In Chapter 5, we learn that Snowball has been reading back issues of Farmer and Stockbreeder, so he is making a real effort to learn about farming and how to make their lives better. When Snowball shares these ideas with the other animals, Napoleon says Snowball's plans "would come to nothing, and seemed to be biding his time." This is one of many points Snowball and Napoleon disagree on. Snowball wants to incite rebellions in other farms. Napoleon wants to focus on their own farm.
So, it is not surprising when Napoleon and Snowball disagree on the windmill. Snowball wants to modernize the farm. Snowball says the windmill will provide energy for the farm in a number of ways.
This would light the stalls and warm them in winter, and would also run a circular saw, a chaff cutter, a mangel-slicer, and an electric milking machine.
Snowball spends hours drawing up the plans. The animals are amazed and excited, even if they don't understand the mechanics. But Napoleon says he was against the windmill from the start. To show his contempt, he urinates on the windmill plans. Napoleon claims he wants to focus more of their efforts on food production. This created a polarization on the farm. Some animals favored Snowball's plan and some favored Napoleon's:
The animals formed themselves into two factions under the slogan, "Vote for Snowball and the three-day week" and "Vote for Napoleon and the full manger."
They intend to vote on the windmill, but Napoleon sabotages the vote and runs Snowball off of the farm. A few weeks later, Napoleon, the true hypocrite, says the windmill will be built. He even has Squealer tell the other animals that he was behind the idea for the windmill from the start.
That, he said, was Comrade Napoleon's cunning. He had seemed to oppose the windmill, simply as a maneuver to get rid of Snowball, who was a dangerous character and a bad influence. Now that Snowball was out of the way, the plan could go forward without his interference.