Sunglasses are surplus to requirements when walking through the labyrinth of alleyways that make up much of Lebanon’s Shatila refugee camp. High buildings locked in an embrace conspire with low-hanging electricity cables and water pipes to shield the camp’s 22,000 inhabitants from the sun.

But roofs are Shatila’s secret weapon: not just places to dry clothes and store water, they can help harness the sun and convert it into much-needed power.