Simson will take her place in the new-look governance team set to take office from 1 November.
In a mission letter to Simson, von der Leyen wrote she wanted the focus of the role to be "on the rapid implementation of energy efficiency and renewable energy legislation".
"You should work closely with the member states to set out their national energy and climate plans."
"To speed up the deployment of clean energy across the economy, you should promote a power system largely based on renewables, with increased interconnectivity and improved energy storage. You should look at how to facilitate the smart integration of the electricity, heating, transport and industry sectors," von der Leyen added.
Simson was Estonia’s minster for economic affairs in 2016-2019 and previously spent ten years in the country’s parliament as a member of the Estonian Centre Party.
After the European Union agreed to increase the renewable energy target to 27% by 2030 in December 2017, she said: "The debate in the council has shown the determination of all member states to create a resilient energy union."
Before the new executive team was announced, trade body WindEurope set out what it believes should be on the commission’s agenda.
This included a focus on increased ambition and delivery of decarbonisation, a smart approach to electricity and gas, investment in infrastructure, growth of research and innovation, and a low-carbon industrial policy "with renewable energy as the backbone".
"[Simson] will have a full in-tray of challenges, not least putting Europe’s energy system on track for net-zero carbon by 2050," said WindEurope chief executive Giles Dickson.
"The cheapest and most efficient way to decarbonise energy is the electrification of heating, transport and industry. And wind energy will play a central role," he added.
Elsewhere in von der Leyen’s new leadership team, Dutch lawmaker Frans Timmermans has been named executive vice president for the European green deal. Timmerman’s is currently serving in the Jean-Claude Juncker commission.
"I want the European green deal to become Europe's hallmark. At the heart of it is our commitment to becoming the world's first climate-neutral continent," von der Leyen said.
"It is also a long-term economic imperative: those who act first and fastest will be the ones who grasp the opportunities from the ecological transition. I want Europe to be the frontrunner. I want Europe to be the exporter of knowledge, technologies and best practice," she added.
Under the European green deal initiative, a key pledge in von der Leyen’s campaign for the presidency, the new commission is targeting an increase its 2030 emissions reduction target to at least 50%, up from the current aim of 40%.
The appointments are subject to European Parliament approval and hearings are expected later this month.
The former commission vice-president for the energy union in Juncker’s administration, Maroš Šefcovic, has a new role in von der Leyen’s team leading inter-institutional relations and foresight.