For centuries, fossil fuels have been the primary sources supplying most of the energy needs of industrialized society.

In recent years, problems with fossil fuels have come up, such as carbon dioxide and sulfur dioxide emissions, global warming, energy crisis (depletion of fossil fuels) and so on. It is well known the energy crisis and environmental pollution impose a huge burden on modern society, especially for developing countries.

Renewable energy, such as solar, wind and hydropower, hydrogen and biomass are the promising alternatives to fossil fuels. Renewable energy is relatively clean and the supply is unlimited. The technologies for converting renewable energy to electricity are impressively developed and are now commercially available.

Although the cost of renewable generation has come down, renewable energy is still more expensive than fossil fuels in electricity generation. For electrical engineers, one of the advantages of using renewable generation is that electricity can be generated in close proximity to end users. For example, we can install photovoltaic panels and wind turbines on the roof of buildings to provide electricity to customers in the building. This forms a type of power system, called a micro grid, which is in contrast to the traditional large-scale power grid. Installing distributed generation close to customers can avoid the expensive cost on long distance power transmission and distribution.

Moreover, the customers can use the electricity generated by their own solar panels and wind turbines, and even sell their surplus electricity to the power company. People now have more and more adaptors and chargers for their electronic equipments. In fact, most of that equipment uses direct current (DC) power supply. Rectifiers and transformers are used to transfer 220-volt alternating current to low voltage DC for the equipment. Powering the equipment directly with DC micro grid can bypass the rectifiers and transformers and eliminate conversion losses.


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