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Hot Pot is a great solar cooker, but was designed for the Tropics
on April 7, 2011
The Hot Pot Solar Cooker, specifically the original 5-liter model with the folding polished aluminum reflector (as sold here) was primarily designed for the third world and developing countries, to function most effectively in the Tropics, between the Tropic of Cancer at latitude 23.5°N and the Tropic of Capricorn at latitude 23.5°S (=11.75° average latitude). This amazing device allows for a 6 hour cooking window, on a typical day, in impoverished areas that often have meager resources for fire and cooking.
But most of those who purchased the solar cookers, specifically the original 5-liter model, partially subsidizing Hot Pot ownership in the third world, live in the Temperate Zone (=45° average latitude). And we are often frustrated with the short 2-4 hour cooking window, and that is usually only during the summer months, as well as difficulty in reaching optimum cooking temperatures.
The issue here is that the optimum solar cooking angle of the Hot Pot folding aluminum reflector is 65° (90° is the sun directly overhead, 0° is the sun on the horizon, shining into the front of the Hot Pot cooker), as measured from the shiny flat aluminum base the Hot Pot rests on. And tilting the Hot Pot and reflector together to focus on that optimum 65° solar angle, to really get things cooking, is a messy and dangerous juggling act. For example, where I live, I have to often tilt the reflector, with a full Hot Pot, about 30°, until the hinge of the angled front reflector is parallel the the ground.
But it's not as simple as latitude. But do this simple Google search to find this handy global map:
"world_solar_insolation_data" (but don't key in the "")
The map shows the amount of effective solar energy, in hours, received each day on an optimally tilted photovoltaic panel surface during the worst month of the year (based on accumulated worldwide solar insolation data). But, with the Hot Pot solar cooker, the hours posted on the global map can, likewise, be fairly accurately taken as the effective daily cooking hours, during the best month of the year. This quickly explains why Hot Pot owners in Arizona and New Mexico give glowing reviews of this device, while Hot Pot owners in America's southeast states (same latitude), or Brazil, or Spain or China, quietly repack their Hot Pots and ship them back the their retailer.
But to get to the point, be sure to heed the "world_solar_insolation_data" chart. If you live in a region that has 2.0-2.9 solar cooking hours a day, or less, during the warmest month of the year, taking out and using your Hot Pot will be a rare, and disappointing, culinary event.
The "world_solar_insolation_data" chart indicates, for example, 3.0 - 3.9 solar cooking hours, a day, during the best summer month of the year, for my area. So I should be able to cook, maybe, through May, June (warmest month), July, and halfway through August. But for simply heating up water, the Hot Pot season is from April - mid-September.
When using my Hot Pot, I really want to make the decision, to cook, the day before, so as to be able to plan my meal, and maybe invite dinner guests. And that decision is based on living in a suitable zone on the "world_solar_insolation_data" chart, the time of year, and favorable weather forcasts: Mostly sunny skies, with a minumum temperature, at high noon solar time, of 70°F, and a minimum solar elevation, at high noon, of 65°. This information is transferable to those in other latitudes.
If the "world_solar_insolation_data" chart indicates that you live in a region that is favorable Hot Pot cooking, you'll then need to find out what months of the year that you can use it: For your seasonal altitude of the sun, the University of Oregon offers their "Online sun path chart program". It's the simplest, and most intuitive, I've found.
But do this simple Google search to find the University of Oregon Solar Radiation Monitoring Laboratory's Sun Path Chart Program:
"Online sun path chart program" (but don't key in the "")
At their site, enter the information for your area:
*Latitude (decimal degrees)
*Longitude (decimal degrees)
*(south latitude and west longitude are given in negative degrees)
or... ZIP code, instead of Latitude and Longitude
Your time zone
*Plot dates 30 or 31 days apart, between solstices, December through June
*Plot dates 30 or 31 days apart, between solstices, June through December
*(only select one at time, for the printout)
Plot hours in local solar time
I simply use default:
Extend azimuth axis from 0° to 360°
Extend elevation axis to 90°
Show hours in AM/PM style
I generally title it:
"Noon Solar Altitude for"
"(your City, your State)
Default: Place label in upper left corner
PDF (Portable Data Format)
Simply enter the posted verification code
This will generate, after two times through the steps above, two landscape, 11" x 8.5" charts that show the angle of the sun, at high noon (solar time), in your area, for different months and days throughout the year. Don't be distracted by the hours on the chart, as high noon is the only position you should be concerned about.
90 degrees, on the chart, is directly overhead. 0 degrees, on the chart, is on the horizon.
With this information, the optimum solar elevation, as well as optimum cooking window, in the Temperate Zone will usually begin at about 10:00am, solar time, and end at about 2:00pm, solar time, but afternoon temperatures are usually warmer than mornings, so an adjusted cooking window of about 10:30am to 2:30pm may be in order.
Well aware of the performance issues, a new Hot Pot solar cooking kit is now being manufactured, and introduced to those in the Temperate Zones. It includes the original reflector, but now a much smaller, 3-liter black enameled steel pot. The clear glass lid seems to be the same size as the original 5-liter kit, but the 3-liter steel pot and clear glass bowl is much shallower, and with a much lower profile. If you live in the Temperate Zone, just be sure that you're ordering the new 3-liter version. Many Hot Pot enthusiasts, in the Temperate Zone, report success when cooking in a half-full 5-liter Hot Pot. But, still, many online vendors have temporarily suspended, or dropped the product because of 5-liter Hot Pot's inability to perform well in the temperate latitudes. In fact, when I received my 5-liter Hot Pot shipment, I noticed that the protective plastic film had been removed from the polished aluminum reflectors, indicating that it had been a returned item. But I didn't complain, since it was a discount purchase.
