Off-Peak Electric Heating and Integration of Solar Water Heaters for Domestic Hot Water in the Nordic Climate

This study assessed the cost-saving potential of off-peak electric heating and solar water heating for domestic hot water (DHW) in the Nordic climate. A TRNSYS model of a typical four-apartment building with 10 occupants was used to simulate three scenarios: thermostat-controlled heating, off-peak time-controlled heating, and off-peak heating combined with solar thermal collectors. Simulations were conducted for five Norwegian cities representing different electricity price zones using spot prices from 2022 to 2024. Off-peak electric heating reduced DHW energy costs by 10–19% while integrating solar collectors increased savings to as much as 50%. Economic analysis showed that solar DHW systems are financially viable in Oslo, Bergen, and Stavanger, where higher electricity prices and greater solar resources improve returns. However, the investment was not economically attractive in Trondheim or Tromsø because of lower solar irradiation and lower electricity prices.