Energy Glossary
Technical terms and concepts related to battery storage and residential energy systems explained in clear, accessible language.
Technical terms and concepts related to battery storage and residential energy systems explained in clear, accessible language.
The energy storage industry uses specialized terminology that can be confusing for homeowners. This glossary explains key concepts in practical terms.
The amount of electrical energy a battery can store, typically measured in kilowatt-hours (kWh). A 10 kWh battery can theoretically deliver 1 kilowatt of power for 10 hours, or 10 kilowatts for 1 hour. However, usable capacity is typically lower than nominal capacity due to depth of discharge limitations and system reserves.
The percentage of battery capacity that has been discharged relative to total capacity. A battery discharged from 100% to 30% has undergone 70% depth of discharge. Manufacturers often limit maximum DoD to extend battery lifespan—a battery rated for 10 kWh might only allow 8 kWh usable capacity to protect the cells.
The ratio of energy retrieved from a battery to energy put into it during a complete charge-discharge cycle. If you store 10 kWh and retrieve 9 kWh, round-trip efficiency is 90%. The missing energy is lost to heat and conversion inefficiencies. Higher efficiency means less energy wasted during storage.
The number of complete charge-discharge cycles a battery can perform before its capacity degrades to a specified level, typically 70-80% of original capacity. A battery rated for 6000 cycles at 80% DoD should retain at least 70% capacity after 6000 full charge-discharge sequences under specified conditions.
The maximum rate at which a battery can charge or discharge, measured in kilowatts (kW). A battery with 5 kW power rating can deliver or accept up to 5 kilowatts at any moment. This is separate from capacity—a 10 kWh battery with 5 kW power rating takes at least 2 hours to fully charge or discharge.
Methods for connecting batteries to solar systems. DC-coupled systems connect batteries directly to solar panels through a hybrid inverter, offering higher efficiency but less flexibility. AC-coupled systems use separate inverters for solar and batteries, allowing easier retrofits to existing installations but with slightly lower efficiency.
A device that converts DC (direct current) electricity from solar panels or batteries into AC (alternating current) electricity used by household appliances. Hybrid inverters can manage both solar panels and batteries. Battery inverters specifically handle battery charging and discharging.
Electronic systems that monitor and control battery operation, managing cell balancing, temperature, charging rates, and safety functions. The BMS protects batteries from overcharging, over-discharging, and thermal issues while optimizing performance and lifespan.
The percentage of solar-generated electricity consumed directly by the household rather than exported to the grid. Battery storage increases self-consumption by storing excess daytime solar generation for use during evening hours when solar panels aren't producing.
Electricity pricing structure where rates vary by time of day, typically with higher prices during peak demand periods and lower prices during off-peak hours. Batteries can exploit ToU tariffs by charging during low-price periods and discharging during high-price periods.
The total cost of a battery system divided by the total energy it will store and discharge over its lifetime. LCOS accounts for upfront costs, installation, maintenance, and replacement, providing a per-kWh cost for stored energy. Lower LCOS indicates more economical storage.
Systems that regulate battery temperature to maintain optimal operating conditions. Batteries perform poorly in extreme temperatures—heat accelerates degradation while cold reduces capacity. Thermal management may include passive cooling, active cooling, or heating elements depending on chemistry and climate.
A lithium-ion battery chemistry known for long cycle life, thermal stability, and safety. LiFePO4 batteries typically offer 3000-6000+ cycles and operate safely at higher temperatures. They have lower energy density than other lithium chemistries, resulting in larger physical size for equivalent capacity.
Battery warranties typically specify both a time period and cycle count, with coverage ending when either limit is reached. Warranties also define capacity retention—commonly 70-80% of original capacity at warranty end. Understanding warranty terms helps evaluate expected system lifespan and replacement timing.
Battery systems configured to provide electricity during grid outages. Not all battery systems include backup functionality—some are designed only for self-consumption optimization. Backup-capable systems require additional equipment including automatic transfer switches and islanding capability.
Battery capacity degradation that occurs simply due to time passing, regardless of usage. Even unused batteries lose capacity over years due to chemical processes within cells. Calendar aging means batteries have finite lifespans even with minimal cycling.
Battery datasheets contain numerous specifications, but not all are equally relevant for residential applications. Key specifications to focus on include usable capacity, round-trip efficiency, power rating, cycle life at specified depth of discharge, operating temperature range, and warranty terms.
When comparing systems, ensure specifications are measured under comparable conditions. One manufacturer might rate cycle life at 80% DoD while another uses 100% DoD, making direct comparison misleading without understanding the testing parameters.
If technical concepts remain unclear or you need clarification on specific terminology, we're available to help explain.
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