Alternative energy advice from Ask Jeff Yago. Volume #12

Ask Jeff Yago
Solar & Energy-Related Issues

By Jeffrey Yago, P.E., CEM
Jeff Yago

Sorry. Jeff no longer answers questions online

Corn stoves


Why do some people use crushed oyster shells with their corn stoves?



Some people who have been heating for years with a corn stove swear adding alayer of crushed oyster shells in their corn stove burner reduces ash and promotes cleaner burning. I am not sure how well this works, as I perfer putting the whole oyster over the flame. Makes a great snack!


Heating a four-season room

Dear Jeff,

We recently built a 14×18 four season room on top of our deck, which is about 4′ of the ground. The builder told us our four season could be used all year round in Michigan with exception of maybe two months in the winter.

Well, I don’t really find that to be very true. The room has a R-13 insulated roof, and glazed full length glass window/walls. I was wondering how we could heat it efficiently (and easily)? We have access to get under the room. Any suggestions?



I think I ran into your builder on the Internet trying to sell the Brooklyn Bridge. As you found out, this arrangement will NEVER provide enough solar heat in the winter to keep it warm, and you will soon find out the greenhouse will be about 120 degrees in the summer! The reason is the fact that you built above ground and have very little insulation or thermal mass in the floor or rear wall. We install R-19 insulation in walls and floors and R-32 in ceilings – and that is in Virginia where it almost never gets really cold.

We have been in our solar home now since 1994 which includes a 24 X 12 greenhouse having double-glass construction and is TOTALLY heated by the sun, and still does not over-heat in the summer. Yes, it does get down to around 50 degrees in the greenhouse on a winter night which seems freezing to me, but most plants are fine for even lower temperatures.

The secret is, I built the pre-fab greenhouse against an exposed stucco over heavy concrete block wall of the south wall of the house, and the greenhouse floor is a 6″ concrete slab over a layer of gravel then 2″ high density foam insulation board under the slab and around the perimeter baseboard walls. The sun heats up this heavy mass all day, then this mass will give up its heat at night to the cooler interior air. In the summer, the high mass absorbs most of the daytime heat which keeps the greenhouse from overheating.

Without lots of thermal mass in addition to insulation, all you really have is another room on your added to your house that has lots of windows, which you will need to heat the same as other rooms. Many plants do not like fumes from open propane or gas heaters, so be careful what you use to provide the heat. The best type of heating for many plants is to heat under or in the bottom of the dirt beds to warm their roots which can allow much lower room air temperatures.

I like hydronic heat for greenhouses, but plants like blowing air to keep their leaves moving. This also helps reduce insect problems, so if you use electric or hot water radiators, you may want to run a small circulating fan during the day.

If you do not plan to have plants, then you are free to use any conventional hot water, forced air, electric baseboard, or unit heating system.

Good luck!

Jeff Yago

Wind generator placement

Mr. Yago,

I am buying a Bergey 1kwh wind turbine. I have read for optimum performance the requirement is a 300′ circumference. If I can’t get 300′ how high above the treeline do I have to go to get clean air?

I am also wanting to place the turbine within 60′ of a cliff but a neighbor told me that was a no-no. I was told that the air I recieved would be turbulent air and not the steady air needed. As I am a rookie I would appreciate any advice you could give me.




For a rookie you have selected a good model to work with. Cliffs are fine – as long as you are on top of them! Your neighbor is correct, as a still living ex-commercial helicopter pilot I can tell you the “down wind” side of any mountain or cliff can be very, very turbulent. I have a wind turbine on my house that is very close to the tree line as I could not cut down my neighbors trees! Its not the best arrangement, but my wind turbine is still working after 12 years.

The real secret to wind turbines is height above ground. Anything less than 35 feet is a waste of time. Many residential towers are in the 75 to 125 foot range. The higher you are, the smoother and more constant the air flow, but this is ideal and most sites are a compromise. Just get as high as you can, and as far away from trees as you can, and stay away from the downhill side of cliffs and mountains!

Jeff Yago

Solar-powerd bike fridge?


Summary: Is it possible for a portable DC cooler to be made with a low (1-2) amp draw?

I am planning a cross Canada bicycle trip to promote clean alternatives (life style and technology). I plan to demonstrate solar power using 3x 1.2 amp (3.6 amps) solar panels on my bike (set up will likely allow 2/3’s effective aiming of the panels). I would also be using a 12 Amp/hr battery pack. (current target supplier for both is Modern outpost) (This is the current plan anyways – could be modified with a small trailer to a few extra amps of solar or battery but may not be worth it). I will be demonstrating other technologies and am willing to carry the extra weight with in reason.

