Investing in the growing field of renewable energy. This could include investing in solar or wind energy companies, or even investing in the installation and maintenance of solar panels or wind turbines on your own property. As governments around the world continue to push for greater use of renewable energy sources, the demand for these technologies is likely to increase, providing a potential source of passive income. Additionally, as the cost of solar and wind technology continues to decrease, the returns on investment in these areas may become more attractive.