One of the policy targets of the European Union (EU) for the year 2020 is to achieve a renewable energy resource share of 20% in the end consumption. In Latvia, the corresponding target for this time period is 40%. The EU target for the year 2030 is to achieve at least 27%. One group of end users consists of households, to which many EU countries, including Latvia, applies a net billing system with the aim to increase the share of renewable energy resources. Net billing of electricity is an instrument that stimulates efficient use of energy and installation of low-capacity electricity generation equipment at households, at the same time increasing the individual power supply reliability for households. In order to reach the target defined by the EU and by Latvia, it is necessary to foster wider use of the net system, at the same time observing the interests of other electricity users. Solar and wind power plants provide the most frequently used renewable energy resources at households, which at the same time allows diminishing the electricity tariff/bill and increasing the share of renewable energy resources. The passive use of the existing net billing system is characterised by high initial investments, a low economic gain and a long payback period — from 10 to 25 years. The optimum payback period of renewable energy resources is up to twelve years, which is equal to the warranty period of the equipment. One of the main prerequisites for ensuring an optimal equipment payback period is as high as possible a proportion of auxiliary consumption against the amount of produced electricity. By introducing an optimal net system in Latvia, the share of renewable energy sources at households can be increased several times, without exceeding the technical limitations in the distribution and transmission networks. Corresponding to the existing model, a household producing energy by renewable energy resources pays for the electricity used for auxiliary needs only by the fee for ensuring the connection and the mandatory procurement component of capacity for the connection; regarding the electricity received from the grid there is an additional payment for power distribution and the mandatory procurement component (MPC); as regards the net electricity consumption (the difference between the received amount of electricity and the amount provided to the grid), it is also necessary to pay for the electricity. The user of the net system is to be considered a producer of renewable energy resources, hence special electricity tariff conditions apply, i.e. the mandatory procurement component burden is to be diminished and/or support for initial investment is to be encouraged. To determine the optimal payback period, a model of an energy-producing household was created, which demonstrates that, by diminishing the MPC or increasing the initial investment support for the electricity provided to the grid, the equipment payback period reaches the length of the equipment warranty period. Optimal use of renewable energy resources in a household provides a long-term economic gain, increasing the competitiveness of households, diminishing the amount of CO2 emissions, increasing the share of renewable energy resources used in the country and stimulating the attraction of investment.