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Energy is a measure of a system's ability to do work.  In other words, the amount of energy in a system is that system's ability to cause change or movement.

For a simple example think of a spring with a ball on it.  When you push the ball down onto the spring you are storing energy in the spring.  This stored energy is called potential energy.  The ability of the spring to cause movement and shoot the ball into the air depends on how much you compress the spring.  The more you compress the spring the more potential energy you store in it.  The greater the potential energy the more ability it has to do work.  When you release the ball the spring does work on the ball and shoots it into the air.  The energy in the spring is transformed into energy in the ball.  The ball now has kinetic energy, the energy of motion.

Energy comes to earth from the sun in two main forms that we can use directly, heat and light.  We use heat energy for solar heating and we transform the light energy into electrical energy.  Solar heating is used for water heating systems as one example.   A panel with water pipes in it collects heat energy from the sun and transfers that heat energy to the water in the pipes to provide hot water.   Light energy can be transformed into electrical energy that is used immediately or stored in batteries.  Photovoltaic (PV) panels are devices that are used to convert light energy into electrical energy.

Energy can only change from one form to another.  It can not be created or destroyed.  This is The Law of Conservation of Energy. 

Let's look at a solar vehicle as a simple example in the transformation of energy from one form to another.

Sunlight hits the PV panel and the panel transforms the light energy into electrical energy.  The electrical energy (electricity) passes through the wire circuit to the motor.  The motor transforms the electrical energy into mechanical energy and spins the drive shaft which spins the wheel.  The front wheel rotates on the ground to pull the car transforming mechanical energy into vehicle motion (kinetic energy).

Solar Vehicle Ideal Energy Chain:

Light Energy » Electrical Energy » Mechanical Energy » Kinetic Energy

The above case is ideal because not all systems are perfect and in reality there will be losses of energy from our system.

In a simplified view of this case some losses will be from:

  1. friction of electrons passing through the wires;  this is released as heat energy although you may never notice it in the case of the solar explorer.
  2. friction of the wheel on the ground;  this is released as either heat or sound energy.

Even with the losses the law of conservation of energy still holds.  The amount of energy into a system will always equal the amount of energy out of a system. If energy can not be created and can only be transformed from one form to another, how do we get heat and light energy from the sun?

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