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Across 4. there are ? broad categories of solar enrgy systems 6. solar water heating requires a very ? set up 7. passive solar heating produces little ? pollution as there is no moving mechanical parts involved 12. the process in concentrated solar systems involves ? being focused on mirrors to create a high-intensity heat source to power a mechanical generator to generate electricity 13. in solar water heating, light from the sun heats up an ? plate in the solar collector, and this heats the water running through the tubes in the solar collector. 14. the carbon footprint per year and per person should be ? to less than 2000kg Carbon Dioxide to ensure sustainable development for our earth 15. in solar cookers, a basic cooker is a one with an ? box which has a glass top 16. carbon footprint helps countries to monitor their ? gas emissions and in the medium-and long term

Down 1. solar water heating requires 2/3 ? energy than other methods,making it more energy-efficient 2. solar cookers are not suitable for ? areas, and for places with not much sunlight/hot weather 3. solar water heating is very ?-consuming,and not ideal for areas with high density buildings 5. passive solar heating does not require any solar collectors, but instead are heat-absorbing materials placed on ? 6. carbon footprint is the total amount of ? Dioxide gas produced directly or indirectly from human activities 8. in solar water heating, the heated water will then be pumped to a ? tank, and the heat produced can power heating or cooling systems. 9. solar cookers are useful in very ? areas, and also practical for survival means 10. passive solar heating does not produce a lot of electricity compared to other methods, less efficient as it cannot change its ? to face areas with more sunlight 11. solar water heating is a clean and ? source of energy