EDGE recognizes renewable energy sources for their contribution to reducing carbon emissions in hot water production. The EDGE User Guide defines renewable hot water technologies: "Solar hot water collectors are considered a renewable source in EDGE, as they directly use solar energy to heat water, reducing reliance on fossil fuel-based energy" (EDGE User Guide, Section 4.2: Energy Efficiency Measures). Option B, solar hot water collectors, matches this description as it harnesses solar energy, a renewable resource. Option A (ground source heat pump) uses electricity to transfer heat from the ground, which is efficient but not renewable unless the electricity is from a renewable source: "Ground source heat pumps are efficient but rely on electrical input, not classified as a renewable source in EDGE" (EDGE Methodology Report Version 2.0, Section 5.1: Energy Efficiency Metrics). Option C (high efficiency boiler) typically uses gas or electricity, not a renewable source: "Boilers, even high-efficiency ones, are not renewable as they burn fuel or use grid electricity" (EDGE User Guide, Section 4.2: Energy Efficiency Measures). Option D (preheating water using waste heat from the generator) is a heat recovery method, not a renewable source: "Waste heat recovery improves efficiency but is not considered a renewable energy source in EDGE" (EDGE Methodology Report Version 2.0, Section 5.3: Energy Measures). Thus, solar hot water collectors (Option B) is the renewable source technology.