Quick answer
Alternating Current (AC) is electric current that reverses direction many times a second; in the US it completes 60 cycles per second (60 Hz).
The grid and every household outlet run on AC because transformers can step its voltage up for long-distance transmission and down for safe use. Solar panels make direct current, so every grid-tied system needs an inverter to produce AC.
Quick facts
The key facts about alternating current, with sources:
- US frequency
- 60 Hz (reverses direction 120 times a second) 1
- US home service
- 120/240 V split-phase 5
- Made in a solar system by
- The inverter (string, micro or hybrid) 2
- AC rating on quotes
- kW AC: the inverter's output limit
- Grid connection standard
- IEEE 1547-2018 6
Key takeaways
- AC is current that flips direction. In the US it does a full cycle 60 times a second.
- Homes, outlets and the grid all use AC. Panels make DC, so an inverter converts it.
- The inverter is where DC becomes AC: on the wall, behind each panel, or in a battery.
- A grid-tied inverter follows the grid and shuts off in a blackout unless a battery can take over.
- Quotes list kW AC, the inverter’s output, next to kW DC, the panels.
Back and forth, sixty times a second
In an AC circuit the electrons do not travel from the power plant to your toaster. They shuffle back and forth in place, and the energy moves along the wire as a wave.
DOE describes AC as current that reverses direction a set number of times per second: 60 cycles in the US, 50 in much of the rest of the world.
Another DOE page puts it this way: in AC, electricity flows both ways in the circuit as the voltage swings from positive to negative. Each full swing is one cycle. The number of cycles per second is the frequency, measured in hertz (Hz).
Why the grid runs on AC
AC won the late-1800s "war of the currents" against direct current for one practical reason. A transformer can raise its voltage for efficient long-distance lines and lower it again near your house. DC could not be converted that easily until modern power electronics.
EIA explains that higher voltage makes long-distance transmission more efficient and less costly. Transformers at substations step it up or down for each stage. Lower-voltage lines then carry it to homes, where it is safer to use.
How an inverter makes AC from solar DC
Solar panels make direct current, which flows one way. The DOE says an inverter turns it into AC by switching the direction of the DC input back and forth very quickly. Modern inverters do this with transistors, solid-state parts with no moving pieces.
A grid-tied inverter watches the grid’s voltage and frequency and matches them. It does not set its own rhythm. Smart inverters can also respond to changes in grid voltage or frequency to help keep the grid stable, the DOE notes.
Sources: [2]
Where DC becomes AC in a solar home
- Sunlight → panels make DC → inverter converts DC to 240 V, 60 Hz AC → main electrical panel → your appliances, with any surplus → utility meter → grid
Three places the conversion can happen
| Design | Where DC turns into AC | What it means for you |
|---|---|---|
| String inverter | One box, usually on a wall near the electrical panel | High-voltage DC runs from the roof to that box. One unit to replace. |
| Microinverters | Behind each panel on the roof | Only AC leaves the roof. The Enphase IQ8M outputs 240 V split-phase at 60 Hz 4. |
| Hybrid / battery inverter | In the battery or inverter unit, which also charges the battery | Powerwall 3 accepts DC solar and delivers 120/240 VAC 5. |
Example: AC numbers on a microinverter data sheet
Output lines from the Enphase IQ8M data sheet (DSH-00243-3.0, December 2024), with what each one tells a homeowner.
| AC spec | Value | Meaning |
|---|---|---|
| Nominal grid voltage | 240 V split-phase 4 | Connects to a standard US 240 V circuit |
| Allowed grid voltage | 211–264 V 4 | Outside this the inverter stops exporting |
| Nominal frequency | 60 Hz 4 | Locked to the US grid |
| Maximum continuous output | 325 VA, 1.35 A 4 | AC power and current per panel |
| CEC weighted efficiency | 97.5% 4 | About 2.5% lost turning DC into AC |
A grid-tied inverter follows the grid's voltage and frequency rather than setting its own. When the grid goes down it must stop, which is why panels alone do not power a house in an outage; that takes a battery or an inverter designed to form its own AC.
