Shading affects the output of the entire string of solar panels. It blocks the flow of the electrical current, which in traditional solar strings without optimisers, effects the entire string equally. For example, shading 50% of one panel would reduce the entire system efficiency by 50%.
More importantly, there is a solution to shading, bsolar recommends optimisers, which can be included in all our solar power systems. This will increase the energy output from PV systems by constantly tracking the maximum power point (MPPT) of each module individually achieving the optimal output.