CAPE TOWN, South Africa  — President Barack Obama on Sunday will announce a new initiative to double access to electric power in sub-Saharan Africa, part of his effort to build on the legacy of equality and opportunity forged by his personal hero, Nelson Mandela.

Pres. Obama, who flew from Johannesburg to Cape Town on Sunday, is paying tribute to the ailing 94-year-old Mandela throughout the day. The president and his family visited Robben Island, where the anti-apartheid leader spent 18 years confined to a tiny cell, including a stop at the lime quarry where Mandela toiled and developed the lung problems that sent him to the hospital for most of the month.

The White House said Pres. Obama’s guide during the tour was 83-year-old South African politician Ahmed Kathrada, who also was held at the prison for nearly two decades and guided Pres. Obama on his 2006 visit to the prison as a U.S. senator. The president also saw the prison courtyard where Mandela planted grapevines that remain today, and where he and others in the dissident leadership would discuss politics, sneak notes to one another and hide writings.

After the tour, Pres. Obama visited with retired archbishop Desmond Tutu before delivering what the White House has billed as the signature speech of his weeklong trip, an address at the University of Cape Town that was infused with memories of Mandela.

Pictured: President Barack Obama walks from Section B, prison cell No. 5, on Robben Island, South Africa. This was former South African president Nelson Mandela’s cell, where he spent 18-years of his 27-year prison term on the island locked up by the former apartheid government.