In response to climate change and sustainability challenges, various incentive programs have increased solar photovoltaic (PV) generation interconnection in the low voltage electrical distribution system. However, electric utility support of PV generation is limited by reverse power flow into the electricity network at high penetration levels. This limits the ability to achieve Zero Net Energy (ZNE) behind individual meters and in whole communities. In parallel, district level energy systems, and Advanced Energy Communities (AEC) that include storage, offer a great prospect for integrating high levels of Distributed Energy Resources (DER) into the built environment. Optimally designing such systems to serve communities, commercial, and industrial loads, while maximizing the penetration of solar PV, has been a challenge to Distribution System Operators (DSO) and city planners. This paper proposes a Mixed Integer Linear Program (MILP) optimization to decide the best DER portfolio, allocation, and dispatch, for an AEC that achieves ZNE and islanding while respecting electrical grid operational constraints, with a focus on distribution transformer overloads. The main strategies to avoid transformer overloads were found to be judicious sizing and siting of battery energy storage and also optimally re-distributing PV throughout the community, which increased the ability of the electric infrastructure to support a PV deployment that is 1.7 times larger than the existing transformer capacity without the need for infrastructure upgrades. This work highlights the importance of including local infrastructure capacities, such as distribution transformer constraints when developing projects that result in high renewable penetration throughout the distribution network.