With an increasing integration of intermittent distributed energy resources (DERs)

the consequent voltage excursion and thermal overloading issues limit the self-sufficiency of distribution networks (DNs). The concept of soft open point (SOP) has been proposed as a promising solution to improve the hosting capacity of DNs. In this paper

considering the ability of building thermal storage (BTS) to increase the penetration of renewable energy in DNs

we provide an optimal planning framework for SOP and DER. The optimal planning model is aimed at minimizing the investment and operational costs while respecting various constraints

including the self-sufficiency requirement of the DN

SOP

building thermal storage capacity and DER operations

etc. A steady-state SOP model is formulated and linearized to be incorporated into the planning framework. To make full use of the BTS flexibility provided by ubiquitous buildings

a differential equation model for building thermal dynamics is formulated. A hybrid stochastic/robust optimization approach is adopted to depict the uncertainties in renewable energy and market prices. IEEE 33-bus feeder and a realistic DN in the metropolitan area of Caracas are tested to validate the effectiveness of the proposed framework and method. Case studies show that SOP/BTS plays a complementary and coordinated coupling role in the thermo-electric system

thereby effectively improving the hosting capacity and self-sufficiency of DNs.