{ "node": { "id": "term:energy-efficiency", "type": "Term", "label": "Energy efficiency", "properties": { "id": "energy-efficiency", "name": "Energy efficiency", "aka": [ "round-trip efficiency" ], "section": "topic-ratings", "definition": "Energy out divided by energy in over a full cycle. It is lower than coulombic efficiency because the charge voltage sits above the discharge voltage; cells reach 95–98 %, and a full storage system 85–92 % after power electronics and cooling.", "unit": "%", "related": [ "coulombic-efficiency", "voltage-hysteresis", "ir-drop", "stationary-storage", "voltage-efficiency" ], "url": "https://lemonergy.com/learn/glossary/energy-efficiency/", "mentions": [] } }, "edges": [ { "id": "edge:53", "source": "term:energy-efficiency", "target": "workflow:loss-accounting", "type": "usedIn", "properties": { "sourceFile": "wiki-blocks.json" } }, { "id": "edge:978", "source": "term:energy-efficiency", "target": "topic:topic-ratings", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:979", "source": "term:energy-efficiency", "target": "term:coulombic-efficiency", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:980", "source": "term:energy-efficiency", "target": "term:voltage-hysteresis", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:981", "source": "term:energy-efficiency", "target": "term:ir-drop", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:982", "source": "term:energy-efficiency", "target": "term:stationary-storage", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:983", "source": "term:energy-efficiency", "target": "term:voltage-efficiency", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:984", "source": "term:energy-efficiency", "target": "visual:efficiency", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } } ], "neighbors": [ { "id": "workflow:loss-accounting", "type": "Workflow", "label": "Compare grid and battery energy", "properties": { "id": "loss-accounting", "title": "Compare grid and battery energy", "kind": "studio", "summary": "Separate energy and loss signals make efficiency visible.", "steps": [ "Keep battery settings fixed.", "Change converter efficiency." ], "example": "7 kW battery-side power at 95% efficiency requires about 7.37 kW grid power and produces about 0.37 kW converter loss.", "observe": "Battery I²R loss differs from converter loss.", "limits": "A loss signal is not a predicted temperature. This network takes external temperature.", "url": "https://design.lemonergy.com/cosim.html?example=charging-home", "label": "Open the Studio example", "evidence": [ "js/charging-control.js", "js/charging-scenarios.js", "docs/CHARGING_BLOCKS_SPEC.md" ] } }, { "id": "topic:topic-ratings", "type": "Topic", "label": "Capacity, energy, power and ratings", "properties": { "id": "topic-ratings", "name": "Capacity, energy, power and ratings", "lede": "The numbers that size a cell and let two cells be compared.", "context": "Separate nameplate ratings from test results.", "example": "5 Ah at 3.6 V gives 18 Wh nominally. Integrated measured terminal power may give a different result.", "lesson_url": "https://lemonergy.com/learn/fundamentals/capacity-and-c-rate/", "lesson_label": "Open capacity and C-rate" } }, { "id": "term:coulombic-efficiency", "type": "Term", "label": "Coulombic efficiency", "properties": { "id": "coulombic-efficiency", "name": "Coulombic efficiency", "abbr": "CE", "section": "topic-ratings", "definition": "Charge delivered on discharge divided by charge put in on the previous charge. A healthy lithium-ion cell exceeds 99.9 %; the missing fraction is lithium lost to side reactions, so CE is an early and sensitive aging signal.", "formula": "CE = Q_discharge / Q_charge", "unit": "%", "related": [ "energy-efficiency", "loss-of-lithium-inventory", "sei", "formation" ], "example": { "title": "Compare charge in and charge out", "text": "If a defined test charges 5.00 Ah and subsequently discharges 4.95 Ah over the chosen voltage window, its coulombic efficiency is 99%. This ratio alone does not include voltage-related energy loss." }, "url": "https://lemonergy.com/learn/glossary/coulombic-efficiency/", "mentions": [] } }, { "id": "term:voltage-hysteresis", "type": "Term", "label": "Voltage hysteresis", "properties": { "id": "voltage-hysteresis", "name": "Voltage