Grid-Tied Solar: How It Works and What Happens in an Outage

A grid-tied solar system, also called a grid-connected PV system, is the most common residential solar design. It is connected to the local utility grid, allowing electricity to flow both to and from the home. This page explains how such a system operates, what happens when the grid goes down, and which rules depend on where you live.

How a Grid-Tied System Works

A typical grid-tied system consists of solar panels, an inverter, and a meter. The panels produce direct current (DC) electricity when exposed to sunlight. The inverter converts that DC into alternating current (AC) that matches the utility’s voltage and frequency. The AC power then feeds the home’s electrical panel, supplying loads like lights and appliances.

When the solar array produces more electricity than the home uses, the excess is exported to the grid. When the home uses more than the array produces, power is drawn from the grid. This exchange is measured by a bi-directional meter, which can record both imports and exports.

The inverter is the key component that enables grid connection. It must synchronize its output with the grid’s voltage and frequency, and it must disconnect from the grid if those parameters fall outside acceptable ranges. This is a safety requirement, not an optional feature.

Anti-Islanding: Why the System Shuts Off During an Outage

The most misunderstood aspect of grid-tied solar is its behavior during a power outage. When the grid goes down, a grid-tied inverter immediately shuts off the solar system. This is called anti-islanding.

An “island” is a section of the grid that remains energized while the rest is dead. If a solar system kept feeding power into a downed grid, it would create an island. That would endanger utility workers who might be repairing lines, and it could damage equipment when the grid reconnects. To prevent this, inverters are required to detect a loss of grid power and disconnect within a fraction of a second.

Consequently, a standard grid-tied system does not provide backup power during an outage. This surprises many homeowners, but it is a deliberate safety feature. If backup power is needed, the options are a battery storage system with islanding capability, a generator, or a hybrid inverter that can intentionally island.

Net Metering and Export Compensation

Net metering is a billing arrangement that credits solar owners for the excess electricity they export. Under net metering, the utility credits the full retail rate for each kilowatt-hour sent to the grid, offsetting consumption at other times. However, net metering is not universal. Some states and utilities have replaced it with net billing or feed-in tariffs, which pay a lower rate for exports. Others have time-of-use rates that change the value of exports depending on the hour.

These rules are set by state and by utility, and they change. What applies in one jurisdiction may not apply in another. Before relying on any financial projection, check the current interconnection rules, export compensation, and net metering policy in your area. Your utility or state public utility commission is the authoritative source.

Physical Interconnection

Connecting a solar system to the grid involves an interconnection agreement with the utility. This agreement specifies the technical requirements, such as inverter certification, disconnect switches, and metering. The utility may require an inspection before granting permission to operate. The process varies by utility, and some have capacity limits or application fees.

In most places, the actual connection to the grid must be performed by a licensed electrician, and any work on the utility side of the meter is the utility’s responsibility. Never attempt to modify the meter or the service entrance yourself.

Comparison of System Types

What People Get Wrong About Grid-Tied Solar

A common mistake is assuming that a grid-tied system will keep the lights on during a blackout. This is a natural assumption because the solar panels are still producing power during the day. The confusion arises because the inverter is designed to shut down for safety, not because it cannot produce power. The misconception is understandable: the system works perfectly when the grid is up, so it seems logical that it would continue during an outage. The reality is that anti-islanding is a mandatory safety feature, and disabling it is illegal and dangerous.

Another misdiagnosis is thinking that net metering is a federal program or that it applies everywhere. Net metering is a state-level policy, and some states have no net metering at all. A homeowner might see a neighbor’s net metering arrangement and assume it applies to them, only to find their utility offers a different compensation scheme. The correct approach is to read the utility’s interconnection tariff.

Checking Your Local Rules

Because rules vary, the only reliable way to know the specifics is to consult the utility and state authorities. Look for:

• The utility’s interconnection agreement and tariff.
• The state’s net metering or export compensation policy.
• Any local permitting requirements.

These documents are usually available online. If they are unclear, a licensed solar installer can help interpret them, but the responsibility for compliance rests with the system owner.

Safety Considerations

A PV array produces dangerous DC voltage whenever light hits it, and it cannot be switched off at the panel. Never open a combiner box, probe a live string, or disconnect an energized connector. Only qualified personnel should work on the DC side. Roof work and mains connection are also licensed trades in most jurisdictions.

Summary

Grid-tied solar is a straightforward way to offset electricity consumption, but its operation is tied to the grid’s presence. The system shuts down during outages to protect workers and equipment. Net metering and other export rules are local and change over time. Always verify current policies before making decisions.

For more on system design, see the related pages on inverters and battery storage.