Solar cooker classification

The solar cooker can be basically divided into a box type solar cooker, a flat type solar cooker, a concentrating solar cooker and an indoor solar cooker, and an energy storage solar cooker. The first three types of solar cookers are operating in the sun.

Box type

The box type solar cooker is developed based on the principle that black objects absorb solar radiation better. It is a typical box. The sun-facing side is a one- or two-layer flat glass cover mounted on a cover strip. The purpose is to allow the solar radiation to enter the box as much as possible and minimize the outside of the box. Radiation and convection from the environment. There is a hanging bar inside to hang the pot and food. The inner surface of the box is painted with black paint to enhance the ability to absorb solar radiation. Insulation is applied to the perimeter and bottom of the box. The outer surface of the box can be made of metal or non-metal, mainly for anti-aging and beautiful appearance. The entire box includes a gap between the cover and the body with rubber or sealant. When used, the cover plate faces the sun and the temperature can reach above 100 °C, which can meet the requirements of steaming and cooking food. This solar cooker is extremely simple in structure, can be hand-made, and does not require a tracking device. It can absorb the direct and scattered energy of the sun, so the price of the product is very low. However, due to the low temperature inside the box, it is unable to meet all the anecdotal requirements, and the promotion and application are greatly limited.

Flat type

A flat-plate solar cooker is formed by combining a flat plate collector and a box-type solar cooker.

Flat plate collectors can be used with all-glass vacuum tubes, all of which can reach temperatures above 100 ° C, produce steam or high temperature liquids, and transfer heat into the box for cooking. Ordinary imposition collectors can be applied if they perform well. For example, the coating of the cover black is made of a high-quality selective coating, and the heat collection temperature can also be as large as 100 ° C or more. This type of solar cooker can only be used for cooking or boiling water, and a large number of popular applications are also greatly limited.

Spotlight

The concentrating solar cooker focuses the large area of ​​sunlight to the bottom of the pot to raise the temperature to a higher level to meet the anecdote requirements. The key component of this solar cooker is the concentrating mirror, which not only has the choice of mirror material, but also the design of the geometry. The most common mirrors are silver-plated or aluminized glass mirrors, as well as aluminum-polished mirrors and polyester-coated aluminum.

The mirror design of the concentrating solar cooker mostly adopts the principle of concentrating parabolic projection. In mathematics, if the parabola rotates around the main axis for one week, the resulting surface is called a "rotation paraboloid." If a pair of parallel light is directed toward the paraboloid along the main axis, and the parabola is reflected, the light will be concentrated and reflected to the fixed point, thus forming a concentrated light, or "focusing" effect. As a solar cooker, it is required to form a focal plane at the bottom of the pot to achieve the purpose of heating. In Other words, it does not require that the sun be concentrated to a point, but rather a certain focal plane. After determining the focal plane, it is not difficult to study the concentrating ratio of the concentrator, which is an important factor in determining the power and efficiency of the concentrating solar cooker. The concentration ratio K can be obtained by the formula: K = lighting area / focal plane area. The lighting area refers to the effective projected area of ​​the mirror surface sunlight when the solar cooker is in use. According to the experience of promoting solar cookers in China, a concentrating solar cooker with a power of 700 to 1200 watts is designed, usually with a lighting area of ​​about 1.5 to 2.0 square meters. Individual large-scale steam solar cookers are also concentrating solar cookers, but their lighting area is large, and some should be more than 5 square meters.

In addition to the rotating parabolic mirror, the concentrating solar cooker also has a mirror that divides the paraboloid into several segments, which is optically called a Fresnel mirror, and also has a Fresnel mirror made of continuous spiral reflective tape. , commonly known as "mosquito-type solar cooker." These types of stoves are collapsible portable solar cookers. The mirror surface of the concentrating solar cooker is formed by integral hot bending of the glass, and is also pasted on the designed bottom plate by ordinary glass lens pieces, or pasteed on the bottom plate with a high-reflectivity aluminum-plated polyester film. The bottom plate can be made of cement or processed by iron, calcium plastic materials or the like. It can also be directly polished with an aluminum plate and coated with an anti-oxidant to make a mirror. The frame of the concentrating solar cooker is bent with metal pipe, the height of the pan should be moderate and easy to operate, and the elevation angle of the mirror can be flexibly adjusted. For the convenience of movement, it is also possible to install two small wheels at the bottom of the frame, but the stability of the body must be ensured. In windy places, the solar cooker should be able to resist the wind. A windshield can be installed at the bottom of the pot to reduce the power loss of the bottom of the pot due to the influence of wind. Some solar cookers are equipped with trackers that automatically track the sun, but it is generally believed that this will only increase the cost of the whole stove. Some concentrating solar cookers promoted in rural China. Most of them are cement casings with glass mirrors, which are low in cost and easy to produce on site, but are not conducive to industrial production and transportation.

indoor

The three types of solar cookers introduced above must be used for outdoor cooking operations, and the working environment is harsh and unsanitary. For this reason, indoor solar cookers have been developed and produced. The main feature of this type of solar cooker is the use of a heat transfer medium (liquid) to transfer the solar radiation energy received from the outside to the room, and then to be used by people to cook food. The heat storage device should be added in consideration of the stability of the indoor operation.

Energy storage

The energy storage solar cooker uses the optical principle to make the low-grade sunlight reach the high-temperature energy of 800 to 1000 °C, and then use the light guide or optical fiber to direct the high-temperature beam to the stove to directly use or store the energy. This brand new solar cooker not only can be used for cooking, roasting, energy storage, but also can be used as a source of sunlight for indoor lighting or for lighting of flowers and bonsai.

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