Transforming and Storing Energy
After energy has been collected and transported, it must be transformed into a form that can be directly used or stored for later consumption. Transformation is where energy finally becomes useful for everyday applications in a household.
Why Energy Transformation Matters
Energy rarely arrives in the exact form required by end uses. Electricity may need to be converted between DC and AC, heat may need to be stored or distributed, and production must be aligned with consumption in time.
Each transformation step introduces losses, but it also provides flexibility and usability. Designing an efficient system is about choosing the right transformations and minimising unnecessary conversions.
Electrical Energy Transformation
Photovoltaic systems produce direct current (DC), while most household appliances and public grids operate on alternating current (AC). Electrical transformation ensures compatibility between sources, storage, and loads.
DC to AC Conversion
Inverters convert DC electricity into AC. Their efficiency, waveform quality, and control capabilities directly affect system performance.
- Grid-tied inverters: Synchronise with the utility grid.
- Off-grid inverters: Supply isolated loads.
- Hybrid inverters: Manage PV, batteries, and grid interaction.
AC to DC Conversion
Many devices internally operate on DC. Rectifiers and power supplies convert AC back to DC, illustrating that unnecessary conversions should be avoided when possible.
Storing Energy
Storage decouples energy production from consumption. It allows excess energy produced during sunny or windy periods to be used later when production is low.
Electrical Storage (Batteries)
- Lithium-ion: High efficiency, high energy density, long cycle life.
- Lead-acid: Mature technology, lower cost, heavier and shorter lifespan.
- Flow batteries: Scalable capacity, mainly for larger installations.
Battery management systems (BMS) monitor voltage, current, temperature, and state of charge to ensure safety and longevity.
Thermal Storage
- Hot water tanks: Simple and efficient storage for domestic heat.
- Phase change materials: Store heat at nearly constant temperature.
- Underground storage: Seasonal storage of thermal energy.
Transforming Heat into Useful Services
Heat collected from the sun can be used directly or upgraded using heat pumps. The usefulness of heat depends largely on its temperature level.
- Direct heating: Domestic hot water and space heating.
- Heat pumps: Increase usable temperature by moving heat from one place to another.
- Absorption cooling: Use heat to provide cooling instead of heating.
Low-temperature heat is often abundant and efficient to collect, but requires appropriate distribution systems such as underfloor heating.
Sector Coupling: Electricity, Heat, and Mobility
Modern energy systems increasingly connect different sectors. Electricity can be converted into heat or mobility, while thermal storage can reduce electrical demand.
- Power-to-heat: Using excess electricity for heating.
- Power-to-mobility: Charging electric vehicles.
- Smart control: Prioritising local consumption over grid export.
Transformation Efficiency and Monitoring
Monitoring transformation stages helps identify losses and optimisation opportunities. Key indicators include conversion efficiency, battery state of charge, inverter loading, and thermal storage temperature.
These indicators are essential to understand whether the system behaves as expected under varying weather and consumption patterns.
Closing the Loop
Collecting, transporting, and transforming energy are tightly connected. Monitoring all three stages provides the insight needed to improve efficiency, resilience, and self-consumption.