The heat and light of the sun in the summer should be fully used. We may dry our washed clothes quickly in the hot sun. And the sunlight can be used to heat water. Solar cookers have been invented and put to use. The electric source of the road lamps can be converted from the sunlight through the solar panels installed beside. I still remember the way of producing salt in summer in our native village. First, made the water filter through the salty soil and caught the drips below. Then exposed the new liquid in a large shallow saucer made by a plastic sheet under the sun. Later salt would come into being.