recently there are some reports of Pres. Trump using solar panels as the wall. As shown by China's great wall, its best to own land both sides of the wall. And solar obviously does not like trees. Anyway, some back of the envelope calcs length approx, 3,000km or 3,000,000 metres a module is about 40cents per watt Price Quotes_EnergyTrend PV so 250W module is about $100 a module is about 1m wide and 1.5m high so roughly a fence 1 module high would contain 3,000,000 PV modules at between 250-350W each 3,000,000 * 0.250kW = 750 MW 3,000,000*0.350kW = 1,050 MW a four module (6m) high fence would be 3,000MW to 4,000MW hmmm, very rough calcs, but the incremental cost of using solar seems very sensible for that application.