Since they derive their energy from the same solar irradiance, many times they are described the same way (“solar”) but some people like to distinguish “solar” and “photovoltaics” separately as follows:
Photovoltaic (PV) panels convert sunlight to electricity that can be used to supplement or replace the electricity supplied by the utility grid. PV panels are most commonly installed on rooftops, and are most effective with a southerly exposure that provides full sun. Other possible installations include a ground mount, a pole mount, and atop a porch, carport, or other shaded area.
Solar thermal energy, or solar hot water, uses collector containers/plates to harness the sun’s energy to heat water for use in businesses, homes, and pools. The installation and appearance can be much like those of the PV panel, and the collectors are best installed facing south, under unobstructed sunlight. Unlike PV panels, solar thermal collectors do not convert sunlight to electricity, but transfer the energy directly to the water. Solar thermal systems displace the electricity or natural gas that would otherwise be required to heat water.
Here are some examples of different designs of solar hot water systems…