Power prices are set by demand and supply just like most other goods in a liberal market economy. Yet, power markets are also a highly regulated with a lot of security requirements to avoid blackouts or accidents. This means that power prices are constantly adjusted and determined by demand and supply within a clearly defined set of rules. In consequence, either side - demand or supply - can have an influence on the price.
If you have a lot of wind and sun, supply increases and since renewable energy sources generate power at zero marginal cost, prices decrease. At the same time, a moment without wind or sun with more expensive power from for example gas-fired power plants increases the price. Here is a graph where you can visually see the affect of wind and sun on the price:
☀️ sun 🍃 wind 🔵 price
Most northern European countries therefore have so called consumption peaks around lunch time and/or in the early evening - therefore prices tend to be higher in those time frames. On a Sunday night or an early morning for example, most industrial or commercial consumption is basically zero and private consumption is also limited. So demand is lower and therefore prices decrease.
In addition to those main factors regarding demand and supply, there are many more, such as fuel prices, power imports and exports to neighbouring countries or carbon taxes or energy subsidies that can affect the price.
If you want to get a feeling for the average price per month you can go on our website, whether it is for Norway, Sweden or Germany, put in your postal code and see the average monthly prices for the last 12 months.