Solar panels are now mandatory on all new and renovated buildings as a result of an ongoing effort to update the country's building code. Spain's building code has not changed since the 1970s and has done little to promote energy efficiency. The new law, which was implemented September 29th, requires homes to heat 30 to 70 percent of their hot water with solar power. "'We have to make up the time we have lost,' Environment Minister Cristina Narbona said.