Solar Energy System Glossary for Homeowners
If you’ve ever sat through a conversation about solar power and felt like you accidentally walked into an electrical engineering class, you’re not alone. The solar industry has its own language, full of acronyms, technical terms, and buzzwords that can make even the most enthusiastic homeowner’s head spin. Whether you’re just starting your solar journey or looking to sharpen your understanding, we’ve gathered some of the most common solar terms and broken them down into plain English.
AC Coupled
“AC coupled” refers to solar systems that connect alternating current (AC) sources, such as microinverters or secondary inverters, to an energy storage system through an inverter’s AC input—commonly the generator (Gen) port. For example, Sol-Ark inverters allow for this configuration to integrate various AC sources.
Amp-Hours (Ah) & Kilowatt-Hours (kWh)
These units measure energy capacity. Amp-hours (Ah) are often used in battery specifications, while kilowatt-hours (kWh) are more common for overall system energy usage. The average U.S. household uses approximately 30–60 kWh per day, depending on region and season (U.S. Energy Information Administration [EIA], 2023). A 51V nominal battery delivering 1,176 Ah equals roughly 60 kWh.
Battery Chemistries
- Lead-Acid: Traditional and affordable, like car or golf cart batteries.
- AGM (Absorbent Glass Mat): A sealed, maintenance-free variant of lead-acid with improved safety and performance.
- LiFePO₄ (Lithium Iron Phosphate): The industry standard for solar applications due to its long cycle life and thermal stability
Learn more about How To Choose The Best Battery Chemistry
Black Start
This term describes an AC-coupled system with depleted batteries attempting to restart. If the inverter can generate a grid-forming signal (120/240V, 60 Hz), it can allow AC sources to power the system—thus enabling the “black start” functionality.
Closed Loop vs. Open Loop Communication
- Closed Loop: The inverter communicates directly with the battery’s Battery Management System (BMS), optimizing performance and safety.
- Open Loop: No BMS communication; the inverter operates based on general parameters without direct feedback from the battery.
Continuous Power
Defined by the National Electrical Code (NEC) as power deliverable for three hours or more. Systems with higher voltage batteries often perform better due to breaker limitations. It is important to validate inverter claims with real-world tests, as some systems overheat under sustained loads (National Fire Protection Association [NFPA], 2020).
CTs (Current Transformers)
These devices measure the current passing through a conductor. Shaped like rings or donuts, CTs allow the inverter to monitor system performance and control energy flows accurately.
DC Couple
A system where direct current (DC) sources like traditional solar panels connect directly to the inverter’s Maximum Power Point Trackers (MPPTs). This approach is efficient and common in residential solar installations.
Grid
The traditional power supply provided by the utility. Grid power enters through your utility meter and is used when solar production or stored battery energy is insufficient.
Grid-Tied vs. Off-Grid
- Grid-Tied: Connected to the utility grid.
- Off-Grid: Fully self-sufficient, with no grid access or backup.
Hybrid Inverter vs. String Inverter
- Hybrid Inverter: Supports both solar generation and battery storage.
- String Inverter: Connects solar panels in series (a “string”) but usually lacks battery capabilities. Common in large-scale projects.
Learn more about Sol-Ark® Home Hybrid Inverters and Commercial Hybrid Inverters
LRA (Locked Rotor Amps)
Refers to the inrush current required to start an appliance motor—commonly noted for air conditioning units.
Load
Refers to the electrical circuits or devices being powered by your solar or backup system.
Microinverter
Installed at the module level, microinverters convert DC to AC right at the panel. They offer panel-level optimization and rapid shutdown capabilities, increasing system resilience and performance.
Ohm’s Law
These equations help determine power flow from PV panels, batteries, the grid, and loads. Ohm’s Law is the foundation of electrical theory.
- V=I×R (Voltage = Current × Resistance)
- P=V×I (Power = Voltage × Current)
Optimizer
A device that allows panels to bypass shaded or malfunctioning modules in a string. This maximizes total energy output and often includes rapid shutdown features.
Overcurrent Protection Devices
Includes fuses and circuit breakers. Fuses must be replaced after tripping, while breakers can be reset. Both protect wiring and equipment from excessive current.
Peak Shaving
A strategy to reduce demand charges by limiting how much power is drawn from the grid during peak times. Hybrid inverters can pull energy from batteries instead of the grid, reducing energy bills.
Learn more about How Businesses Can Maximize ROI with Peak Shaving
PV (Photovoltaic)
A term used to describe the process of converting sunlight into electricity. Also shorthand for solar panels or modules.
RSD (Rapid Shutdown)
A fire-safety feature that allows PV systems to stop producing power quickly. NEC codes require RSD for systems on buildings to protect first responders.
SOC (State of Charge)
Indicates how much energy remains in a battery, similar to your phone’s battery percentage. Most lithium batteries should not discharge below 20% SOC to maintain longevity.
Soft Start
A device added to high-LRA appliances (like air conditioners) that gradually increases current, reducing stress on both the appliance and inverter during startup.
SOH (State of Health)
A measurement of a battery’s current capacity versus its original design capacity, usually expressed as a percentage. Indicates long-term battery health.
TOU (Time of Use)
A battery discharge strategy that uses stored energy during high-rate utility billing periods. This reduces grid dependency and can lower costs significantly.
VPP (Virtual Power Plant)
A network of distributed energy storage systems (like residential batteries) that aggregate their stored power and sell it back to the grid. VPPs help balance grid demand and can earn homeowners incentives (Lund, Lindgren, Mikkola, & Salpakari, 2015).
Learn more about VPPs
UPS (Uninterruptible Power Supply)
The ability of the system to switch from grid to battery backup nearly instantaneously, measured in milliseconds. This prevents disruptions to sensitive equipment.
References
- Dunn, B., Kamath, H., & Tarascon, J. M. (2011). Electrical energy storage for the grid: A battery of choices. Science, 334(6058), 928–935. https://doi.org/10.1126/science.1212741
- Lund, H., Lindgren, J., Mikkola, J., & Salpakari, J. (2015). Review of energy system flexibility measures to enable high levels of variable renewable electricity. Renewable and Sustainable Energy Reviews, 45, 785–807. https://doi.org/10.1016/j.rser.2015.01.057
- National Fire Protection Association. (2020). National Electrical Code (NEC) 2020 Edition. https://www.nfpa.org/
- U.S. Energy Information Administration. (2023). How much electricity does an American home use? https://www.eia.gov/tools/faqs/faq.php?id=97&t=3