Cooking with Just the Sun’s Rays: GoSun Sport-E Solar Oven Review

Sections to Follow: The Case for Solar Cooking; Types of Solar Cookers; Cooking with Solar Ovens; Review of Purchased GoSun Sport-E Solar Oven; Why This Article on This Blog

The Case for Solar Cooking

Although domestic cooking in developed countries comprises only a tiny fraction of total energy consumption, this is not true in some regions. Some 2 billion people still cook over fires of wood, charcoal, or animal dung. Foraging for wood can contribute to deforestation in arid or densely-populated regions. It is usually the women doing the cooking over these fires, inhaling smoke with all its consequences. Also, it is again women who largely end up gathering the fuel. All this gathering and fire-tending consumes time which takes away from other tasks like raising food. Also, women can be assaulted in the forests while they are gathering fuel.

It is possible to construct devices which capture enough of the sun’s rays to cook food (more technical details below). Various non-governmental aide organizations (NGOs) help people in poor, mainly sunny/tropical regions and in refugee camps to purchase or construct solar cookers. It is possible to set up cottage industries for locally making and selling these devices at low cost. This a win-win.  Solar Cookers International specializes in this work, and has developed and shared some of the most useful technology here. They claim some four million solar cookers are in use, and present figures for how much CO2 emissions and money for fuel are saved.

Why is this relevant to us in the West? Well, if we care to help the lot of the less-fortunate, we can give money to support these solar cooking initiatives. As noted, they can help the well-being of people, especially women, in many ways. A less-obvious  impact of us using solar cookers in our own homes is that folks in other lands are aware of our life-styles. It turns out that a non-trivial barrier to wide-spread adoption of solar cooking is that they are suspicious of Western aid workers promoting a method of cooking that no one back in the developed countries uses. If solar cooking could be more visible in our lifestyles it would have a significant effect in lands where it is really needed.

Without descending into a tussle over exactly how man-made it is or whether it is part of a natural cycle which may turn someday to plunge us into yet another ice age, it does seem clear that the earth is experiencing a warming trend with possible serious consequences, and it is obvious that fossil fuel reserves (oil, natural gas, coal) are finite. Thus, it is a responsible choice to reduce fossil fuel use as reasonably practical. This furnishes another motivation for us to employ solar cookers, although granted that the amount of CO2 saved will likely be modest.

And for more personal motivations – it is kind of intriguing and rewarding to cook directly from the sun. On a hot day, it can mean cooking a casserole without heating the oven/kitchen or stressing the air conditioner. You can do great projects with kids (your own or others), designing and making and using solar ovens.

If you find yourself in some situation when you have no other means to cook, a solar cooker could be very helpful. To temper this reality, however, in most  temperate regions there will be many days without sufficient sunshine to make these work. Also, they are slower to heat up and cook than conventional stoves, so you need to plan ahead. That said, if you have a sunny morning or afternoon, you can put your pot of rice or whatever out to cook in the sun, go about your business, and come back in 2-3 hours, knowing your “solar crock pot” will have simmered your dish without burning it.

Types of Solar Cookers

I find the technical details here fascinating, but I will skip the juicies here and just briefly describe how these things are made and how they work. In all cases, there are some mirrored reflecting surfaces which concentrate the sun’s rays onto a cooking pot. For reflecting surfaces, one can glue aluminum foil onto cardboard. However, regular foil grows dull with time and use, so it is better to use some kind of aluminized plastic surface, such as car windshield reflectors, mirrored craft adhesive sheeting, or even the insides of potato chip bags. Usually, the pot is in some kind of enclosure which is transparent to let the sunlight in but traps heat around the pot. 

There are a number of configurations that work. A description of various designs, with illustrations, is here  and here.

Panel and Box Solar Cookers

Perhaps the most minimalistic solar cooker is the panel cooker. Here, the pot is enclosed in a clear  oven bag or within two glass bowls. Segmented or curved reflective panels are arranged to reflect the sun on the pot from multiple angles. Solar Cookers International’s Cookit ($50) is said to be the most widely produced solar cooker, and it is of this design.