So, to cook with the 5-liter Hot Pot at my house, in the Temperate Zone (latitude: 37.5° north), I had to resort to drilling out a 1/2" diameter hole, in the center of the flat reflector base, 1-3/8" forward of the very center. I then drilled out a 3/8" hole in the center of a sturdy four legged wooden foundation, from an old chair, and inserted a 6-1/2" long, 3/8" threaded lamp pipe, vertical (perpendicular to the ground), with the Hot Pot resting on very top of the pipe, on an inverted round black steel lamp base, bolted to the top, that conforms to the glass bottom of the Hot Pot. The jet-black makeshift lamp base actually is the hottest spot in the cooking process, as the water begins to boil there, as well as intense heat rises up from the metal base and into the 1/2" double-wall area of the bowl. Capitalizing on this effect, I spray painted the upper 1-1/2" of the threaded lamp pipe, as well as the supporting nut and washer, jet-black. The folding aluminum reflector can now safely be periodically tilted and turned to focus the sun's rays, while the boiling Hot Pot firmly and safely remains stationary. This provides a potential for a 3-5 hour cooking window, depending on the time of year and latitude. I would upload photos of my rig, but it would only create confusion and misunderstandings with Amazon.com customer service.
But do this simple Google search to find my webspace with the photos and the details:
"hot pot solar cooker instructables" (but don't key in the "")
With this setup, I am able achieve the best results possible, for the latitude. For example, on a sunny day, no clouds, light breeze, April 5th, northern hemisphere, 37.5° latitude, I poured a gallon of 60°F water into the Hot Pot, the ambient temperature was also 60°F. I chose to test one gallon of water, as I see no sense in solar cooking, for hours, to cook a half-gallon meal:
Above times are solar time. And, with these results, it's obvious that, where I live, I'll only be able to solar cook, maybe, 4 months out of the year (May - August). The solar altitudes were included on the chart so anyone can apply these results to wherever they live on the planet. And while one can always tilt and rotate the Hot Pot to track the sun at the optimum 65° solar angle, the solar cooker becomes less and less effective as one moves away from the equator, since the sun's rays are filtered out and weakened by more and more of the atmosphere as the altitude (angle) of the sun decreases. Ambient temperatures were also noted, as that will prove to have a major effect on cooking times.
I suspect that the maximum heating capacity of the Hot Pot, filled with a gallon of water is, mavbe, 105°F above ambient temperature, since the Hot Pot is not an insulated type of solar cooker. Many Temperate Zone Hot Pot users report that their solar cookers can maintain temperatures of 250-300°F, and even a maximum of 350-400°F, but I've found that those temperatures are only possible in an empty Hot Pot, and pointless information to post and circulate. Wind conditions also reduce the heating capacity of the Hot Pot.
The hot water, from the solar cooker test, was poured into a one gallon glass-lined vacuum airpot. A stainless steel-lined vacuum airpot, while far more tough and rugged, simply does not hold their heat for more than a couple of hours. But a glass-lined vacuum airpot will keep my hard-earned hot water, hot: Scalding hot 24 hours later, hot 48 hours later, and warm 72 hours later. A 3/4 gallon airpot of warm water may not sound like much of a resource, but someone in a developing country would be able to completely bathe, shave, and rinse off, and also hand wash and rinse their clothes from the day before. 3-day old warm water can also be much more quickly brought back up to boiling temperature by pouring it back into the Hot Pot and reheating it. A real convenient feature of airpots is that they have a convenient push-button, or lever-pump, top that allows it to function as a portable hot water faucet, to be placed throughout a summer cabin in the kitchen, dining room, bathroom, or generously loaned to a neighbor.
Some Hot Pot owners, in temperate latitudes, report success by fashioning a clear plastic oven roasting bag and stretching it over a lightweight frame, forming a reusable, snug-fitting cover over the reflector. I may try that method, but am not wild about adding clutter to the process, although it could provide strength and rigidity against wind gusts. Other Hot Pot owners suggest preheating the black metal cooking pot and its contents to a full boil, on the kitchen stove, and then taking it outside and placing it inside the clear glass bowl and lid, inside the reflector. Oh puhleeze! What's the purpose of solar cooking, if one has to burn fossil fuels to prepare their meals. Really.
But one still has to respect the heat output of the Hot Pot reflector. Always wear sunglasses when using the device, and it's sometimes necessary to turn the reflector 180° away from the sun when stirring the pot and making certain adjustments. The raw sunlight radiating out from the reflector sometimes feels like a blast furnace, not to mention the insanely bright sunlight in the face. And never leave the Hot Pot solar cooker unattended, as children are naturally attracted to it. The Hot Pot solar oven is an excellent first solar cooker project for the beginner, allowing one to practice the basics of solar cooking safety and precautions, before moving up to larger, and potentially more dangerous solar cookers.
Stay posted for late spring, summer, and early fall boiling tests, as I'm eager to plan delicious dishes on the optimum cooking days, once I find out which days, and weather, is most promising.