Solar System Performance: Is Your System Producing Enough Power?

Solar system performance isn’t always easy to evaluate. Your monitoring app may say everything is working, but how do you know whether your system is actually producing as much electricity as it should?

There are no error messages, your inverter is online, and the system is generating electricity. But that doesn’t necessarily mean it’s performing properly.

A solar system can continue producing electricity despite failed components, configuration problems, or other conditions that reduce its output. Some of these issues can go unnoticed for months or even years.

So how can you tell if your solar system is underperforming? The answer starts with understanding what your system should be producing in the first place.

Understanding Solar System Performance: How Much Power Should You Produce?

There isn’t a single production figure that applies to every solar installation. Two systems with identical equipment can produce significantly different amounts of electricity depending on their installation and operating conditions.

Some of the most important factors include:

• System size: The total rated capacity of the solar panels, typically expressed in kilowatts (kW).
• Panel orientation: The direction the panels face affects when and how much sunlight they receive.
• Roof pitch: The angle of the panels influences seasonal production.
• Shading: Trees, neighboring buildings, and other obstructions can reduce output.
• Equipment efficiency: Inverters, wiring, and other components introduce electrical losses.
• System age: Solar panels gradually lose some of their production capability over time.
• Weather and temperature: Cloud cover, seasonal daylight hours, and panel temperature all affect production.

For homeowners in Sacramento and surrounding communities, our long, sunny summers provide excellent solar production potential. However, high summer temperatures can also reduce panel efficiency, meaning the hottest day of the year isn’t necessarily the day your system will produce the most power.

How to Check Your Solar System Performance

1. Compare Current Production to Previous Years

One of the easiest ways to identify potential performance problems is to compare your system’s production history.

Most monitoring platforms, including SolarEdge, Enphase, and Tesla, allow homeowners to review historical production data.

Compare the same month across multiple years rather than comparing consecutive months. For example, compare September 2026 with September 2025, not September with August.

Some year-to-year variation is normal due to weather. Solar panels also experience gradual degradation, commonly estimated around 0.5% annually, although the actual rate depends on the equipment and operating conditions.

A substantial or persistent reduction in production that cannot be explained by weather, shading, or normal aging deserves further investigation.

2. Review Your Daily Solar Production Graph

Your daily production graph can reveal problems that aren’t immediately obvious from total energy production.

On a clear day, an unobstructed solar array will generally produce a relatively smooth curve, with production increasing through the morning, peaking around the middle of its solar day, and declining toward evening.

Depending on the system’s orientation, inverter capacity, and configuration, the curve may be asymmetrical or have a flattened peak.

Things worth investigating include:

• Unexpected drops in production during otherwise clear conditions.
• Repeated interruptions or gaps in production.
• Unusually low output compared with similar clear days.
• Changes in the shape of the production curve that weren’t present previously.

These patterns don’t necessarily indicate a malfunction. Shading, utility interruptions, battery charging behavior, and export restrictions can produce similar results.

The important part is identifying whether the behavior is expected for your particular system.

3. Compare Actual Production Against an Independent Estimate

Historical production is useful, but what if your system has been underperforming since it was installed?

In that situation, comparing this year’s production with last year’s won’t tell you much.

A better approach is to compare actual production against an independently calculated estimate.

The National Renewable Energy Laboratory provides a free tool called PVWatts, which estimates solar electricity production using location, system capacity, panel orientation, and other operating characteristics.

While these estimates aren’t exact, they provide a useful baseline for evaluating solar system performance.

For a meaningful comparison, the model should account for actual equipment specifications, shading, system age, and other site-specific conditions.

5 Common Problems That Reduce Solar System Performance

1. Failed Solar Panels or Microinverters

On systems equipped with module-level electronics, an individual panel or microinverter can fail while the rest of the array continues operating normally.

For example, if one microinverter fails on a 30-panel system, the homeowner may lose roughly 3% of the system’s production capacity without noticing a dramatic change in overall output.

Some monitoring platforms identify these failures automatically. Others require reviewing module-level production data or performing additional testing.

2. Inverter or String-Level Problems

String inverter systems can experience problems affecting an entire group of solar panels.

Failed connections, electrical faults, damaged conductors, or inverter input problems can reduce production without necessarily shutting down the entire system.

In systems with multiple strings or maximum power point trackers (MPPTs), one portion of the array may be operating normally while another produces little or no power.

