Carry, take, etc. coals to Newcastle
Definition 1 of 1
Pro Tip 1/3Cultural Origin
The phrase originates from Newcastle, England, known for its coal production. 
Explaining snow to an Eskimo is like carrying coals to Newcastle.
Pro Tip 2/3Idiomatic Usage
Use this phrase to express that an action is redundant. 
Donating ice in the Arctic is like taking coals to Newcastle.
Pro Tip 3/3Cultural Understanding
Understand the irony by knowing Newcastle doesn't need more coal. 
A solar panel salesman in the Sahara is like taking coals to Newcastle.