<P> Latent heat can also be stored in technical phase change materials (PCMs). These can be encapsulated in wall and ceiling panels, to moderate room temperatures . </P> <P> Liquid hydrocarbon fuels are the most commonly used forms of energy storage for use in transportation, followed by a growing use of Battery Electric Vehicles and Hybrid Electric Vehicles . Other energy carriers such as hydrogen can be used to avoid producing greenhouse gases . </P> <P> Public transport systems like trams and trolleybuses require electricity, but due to their variability in movement, a steady supply of electricity via renewable energy is challenging . Photovoltaic systems installed on the roofs of buildings can be used to power public transportation systems during periods in which there is increased demand for electricity and access to other forms of energy are not readily available . </P> <P> Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass . In analog filter networks, they smooth the output of power supplies . In resonant circuits they tune radios to particular frequencies . In electric power transmission systems they stabilize voltage and power flow . </P>

Materials which can store electrical energy are called