees you have to heat it all the way to 104 degrees F to get a hot shower or bath. If you run that incoming water through a car radiator with a blower forcing outside air through it on a warm day the temperature to the tank will be much higher so you will have to heat the water much less or not at all. This system uses the miles of warm land around you as the collector.
During the summer when the attic is very hot, a blower forcing that air through a small heat exchanger would heat water quite well. It takes a lot of hot air to heat water, but there is a lot of hot air in an attic.
The attic set-up should give you all the hot water you need on a warm day. The normal roof is about 1000 square feet. 1000 x 50 = 50,000 watts or 50 kilowatts. That's a lot of power.
A Flat plate collector is just that, a flat plate with the sun shining on it. You have seen its effect when you laid your hand on the roof of a black car at noon. Wow! Put a plate of tempered glass in front of it to reduce heat losses and you have the basic design.
Its temperature will rise until its hot enough that it radiates heat at the same rate it is receiving energy from the sun. Any drafts will suck off heat and the temperature will drop.
A flat plate collector is simple and does not need to track the sun at all if you are not too concerned about efficiency, works well if the output temperature doesn't need to be high and the outside temperature is not too low.
Take a old bathtub and throw a dark towel inside, fill it , drape a sheet of plastic over the top. Insulate the sides somehow. Fill it in the morning with 55 degree water from the well and at the end of a summers day you will be able to take a bath in warm water. It doesn't get much simpler than that.
Receivers are used on focusing or concentrating collectors.
A receiver is nothing more than a flat plate collector placed to catch the reflected sunlight from mirrors. It may have a piece of tempered glass in front of it to keep the breeze off the plate to reduce heat loss and reflect some of the heat radiated by the flat plat back to it to further reduce heat loss. The back is often insulated with something that will not melt or catch fire. Water pumped through the collector carries off the heat to do useful work. When the pump fails the water boils or flashes into steam and you will have problems. Possibly catastrophic problems.
Focusing or concentrating collectors are more complex, have to always track the sun, and will quite possibly fry themselves if you don't pull heat out of the receiver fast enough. They easily give very high temperatures.
A full focusing collector uses a highly polished spherical or parabolic reflector and gives the highest heat concentration. It actually reflects a small image of the sun on the receiver. Its good for melting things, starting fires, burning yourself and damaging your vision. You probably really don't want one one unless your are trying to melt something. Besides that, curved mirrors are much more expensive.
A half focusing collector is good for heating pipes and hot dogs. Simply bend a flat mirror to get a cylindrical reflector or parabolic reflector. Remember that the focused sunlight is still extremely intense at the focus where the receiver (hot dog) sits. Not quite as dangerous as a full focusing collector, it gives a long line of very intense heat at the focal point.
A Non focusing concentrating collector uses
2 or more flat mirrors reflecting sunlight on the receiver. Size the mirrors
the same size as the receiver. The power hitting the receiver then equals
the total power hitting the mirrors minus some loss. If the mirrors are
mounted separately from the receiver and driven by motors to track
the sun then the system is called a heliostat. Its cheap, it works and
danger is greatly reduced if the number of mirrors is kept small.
Room temperature water in a black
cup measured 125 degrees after 1/2
hour. I had to move the two outer
mirrors once to keep the reflected
sunlight on the black cup. The
temperature stopped rising at that
point so I drank the tea after the
handle had cooled enough to hold. Just
One foot mirror tiles sell for .$50 to $1.00 each.
Nine one foot mirror tiles mounted on a piece of plywood so they reflect to the same square foot give us 450 watts, probably just enough to fry with. If all the heat goes directly into the bottom of a skillet, then the numbers should work.
Nine suns density of energy is plenty dangerous, but not as dangerous as the hundreds or thousands suns density of half or full focusing mirrors. Keep the focus short so that the space where eye damage might occur is restricted. A long focus is more like a death ray. Good for accidentally setting your house on fire.
Focusing or concentrating collectors must not be used where children may wander through the focus. Adults do stupid things too. Guard the focus somehow so that no one/anything, is harmed. One of the problems with large high concentrating collectors using a target on a tower is that it blinds and sets birds on fire. They don't understand what is happening and so don't stay out of the focus.
Don't concentrate more than you need to. Enjoy the cost advantages of a small but not tiny receiver and lower cost for materials and avoid the danger and difficulty of designing the receiver with very concentrated sunlight.
Little is to be gained on a larger concentrating system by individually pointing 1 foot mirrors. You have to do more work to point all the little mirrors and may end up with hot spots on your tiny flat plate. Tracking becomes more of a problem. On a larger system consider mounting the cheap one foot mirrors flat on however many 4x4 sheets of plywood and then use as many of these built up 4x4 mirrors as you wish to point at a 4x4 receiver.
A few words about solar box cookers:
This information was gleaned from several years reading the solar cooking list.
Yes, you can get food poisoning if the food temperature stays in the range bacteria can grow in for too long. Don't get the food just barely warm and keep it there for hours.
A solar box cooker is a insulated box with a glass top. Food is cooked inside a pot sitting in the box.
They work great on sunny days once you figure out the construction details.
Insulate the sides and back with insulation that won't melt or out gas fumes.
Use tempered glass or risk the heat cracking or shattering the glass.
Line the inside sides with aluminum foil to reflect heat onto the cooking container. Experiment has shown this works better than having the interior of the box all black.
You might want to slant the sides at 45? degrees so the light reflected off them hits the pot. This should (?) increase the heat delivered to the pot, but is apparently not important enough to become mentioned often. A series of experiments could put this question to rest.
Paint the inside bottom black or better, put in a thin sheet of black metal 1/2 inch above the foil lined bottom.
Make it fairly airtight to keep heat in. Less airtight if the glass fogs up. Make the fit of the glass accurate so the heat stays in. Don't use rubber gaskets, they may melt.
Use a lighter weight food container so you don't waste time heating the container.
Black food containers work much better than shiny ones, if you paint a container use heat safe non toxic paint. Dark tinted oven glassware also works well.
The smaller the weight of the food and water, the quicker it will come to cooking temperature.
Available power to heat the food goes up with the size of the window opening and the number of outside reflectors.
Put an oven thermometer inside your pot so you know how its working.
Use a roast thermometer to see how the food temperature is doing.
The empty pot temperature will be higher than the oven temperature after a while as the black pot is really the heating element in the box. Light not reflected turns into heat. The pot also gets heated by the heat rising from the black bottom, from the top by the sun, and from 4 sides (with luck) with sun reflected off the sides.
Food in the pot absorbs heat from the pot sides. So liquid food will keep the pot sides cool till the water has time to heat and will get no higher in temperature than the boiling point of water.
Chunky drier foods, like a potato or meat chunk, will be heated by the heat radiated from the sides of the pot and convected through the air inside the pot. So this type of food will be heated as if it was in an oven, the pot being the little oven. So the sides of the pot may get well above boiling while the food temperature will stop rising at the boiling point. Given long enough the food starts to brown or burn when most of the water is boiled out of it.
Keep it facing the sun.
The experts have it all at:
Books: "Direct Use of the Suns Energy" by Farington Daniels is the best book I have run across after 30 years of reading on solar energy. I've gone through 4 copies of it, read it many times. Don't loan it out unless you have 2 copies... If you run across a better book please let me know.