LAUSR

Abstract With a great reduction in the cost of rooftop photovoltaic systems (PVs), many new business models of PVs and the behind-the-meter scheme (BTMS) have been launched, especially the solar power purchase agreement (SPPA). The SPPA is a model that the potential investors supply and sell the PV output power to customers with the discount rates, directly. If the excess energy supplied to the grid is allowable, the investors will get additional revenue from the reverse power. The proposed rates from the investors are practically formulated in term of the SPPA discount rates on utility’s retail rate. Therefore, to convince the customers while retaining revenue of the investors, attractive and feasible SPPA discount rates should be investigated thoroughly. The proposed methodology in this paper to determine the SPPA discount rates for rooftop PVs under the SPPA and BTMS is presented. The cost optimization was developed and proposed to minimize the SPPA electricity charges while maintaining an acceptable internal rate of return (IRR). The benefit of the customers is the lower electricity charges, while the benefit of the investors is the sold power from rooftop PVs. Furthermore, with the proposed methodology, the large general service load in Thailand to assess the effect of the rate of excess energy and size of rooftop PVs. From the result, it showed that an oversized rooftop PVs will restrict the SPPA discount rates. The customers will get the higher SPPA discount rate if the rate of excess energy increases.