There are four main types of solar technology: 1. Photovoltaic (PV) systems, which convert solar energy directly into electricity using photovoltaic cells made of semiconductor materials. 2. Concentrated solar energy (CSP) systems that use reflective devices such as tanks or glass panels to concentrate solar energy to generate heat, which is then used to generate electricity. 3. Solar hydrothermal system, consisting of a solar collector facing the sun, using this collector to heat water directly, or heat the continuously flowing 'working liquid' and then heat the water device. 4. Solar steam collectors, or 'solar walls,' use solar energy to preheat the air circulating in the building.