This thesis investigates the cost optimal dimensioning of the solar photovoltaics (PV) system into a Nordic electric heated detached house and profitability of load control system to be designed for the site based on current electrical load possibilities. The cost-optimal dimensioning is carried out using hourly level simulation model and hourly data used in simulation consist of electricity SPOT price for 2021–2022, PVsyst-simulation for PV production and measured electricity consumption for 2021–2022.

The planned load control system can be used to control biggest electric loads including heating of the domestic water, in order to optimize the energy cost and profitability of the PV system. The control uses the electricity SPOT price, the “perfect” forecast for PV power generation and measured consumption data, as well as calculated estimates of load consumption. The block diagram of the load control is designed and bill of material (BOM) is defined to calculate the profitability. The plan for load control is designed, but load control is not implemented. Related to load control, numerical weather prediction (NWP) method for solar production estimation and method for interior heat demand estimation are introduced. At the end, commercial solutions for load control are investigated.

As a result of the research, the 11.2 kWp system was found to be the most profitable solar PV system. The load control system was found to be profitable depending on the SPOT price. The benefits decreased as the SPOT price increased, even making control of the smallest system loads almost unprofitable.