I would like to be able to demonstrate a portable cooler as part of this setup. (as well as to keep me well fed on the 100 days).

Most of the small DC coolers I have looked at have AMP draws that are too High (3-5 amps) for what I envision. Are their other options (besides thermoelectric) Is a lower amp cooling system even possible? Should I keep looking or should I give up because no such beast is possible. Any suggestions for this type of set up?

Thank you

Drew Stevenson


First, as I just wrote in the last article on DC refrigerators, that you should not even think about a thermoelectric model, as these really have a hight amp draw that is constant, and they still do not cool that well. Although a compressor type refrigeration unit has a much higher amp draw, they cycle on and off and are not a constant load.

You may also want to re-consider your solar module plans, as any solar module large enough to do any real good will be like a sail on your bike in high winds (unless the wind is behind you!). There is nothing wrong with an ice chest, and if you take a really well-insulated model and then spray more foam insulation all over it, you should be able to keep food cold for 4 to 5 days at a time. This would demonstrate how energy in-efficient most refrigerators really are.

I suggest making or buying one of the small “trailers” you see advertised to pull behind a bike that have bicycle spoke type low-resistance wheels. I would build a very lightweight box with a hinged lid and have half for dry storage and half for the modified ice chest. I would mount a large solar module over the top of this trailer in the flat position while riding. When you stop anywhere you can tilt up or re-position this trailer so the solar module is facing directly toward the sun.

I would want at least one or two solar modules that total at least 40 watts (75 watts even better), otherwise you will not be able to power much more than an LED night light and radio. The battery should have at least 2 to 3 times the daily output of the solar module, which would be at least a 25 amp-hour gel cell. If this is too heavy, down-size everything, but you will not have very much useful power.

Kyocera is one of the few manufacturers that make an almost square solar module. Their 40 watt module would fit perfectly on top of a trailer this size.

Send a few photos and good luck!

Jeff Yago

Printable solar panels

Hello Jeff Yago:

I find your articles in BHM to be outstanding. Keep up the good work.

Recently stumbled into, and am wondering if you know anything about these printable solar panels they claim to be able to make. Since very little information is furnished on the site (and me being a bit of a skeptic), I am wondering if this is mostly hype.

If they can actually print solar panels that are cheap, reasonably efficient, and will stand up to the elements, that would be of great interest to many. Thought this might be an idea for one of your articles.


John Oler


Remember that old rule – you get what you pay for. I do not know about this specific product, but I do know all the major solar manufacturers have been trying for years to make solar modules without the high cost of slicing silicon crystal into thin wafers. The problem so far is, they can cut the cost of manufacture in half, but the results are modules having half the wattage. This means for a given wattage, you need twice the roof area, twice the number of modules, and end up with the same total cost and total wattage. There is a real mis-understanding out there that solar modules are made in some guy’s garage, and the prices will drop as soon as the start mass production. I have toured several major solar module manufacturer’s plants and they are almost fully automated and required millions of dollars in production equipment to get started. In one plant I visited, the first time the solar module was handled by a human was attaching the two wires on the back junction box when it was completed!

One manufacturer just closed down a major fully automated plant that was making solar modules by “plating” the silicon material on the glass like you chrome plate a bumper. Of course this requires many steps and layers to complete before a computer driven laser “cuts” the single silicon layer into separate cells. This is about as cheap as you can make a module, yet the output was only about 50% of other modules. SO far they have tried growing silicon crystals, using scrap silicon, producing the silicon in an endless ribbon, slicing crystals, you name it, but still not there.

I think you will see solar cell efficiency increase a few more percentage points every few years, but don’t expect the costs to drop very much, as the cost for copper, glass, and aluminum needed to make a solar module keeps increasing, and the electronics industries are bidding up the price for the limited supply of raw silicon.

Hope this helps,

Jeff Yago

Solar or Wind, that is the question


I am project director of a charity project that will be working in Togo, West Africa. We are building a schoolhouse which will have a few computer labs, with approximately 40 computers. We need only power lights, a few projectors, the computers, and video camera battery chargers. I imagine we could probably do this in under 1000 KWh/month, correct me if you think I’m way off. Anyway, the village we are building in does not have power, we intend to power the school and eventually create a grid for the entire village, or show individuals how to generate their own power.

