The secondary research process involved comprehensive analysis of energy regulatory databases, industry policy documents, technical standards publications, and authoritative renewable energy organizations. Key sources included the US Department of Energy (DOE), International Energy Agency (IEA), International Renewable Energy Agency (IRENA), National Renewable Energy Laboratory (NREL), Federal Energy Regulatory Commission (FERC), California Energy Commission (CEC), European Commission Directorate-General for Energy, China National Energy Administration, India Ministry of New and Renewable Energy (MNRE), Solar Energy Industries Association (SEIA), Solar Power Europe, China Photovoltaic Industry Association (CPIA), Energy Storage Association (ESA), International Electrotechnical Commission (IEC) standards, BloombergNEF, Wood Mackenzie Power & Renewables, and national energy ministry reports from key markets.
Installation statistics, policy incentive data, grid interconnection standards, technology cost trends, and market landscape analysis for lithium-ion batteries, lead-acid systems, customer-owned installations, and utility-scale residential storage programs were gathered using these sources.