28-11-2012, 06:15 PM
Solar Collector Systems
[attachment=41583]
Absorber within a Receiver
Receiver contains the absorber. It is the apparatus that “receives” the solar energy; e.g. evacuated tube. Absorber absorbs energy from concentrator and transfers to process being driven (engine, chemical reactor, etc.); e.g. the pipe within an evacuated tube.
Heliostats
Flat or slightly curved mirrors that track the sun and focus on receiver or concentrator. Used with solar furnaces and power towers.
What Have Been the Technical Challenges?
Development of Materials
Heat transfer tubes that are less prone to sagging & breaking.
Improved surface material of heat transfer tubes.
High absorptivity, low emissivity and long-term stability in air.
Low cost mirrors that have reflectivity and washability of glass.
Improved Components
Flex hoses used to join sections of pipe loop were prone to failure Replaced with ball joint design.
Ability to track on tilted axis
Improved Processes
e.g. Generate steam directly instead of running heat transfer fluid through heat exchanger - Improves efficiency but more difficult to control.
Why Solar Cookers are needed
High cost or Unavailability of commercial fuels – Kerosene, Coal, Gas, Electricity
Deforestation caused by Increasing Firewood Consumption
Use of Dung and Agricultural Waste as Fuels Instead of for Soil Enrichment
Diversion of Human Resources for Fuel Gathering
Principle of Cooking
The quantity of heat required for physical and chemical changes involved in cooking are small compared to the sensible heat of increasing food temperature and energy required for meeting heat losses that normally occur in cooking.
Once the contents of the vessel have been sensibly heated up to the cooking temperature (100C), the speed of cooking is practically independent of heat rate as long as thermal losses are supplied.
Differences in the time required to cook equal quantities of food in cookers of various heat supply capabilities are due mainly to different sensible heating up periods.
Types of Solar Cookers
Direct or focusing type solar cooker
In these cookers some kind of single or multifacet solar energy concentrator (parabolic, spherical, cylindrical, fresnel) is used which when directed towards the sun focus the solar radiation on a focal point or area where a cooking pot or frying pan is placed. In these cookers the convection heat loss from cooking vessel is large and the cooker utilizes only the direct solar radiation.
Indirect or Box type Solar Cooker
In these cookers an insulated hot box (square, rectangular, cylindrical) painted black from inside and insulated from all sides except window side which is double glazed is used. Single plane or multiple plane reflectors are used. Some times these are also known as oven type solar cookers. These can be electrical cum solar cookers and some cookers utilize a kind of latent heat storage material.
[attachment=41583]
Absorber within a Receiver
Receiver contains the absorber. It is the apparatus that “receives” the solar energy; e.g. evacuated tube. Absorber absorbs energy from concentrator and transfers to process being driven (engine, chemical reactor, etc.); e.g. the pipe within an evacuated tube.
Heliostats
Flat or slightly curved mirrors that track the sun and focus on receiver or concentrator. Used with solar furnaces and power towers.
What Have Been the Technical Challenges?
Development of Materials
Heat transfer tubes that are less prone to sagging & breaking.
Improved surface material of heat transfer tubes.
High absorptivity, low emissivity and long-term stability in air.
Low cost mirrors that have reflectivity and washability of glass.
Improved Components
Flex hoses used to join sections of pipe loop were prone to failure Replaced with ball joint design.
Ability to track on tilted axis
Improved Processes
e.g. Generate steam directly instead of running heat transfer fluid through heat exchanger - Improves efficiency but more difficult to control.
Why Solar Cookers are needed
High cost or Unavailability of commercial fuels – Kerosene, Coal, Gas, Electricity
Deforestation caused by Increasing Firewood Consumption
Use of Dung and Agricultural Waste as Fuels Instead of for Soil Enrichment
Diversion of Human Resources for Fuel Gathering
Principle of Cooking
The quantity of heat required for physical and chemical changes involved in cooking are small compared to the sensible heat of increasing food temperature and energy required for meeting heat losses that normally occur in cooking.
Once the contents of the vessel have been sensibly heated up to the cooking temperature (100C), the speed of cooking is practically independent of heat rate as long as thermal losses are supplied.
Differences in the time required to cook equal quantities of food in cookers of various heat supply capabilities are due mainly to different sensible heating up periods.
Types of Solar Cookers
Direct or focusing type solar cooker
In these cookers some kind of single or multifacet solar energy concentrator (parabolic, spherical, cylindrical, fresnel) is used which when directed towards the sun focus the solar radiation on a focal point or area where a cooking pot or frying pan is placed. In these cookers the convection heat loss from cooking vessel is large and the cooker utilizes only the direct solar radiation.
Indirect or Box type Solar Cooker
In these cookers an insulated hot box (square, rectangular, cylindrical) painted black from inside and insulated from all sides except window side which is double glazed is used. Single plane or multiple plane reflectors are used. Some times these are also known as oven type solar cookers. These can be electrical cum solar cookers and some cookers utilize a kind of latent heat storage material.