For now I’m just trying to decide what is going to be the most effective, horizontal-axis wind generators, or solar panels. Eventually I would love to create a power farm to generate power for more than just our building. The land won’t be a problem for wind or solar. Togo is right near the equator, so it should be prime for solar, no?

From what I’ve read it looks like wind might be the cheaper route to go, but again, my knowledge is minimal on this subject.

Thanks for your help,

Dave Harding


Totally depends on location. Most people think its windy where they are, but actually its usually only certain areas that have a constant wind and this is usually high above the ground. Since a system like you describe will require inverters and batteries to handle those hours at night or no wind, you will have a large battery bank. The good thing is, both a solar array and a wind turbine can charge the same battery bank, so you may be better off having both. For your location the solar array can be almost flat so your could use as some kind of roof over a shelter or for shade. Unless you are on the coast, you will probably need a tower at least 50 to 75 feet high for a wind turbine unless you are where the wind blows your hat off the entire day at ground level.

Solar modules are expensive, but you can add to them without loosing what you already purchased. However, inverters, charge controllers, and batteries do not up-size very well so its best to size these for a much larger solar array so they will not be under-capacity when you add more modules later. For your location you may have about 7 to 8 hours of good solar, where we in the states usually find only 4 to 6 hours per day due to lower sun path in sky. Solar modules are rated for the type of intense sun you have, so you may not need to de-rate the modules. For example, a module with a 150 watt nameplate rating will probably have this output during 9 AM to 3 PM, and still have a good power output before and after these hours.

Example – Two solar modules, 150 watts each nameplate rating, 7 hours sun per day:

(2)(150)(7) = 2100 Watt-hrs = 2.1 kWh per day. Assume about 15 to 20% losses for charging batteries and another 5 to 10 % loss for dis-charging batteries under load. Of course if you use most of the power during the day while its being generated, you only losses is in the efficiency of the inverters, and these are fairly efficient, with an average of 8 to 10% loss depending on loading.

Work backwards to see what you need for the loads you are expecting.

Good luck,

Jeff Yago

Self-powered corn stove?

Hi Jeff:

First off, I love your articles. They have really inspired me, and I believe, helped me put my finger on my true calling. I'm a practicing engineer by trade, and a self-reliant country-boy by heart. I currently work in R&D in an off-road vehicle industry, and it just so happens one of my areas of responsibility is "alternate energy". That covers a lot of ground, and allows me to investigate a number of interesting areas.

My first question has to do with corn stoves. I live in the heartland where corn is one of the most abundant resources, as is proof by all the ethanol plants sprouting up. I love the idea of a corn burning stove, but for my purposes of back-up or off-grid heat, is not practical due to the electricity draw required for controls, blowers, feeders, etc. I'd like to own a self-sustaining corn stove that burns efficiently under its own power, and since I haven't found one commercially, am considering developing one on my own.....if it's possible. It would likely have to use stored energy (mechanical or electrical) during the warm-up phase, and then use its own heat to generate power and sustain itself. There a few methods I'm aware of that can convert heat into mechanical energy, and based on those I have a couple design concepts roughed out. Generally speaking, it appears within reason, but still lots of unknowns. Have you ever heard of such a contraption on the market? If not, what are your thoughts on the practicality of developing one? If it were developed and not too costly, do you think there would be any market demand for off-grid or back-up heat?

Question two, has to do with career path. I'm finding a real passion in the areas of energy and energy management, and want to pursue this direction. I have a graduate degree in mechanical engineering and 10 years industry experience, but am not PE certified. Can you give some advice or background on requirements to become a CEM, and what types of career opportunities are available in this area? Also, are there universities that offer programs of study in this area? With the inevitable energy crunch and alternate energy technology developments in process, "energy for self-reliance" looks like a good and exciting place to be for the future. If you could point me in the right direction, I'd be grateful.


Nick Hiser
Beatrice, NE


Lots of questions!

First, the last time I mentioned corn stoves in one of my articles I nearly had my head handed to me as someone out there thinks they are the ONLY stove that should be made and they will save the earth! Actually, my point was they are like all other stoves – they sell best where the fuel is cheap. Like coal stoves in coal country, wood stoves where its wooded, and yes, corn stoves where you can find a local supplier of corn.

