The names explain the purpose: pyramids are graphical representation of different aspects of ecosystem. Pyramid of energy is always upright which may not be so for pyramid of numbers or pyramid of biomass.
Energy pyramid depicts flow of energy in the ecosystem: source of all energy in ecosystem is the SUN. Producers are only organisms in ecosystem who can trap the solar enrgy. So base of energy pyramid is always wide.
Now let us see a pyramid of number : in an orchard producers are some large trees but the trees will support a large number of consumers such as insects and birds. Pyramid of number in such ecosystem will be inverted as seen in the following illustration:
An inverted pyramid of biomass could be seen when we study aquatic ecosystems like a lake. The phytoplanktons at a given time is less in biomass but their lifecycle is very short; they actually reproduce faster than the consumers dependent on them.