AC vs DC at a glance
| Alternating current (AC) | Direct current (DC) | |
|---|---|---|
| Direction | Flips back and forth | One way |
| US frequency | 60 Hz | None (0 Hz) |
| In a solar home | Inverter output, panel box, outlets, grid | Panels, battery cells, string wiring |
| Voltage change | Easy with a transformer | Needs power electronics |
| Rating on a quote | kW AC | kW DC |
kW AC vs kW DC on a quote
A proposal may list both. kW DC is the panels' lab rating; kW AC is what the inverter can deliver.
Powerwall 3, for example, accepts up to 20 kW of DC solar but its continuous output is 11.5 kW AC. Utilities usually set connection limits in kW AC.
The ratio between the two is a design choice called the DC-to-AC ratio.
Sources: [5]
Benefits and limits of AC in a solar system
Benefits
- Works with every outlet, appliance and the utility grid.
- Lets you send surplus power to the grid for credit.
- Microinverter designs keep only AC on the roof.
Limits
- Each conversion loses a little energy; the IQ8M is rated 97.5% efficient.
- Batteries store DC, so AC-coupled designs convert twice.
- Grid-tied AC output stops in a blackout without backup gear.
Losses from converting back and forth
Every DC-to-AC step loses some energy as heat. Tesla lists Powerwall 3 at 97.5% efficient from solar straight to the home or grid. Going solar to battery to home, it lists 89%, because the energy is stored and converted more than once.
These losses are small but real. They are already in a good production estimate. They are also why a design that sends solar to the home first, then to the battery, can make the most of each kWh. See inverter efficiency.
What drives the cost of the AC side
The inverter is the main cost on the AC side. Price depends on its kW AC rating, the type (string, micro or hybrid), and whether it can run the home in an outage.
Other AC costs: the breaker in your main panel, an AC disconnect if your utility needs one, wiring, and sometimes a panel upgrade.
Inverters often wear out before panels. Many string inverters need replacing during a panel’s life, while microinverters and batteries carry their own warranties: Tesla lists 10 years on Powerwall 3 5. We do not list prices; see solar cost and the inverter replacement planner.
How the AC connection is made
- The designer picks an inverter whose kW AC fits your panel, utility cap and needs.
- Plans show the AC breaker, disconnect and meter; the building department reviews them.
- A licensed electrician connects the inverter output to your main panel or service.
- An inspector checks the AC wiring and labels.
- The utility reviews the connection under its rules, may swap the meter, then grants permission to operate. See interconnection.
Keeping AC output steady
Inverters need little care. Keep their vents and the area around them clear so they stay cool. Check the monitoring app for error codes and for days when AC output is zero in daylight.
Grid settings matter. The IQ8M ships with defaults that meet IEEE 1547, and only the installer or utility should change them, using Enphase’s gateway. Inverter software updates may also arrive over the internet, so keep the system online.
Sources: [4]
Warning signs and when to call a pro
OSHA lists shock, electrocution and fire among electrical dangers. Call your installer or a licensed electrician if you see:
- Repeated inverter faults for grid voltage or frequency.
- An AC breaker for the solar circuit that trips often.
- Zero AC output on sunny days. See when monitoring shows zero.
- Heat, buzzing or a burning smell near the inverter or panel.
Sources: [7]
Standards and rules for AC from solar
Grid connection. IEEE 1547-2018 sets how home generators like solar connect to the grid, including how they respond to voltage and frequency changes and how they avoid powering a dead line, called islanding.
Inverter safety. The Enphase IQ8 and Powerwall 3 sheets list UL 1741, the safety standard for inverters, including its SA and SB grid-support versions.
Wiring. Your local building department enforces its adopted edition of NFPA 70, the National Electrical Code. Utilities add their own connection rules under state oversight.
Common myths about AC and solar
- Myth "Solar panels make the same power as my outlets."
- Reality Panels make DC. Only the inverter makes AC.
