Basic knowledge about energy field

1. ppa: power purchase agreement
2. Renewable energy is energy that is collected from renewable resources, which are naturally replenished on a human timescale, such as sunlight, wind, rain, tides, waves, and geothermal heat.^[3] Renewable energy often provides energy in four important areas: electricity generation, air and water heating/cooling, transportation, and rural (off-grid) energy services.^[4]
3. scenario, reference scenario; 参考方案。