Solar Cooking
Last edited: 5 July 2009      
EZ-3 with booster

EZ-3 up and running, with booster in place.

Designed by Sharon Cousins (standing on the shoulders of giants), the EZ-3 Solar Cooker might best be classified as a small hybrid panel-oven, since the whole cooker goes into the cooking bag (eliminating the need to bag the cooking vessel). A cut out, foiled box corner is sized so that the whole cooker can be eased into a Reynolds turkey sized oven bag. Distance from the corner along the bottom edge can be 12" - 13", and the vertical measure can be 17" - 18" (which can include the box flaps, taped upright with duct tape or other heavy-duty tape). This is a surprisingly efficient little cooker for up to one quart of food and works very well with either small, dark pots or pint or quart cooking jars. It is Sharon's favorite cooker for heating up her solitary summer lunches. To make an EZ-3, measure, mark, and cut out the box corner (first taping up the top flaps if you need them to attain the proper height). One or two small triangles of bottom flap will usually come loose in the process. Glue these triangles back in place with white or wood glue. Do not glue the whole bottom together if you want to be able to fold the cooker flat for storage and transport! When that glue is dry, foil the inside of the cooker.

EZ-3 in action

The first prototype EZ-3 taking advantage of the August sunlight.

The whole cooker is enclosed in a Reynolds turkey size oven bag. When setting up the EZ-3, use a binder clip to secure the cooker. A 6" cake cooling rack or three or four small pebbles elevates the food so light can get under it, improving the efficiency. The cooker is gently eased into the oven bag. The opening of the oven bag is rolled up at the back of the cooker and secured with two clothespins. When folding for storage (after making sure any vapors have dried from the cooker and bag), remove the binder clip and fold flat, with the folded oven bag inside the cooker, and secure with the binder clip.

EZ-3, back detail

The whole cooker is enclosed in a Reynolds turkey size oven bag. The opening of the bag is rolled up at the back of the cooker and secured with a couple of clothespins

This is an ideal cooker for youth projects, as it is easy to make, is easy to aim using the shadow, and it works well. The recipe SharonID's Solar Project Soup in the Soup section of Recipes was developed for EZ-3 youth projects. It lets each person/youth make an individual pot of vegetable soup, with the vegetables set out so that each person fills their measure with ones they like.

The EZ-3 is also a good cooker for couples or people who live alone and only cook small quantities of food (for more than one food, make additional cookers) or for people who want a small cooker for backpacking or traveling. Homeless people in some circumstances might find it useful (you can even heat prepared food in the can if you open the can slightly to vent and slide it into a thin, black sock), and families with one member with special dietary needs might find it useful for small amounts of special foods. It's a great cooker for cooking up to a quart of anything, from soup stock to rice to fruit sauces (see Fruit ). It is also ideal for making a quart of solar coffee (see Beverages ). With the addition of a small, dark lidded pot (3-4 cups or .75-1 liter) the EZ-3 does a very good job of baking cake, cornbread, yeast bread, a big fat cookie, brownies, scones, a giant muffin, and more. Weight watchers might find it useful to be able to make a small amount of a special treat to avoid the temptation to overeat.

To increase the efficiency of an EZ-3, a small front booster panel can be made by tracing the bottom of the cooker on a flat piece of cardboard and marking a rectangle the width of the cooker and seven-ten inches deep (the farther south, the more front booster is needed). Cut out this triangle+rectangle shape (it will look a bit like a child's outline of a house) and score a fold along what would be the front edge of the cooker (between the triangle part and the rectangle part) and foil it.

EZ-3 booster

EZ-3 booster — cut, scored, and foiled

In use, place the cooker on the triangle part of the booster and use a small pebble or two underneath to elevate the booster reflector to a good angle for shining into the cooker and onto the pot or jar.

EZ-3, side-by-side

EZ-3 assembled and folded flat for storage and transport.

For better winter cooking efficiency, make two EZ-3s in slightly different sizes, so you can nest two for the added insulation and bag the nested pair. In combination with a front booster panel, this double EZ-3 arrangement reached temperatures of 225F on a clear day in January, at 47 degrees north latitude, with ambient outdoor temperatures in the upper twenty degree (F) range.

EZ-3 close-up detail

Close-up detail of rack and binder clip.

Sharon has recently found a source for a larger sized cooking bag and is developing an slightly larger EZ-3 in hopes of coming up with one that can do a good job with a half-gallon cooking jar. She also reports that the oven bags used to enclose an EZ-3 last much longer than bags used to enclose cooking vessels. Sharon is primarily cooking at 47 degrees north latitude with an occasional foray into the San Jose CA area. She suspects that further south the EZ-3 will work better if it is tipped back a bit, with a stick or small board or pebbles under the front of the cooker to lift it. Level out the bottom with a false bottom (foiled, of course) and figure out some way to shim the corner so your pot or jar will still be reasonably level. Also, opt for slightly shorter and slightly wider at the bottom, within the limitations of your bag. Further south, you need less height and more side-wall.

EZ3-S1 S2 S4 N1

Scale drawings of side-view for four EZ-3 models. N1 is the original northern model, designed at 47N. S1, S2, and S4 all work better farther south, when tested a little below 38N, esepcially with a simple additional black bottom piece.

