Every term you need to understand solar panels, batteries, inverters, and off-grid systems — explained in plain language with formulas where applicable. The most complete solar glossary for beginners and professionals.
A system design where an off-grid inverter and a grid-tie inverter are connected on the AC side, allowing solar energy to charge batteries through the off-grid inverter.
Electric current that periodically reverses direction. Used in homes and the grid. Solar panels produce DC which inverters convert to AC.
The temperature of the surrounding air. High ambient temperatures reduce solar panel efficiency and battery performance.
A unit of electric charge representing the amount of energy a battery can deliver. A 100Ah battery can deliver 10A for 10 hours.
A group of solar panels connected together (in series, parallel, or both) to form a single power-generating unit.
The number of days a battery bank can power loads without any solar input. Also called "days of autonomy."
All components of a solar system except the panels themselves — wiring, combiner boxes, mounting hardware, charge controllers, inverters, and monitoring.
Multiple batteries wired together to increase total voltage, capacity, or both. Series wiring increases voltage; parallel wiring increases Ah capacity.
An electronic system that monitors and protects a battery pack. Manages cell balancing, temperature, overcharge, over-discharge, and short-circuit protection.
A measure of a battery's current capacity compared to its rated capacity when new. Expressed as a percentage. Degrades over charge cycles.
A diode inside a solar panel junction box that redirects current around shaded or damaged cells, preventing hot-spot damage and reducing power loss.
The rate at which a battery is charged or discharged relative to its capacity. 1C means fully charging or discharging in 1 hour. 0.2C means 5 hours.
A device that regulates the voltage and current from solar panels to batteries. Prevents overcharging and over-discharging. Two main types: PWM and MPPT.
Fuses or circuit breakers required between the battery and inverter, and between arrays and charge controllers, to protect wiring from overcurrent.
An electrical enclosure that connects multiple solar strings into a single output. Contains fuses or breakers for each string.
A utility-scale technology that uses mirrors or lenses to focus sunlight onto a small area to generate heat and electricity. Different from photovoltaic (PV) systems.
See Autonomous Days. The number of cloudy days a fully charged battery bank can cover without solar recharge.
A system design where solar panels charge batteries directly through a charge controller. More efficient than AC coupling for energy storage.
The percentage of a battery's capacity that has been used. A 100Ah battery discharged to 50% has a DoD of 50%. Deeper DoD shortens battery lifespan.
A semiconductor device that allows current to flow in one direction only. Used in solar systems as bypass diodes and blocking diodes.
Electric current that flows in one direction. Solar panels produce DC electricity. Batteries store and deliver DC. Inverters convert DC to AC.
The amount of energy stored per unit of weight (Wh/kg) or volume (Wh/L). Higher energy density means lighter or smaller batteries for the same capacity.
The total amount of electrical energy a solar system produces over a given period (day, month, year), expressed in kWh.
A controlled overcharge applied to flooded lead-acid batteries to balance cell voltages and remove sulfation. Not suitable for sealed or lithium batteries.
A measure of solar cell quality. The ratio of the maximum power output to the product of open-circuit voltage (Voc) and short-circuit current (Isc).
A lightweight solar panel that can bend slightly, suitable for curved surfaces like RV roofs and boats. Generally lower efficiency than rigid panels.
A maintenance charging voltage applied to a fully charged battery to compensate for self-discharge and keep it at 100% without overcharging.
An inverter that synchronizes with the utility grid and feeds excess solar energy back to the grid. Requires grid power to operate — shuts off during outages.
A hybrid solar system that can export to the grid and also store energy in batteries for use during grid outages.
A safety device required in solar PV systems to detect ground faults and interrupt the circuit to prevent fires and electric shock.
An inverter that combines the functions of a grid-tie inverter and an off-grid inverter. Can manage solar panels, battery storage, grid, and loads simultaneously.
A solar system connected to both the utility grid and a battery bank. Can use solar, batteries, and grid power interchangeably based on availability and programming.
The power of solar radiation per unit area, measured in W/m². Standard Test Conditions use 1000 W/m². Also called solar irradiance.
Maximum Power Point Tracking charge controller. Uses electronics to find and operate the solar panel at its maximum power point. Up to 30% more efficient than PWM.
1,000 watts. A unit of power. A 5 kW solar system has panels with a combined peak output of 5,000 watts.
A unit of energy equal to 1 kilowatt of power used for 1 hour. The standard unit on electricity bills. A 5 kW system producing for 4 hours generates 20 kWh.
The oldest rechargeable battery technology. Affordable and reliable. Two types: flooded (FLA) and sealed (AGM/Gel). Shorter lifespan and lower DoD than lithium.
Lithium Iron Phosphate battery. The safest lithium chemistry for solar storage. Supports 80-100% DoD, 2,000-6,000+ cycles, and requires no maintenance.
