LONDON (Bloomberg) — Centrica Plc, the UK's biggest energy supplier, and the British unit of Iberdrola SA said the country must upgrade aging electricity infrastructure to achieve a 2020 renewables target. "The grid is a problem," Sue Wheeler, head of new energy at Centrica, told reporters yesterday at the annual British Wind Energy Association conference in London. "The targets are challenging but achievable" if grid connections receive sufficient investment, she said. The UK has a goal to get 15 percent of its energy from renewable sources by 2020, under a European Union proposal. The country, Europe's third-biggest electricity consumer, has expanded wind-power capacity to become the world's largest offshore operator.