Another trip south provided opportunity for further development, and there are now three versions of the EZ-3—still all basically simple box corners—that will work much better farther south than the original model (N1), especially with the addition of a simple additional black bottom piece. The more southerly models go into the turkey-size oven bags sideways instead of feet-first. S1 is a little simpler to make and has an amazing little late-day burst, S2 had the strongest performance in terms of reaching high heat and holding it until the first drop, but it only showed a late-day surge right at the end of the time of surge. S4 had a factor (newest model, still some glue moisture probably) that may have skewed its tests. I think it should have done better than it did and might be worth a try still. All of the southern models will work better with an additional black bottom layer. One way to achieve this is to trace the interior floor of the cooker and cut out a piece of corrugated cardboard. Trace and cut out a piece of black poster-board and glue it to the cardboard—you will need to smooth it flat and press it with some weight to make sure there is good contact. When dry, paint with two coats of black tempera mixed with a little white glue (Elmer's, PVA) or non-toxic-when dry spray paint. Without paint, the paper will fade very quickly, and the paint will go on more efficiently on the poster-board than it does on brown corrugated. An alternative to this black bottom might be two triangles from a 6" ceramic tile cut corner-to-corner, black or painted black, to put in the two front corners. Silver directly under and in front of the pot is good in the south, having a heat sink in the corners—even blackened cardboard—gives it an amazing boost. Sharon made the corrugated-plus-poster-board and paint bottoms for her side-by-side tests, with a thin center panel of foil folded over poster-board—just enough support for the foil to keep it flat. This arrangement was clearly superior to the original silver bottom in the trials near San Jose CA. Sharon will send a free pair of cut, painted ceramic triangles to the first person from farther south to contact her and let her know they have an EZ-3 built and ready for testing in exchange for test data.

EZ-3 also handles wind fairly well, if you give it a little support so it doesn't just blow away. You can put a couple of foiled chunks of rocks in it to add a little weight, and it can be braced behind with anything heavy—water jugs, big rocks, wood chunks, bricks, etc. Close it as tightly as you can if it will be cooking in the wind, to keep billowing to an absolute minimum

R&S group shot

Youth from an Idaho based Roots and Shoots club celebrate the end of a successful EZ-3 solar cooker project

Using the EZ-3[]

Unfold the cooker, set up, secure with your binder clip, and ease the cooker into the oven bag (ease the front edge in first; you won't get the back corner in until the front corners are in and the edge of the bag pulled a good way up the sides, or for a southern model, where the cooker goes in sideways, you still have to get two corners in far enough before you can get it over the top corner). Put a small (6") rack or four small, foiled pebbles or a thick glass candle plate or ash tray on the bottom of the cooker to raise your pot or cooking jar so the light can get under it. If you want to, you can also put a small oven thermometer in, though it is not essential but it can be interesting. Your EZ-3 with food inside will probably run at least 200-225°F when the sun is high, which is plenty for most foods, as cooking actually begins at 180 degrees.

Put the food (in a covered dark pot or a blackened cooking jar) into the cooker. Roll the opening of the bag closed at the back and secure with two clothespins (if you have a southern model, there'll be some extra plastic you need to roll up, so you're only putting heat into the business area of your cooker). Put on your sunglasses; if you don't have sunglasses, be especially careful to look at the foil as little as possible.

Put your EZ-3 outside, facing the sun. Do not look at the sun to aim. Look at the shadow of your EZ-3. When the shadow is straight and even behind the cooker, it is pointed straight at the sun. Since you don't want to be turning the cooker every couple of minutes, you want to push it ahead of the sun a bit, so there is more shadow to the right than to the left (looking from behind cooker). If you think of the shadow as a sundial, you will soon get a feel for how much you can push it ahead to leave it for varying lengths of time. As you get a feel for it, shoot for pushing it about an hour ahead when you can, so the sun will sweep across the top of the food once per hour, which makes for more even baking

If you use the booster, which will always help your cooker work faster and hotter, especially in marginal cooking conditions, set the cooker on the triangular part and use a stick or a couple of small rocks under the reflector part to angle it up until the shadow underneath is about half the width of the booster.

If it is windy out, use something like a couple of rocks or bricks or jugs of water behind your cooker so it won't blow away or blow over, and cover a couple of flattish rocks with foil to put on your booster panel to keep it from flapping up. Once your cooker is all set, you can play or relax or do chores while the sun takes care of your food. Foods will not burn in your EZ-3, and most foods will not overcook, so except for adjusting the direction now and then, you are free to do other things while your food is cooking.

Cooking is hottest and fastest on a day when you can see your shadow most of the time, and during the time of day when your shadow is shorter than you are, but if you get food hot earlier in the day, your EZ-3 can keep it hot or simmering well into the afternoon or even early evening.

You can most foods cook fairly well with up to 25% clouds or a light haze, but when the sky is less than ideal it is especially important to get the food out early and use your booster. If you want to make baked goods, like muffins or cake or cornbread, set the cooker out by 10am if you can, or 11am at the very latest. It may help to preheat the empty cooker for a little while before putting in baked goods.

Foods will be HOT when you take them out. Remember to use potholders or a folded bandana to lift your pot or jar out!

Your EZ-3 will work best from late spring through early fall. You can use it in the off-season, if the weather is clear and sunny, but you should choose foods that cook relatively easily.

Remember, your EZ-3 cannot start a fire and will not make smoke. As long as you handle your pot with potholders, it cannot hurt you or the environment. You can take it with you on trips and use it to heat or cook food in places where a fire would be dangerous or against the rules. If anyone asks what it is and what you're doing, you have a perfect opening to be an advocate for solar cooking.

See also[]


See Sharon Cousins.