Any device that consumes electrical energy in a circuit. In solar design, loads are all the appliances and equipment the system must power.
A record or estimate of the daily, weekly, or seasonal pattern of energy consumption — which loads run, for how long, and at what wattage.
The point on a solar panel's I-V curve where the combination of voltage and current produces the maximum power output.
Passivated Emitter and Rear Cell technology. Adds a reflective rear layer to monocrystalline cells to improve efficiency by capturing more light.
Solar panels made from a single crystal of silicon. Higher efficiency (18-23%) and longer lifespan than polycrystalline. Recognizable by uniform black appearance.
A billing arrangement where excess solar energy exported to the grid offsets the electricity drawn from the grid, reducing the electricity bill.
The standard operating voltage assigned to a battery or system — commonly 12V, 24V, or 48V for off-grid systems.
A solar power system completely independent from the utility grid. Relies entirely on solar panels and battery storage to power loads.
The maximum voltage a solar panel produces when not connected to any load. Used to size charge controllers and verify panel health.
Fuses and circuit breakers that protect wires from carrying more current than their rated capacity, preventing overheating and fire.
The gradual reduction in a solar panel's power output over time. Most panels degrade at 0.5-0.8% per year and are warranted to retain 80% output after 25 years.
Connecting multiple panels or batteries positive-to-positive and negative-to-negative. Increases total amperage (Ah or A) while keeping voltage constant.
The time it takes for the energy savings from a solar system to recover its initial installation cost.
The number of hours per day when solar irradiance averages 1,000 W/m². Used to estimate daily energy production. Varies by location and season.
The physical process by which semiconductors convert sunlight directly into electricity. The basis of all solar panel technology.
Solar panels made from multiple silicon crystals. Lower efficiency (15-18%) than monocrystalline but historically cheaper. Recognizable by blue speckled appearance.
The rate at which energy is transferred or used. In solar, measured in watts (W) or kilowatts (kW).
Pulse Width Modulation charge controller. The simpler, more affordable type. Works best when panel voltage closely matches battery voltage. Less efficient than MPPT.
A measure of the financial gain from a solar investment relative to its cost, expressed as a percentage.
The ratio of energy output from a battery to the energy input used to charge it. LiFePO4 achieves ~95-98%. Lead-acid achieves ~70-85%.
The rate at which a battery loses charge when not in use. LiFePO4 loses ~2-3% per month. Lead-acid loses ~5-15% per month.
Connecting panels or batteries positive-to-negative in a chain. Increases total voltage while keeping current (Amps) constant.
The current produced by a solar panel when its output terminals are shorted. The maximum possible current at zero voltage.
See Charge Controller. Regulates power from solar panels to batteries to prevent overcharging.
The power of sunlight per unit area reaching a surface. Standard Test Conditions use 1,000 W/m² at 25°C.
A pre-packaged set of solar components — typically panels, charge controller, battery, and inverter — designed to work together as a complete system.
The percentage of sunlight energy that a panel converts into electricity. Commercial panels range from 15% to 23%. Top premium panels reach above 22%.
The annual energy output of a solar system per installed kilowatt peak (kWh/kWp). A useful metric to compare performance across different system sizes and locations.
The current charge level of a battery expressed as a percentage of its full capacity. 100% = fully charged. 0% = fully discharged.
A series-connected group of solar panels. The string voltage equals the sum of all individual panel voltages.
The peak power an inverter can deliver for a short time (typically 1-5 seconds) to start motor loads like pumps and compressors. Usually 2-3x the rated continuous power.
The rate at which a solar panel's power output decreases as temperature rises. Typically -0.3% to -0.5% per °C above 25°C.
A type of solar panel using a thin layer of photovoltaic material on glass or metal. Cheaper to manufacture but lower efficiency (10-13%). Better in low-light conditions.
A measure of inverter output waveform quality. Lower THD means cleaner power. Pure sine wave inverters have THD below 3%, making them safe for sensitive electronics.
The actual energy available from a battery after applying the maximum Depth of Discharge limit. A 100Ah battery with 80% DoD has 80Ah usable.
The unit of electrical potential difference. In solar systems: 12V, 24V, and 48V are the most common system voltages.
The reduction in voltage along a wire due to resistance. In solar systems, wire must be sized to keep voltage drop below 3% to avoid energy loss.
The basic unit of electrical power. 1 Watt = 1 Volt × 1 Ampere. A 400W solar panel produces 400W at peak conditions.
The rated power output of a solar panel under Standard Test Conditions (STC): 1000 W/m² irradiance, 25°C cell temperature, AM1.5 spectrum.
A unit of energy. 1 Wh = 1 watt used for 1 hour. Used to measure battery capacity and daily energy consumption.