This guide explores how to build a solar energy system for your home and will review the best free tools for designing it. OpenSolar is a free, web-based solar design and sales platform. It offers tools for designing PV systems, allowing users to create accurate solar proposals and. Building your own DIY solar system is one of the most rewarding projects you can take on — it's affordable, sustainable, and puts you in full control of your power. In this guide, we'll break. Designing a residential solar system is a meticulous, multifaceted undertaking that requires balancing your energy needs, the practical conditions of your property, and the financial aspects of the investment.