Clean Energy Technology

Biomass can be thermally converted to gaseous products via gasification. Biomass with a high lignocellulosic content (e.g. wood, straw, residues from forestry and agriculture, municipal solid waste) is heated, but not combusted, in an oxygen-restricted environment, producing a mixture of mostly hydrogen (H2) (20-30%), carbon monoxide (CO) (~20%), carbon dioxide (CO2) (~15%), and other hydrocarbons. Small-scale gasifiers (

Similar to the biomass gasification and catalytic methanation route (aka the bioSNG route), but with the addition of CO2 capture and compression following the CO2 removal step during syngas cleaning prior to methanation. Adding carbon capture and storage (CCS) is relatively easy given the pure stream of CO2 inherently produced in the process. Storing the CO2 rather than utilising it creates negative emissions that can offset hard-to-abate emissions elsewhere in the energy system. See non-CCUS variant for more detail.

Large, industrial size heat pumps can use renewable energy from air, water or ground but also waste energy from buildings and processes to provide heating and cooling. Heat pumps are considered large if they exceed capacities of 100 kW. Current technology can easily reach the one to several megawatt range with the largest units providing 35 MW in a single machine.

Latent heat storage (LHS) takes advantage of the energy absorbed or released at constant temperature during a phase change of the material. In most cases, solid/liquid phase change is utilised, with melting used to store heat and solidification used to release heat. For low temperature storage, water (ice storages) and aqueous salt solutions (for temperatures below 0 °C) have been commercialised and deployed on a large scale, e.g. the phase change of water at 0 °C is used for storage of cold for air conditioning and supply of process cold. Many low-temperature products using latent heat technology in buildings, mini-storage for food, and cooling for medication have been commercialised (TRL 9).

Similar to the catalytic methanation route to produce bioSNG, biomass is first gasified into syngas, and then the CO, CO2 and H2 in the syngas are biologically converted into biomethane via the use of microbes.

Similar to petroleum refineries, but solely using biomass resources. A biorefinery is an integrated system that converts a variety of biomass resources via several biofuel production processes into multiple biofuels and bioproducts.

Solar district heating plants employ sizeable fields of solar thermal collectors to supply or upgrade the heat in district heating networks. The technology is highly modular, and can therefore be applied - subject to space - to district heating networks from block to city sizes. The solar collector fields can be deployed on the ground, but can also be integrated into building-roofs. The technology necessary provides only a share of all heat, which typically hovers around 10-50% of system needs. A key constraint is the space required for renewable energy such as solar thermal. In order to keep costs to a minimum, they need to be installed close to the heat consumers, where land availability is the most scarce.

Energy is used to heat the storage medium, such as molten salt, without changing its phase, where it is stored as heat and used when needed. Electricity can be generated by using the heat stored in the molten salt to produce steam to drive a turbine but also, the heat can be directly used. Molten salts are inorganic chemical compounds, typically a mixture of nitrate/nitrite salts (e.g. a mixture of potassium and sodium nitrate), which have high boiling points, low viscosity, low vapour pressure and high volumetric heat capacities, i.e. they require a relatively small storage tank. When selecting the chemical mixture, it is advantageous to have the lowest possible melting point and the highest possible boiling point to maximise the available temperature range for the molten salt. Salts that would normally be solid at ambient temperatures are maintained at temperatures above their melting points so that they are always in liquid, i.e. molten, form and can be heated to around 560°C.

Often referred to as the bio-synthetic natural gas (bioSNG) route, biomass is first gasified into syngas and the syngas is then converted into biomethane via methanation. Biomass with a high lignocellulosic content (e.g. wood, straw, residues from forestry and agriculture, municipal solid waste) is gasified via heating in an oxygen-restricted environment, producing a mixture of mostly hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), and other hydrocarbons. This "syngas" is then cleaned, CO2 is removed and vented, and the remaining syngas is dried before undergoing catalytic methanation. Prior to methanation, a partial water-gas shift (WGS) reaction may be used to adjust the H2/CO ratio. Technical challenges revolve around tar buildup and removal during gasification.

Double-cropping is the practice of planting a second crop (cover crop) during the idle season of the first (main) crop. If the main crop is a food crop and the cover crop is an energy crop, it reduces competition between food and energy, and can potentially increase the amount of sustainable biomass that can be produced for energy. Having a cover crop also prevents soil erosion. However, more fertiliser is required to provide nutrients for the second crop.

Latent heat storage (LHS) takes advantage of the energy absorbed or released at constant temperature during a phase change of the material. In most cases, solid/liquid phase change is utilised, with melting used to store heat and solidification used to release heat. Applications in the power sector are solar thermal power plants, allowing the plant to provide electricity after sunset. Salt hydrate and paraffin wax systems are partly commercialised for temperatures below 100 °C (TRL 6-8). High-temperature LHS with integrated finned-tube heat exchangers has been constructed and operated with variable phase-change temperatures between 140 °C and 305 °C (TRL 7).

Energy is used to heat a solid storage medium, such as rocks, pebbles, metals or other refractory materials, without changing its phase, where it is stored as heat and used as heat or electricity when needed. The storage unit is packed with the solid storage medium through which a heat transfer fluid is circulated and can be used up to high temperatures (around 600°C). Solid storage media are considered mainly for cost reasons, as the cost of an equivalent mass of solid materials can be one or even two orders of magnitude lower than that of molten salts. Some solid storage materials also have a wider operating temperature range, freezing is not an issue, evaporation or leakage is not a problem. However, heating the solid is usually more difficult than heating a liquid such as a molten salt. A wide range of materials can be used as solid media storage. Any suitable candidate materials must be chemically and thermally stable and should be applicable over a wide temperature range. The maximum application temperature depends on the specific material and can be over 1000°C for ceramics such as magnesia bricks.