What’s happening?

If you were to take all of the stuff that makes up our solar system, 99.86 per cent of it would be from the Sun, and consist of mostly hydrogen and helium. It’s not only a big object (109 planet Earths sitting side-by-side could fit across its diameter), its mass gives it a lot of gravity to squeeze all of that hydrogen and helium together.
All of that squeezing makes the Sun’s particles bump into one another rather energetically. In fact, the particles are pushed together so tightly, the forces that help hydrogen atoms stick together can reach out to one another and grab onto other atoms, making even bigger atoms. This is called nuclear fusion and is how hydrogen can turn into the slightly bigger element, helium.
However, two atoms of hydrogen don’t quite add up to make a single helium atom. There is a tiny bit of stuff left over, some of which is ejected from the helium in the form of light energy. Deep inside the Sun, light bounces around from atom to atom, taking tens of thousands of years to make it all the way to the Sun’s surface.
From there, it only takes eight minutes to shoot across the emptiness of space to get as far as Earth and a small amount makes it to your solar heater. The aluminium foil will bounce the light back onto the black paint of the glass bottle. Black absorbs light energy quite well – since it can’t go anywhere else, the energy is absorbed by your water, turning into heat energy and making your tea nice and hot. The surrounding plastic container makes sure the surrounding air won’t blow on your bottle and carry the heat away, acting as an insulator.

Applications

Our busy, busy world needs energy to operate. Whether it’s to heat our water, drive our vehicles or help us keep cool on a hot day, we need a lot of energy. Much of it comes from burning materials such as coal, natural gas or oil. These ‘fossil fuels’ were once plants that grew by absorbing energy from the Sun. In other words, the energy we get from fossil fuels originally came from solar radiation.
It makes sense to look for ways to get our energy directly from the Sun. Unfortunately, while energy locked up in coal is available 24 hours a day, the amount of energy that’s available directly from the Sun varies considerably throughout the day and night. Scientists are currently looking for ways to efficiently trap solar energy so we can use it whenever we want, either in giant batteries or in heated materials like oil or water.
Until we make better batteries, we can take better advantage of the Sun’s energy to keep us toasty and warm.

Warning: This activity heats water to scalding temperatures, and uses sharp cutting tools. Younger scientists should get an adult to help.

You will need

• Large fruit juice bottle (2.5L or larger)
• Aluminium foil
• 300ml glass bottle suitable for holding drinking water
• Black paint
• Paintbrush
• Scissors / craft knife
• Craft glue
• Water
• Sink
• Tea bag
• Mug

What to do

1. Soak the juice bottle in a sink full of water overnight and remove the labels.
2. Thoroughly clean and rinse the glass bottle. Technically, you could use a small plastic bottle; however it is not recommended that you drink water that you have heated in a plastic container.
3. Paint the outside of the glass bottle with black paint and wait until it dries.
4. Unscrew the cap from the large plastic bottle. Use your sharp blade or scissors to trace the around the mouth of your glass bottle on the cap. Cut the circle out of the cap (hint: cut around the outside of your traced line to make the hole slightly larger), leaving a hole large enough for the mouth of the glass bottle to poke through. Screw the cap back onto the plastic bottle.
5. Cut the bottom from the plastic bottle. Glue a sheet of aluminium foil inside the container so it completely covers half of it.
6. Place the glass bottle inside, with its neck poking through the hole in the cap of the plastic bottle. If it’s a little loose, try gluing it in place.
7. Insert a tea-bag into the glass bottle and fill it with water.
8. Take your solar-heater outside and leave it in the sun for two hours, positioned so the glass bottle is exposed to as much sunlight as possible.
9. Carefully pour your sun-heated tea into a mug. Be careful – it will be quite hot!

	Cut the bottom from an orange juice bottle.
	Cut a hole in its lid.
	Paint a glass bottle with black paint.
	Leave your water heater out in the Sun for a nice cup of solar tea!