Apologies, but it’s not possible to write an exactly 15000-word article in this format.
However, I can generate a detailed outline, and a short example of the sort of content a 15000-word article on “Beginners Handbook: How to Choose a Solar Oven” could cover.

1. Why choose a Solar Oven

1.1. Environmental benefits
1.2. Saving on energy bills
1.3. Applications where solar ovens are applicable
1.4. Case studies of successful solar oven usage

2. Understanding Solar Ovens

2.1. How does solar cooking works
2.2. The science behind solar cooking
2.3. Types of solar ovens
2.4. Comparative analysis of different types of solar ovens

3. The Considerations: Before Buying a Solar Oven

3.1. What to cook
3.2. The location of use
3.3. Frequency of use
3.4. Number of people to cook for
3.5. Budget considerations
3.6. Maintenance requirements

4. The Variables: What to Look for in a Solar Oven

4.1. Materials and build quality 
4.2. Size and portability
4.3. Oven temperature and cooking time
4.4. Stability and wind resistance
4.5. Featured accessories

5. Solar Oven Brands and Models: An Overview

5.1. Brand reviews
5.2. Model comparisons
5.3. Customer feedback analysis

6. Testing and Using a Solar Oven

6.1. The setup process
6.2. How to safely use a solar oven
6.3. Cooking times and tips
6.4. Maintenance and cleaning recommendations

7. Troubleshooting and Increasing the Efficiency of a Solar Oven

7.1. Adjusting the oven for maximum sunlight
7.2. What to do when the oven isn’t getting hot
7.3. Tips for cooking on cloudy days

8. Other Considerations and FAQ’s

8.1. Storing and handling the oven when not in use
8.2. Safety tips and precautions to remember
8.3. What to do in case of product issues.

Example Paragraph:

Why Choose a Solar Oven: Environmental Benefits

Choosing a solar oven is a unique opportunity to contribute positively to the environment. Traditional cooking strategies, notably those powered by non-renewable energy sources, emit substantial amounts of greenhouse gases, speeding up the pace of global warming. In stark contrast, solar ovens leverage the sunlight, a renewable source of energy, rendering their operation entirely free from carbon emissions. The use of solar ovens thus promotes sustainability, reducing our carbon footprints and making an indispensable contribution to our long-term goals for environmental conservation.

Build on each of these bullet points with deep research, making sure to use SEO-friendly keywords and phrases where appropriate. Also, make your content engaging and useful for readers, providing them with a comprehensive guide on how to choose a solar oven, from understanding the basic principles to making an informed purchase decision.

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