In the 2030 new energy mix suggested by 6th Strategic Energy Plan, the ambitious upper limit of photovoltaics (PV) installation rate was set to 117.6GW, which is about two times of the present installation level. PV installation in household is a key factor forward realization of the 2030 new energy mix. However, PV is a variable renewable energy (VRE) which increases power system stabilization cost. Hence, its evaluation and reduction counterplan on the demand side are considered important for the realization of both massive PV installation and power system stabilization. In this paper, we will analyze power system’s supply and demand for both the case of controlling household distributed energy resources (DER) as usual and the case of optimal control of DER based on variable electricity prices in 2030 Kyusyu area. Thus, we will suggest effect of optimal demand control for both demand side benefit which is electricity bill reduction and supply side benefit which is power system stabilization cost.