The PV Data Display shows electrical energy in units of kWh (kilowatt hour). This is the everyday unit for electrical energy. A definition of a kWh is covered under "Electrical Power and Energy Terms". A quasi scientific overview of "energy" is given here.

Energy is a characteristic of a state that is capable of doing work. Work is the product of force acting through a distance. Pushing a box across a floor is work. The greater distance you push the box the more work you do. A heavy box requires more force (to overcome friction) to push it than a light box. Consequently, pushing the heavy box a given distance involves more work than pushing the light box. This matches with our everyday experience. At an atomic level, the processes involved in producing electricity from PV panels - getting an electron to break free of its bonds, move through a semi conductor and then, power equipment via a circuit – all requires work.

Energy can take many forms; potential or stored energy, the kinetic energy of a moving mass and electro-magnetic energy, to name a few. Fossil fuels have chemical potential energy that is released when they are burnt and this can be transformed into electricity via heat engines – steam boilers and turbines. The kinetic energy of wind can be converted to electrical energy via wind turbines. Sunlight is electro-magnetic energy. PV systems convert sunlight into electrical energy. Electrical energy can then be used to do what we more readily perceive as work; such as to power motors that push and pull things around.

Energy can be transformed from one type to another. Sunlight can be converted to electricity using PV technology, for example, and this electricity can be used in a lamp to produce light. During this transformation some energy is, in common parlance, "lost". Energy is, however, always conserved. What is really happening is that some of the energy is not captured by the process at all (e.g. light may be reflected off PV panels) or some is transformed into forms that are less useful in terms of human utility.  During the conversion of light to electricity and vice versa some of the energy involved in the conversion processes is converted to heat, or infrared energy, which is not useful if the objective is to produce visible light..

Increasing the efficiency of converting sunlight to electricity (by improving capture and reducing losses) is a major focus of PV research.

The scientific community uses the "joule" or "newton-meter" (N x m) as the units for energy or work. The "newton" is the scientific unit for force and was named in honor of Sir Isaac Newton who described the three laws of motion that form the basis of mechanics. He also identified the specific relationship between force, mass and acceleration (F=MA). The alternative energy unit, "joule", is named after the English physicist James Prescott Joule who pioneered the field of thermodynamics. He discovered the relationship between heat and mechanical energy, a relationship that underpins the conversion of fossil fuels into kinetic energy (a spinning turbine) and then electrical energy today.