A photovoltaic cell (also known as a solar cell) converts energy from the sun into electrical energy.

Connecting the 8 batteries in series multiplies their voltage while keeping their current the same yielding a 72V 5A configuration. Connecting the 8 batteries in parallel multiplies their current while keeping their voltage the same yieleding a 9V 40A configuration. Using a series-parallel connection, 4 batteries can be connected in series and 4 can be connected in parallel resulting in a 36V 20A configuration.

Resistors are used to limit voltage and/or current in a circuit and can have a fixed or variable resistance.  Variable resistors (often called potentiometers or rheostats) are used when dynamic control over the voltage/current in a circuit is needed, for example, in a light dimmer or volume control.

Semiconductors have valence shells that are exacly half full and can conduct electricity under some conditions but not others. This property makes them useful for the control of electrical current.

An electrical circuit is a path through which electricity flows. This path contains one or more components that create a load (something that is using electricity) and that load acts as resistance to the passage of electricity through the circuit. Electricity can only flow through a circuit when the path is closed and cannot flow through an open circuit.