There are many DIY designs floating around for panel cookers, including ones made from car windshield sun screens. Several commercial models are available for purchase, from the makers or on Amazon. I think the best price/performance panel solar cooker is the Haines 2 ($100). When the sun is reasonably high in the sky, this heats a pot of water faster than other panel cooker do, it is straightforward to assemble, and it comes ready to go with a 4.5 quart cooking pot and insulating sleeve. Another option is the All Seasons Solar Cooker. For a similar price, this cooker does not include a pot or the clamshell pair of pyrex bowls for insulating around the pot (so you will need to buy these, for another $40 or so), and it is harder to assemble, but it can handle a large pot and it more readily adjusts to low sun angles for winter or late in the day.

Another design that people construct at home (see the internet) is a box solar cooker. Typically, you use a smaller cardboard box within a larger box, with the spaces between the two boxes filled with some kind of insulation (e.g., crumpled newspaper). A hinged glass lid and some reflecting panels on top of the box complete the device.

A very expensive ($450) but very effective and convenient box-type solar cooker is the All-American Sun-Oven. Because of good insulation and large light-gathering reflectors, this can function year-round in cooler climates, but takes up a lot of space in storage. Temperatures inside the large cooking space can readily get to 350 F. It has a built-in thermometer.

Cooking with Conventional Panel or Box Solar Cookers

The pot you see inside the Sun Oven above is a 3-quart (3-liter) roasting pan with thin metal walls and dark enamel-ware coloring, used frequently in solar cooking because of being lightweight, inexpensive, and having good heat absorption and conducting properties. That is a reasonable capacity for making a dish to feed a family of four. Although solar cookers are billed as solar “ovens,” it is probably best to think of them more like crock-pots (slow cookers). They heat up relatively slowly, and for most dishes you need to keep a lid on the cooking pot. Otherwise, steam would escape and then condense inside the glass window or on the inside of the clear plastic bag, interfering with the heat transmission. But they excel for watery dishes like stews or rice or beans or soups that are often cooked on stovetops, as well as steaming meats and vegetables. It is can be hard to get food browned in a solar oven, and nearly impossible to get it really crispy. For panel cookers, temperatures may not get much above the boiling point of water.

You can put the pot in the cooker and walk away, letting the food simmer. You may need to adjust the position of the cooker once every two hours to track the sun. It is possible to cook bakery goods like breads and cakes and brownies and cookies with solar cookers. But this would take experimentation. In general, it takes about twice as long to cook food in a solar cooker compared to a conventional oven. This article has discussion and links regarding solar cooking and solar cookers.

Users in relatively sunny regions (in the U.S., that would be the southwest quadrant, and Florida) could get reasonable use out of these cookers. But in the Northeast/Midwest U.S., one could expect to be able to use them less than a quarter of the time. They require typically 2-3 consecutive hours of nearly cloudless sky, with minimal haze. High winds can be problematic, since these cookers are often light, with large, somewhat flimsy reflectors that catch the wind. Also, panel cookers struggle on cold days, due to excessive heat loss. Here is a YouTube by Roger Haines describing all types of solar cookers.

Go-Sun Solar Ovens with Glass Vacuum Tube Insulation

In tropical regions with the sun high overhead, there is some use of a large round parabolic mirror (sometimes made from an old satellite dish antenna) which can focus a very hot spot of sunlight onto the bottom of a pot or pan suspended above the mirror. High heat loss from the pot is compensated by the large size of the mirror.

A more recent, high-tech approach is the line of solar cookers from GoSun. These feature smallish linear parabolic reflectors that focus the rays on a long, skinny cooking tray inserted in a double-walled glass tube with vacuum between the walls (Thermos-type insulation). The sunlight passes through the outer glass tube, then hits a dark coating on the inner glass tube. The inner tube heats up and bakes the cooking tray inside it.

These cookers have only medium size capacity, but heat very quickly and can cook food really hot (e.g., can bake biscuits). So, they are  convenient and versatile cookers in many ways, although they do best with relatively solid foods like hot dogs or breads or cut-up meat or vegetables. They cannot readily handle liquidy loads like stew or adding water to cook dry rice or beans, so they are a different cooking niche than conventional solar cookers. Even cooking hamburger or some fishes is challenging because of all the juices generated; users report they may have to withdraw the cooking tray partway through and carefully pour off boiling hot juices without dumping the food, which is stressful. The glass tube is not happy to get liquid splashed on its hot insides.