I am not aware of a corn stove that does not require power for either a fan or a feed mechanism, but its also possible you are not alone it working on the problem. I have a neighbor with a wood pellet stove that swears by it – at least until she tried to heat her house during a power outage and it would not function!

Although the power requirements are very small for operating this type of stove, there is always room for new ideas. I can envisage one of those long wind up springs like they are using in those wind up emergency radios. You wind it up every 15 minutes or so.

As for becoming a “Certified Energy Manager”, you need to check with the Association of Energy Engineers:

The basic requirements are a 4-year degree (technical or engineering), written documentation of past work history in areas involving power, energy, thermal, utilities, or similar areas. They offer a week long very heavy duty class program ending with a several hour long written test. There is also an annual fee and the class and test run over $1,500. They offer job opportunities listings on their web site. If you think this is something that would help you then go for it. However, if you are doing some kind of “research” , inventing, or starting a business venture, these offer a very good education in their own right that may help you more. I have 5 U.S. Patents after working as a high school student for a true inverter who never made it past junior high. He had over 40 patents and sold each for lots of money. He told me each required many months of research and failed efforts before getting it right and he claimed each patent represented a college degree for him. He once told me “others read and learn from textbooks – but he writes the textbooks”.

I wish you success in your venture!!

Jeff Yago

Home Cooling without AC

Dear Jeff,

My husband and I are looking into independent home energy, and I want to know more about solar energy and cooling a home using large pipes. How can I cool my home using pipes buried in the ground? How deep do they need to be and what size would be good for a 1200 sq ft house?

Thank you,

Amanda Wood
Sandy Ridge, North Carolina


This method of “free” cooling goes back at least as far as the early Romans. It seems like every few years there is an article about a homeowner doing this do-it-yourself type project. Yes, it will work with limited success, but here are the problems you must over-come in the design:

1. The pipes need to slope so water will not collect and breed nasty things that will get into the air flow you will be breathing (think standing water with that funny green color).

2. The pipes must be large enough or you will require lots of fan power to move the air. Remember, air resistance verses pipe diameter is not a porportional relationship. For example, a 4″ pipe is not twice the resistance of an 8″ pipe, its more like 3 or 4 times higher than the next larger pipe size depending on flow rates.

3. The pipes must have enough length and surface area or they will suffer the same problem as an under-sized earth geo-thermal heat pump system – that cold below ground temperature will start to heat up after a few weeks of warm air or warm water it is in direct contact with. Tests have shown this “heating up” can extend far out from the immediate pipe location, making the cooling effect much less until given a period of time to “re-charge”.

4. You must address the problems you could have with insects, animals, dirt, and moisture. Remember, you will be breathing this air!

Hope this helps, and buy a hospital mask for you and yours!

Jeff Yago

Solar panels for rent


Are you aware of a new company, Citizenre, that will be making solar panels available for rent on people’s homes? BTW, I just read your article on “Are hydrogen-fueled cars pie-in-the-sky? ” and couldn’t agree more. Most people just don’t get that hydrogen is a form of fuel (i.e., a way to store and deliver power), not a source of energy.

Keep up the good work.

Geo. McCalip


Yes, there are several firms getting into this at the home-owner retail level. Its like leasing a car – it might make sense for some people, while others will find they would have been better off buying. Read the small print!

Jeff Yago

Satellite dish solar collector


Would converting an old large satellite dish to a solar collector be viable for solar energy if the photovoltaic array is at the focal point? If so how much could efficiency be affected?



Anytime you can concentrate the sun you can increase temperature, but you are collecting the same energy per square foot of sunlight. As to placing a solar electric cell at the focal point, you would increase power output right up to the point you melt it! There are solar arrays that concentrate sunlight, but these solar cells are designed for much higher temperatures than a standard solar cell. I have a few solar modules scrapped from a large test array that had side mirrors that increased the amount of sunlight hitting the cells and these color and finish damage from the heat. However, these reflectors were used more to re-direct sunlight that would be lost back onto the cells, and did not concentrate the sun’s rays onto a single point like a magnifying glass.

You would have more look by making this into a solar cooker or to heat water. You can even generate steam and really reach some very high temperatures. The downside with any solar reflector system is they require a “focusing” sun. This means blue sky and no clouds blocking the sunlight or you will not heat anything. You will need a “mirror” finish on the dish, so I assume you are going to cover it with reflective mylar or similar material.

Good Luck!

Jeff Yago

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