Exxaro and Seriti are Eskom's two biggest coal suppliers, together accounting for about 80%.
The first phase was expected to include a number of solar photovoltaic facilities both on-mine and at related Eskom sites, and future projects could include energy storage and wind power.
"This is a significant, landmark development in South Africa's energy transition to a low carbon economy for three of South Africa's largest players in the mining and energy sectors," Exxaro CEO Mxolisi Mgojo said.
The trio said the MOU was a step towards achieving a just transition, without jeopardising the country's fragile energy supply or livelihoods, saying the new projects would create jobs and re-skilling opportunities.
"This is one of the many initiatives Eskom has embarked on to achieve a NetZero status by 2050," Eskom CEO Andre de Ruyter said.
Under the MOU, Exxaro envisaged reducing CO2 emissions by up to 130,000 tonnes per annum at its Matla coal mine, a saving of about 70%.
Seriti was aiming for a cut of 350,000tpa, which it said was more than half its current emissions of 700,000t of CO2-equivalent through the consumption of coal-fired electricity generation.
"As a company we are fully committed to decarbonisation and a just transition, and in working with our partners - in business, government, labour and communities - in achieving this, and have formed a new subsidiary, Seriti Green to pursue this," Seriti CEO Mike Teke said.
The companies committed to begin the projects "as soon as possible", subject to regulatory approvals.
South Africa's miners were hobbled by unprecedented power outages two years ago and the country continues to experience both scheduled "loadshedding" and unplanned outages, hindered by increasing theft and vandalism.