With a significant growth of the rooftop photovoltaic systems (PVs) under the behind-the-meter scheme (BTMS), the battery energy storage systems (BESS) have been developed to enhance the performance of rooftop PVs in many aspects, especially the electricity charge savings. The BTMS can be typically classified into three schemes of self-consumption scheme, net-metering scheme, and net-billing scheme. Other than these schemes, the solar power purchase agreement (SPPA) has been developed to be one the most attractive business models. The SPPA is the scheme where the investors propose to directly sell an electricity from rooftop PVs with BESS to the customers without passing through the utility’s infrastructure, such as electricity meter, distribution line, etc. The proposed rates are typically performed in terms of the discount rates on Time-of-use (TOU) tariff. Therefore, this dissertation proposes a novel methodology to investigate the battery capacity, operation schedule of the BESS and SPPA discount rates for rooftop PVs under the BTMS and SPPA. The mode-based operation of the BESS was adopted and developed for self-consumption, net-metering, net-billing schemes, and SPPA. For the typical BTMS, the objective was only to minimize the electricity charge of the customers. For the SPPA, the main objective was to minimize the electricity charges of the customers while maintaining the internal rate of return of the investors. In addition, as a working example, the TOU tariff with demand charges for large general service load in Thailand was implemented with the proposed methodology to evaluate the effects of installed capacity of rooftop PVs, battery capacity, rate of excess energy and battery degradation. The result showed that the installed capacity of rooftop PVs, the rate of excess energy and the battery degradation have significant effects on the battery capacity, operation modes of the BESS and SPPA discount rates. Under the typical BTMS, it is obvious that an increase of the installed capacity of rooftop PVs will extremely increase the battery capacity and operation modes in charging and discharging modes when the reverse power flow is available with high rate of excess energy. In addition, the consideration of battery degradation will lead to an increase of battery capacity. Under the SPPA, the proposed SPPA discount rates from the investors will be constrained when the battery capacity is increased, and the installed capacity of rooftop PVs is oversized. The consideration of the battery degradation will also limit the proposed SPPA discount rates.