The right power agreement can affect your monthly bill. It can affect on your budget then and this is why it is important to choose just the right type that will be most favorable to your situation. Every country has different power agreements and this is why it is important that you get oriented with the ones in your country.
In Norway, there are three types of power agreements and they are elaborated in one of the pages of Agva Kraft here These are the following:

Spot Price
This is a type of power agreement that is best suited for those who are looking for more affordable energy rates. In this agreement, the company bases its prices to the spot price from the power exchange, hence the name. However, you should know though that there is a chance you will be paying more on the winter but at least you will pay less most of the time.

Variable Price Flow Agreement
This is the second type of power agreement. This is almost the same as the first type, though the calculations are a little different. Due to the fact that most of the electricity is used at the daytime, the vendors based their calculations on the average used at this time as well. But one downside on this is you have to pay really high during winter days.

Fixed Price Flow Agreement
This is the last type and this is also the most common form. Here you will buy the current at a fixed price assuming this is stable for the entire year. This is the best solution for those who want to prepare the budget for the entire year as they already know how much they are going to pay more or less.