Because energy comes in many different forms such as heat, light, sound, movement, or on a more advanced level, matter, you can choose just about anything you see (or hear) and turn them into some great science projects on energy.
However, there are some things that you should keep in mind when considering how to go about structuring your child's experiment. Here is a list of some of the things worth thinking about:
Be original. This is probably the most important factor in any science project on energy or any other subject: try to think of something unique, or make something commonplace (like baking soda or corn flour) do something unusual.
Establish a clear end goal for your experiment: ask yourself what EXACTLY am I trying to accomplish? A good way to do this is to have a statement in your mind (and in your presentation) such as "I intend to demonstrate that X soda has more energy value than Y soda".
Make sure to document everything you do: just relying on our memory may be good enough in 2nd grade, but as your child progresses, more information will be required by the judging teachers.
Have a conclusion: make sure that they can tell the judges exactly what has been concluded from the experiment. Don't have them read from a script or even try to memorize it word for word. Instead, the project should be understood completely, making it easy for your child to present it fluently to the judges.
For organizing science projects on energy, there are several things that need to be considered.
Firstly, your child will need to have a good knowledge of what they intend to build for their project, so they should read on the subject as much as possible, but not to the detriment of their other lessons of course.
They will need to tell their teacher what they are planning and be sure that the teacher knows enough about the subject to give advice and guidance. The teacher will invariably suggest a different subject if they don't feel that they know enough.
They will need access to the right equipment. If the school can't provide this, you will have to, so make sure that you know you can get the equipment without breaking the bank!
Try not to use pre-packaged kits, because it's likely that other parents are doing exactly this and judges don't like to see repetition. If they do, then the only thing they can judge upon is the presentation.
Science projects on energy can come in many forms of course, but here are some ideas for you:
Showing how movement can be turned into electricity, perhaps with a watermill.
Building a solar oven; this can be likened to a greenhouse, or why cars get hotter than the external temperature on sunny days. This can also be shown to explain the "greenhouse gas" effect on the planet.
Demonstrating how static electricity is produced with a balloon; this one is great for really young children.
The best and most original science projects on energy will come from your imagination. Look at things around you and then think about what your child is ALREADY interested in. Regardless of whether it's playing a musical instrument, or watching TV, energy comes into the equation somewhere.
This last point is very important. If your child is already interested in one element of the project, they will be more inclined to learn more about it, AND they may develop a deeper understanding and appreciation for it.