Harvesting the Sun

How to Harvest the Sun with a Solar Oven

Hot weather and stuffy kitchens are enough to turn anyone off their appetite. Unfortunately, conventional ovens can create a lot of heat, quickly making meal prep a miserable experience for everyone. But there is an easy solution to this problem, a low-maintenance, simple to use oven that required almost no effort to use. Best of all, it runs off the solar system’s most plentiful renewable resource- sunshine. Welcome to the wonderful world of cooking with a solar oven.

Giving one of the Big Laurel bunk house’s a much-needed tidying last fall revealed unexpected rewards when Ian and I discovered a Sun Oven under one of the bunk beds. It was in perfect condition, if a little dusty, so we brought it over to our house where I have experimented with it these past few weeks.

There’s been a lot to like. Here are just a few of the benefits of cooking with a solar oven.

Child friendly: Kids stay safe because solar ovens don’t have exposed flames or a super hot heat source. We can use them during summer camp!

Encourages time outside: Solar ovens need to be out in the sun (obviously) and will consequently keep us out of our stuffy kitchen.

Environmentally sustainable: Relying on the most prevalent form of renewable energy out there, solar ovens don’t need any fossil fuels and don’t create any air pollution.

Low maintenance and easy to use: Using a solar oven means I can start dinner in the early afternoon and simply walk away. In the oven we have food rarely (if ever) needs to be stirred and won’t burn.

Highly portable: Most styles of solar oven are small and light enough to be brought just about anywhere, making them great for camping! Small models like this can be brought just about anywhere, making it especially useful in places with a fire restriction.

Types of Solar Ovens

There are two main types of solar oven available: a parabolic and box design.

Both types of solar ovens work so long as there is sunshine, but the maximum temperatures and time needed to cook food can vary wildly from one design to another. Think carefully about your cooking needs and how you most want to use your oven when deciding on they type you want.

Parabolic Oven

Also called curved concentrator ovens, parabolic ovens get hotter and can cook faster than box ovens, making them useful for grilling and frying. Their rounded walls focus the sun’s heat to the oven’s base where food is placed.

Unlike box ovens, parabolic ovens need to be watched carefully so that the oven stays angled towards the sun and that the oven doesn’t get so hot that it scorches the food. Limited cooking space means that only one dish can be cooked at a time, though each dish will cook faster than in a box oven.

Popular in China, parabolic ovens are used in restaurants more than by families. They are a more expensive option but many people believe their cooking efficiency makes them well worth the cost. If you are looking for a portable version to travel with, this single serving solar oven could be a great choice.

Box Oven

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Our American-made sun oven

Box Ovens are the most common type of solar oven and are popular because their size allows multiple dishes to be cooked at once. Box ovens cook slower than other models and rely on reflective panels that direct sunlight to the inside of the cooker. Box ovens are usually insulated which gives them the advantage of being able to be left unattended for long periods of time. They are also more stable and less likely to tip over than parabolic ovens. They can typically keep temperatures between 200-350 deg F and are great for baking cookies and breads.

Cooking With a Solar Oven

No matter the type, all solar ovens work towards three main goals: capturing, converting, and retaining heat from the sun.

1. Capturing Sunlight: Solar oven need to spend several hours outdoors in sunny spot. Cooking works best from 10am-2pm, but any time will work so long as you keep reorienting your oven to face the best sun. Both parabolic and box ovens have reflective ‘wings’ on the sides that capture extra sunlight from the sides and reflect it to the bottom where the food is.

2. Converting Sunlight into a Fuel Source: Solar oven dishes are best cooked in dark, lightweight containers that attract sunlight and keep heat. This creates crock pot conditions within your oven that allows food to cook slowly while retaining moisture.

3. Retaining Heat: A thin heat trap (either a transparent lid for a box oven or a plastic oven bag for parabolic ovens) lets in sunlight and keeps in the heat, allowing your food to cook for hours even after the peak sunlight is gone.

I recently baked apple bread in our oven and decided to track the interior temperatures throughout the day. The data from this micro experiment is below.

Weather conditions: mid 70s, partly sunny sky.

10:30 am: oven set outside: 102 deg F

10:45: 200 deg

11:00: 235 deg

11:07: bread put in oven temp after reclosing oven: 214 deg

11:45: 212 deg

12:45: 249 deg

1:15: 256 deg

2:00: 245 deg

3:00: bread done and pulled out: 225 deg

In my experiment, the bread took about 4 hours to cook on a partly sunny day. (I wouldn’t have chosen that day for experimenting if I’d known the weather would be so fickle.) The oven never got much hotter than 256 degrees, but the bread still baked! It was moist for sure, but still fully cooked and very delicious. I’d call that success!