In the past I have owned a panel solar cooker (Cookit) and also the high-end Sun Oven box cooker. I live in the Northeast U.S., so (for reasons mentioned above), I got little use out of them. I wanted to get back in the solar cooking game, partly for fun and partly to reduce the load on our A/C during these long, hot summers. The GoSun cookers seemed like a promising approach.  They can often cook with as little as 45 minutes of sunshine, and they can tolerate clouds and haze better. Importantly, they are not affected by cold weather or by wind (within reason), which makes for a much wider operating window compared to panel or box cookers. The reflectors are relatively small, so the cookers can tolerate more wind. Also, the GoSun devices fold up fairly small, at least compared to a box cooker.

Here is a random rave review from Amazon customer: “Wow, this thing is fun! I’m very happy with it. The kids go nuts for anything that comes out of it. We’ve made, brownies, chocolate chip cookies, blueberry muffins, corn muffins (can hold 85% a box of Jiffy brand muffin mix), steak (in strips), hot dogs (fits 8-12), shredded baked potatoes, and tin-foil dinners without the foil (ground beef, potato, carrots, onions, seasonings), and probably a few other items I’m forgetting.”

Here is a YouTube video (made by GoSun) with a head-to-head test of their ovens versus several conventional solar cookers, for baking cornbread. Their ovens did much better than the others. One less-convenient feature of the GoSun ovens is cleaning. Food can cook on hard the tray where something has dripped and then dried out. Lining the food tray with foil can help with clean-up. You have to be concerned about food touching or dripping on the glass tube surrounding the food tray; cleaning the long, narrow inside of the glass tube is a chore, with the possibility of breakage. By comparison, conventional solar ovens have a single large pot which is easy to clean because food rarely dries out.

Review of Purchased GoSun Sport-E Solar Oven

Well, I went ahead and splurged on a GoSun Sport-E solar cooker. This is the middle-sized model, in between the small Go-Pro ($120) and the large Fusion ($500). The prices for the Sport model on the GoSun website are $249 for the base model and $279 for the Sport-E. There are similar knock-off versions of these evacuated glass tube cookers for sale from presumably Chinese manufacturers, but I saw no reason to take a chance on them.

The Sport-E has an added feature of a strip of resistance heating along the bottom of the long, skinny food tray. You can plug that into a 12-volt power source (e.g., Li-ion power pack, or vehicle battery cigarette light outlet) and cook food in the tray, even in the absence of sunlight (e.g., at night or on a cloudy day). That option may not seem too appealing for use at home, but I have seen favorable reviews by folks living out of their RV that it is handy to be able to cook some food at night without firing up a camp stove. You can also use the Sport-E with sunlight, as usual.

Sport-E

Above is a photo of the Sport-E. Note the food tray partly inserted in the glass tube. The heating element is visible on the underside of the tray. The reflectors are hinged to form a parabolic trough reflector when they are opened, and to form a protective clamshell around the glass tube when they are closed.

The prices for these gadgets on Amazon  are sometimes lower than on the GoSun company website. In my case, I happened to see a good deal which enticed me to make a purchase. The package displayed on Amazon was the regular (not electric)  Sport model, with an extra food tray, a carry/storage bag, a set of little rectangular silicone “cupcake cups” for inserting in the food tray, and I think an accessory that inserts into the oven to heat up  maybe 14 oz of water. All this for $199, which was a very good price. (This deal is no longer available).  But what actually came was a Sport-E model, with only one tray and no water kettle. But it did include the carry bag and the silicone cups.

