Chemically stored energy.
Coal, oil and natural gas are energy-dense and dispatchable but require extraction and combustion infrastructure.
Side 45
Energy
Systems
A study of how energy is sourced, converted, transported, stored and used. Energy systems connect physical limits with infrastructure, reliability, cost and the different qualities of heat, electricity and fuels.
source→conversion→transmission→storage→end use
06system layers
05conversion ideas
06grid questions
45Side
Energy sources differ in form, density, variability and location.
The useful question is not merely “how much energy exists?” but what form it takes and how readily it can be converted into the service required.
Energy from nuclear reactions.
Fission produces large amounts of thermal energy from small fuel volumes and requires complex safety and waste systems.
Direct solar radiation.
Photovoltaics convert light to electricity while solar thermal systems convert radiation to heat.
Kinetic energy of moving air.
Turbines convert wind into mechanical rotation and then electricity.
Gravitational potential of water.
Hydroelectric systems convert water head and flow into mechanical and electrical energy.
Heat or stored biological energy.
Both are highly dependent on local resource conditions and conversion pathways.
Every useful energy service requires conversion.
Conversion changes form—chemical to heat, heat to motion, motion to electricity—while thermodynamic losses constrain what is possible.
What energy form enters?
Fuel, heat, light, motion?
Input quality determines which conversion technologies are available.
What device changes the form?
Engine, turbine, motor, cell?
Converters differ in efficiency, scale, controllability and operating conditions.
Where does unusable energy go?
Usually heat.
Energy is conserved, but not all energy remains available to perform useful work.
What useful form emerges?
Electricity, shaft power, heat?
Output form should match or efficiently connect to the end-use service.
How much input becomes useful output?
Useful output / input.
Efficiency is meaningful only when system boundaries and useful output are defined.
Conversion efficiencyη = useful energy output / energy input
Electricity must be balanced continuously across a network.
Power systems coordinate generators, transmission, distribution and loads while maintaining frequency and voltage within acceptable ranges.
Generation
Produce electrical power.
Generators differ in marginal cost, ramp rate, minimum output, availability and fuel dependence.
Transmission
Move bulk power long distances.
High-voltage networks reduce current for a given power transfer and therefore reduce resistive losses.
Distribution
Deliver power locally.
Distribution networks connect transmission substations to homes, businesses and smaller generators.
Balance
Supply must track demand.
System operators continuously manage generation, storage, imports and flexible load.
Reserve
Keep capacity for surprises.
Operating reserves respond to generator trips, forecast error and sudden demand changes.
Constraint
The grid has finite transfer capacity.
Congestion can make location as important as total generation quantity.
Storage moves energy through time.
Different technologies serve seconds, hours, days or longer periods and trade power capability against energy capacity, efficiency and cost.
| Storage | Stores energy as | Strength | Constraint |
|---|---|---|---|
| Battery | Chemical potential | Fast response, modular | Cost, degradation, duration |
| Pumped hydro | Gravitational potential | Large-scale, long-lived | Geographic requirements |
| Thermal | Heat or cold | Cheap for thermal end use | Not always easily reconverted to electricity |
| Hydrogen | Chemical energy | Potential long-duration storage and fuel | Conversion losses and infrastructure |
| Flywheel | Rotational kinetic energy | Very fast cycling | Limited energy duration |
Power and energy are different.
Power measures the rate of energy transfer; energy measures the total quantity transferred or stored.
Energy demand is really demand for services.
People do not consume kilowatt-hours for their own sake; they want heat, mobility, light, computation, motion and industrial transformation.
Temperature is the service.
Boilers, resistance heaters and heat pumps provide heat with very different conversion efficiencies.
Move people and goods.
Fuel energy, electric drivetrains, vehicle mass and utilization determine system-level energy use.
Heat, motion and chemistry.
Industrial demand includes high-temperature processes and feedstocks that can be harder to substitute.
Condition space and operate equipment.
Envelope quality, climate and equipment efficiency drive heating and cooling demand.
Compute and move information.
Servers, networks and cooling convert electricity into computational services.
Provide the same service with less input.
Efficiency gains can reduce demand, though behavioral rebound may offset part of the savings.
An energy technology changes the whole system around it.
Cost, reliability, infrastructure, resource quality, flexibility and environmental effects must be considered together.
Capacity
How much maximum power can the asset produce or carry?
Utilization
How often and how fully is that capacity used?
Dispatchability
Can output be increased when demanded, or is it driven by weather or process conditions?
Infrastructure
What pipelines, grids, chargers, ports, mines or storage systems are required?
Reliability
Which combinations of generation, network capacity, reserve and storage keep service available?
Lifecycle
Extraction, construction, operation, maintenance and disposal all shape total system impact.
A generator has low fuel cost but high capital cost.
Compare utilization and financing assumptions. Capital-intensive assets need sufficient lifetime output to spread fixed cost effectively.
A region adds large amounts of variable generation.
Study correlation of output with demand, geographic diversity, transmission, flexible generation, storage and demand response rather than capacity alone.
A process switches from combustion to electricity.
Measure the full conversion chain. Electrification can improve end-use efficiency while shifting demand upstream to generation and grid infrastructure.
Energy Systems EngineeringVanek, Albright & Angenent · system foundation
Sustainable Energy — Without the Hot AirDavid MacKay · quantitative energy reasoning
Power System AnalysisGrainger & Stevenson · electricity networks
Energy and Human Ambitions on a Finite PlanetThomas Murphy · energy scale and physical limits