Which of the following are the main types of heat pumps?

The main types of heat pumps include air-source and ground-source heat pumps. Air-source heat pumps extract heat from the outside air and transfer it inside for heating or vice versa for cooling. They are widely used due to their efficiency, especially in moderate climates. Ground-source heat pumps, often referred to as geothermal heat pumps, utilize the relatively constant temperature of the ground to provide heating and cooling. They are typically more efficient than air-source systems, especially in extreme temperatures, because the ground temperature remains more stable compared to the air temperature.

While other options like solar, wind, and biomass are related to renewable energy sources and can be part of a wider energy strategy, they are not classified as main types of heat pumps. Instead, they represent alternative methods of generating power or heating rather than mechanisms designed specifically for heat transfer like the air-source and ground-source systems.