To work at your farm you need workers, which help you to make meals and products. Energy can be obtained by buying decorations at your farm. Every decoration gives you Happiness Points. These happiness points will turn into energy which is stored in your workers huts. You can buy the decorations, who gives you happiness point in the shop.
Workers Hut Edit
You can buy a workers hut in the store in exchanges for 3 materials. That will be a oven mitt, worker shoes and a workers hat. You can find these materials in the game while collect items, harvest your crops, in the chests at your land or your neighbours and as bonus for completing quests or the Arena. The first 2 workers hut, you get for free at level 4.
Workers Hut upgrade Edit
You also can upgrade your workers huts so they can reserve more energy for you. Here is a list what a upgrade will cost yu and how many energy you can reserve per workers hut.