Identifying these conditions often requires reviewing inverter operating data and comparing electrical measurements against expected values.

3. Shading and Panel Soiling

Shading conditions can change considerably over the life of a solar installation.

Trees grow, neighboring properties change, and objects that weren’t an issue when the system was installed may eventually obstruct sunlight.

Dust, pollen, bird droppings, and other debris can also reduce production. This is particularly relevant during Sacramento’s long, dry summers.

However, panel cleaning shouldn’t automatically be the first recommendation when production is low. The actual impact of soiling varies, and electrical or configuration problems may be responsible for much larger losses.

4. Incorrect System Configuration

Not every performance problem is caused by failed equipment.

Incorrect inverter settings, mismatched strings, inappropriate operating limits, and other configuration issues can prevent a system from operating at its full potential.

These problems can be especially difficult for homeowners to recognize because the equipment may report normal operation.

On systems with battery storage, incorrect operating modes or metering configurations can also affect how solar energy is used, stored, or exported.

5. Monitoring and Metering Errors

Sometimes the solar system is producing normally, but the monitoring platform isn’t reporting the information correctly.

Current transformers (CTs) installed incorrectly, reversed, or assigned to the wrong electrical phase can produce misleading consumption and grid import/export readings.

These errors are particularly important on solar and battery systems that rely on site metering to make operating decisions.

It’s worth distinguishing between an actual production problem and a monitoring problem before recommending repairs.

Does a High Electric Bill Mean Poor Solar System Performance?

Not necessarily.

One of the most common misconceptions about residential solar is that a higher utility bill automatically means something is wrong with the equipment.

In reality, your electric bill is influenced by several factors beyond solar production, including:

• Changes in household electricity consumption.
• Utility rate increases and time-of-use pricing.
• Seasonal heating and cooling loads.
• Electric vehicle charging.
• Battery operating schedules.
• Changes to your utility’s solar billing arrangement.

A system can produce exactly as designed and still leave the homeowner with a substantial utility bill.

Conversely, a system may be underperforming even when the homeowner’s bill appears relatively low.

That’s why production data and utility billing information should be evaluated separately before drawing conclusions.

For a closer look at this distinction, see our article on why your electric bill may still be high after installing solar.

What Is a Normal Solar Production Loss Over Time?

Solar panels don’t maintain their original rated output indefinitely.

Most gradually lose some efficiency as they age. A commonly used estimate for solar module degradation is approximately 0.5% per year.

At that rate, a system might retain approximately 95% of its original panel output capability after ten years, excluding other changes and losses.

However, normal degradation should generally be gradual. A sudden or unusually large reduction in production is more likely to indicate a specific problem than ordinary panel aging.

The U.S. Department of Energy’s guidance on solar photovoltaic performance provides additional information on performance evaluation, aging, and maintenance.

When Is a Professional Solar Performance Inspection Worthwhile?

If your monitoring data shows a persistent production decline, unexpected behavior, or a substantial difference between actual and estimated production, a professional evaluation may be worthwhile.

A proper solar performance inspection goes beyond confirming that the inverter is powered on.

Depending on the system and available monitoring data, an evaluation may include:

• Reviewing historical solar production and system alerts.
• Comparing actual energy production against modeled expectations.
• Evaluating inverter and MPPT operating data.
• Checking string voltage, current, and other electrical measurements.
• Reviewing module-level production where available.
• Identifying shading, equipment failures, or configuration issues.
• Verifying monitoring and site metering accuracy.
• Documenting findings and recommending corrective action where appropriate.

At McKnight Solar Diagnostics, we evaluate existing residential solar and battery systems throughout Sacramento, Roseville, Rocklin, Folsom, Elk Grove, and surrounding communities.

Our focus is on determining whether the system is operating as intended, identifying the causes of any deficiencies, and providing practical recommendations based on the findings.

Learn more about our solar inspection services in Sacramento.

The Bottom Line: Solar System Performance Is More Than Just Producing Power

A solar system doesn’t have to stop working completely to develop a performance problem.

Failed modules, inverter issues, shading, incorrect settings, and monitoring errors can all go unnoticed while the system continues generating electricity.

The most reliable way to evaluate solar system performance is to compare actual production against realistic expectations, accounting for equipment, age, location, and operating conditions.

If you’ve never evaluated your system’s production beyond checking whether the monitoring app says it’s online, it may be worth taking a closer look.