Sadly, I was unable to get the tray fully inserted into the glass tube. It seems the handle was misaligned on the metal part of the tray by maybe 1-2 mm, so the little silicone ridges on the handle could not enter the tube. A beautiful thing about Amazon is the easy, free return policy. I had saved the packing, so no problem there. I asked for a replacement in kind, instead of a refund. When it came, I first checked the tray insertion. I could wiggle it in, but it was really, really tight, and difficult. I put a wisp of silicone grease on the ridges of the handle. That helped, but only a little. However, buried in an instructional YouTube, which was buried in instructions on the GoSun web site, was the following tip: put a little vegetable oil on these ridges. I did, and that allowed the tray fully insert with no problem. (This vegetable oil tip was nowhere to be found in the written instructions that came with the cooker).

The first thing I cooked was something I knew would be an easy win. These were mini hotdogs wrapped in puff pastry (frozen cocktail party hors d’oeuvres ). These were fairly dry to start with, which is important. They still took about 45 minutes to brown up, compared to 20 minutes in a conventional oven. I pulled the food tray (lined with foil for easier cleanup) out maybe 1/16 inch to let steam escape through the gap. They turned out great:

This confirmed that the GoSun could reach high temperatures if the food was pretty dry. Next up was an apple bran muffin recipe. This was a challenge because the starting mix was reasonably wet:

I loaded the batter in the silicone mini-trays, to keep it clean and under control. I left a small gap at the handle to let steam escape, and there was plenty of steam. I pulled one muffin at 45 minutes. It was hot through, but still very soft, with no crust. It was just too humid in the tube. I opened the gap a little further, and pulled the whole tray at 60 minutes:

The resulting products were a failure as “muffins.” Each one had a somewhat chewy crust around its rim, with a soft, moist middle, a result of extended steaming. They were OK as “bars.” For comparison, we cooked the rest of the muffin batter in a muffin tray in a 400 F conventional oven, and these turned out great after about 14 minutes: nicely domed with a semi-crunchy sweet crust. This was a severe test for a solar oven, and failure here was not unexpected. Anyway, it confirms that this oven should do well with dry foods (especially pastry or biscuits – with a lot of fat, not much moisture) that you want to brown, or with a whole range of foods that you essentially steam (as with conventional solar cookers, crock pots, or microwave ovens). Cakes and cornbread and brownies should work, as well. Although the batters are moist, for these mixes you are not necessarily depending on a crispy crust.

To test the Sport-E for cooking rice, I first plugged the little threaded hole at the far end of the food tray with some aluminum foil, to minimize accidental drippage there. I then loaded the tray with 3/4 cup (177 ml) of my favorite Riso Scotti Venere black rice. (This rice has a nice chewy texture and nutty flavor, and on the stove cooks in only 15-20 minutes, with a 1:1 or so water:rice ratio). I added another 3/4 cup water, and then did a little stirring to moisten the rice grains floating on the surface and try to get them to sink. I very carefully inserted the food tray in the oven and fine-tuned the mirror positions. With such a long, skinny tray, a slight tilt could cause a tidal wave surge of liquids. I did not want to check the contents until essentially all the water had gotten absorbed, since sloshing liquid water on a glass tube after it was heated in the sun could crack it. I pulled the tray out after about 40 minutes, and dipped a spoon in to sample the rice. Maybe it was OK, but it seemed a bit firm, so I gave it another 10 minutes before pulling out the tray. All the water was absorbed (photo below). I got about 1.7 cups of nice cooked rice. The only problem was the rice in the last inch of the tray, away from the handle, was a bit dry and crunchy. It seems the surface on which the solar oven was placed was not level, and so the water ran somewhat towards the other end. Or maybe that far end was simply hotter than the rest of the food tray. I boiled this little bit of dryish rice for a few minutes in the microwave, and it was fine. It would of course had been easier and much faster to simply simmer the rice for 20 minutes on a stovetop, but this experiment showed that one can, in the absence of a stove, make a medium sized portion (enough for maybe three adult meals) of rice using this solar cooker. .

My rice might have been better if I added a little more water. You could probably load the food tray more than I did, maybe up to 0.9 c rice and 1 c water, to make just over 2 c cooked rice. But if your rice takes more than 1:1 water, you’d have to back down on the rice amount. If you are cooking something solid like cut up potatoes where there is no worry about liquid sloshing, I think you could fit nearly 3 cups of food into the tray, without danger of hitting the inside of the glass tube.

