A study of 448 German households provides the first empirical evidence of what investors in direct investments have suspected for the past two years: The combination of solar power, battery storage, and a dynamic rate plan delivers measurably greater cost-effectiveness than any single component on its own. Four universities and a brief study by naturstrom AG show why this model is becoming a standard component of every new photovoltaic system—and which regulatory requirements in 2026 will ensure that it is no longer an optional choice but a mandatory requirement for direct investors.