Architects need to know how well different materials will insulate the building they design. To help them with this they need to know the U-values of different materials.

A U-value of 1 W/(m^{2} ^{o}C) means a 1 metre square area of the material with a 1 ^{o}C temperature difference across the material will conduct heat at a rate of 1 joule per second.

**U-values** measure how effective an insulator something is. The lower the U-value the better the material is at insulating.

## Solar panels

These heat water using the energy from the Sun. The hot water provided can be used to heat homes or to provide domestic hot water.

## Specific heat capacity

This is a measure of the amount of energy required to raise the temperature of 1kg of a material by one degree Celsius.

heat transfered = mass x specific heat capacity x temperature change

(joules, J) (kilogram , kg) ( joules / kilogram ^{o}C) (degrees Celsius, ^{o}C)

Example; How much energy is needed to raise the temperature of 1 kg of water by 30 ^{o}C. The specific heat capacity of water is 4200 J/kg^{o}C.