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yummmm

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Important Safety Information

Harmful food microbes, which includes bacteria and viruses, are killed when heated above 150 deg F, the level where pasteurization happens. Most foods need to be at 180 degrees F to start cooking, which means that solar ovens almost always cook foods at temperatures well above this safety point.

However, with all cooking methods, certain types of bacteria can produce heat-resistant spores that germinate after foods have been cooked. To prevent this, foods should be kept at temperatures above 125 degrees F lest the bacteria spoil the food and cause you food poisoning. Any food that gets below this temperature and stays there for more than four hours should be thoroughly heated again before consumption.

Recipes for Solar Ovens

Most styles of solar ovens can be used to bake, dehydrate, boil and sometimes even fry food. Just about any recipe for a conventional oven can work if you add extra cooking time, but here are two cookbooks with recipes tailored specifically for solar ovens to get you started.


Global Benefits of Solar Ovens

Obviously I really like solar ovens. I love to play around with the maximum temperature I can get and the thought of getting my food cooked for free makes me feel like I’m beating the system. But what I really appreciate about them is the incredible potential that they have to transform the lives of millions of people in the developing world.

Though solar ovens can be a phenomenal alternative to conventional cooking methods in most countries, they have the most potential in tropical, locations due to the consistent climate and sun levels. It just so happens that this is the region of the world that most desperately needs this technology.

An estimated 500 million people around the world have abundant sunshine and suffer from fuel scarcity. Access to solar ovens in these regions has been shown to dramatically improve the quality of life for recipients in several key ways.

Water Pasteurization

Over 1 billion people worldwide do not have safe access to drinking water, and preventable waterborne disease account for about 80% of all illnesses and deaths in the developing world. A simple solar cooker can pasteurize water at a rate of one liter per hour. A Water Pasteurization Indicator (WAPI) can be used to determine when water heated by a has reached appropriate temperatures to make it safe, eliminating risks for families.

Nutrient Retention

The moderate cooking temperatures used in a solar oven help to preserve nutrients in foods, and make it easier to make foods that need long cooking times, like beans or rice.

Time Saving for Women

Millions of women must walk for miles every day to collect fuel for cooking. These trips are a huge burden, both in energy and time. Women often injure themselves and get exposed to dangerous animals and criminals. Solar cooking reduces these risks and burdens, and give them the time to look after their children, grow more food, or farther their education.

The search for fuel consumes the time, energy and health of women and their children. As local wood supplies grow scarce, women risk spinal column damage and uterine prolapse from carrying heavier loads over longer distances. Girls are often kept home from school to help their mothers gather wood, depriving them of educational opportunities. Where wood is unavailable, women cook with inefficient fuels such as animal dung or crop wastes, depriving livestock of fodder and soils of natural fertilizer. This endangers both the nutritional and respiratory health of women and their families.From “Forest Futures: Population, Consumption and Wood Resources”

Solar cooking techniques also require less water and produce dishes that are easy to clean, an important consideration for women who must walk many miles to collect water.

Economics

Cooking fuel is a huge expense for poverty-stricken families, often costing over 25% of their income. In contrast, sunlight is free and easy to come by. Solar ovens are easy to make and can be built in less than an hour for pennies. The money saved from fuel expenses can be used for food, education and health care instead

Benefits to the environment

Around the world over two million people are reliant on wood and charcoal for cooking fuel. This in incredibly taxing to our planet’s finite forest systems. Solar cooking alleviates the difficultly of acquiring fuel and helps to prevent deforestation.

In contrast to heavily polluting biomass and petroleum fueled cooking fires, solar cookers are pollution free and don’t contribute to global warming. Indoor smoke pollution is a leading health burden in the developing world, and moving the cooking process outdoors prevents vulnerable people from being exposed to these toxic chemicals.

In Summary

Where you are ready to experiment with a fun way to play with your food or trying to get off the grid completely, solar ovens are a great way to start this process. Whether you build your own or buy one like mine, solar ovens offer a sustainable, energy-efficient method of cooking that won’t make you rely on the power grid for your food. Have fun with this innovative cooking method and enjoy the process of becoming an accomplished solar chef!

 

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