Energy & Green Tech

On the road to nontoxic and stable perovskite solar cells

Halide perovskite materials show high efficiency for solar energy technologies, but this comes at a cost: The best perovskite materials incorporate toxic lead, which poses a hazard to the environment. Replacing lead with ...

Energy & Green Tech

How to go carbon neutral: Lessons from a Danish island

When fish stocks crashed in the Baltic in the late 1990s, the islanders of Bornholm, Denmark, realised they had to reinvent themselves. Their rocky outcrop, some 200km east of Copenhagen, had been in decline for years. Its ...

Energy & Green Tech

Technique harvests waste heat from untapped sources

Thermoelectric materials convert heat to electricity or vice versa. However, their application to harvest waste heat is limited by challenges in fabrication and materials. Finding cost-effective ways to cover large and potentially ...

Energy & Green Tech

Electric cars better for climate in 95% of the world

Fears that electric cars could actually increase carbon emissions are unfounded in almost all parts of the world, news research shows. Media reports have regularly questioned whether electric cars are really "greener" once ...

Energy & Green Tech

Simple, solar-powered water desalination

A completely passive solar-powered desalination system developed by researchers at MIT and in China could provide more than 1.5 gallons of fresh drinking water per hour for every square meter of solar collecting area. Such ...

page 1 from 8


In physics and thermodynamics, heat is the process of energy transfer from one body or system to another due to a difference in temperature. In thermodynamics, the quantity TdS is used as a representative measure of the (inexact) heat differential δQ, which is the absolute temperature of an object multiplied by the differential quantity of a system's entropy measured at the boundary of the object.

A related term is thermal energy, loosely defined as the energy of a body that increases with its temperature. Heat is also loosely referred to as thermal energy, although many definitions require this thermal energy to actually be in the process of movement between one body and another to be technically called heat (otherwise, many sources prefer to continue to refer to the static quantity as "thermal energy"). Heat is also known as "Energy".

Energy transfer by heat can occur between objects by radiation, conduction and convection. Temperature is used as a measure of the internal energy or enthalpy, that is the level of elementary motion giving rise to heat transfer. Energy can only be transferred by heat between objects - or areas within an object - with different temperatures (as given by the zeroth law of thermodynamics). This transfer happens spontaneously only in the direction of the colder body (as per the second law of thermodynamics). The transfer of energy by heat from one object to another object with an equal or higher temperature can happen only with the aid of a heat pump, which does work.

This text uses material from Wikipedia, licensed under CC BY-SA