- Myth "My solar will run my home in a blackout."
- Reality Grid-tied inverters shut off when the grid fails. Backup needs a battery or a system that can form its own AC.
- Myth "AC is less safe than DC."
- Reality Both are dangerous. Leave all wiring to licensed pros.
AC connection rules in SC, GA and VA
All three states use 60 Hz, 120/240 V service. Each utility sets AC size caps: in South Carolina, Duke Energy Carolinas’ Rider RSC covers systems up to 20 kW AC 8.
Georgia Power caps residential systems at 10 kW 9. Virginia allows net metering up to 25 kW for residential customers of investor-owned utilities 10.
When AC matters to you
- Choosing an inverter: compare kW AC, type and warranty.
- Wanting backup: ask if the system can form its own AC in an outage.
- Adding a battery: ask whether it is AC- or DC-coupled.
- Reading a quote: check the kW AC against your utility’s cap.
Related guides
Questions about alternating current
Do solar panels produce AC or DC?
DC. An inverter converts it to AC so the house and the grid can use it. With microinverters the conversion happens on the roof behind each panel. With a string inverter it happens in one box near your electrical panel.
Why does the grid use AC instead of DC?
AC voltage is easy to raise and lower with transformers, which lets utilities send power long distances at high voltage with lower losses, then reduce it for homes. That advantage settled the choice in the late 1800s.
What is AC power?
Power delivered by alternating current, the kind from your wall outlets. In the US it alternates at 60 Hz and reaches homes as 120/240 V split-phase service. Most appliances are built for it.
Why does my solar stop working when the power goes out?
Grid-tied inverters must follow the grid's AC signal and shut off when it disappears, so they do not send power onto lines that crews may be repairing. A battery system with backup capability can keep supplying your home.
What does 60 Hz mean?
It means the current completes 60 full back-and-forth cycles every second. That is the US grid standard. Inverters sold here, like the Enphase IQ8M, are built to match 60 Hz.
How efficient is converting DC to AC?
Modern inverters lose only a few percent. Enphase rates the IQ8M at 97.5% CEC weighted efficiency, and Tesla lists 97.5% for Powerwall 3 from solar to home. Storing energy in a battery first adds more loss.
What is the difference between AC-coupled and DC-coupled batteries?
An AC-coupled battery connects on the AC side, so solar is converted to AC and back to DC to charge it. A DC-coupled battery charges straight from the panels’ DC. Each has trade-offs in losses, cost and retrofit ease.
Does my utility need to approve the AC connection?
Yes. Grid-tied systems need the utility’s approval before you switch on. The utility reviews the inverter, the size in kW AC and the wiring. It then grants permission to operate.
Sources
- US Department of Energy, The War of the Currents: AC vs. DC Power, retrieved .
- US DOE Solar Energy Technologies Office, Solar Integration: Inverters and Grid Services Basics, retrieved .
- US EIA, Electricity explained: Delivery to consumers, retrieved .
- Enphase Energy, IQ8M and IQ8A Microinverters data sheet (DSH-00243-3.0-EN-2024-12-10), retrieved .
- Tesla, Powerwall 3 Datasheet (2024), retrieved .
- IEEE, 1547-2018 Standard for Interconnection and Interoperability of Distributed Energy Resources, retrieved .
- US OSHA, Electrical safety overview, retrieved .
- Duke Energy Carolinas (SC), Rider RSC Residential Solar Choice (effective 1 January 2026), retrieved .
- Georgia Power, Behind-the-Meter Interconnection Summary for Residential Customers (rev. 15 Aug 2025), retrieved .
- Code of Virginia §56-594 (net energy metering), retrieved .
Expert review
Written by the HyreSolar Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: AC basics from the DOE explainers and EIA. AC output specifications copied from the Enphase IQ8M and Tesla Powerwall 3 data sheets (re-read 2026-10-08). Standard scope from the IEEE 1547-2018 page. Utility caps from the cited tariffs and statute.
Suggest a correction. We fix errors and say what changed.