Biofuels are defined as fuels which are generated directly or indirectly from biomass and can be solid, gaseous, or liquid. Regarding the global energy demand, traditional unprocessed biomass such as fuelwood, charcoal, and animal feces represent the central energy source in many developing and poor countries, especially in Africa and Asia. More advanced and efficient transformation technologies allow the production of biofuels from materials such as wood, crops, and waste material. Biofuels may be produced from forestry, agricultural, or fishery products or municipal wastes, as well as from agro-industry, food industry, and food service by-products and wastes. A distinction is made between primary, secondary, and tertiary biofuels. Primary biofuels are used in their organic form for heating, cooking, or electricity production. Secondary biofuels are generated via the transformation of biomass and include liquid biofuels such as ethanol and biodiesel that can be used in vehicles and industrial processes. Tertiary biofuels are based on integrated technologies that produce feedstock as well as fuel and require the destruction of biomass.
Storage and Conversion
Energy storage is the capture of energy generated at one time for the use at a later time. Energy storage technologies comprise a large set of centralised and distributed designs that are used to offer various services to the energy system. Energy storage is valuable in most energy systems, with or without high levels of variable renewable energy generation. The optimal role for a storage system changes depending on the current energy system landscape and future developments of a particular region. Several studies, which illustrate scenarios of a high usage of renewable energies, refer to a strong connection between power, gas, and heat. This leads automatically to smart and hybrid networks in order to reuse losses in one energy system as sources in the other one. On the one hand, improved load management and opportunities for the intermodal storage of energy in other networks enhance the security of supply. On the other hand, the increase of resource efficiency and the reduction of singular grid expansion costs strengthen economic efficiency. Therefore, the implementation of smart and hybrid networks is crucial for the future energy system. The development of those networks is going to be cost-effective in the long term because of the increased resource efficiency and high-quality and secure supply of energy. The cost-cutting leads to more competitive companies and, at least hypothetically, could also reduce the costs for end costumers.
The existing potential to improve energy use in several sectors of the economy is widely recognized. Investments in more efficient energy technologies represent more cost-effective alternatives when compared to the expansion of the energy supply base. Mandatory efficiency standards in many countries have induced constant modernization of appliances, vehicles, and buildings. Demand-side policies have contributed to the dissemination of efficient technologies and practices, reducing the energy required for energy services.
Waste-to-Energy technologies comprise waste treatment processes that produce energy in the form of electricity, heat or transport fuels from a waste source. These technologies can be applied to various forms of waste (semi-solid, liquid, gaseous). Electricity can be generated and distributed through local and national grid systems. Heat can be produced both at high and low temperatures and then distributed for district heating or used for specific thermodynamic processes. Several types of biofuels can be generated from the organic fractions of waste, in order to be then refined and sold on the market. The development of Waste-to-Energy technologies involves several different perspectives. Besides technical advances it is also essential to account for social, economic, and environmental issues. Growing population, higher urbanization rates and economic growth are changing the issues of (domestic) waste generation rates, waste composition, and transformation technologies.