Direct solar use means using sunlight as heat or illumination for a task without first converting it into electricity. A solar air heater, for example, channels warmed air to dry materials or keep an enclosure above condensation levels. The key idea is simple energy matching: if the job needs heat, you avoid the extra losses and complexity of photovoltaic panels, batteries, inverters, and wiring.
In cyber security, that matters in remote or hardened deployments where power is scarce. Direct solar use can support passive drying, enclosure warming, or solar thermal preheating for cameras, radios, and sensor boxes, reducing failure from moisture and cold. It also changes the threat model: fewer electrical parts can mean fewer points of failure, but off-grid, sun-fed devices may be harder to monitor, log, or physically inspect. Attackers can exploit those assumptions by hiding equipment in low-visibility infrastructure or by relying on environmental power sources instead of mains electricity.