hysteresis", "section": "topic-charging", "definition": "The difference between the open-circuit voltage reached from charging and from discharging at the same state of charge. It is small for most lithium-ion chemistries but large for LFP and silicon, and it limits how precisely voltage can give SOC.", "related": [ "open-circuit-voltage", "ocv-soc-curve", "lfp", "silicon-anode", "energy-efficiency" ], "url": "https://lemonergy.com/learn/glossary/voltage-hysteresis/", "mentions": [ "state-of-charge" ] } }, { "id": "term:ir-drop", "type": "Term", "label": "IR drop", "properties": { "id": "ir-drop", "name": "IR drop", "aka": [ "ohmic drop", "voltage sag" ], "section": "topic-charging", "definition": "The instant step in terminal voltage when current starts or stops, equal to current times internal resistance. It is lost as heat and is the reason a cell’s voltage under load sits below its open-circuit voltage.", "formula": "ΔV = I × R", "unit": "V", "related": [ "internal-resistance", "ohms-law", "polarization", "open-circuit-voltage" ], "example": { "title": "Distinguish a current step from SOC change", "text": "When discharge current jumps from 0 A to 10 A through an illustrative 20 mΩ resistance, terminal voltage immediately drops by 0.2 V. Slower polarization and SOC change are separate effects." }, "url": "https://lemonergy.com/learn/glossary/ir-drop/", "mentions": [ "voltage", "closed-circuit-voltage" ] } }, { "id": "term:stationary-storage", "type": "Term", "label": "Stationary storage", "properties": { "id": "stationary-storage", "name": "Stationary storage", "abbr": "BESS", "aka": [ "battery energy storage system", "ESS" ], "section": "topic-applications", "definition": "Batteries installed in a fixed place — a container at a solar farm, a cabinet in a home — to shift energy in time or support the grid. LFP cells dominate because cost per cycle and safety matter more than mass.", "related": [ "lfp", "energy-management-system", "inverter", "energy-arbitrage", "long-duration-storage", "ul-9540a" ], "url": "https://lemonergy.com/learn/glossary/stationary-storage/", "mentions": [] } }, { "id": "term:voltage-efficiency", "type": "Term", "label": "Voltage efficiency", "properties": { "id": "voltage-efficiency", "name": "Voltage efficiency", "abbr": "VE", "aka": [ "voltaic efficiency" ], "section": "topic-ratings", "definition": "Average discharge voltage divided by average charge voltage over a cycle. The gap comes from resistance, overpotential and hysteresis, so voltage efficiency falls as current rises. Multiplied by coulombic efficiency it gives energy efficiency; a lithium-ion cell at moderate rate reaches about 95 %, a vanadium flow battery often only 80–90 %.", "formula": "VE = V̄_discharge / V̄_charge; EE = CE × VE", "unit": "%", "related": [ "energy-efficiency", "coulombic-efficiency", "overpotential", "voltage-hysteresis", "ir-drop", "flow-battery" ], "example": { "title": "Combine charge and voltage efficiency", "text": "If average discharge voltage is 3.5 V and average charge voltage is 3.8 V, voltage efficiency is about 92.1%. With a matched-cycle coulombic efficiency of 99%, energy efficiency is about 91.2%." }, "url": "https://lemonergy.com/learn/glossary/voltage-efficiency/", "mentions": [] } }, { "id": "visual:efficiency", "type": "Visual", "label": "Charge efficiency versus energy efficiency", "properties": { "title": "Charge efficiency versus energy efficiency", "summary": "Returning most of the charge does not return the same fraction of energy.", "readout": "99% × 92% = 91.08% energy efficiency.", "formula": "η_energy = η_charge × V̄_discharge / V̄_charge", "note": "Matched cycle and measurement boundaries; auxiliary loads omitted.", "software": { "status": "reference", "label": "Reference concept", "body": "For matching cycle boundaries, energy efficiency = charge efficiency × mean discharge/charge voltage ratio. The core nominal-energy helper does not calculate cycle efficiency.", "href": "../fundamentals/capacity-and-c-rate/" }, "html": "
Recovered energy
Recovered energyEnergy put in (Wh) versus Energy recovered (Wh). Ideal 100%; Selected efficiencies. Interpretation follows the graphs.00252550507575100100Energy put in (Wh)Energy recovered (Wh)
Ideal 100%Selected efficiencies (dashed)
" } } ] }