Composition, not consumption

In 2016 Costa Rica ran on 100% renewables for 76 straight days.  Science Alert claims this is possible due to the small size of Costa Rica’s electricity demand.

This is incorrect!

The table below shows the composition of Costa Rica’s electricity supply over this period.  The composition, not the consumption, is what allowed Costa Rica to operate with 100% renewables.

Costa Rica's electricity supply composition (June - August 2016)
Hydro80.27 %
Geothermal12.62 %
Wind7.1 %
Solar0.01 %

The large penetration of hydro power allows Costa Rica to operate fossil fuel free.  Hydro power is unique as it has storage built into the power plant in the form of the water filled dam.

This storage allows hydro power to act in the same role that fossil fuels do in other countries.  Hydro can generate electricity as required, independent of the weather. Dispatchable generation is crucial for electricity as supply must always match demand.

A larger electricity demand with the same penetration of hydro would likely find it as easy to run fossil fuel free as Costa Rica.  Likewise the same sized demand with hydro replaced with wind or solar would need fossil fuels or some form of storage to keep the lights on.