Both solar energy and nuclear energy face significant economic challenges. Sustainable energy costs have traditionally been greater than any of those associated with the growth of fossil fuel power generation, although the costs of renewable energy technologies (especially photovoltaic) have dropped. Furthermore, capital costs remain a big challenge in the nuclear generation. In many nations, the cost of building small nuclear power plants is quite large due to time, technology, and environmental and safety challenges for consumers. Such problems might not be as big for state-owned corporations or controlled industries for which utilities have quick access to cheap resources, and this partially explains why the interest for nuclear reactors in Asia is far greater than in the United States or Europe. Learning could help decrease costs for both types of technologies, but the track record for learning-by-doing in the nuclear sector is not good.