This recipe for apple crisp, scaled down by about 1/3 to fit the tray, worked out well in my GoSun Sport. Because of the steamy environment in the oven with all those apples, the topping stayed fairly soft (not remotely crisp). But I had added an extra layer of chopped walnuts between the apples and the topping, and that gave decent chewy mouth feel.

I only tried the electric feature briefly. I had some angst because the instructions say you need a 15-amp 12-volt power source, and most 12 V power-packs and vehicle cigarette lighter outlets are only rated for 10 amps. But on further investigation it seems that this 15-amp recommendation is probably just a precaution against being sued if someone blows their power source on this device. GoSun’s own promo video states that the Sport-E draws only about 80 watts, which would be about 7 amps at 12 V. So, a 10-amp supply should be fine. I only tested it using a little water in the tray, with a smallish power bank, and it seemed to heat up OK. The GoSun literature indicates the powered tray heats to about 350 F. One user stated that in that mode it cooks like a frying pan, with all the heat from the bottom, so you cannot do baking with it. However, it should work fine for hot dogs or chicken thighs, etc.

Verdict: For someone living in a sunny region who wants to cook large portions of food with minimal drama or cleanup, a conventional, low-tech (panel or box) cooker is probably better than a GoSun oven. For 1-2 people living on a boat in Florida or in an RV in the Southwest, the GoSun Sport could be a win, depending on what they like to cook. The electric cooking feature of the Sport-E would extend its usefulness for off-grid living. For me, living in a house  in the Northeast U.S., the GoSun is definitely better than other solar cookers, since I can use it on cold or less-sunny or most breezy days, and when the sun is low in the sky.  My GoSun Sport-E is basically a toy for me, not a critical tool. The food capacity is relatively small, and it cannot handle liquidy loads. That said, it is a great toy, convenient (because of relatively quick cooking times) for making small, tasty dishes and is fun to share with others in all its well-engineered, high-tech glory.

Why This Article on This Blog

This is generally positioned as a faith-and-science blog. I got started by posting my findings on controversial issues like the age of the earth and evolution, where I was trying to sort out the truth for myself. The faith-and-science discussion also encompasses the moral use of modern technology. Christian theologians find in Genesis 1 that there is a general divine commission laid on mankind to rule over the earth and its creatures. This “cultural mandate” is carried out by means of humanly-devised technology, ranging from stone-tipped spears to genetically-engineered drought-resistant crop strains.

The context of that mandate indicates that humans are to rule to earth, not to plunder it for themselves, but as stewards taking good care of God’s world. Naturally, we can point to many instances where humans have used their powers to harm other species as well as themselves. On the other hand, it is only modern technology (especially artificial nitrogen fixation for fertilizer) that allows the planet to carry 8 billion precious human beings.

Side comment: To anyone who despises the availability of modern technology, I challenge you, with a family, to actually live off of subsistence farming with pre-1500 technology and no trade with larger modern society.  No computers/cell phones, no store-bought nails or lumber or plastic or cloth, and no selling artisan bread and organic microgreens to trendy restaurants in town.  Both of my grandfathers were farmers in the early twentieth century, and it was long days of brutal, back-breaking work; like so many other former farmers, they were glad to be able to get jobs in town and leave the farm for a better life. And if you read current homesteading literature, very often one member of a couple has to work at a conventional job in town, since they cannot get by on just the vegetables and chickens they can raise, even using modern aides to husbandry.

Apart from justified debates on how well humans have used our powers in the past or how we should use them in the future, the inescapable fact is that we do have great power over the physical world (including both “nature” like land and sea, and what goes on inside a factory or an artificial greenhouse). Whether we like it or not, this power will in fact be used, one way or another. And a key component of that power is applied technology. Humans with no tool or weapon in their hands are pretty useless and vulnerable: soft, weak, and slow compared to many other animals.

Thus, applied technology is part of the larger story of humans fulfilling the divine commission to rule the earth. This theological connection is one reason why I occasionally write on such topics on this blog, e.g. on microfinance development and no-till farming. Other motivations are to provide information which might be helpful to readers, and to share findings that I think are just plain interesting.