How Much Solar Production Loss is “Normal”?

Every solar asset loses some production over time. That is expected. The challenge is figuring out when declining performance is simply the natural aging of the system versus when it signals an avoidable operational issue that is quietly eroding financial returns.

For owners managing commercial and institutional solar portfolios, this distinction matters. A small amount of unnoticed underperformance across multiple sites can easily translate into millions in lost savings over the life of the assets.

The good news is, not all production loss is created equal. And much of it is avoidable when identified early.

The Two Types of Solar Production Loss

Broadly speaking, solar production loss falls into two categories:

1. Normal Degradation

Solar modules slowly lose efficiency as they age. This process is unavoidable and is already baked into most financial models and product warranties.

Typical industry assumptions are:

•    ~0.5% annual degradation rate
•    ~9% total output decline over a 20-year period
•    ~14% total output decline over a 30-year period

For example, a 1-megawatt system expected to produce 1,600,000 kWh annually in Year 1 may reasonably produce around 1,491,200 kWh by Year 15 purely due to module aging. That level of decline is normal.

2. Avoidable Production Loss

This is where many portfolios struggle. Avoidable loss stems from operational issues that reduce output beyond expected degradation. Unlike module aging, these issues can often be corrected.

Common causes include:

•    Offline inverters
•    Tracker malfunctions
•    Communication failures masking outages
•    Soiling and vegetation buildup
•    Manufacturer defects in modules

In many cases, the issue is not the failure itself. It’s the length of time the failure goes unnoticed or unresolved. We routinely see sites where systems have been underperforming for months or even years before someone fully investigates the issue.

What Production Loss Benchmarks Are Reasonable?

While every portfolio is unique, here are some practical benchmark ranges for commercial and institutional solar systems:

If a system is underperforming by several percentage points beyond expected degradation, it is often financially worthwhile to investigate. For a 5-megawatt portfolio, a single year at a 15% production shortfall could represent ~$300,000 in lost utility bill savings and revenue.

Why Small Losses Become Big Financial Problems

Production loss compounds quietly. A single offline inverter may seem minor in isolation. But when issues persist across multiple sites, the financial impact escalates quickly between increased utility expenses and lost Renewable Energy Certificate revenue. The longer issues remain unresolved, the more difficult it becomes to identify and address them. This is especially common in older portfolios where:

•    Original installers are no longer involved
•    Monitoring platforms have become outdated
•    Responsibility for performance oversight is unclear
•    Institutional knowledge has faded over time

When Should You Investigate?

Not every fluctuation warrants concern. Weather variability alone can create meaningful month-to-month swings. But there are several warning signs that typically justify a response.

Investigate when:

Utility bills are higher than expected 

Sometimes the first clue is not in the solar monitoring data. It shows up in the utility bills.

Performance suddenly changes 

Sharp drops in production often indicate equipment failures, communication problems, or operational changes.

Monitoring visibility is incomplete 

You cannot manage what you cannot see. Partial monitoring coverage often hides real production losses.

One site materially underperforms comparable sites 

Similar systems in similar climates should generally perform within a reasonable range of each other.

The Importance of Context

One of the biggest mistakes in solar asset management is looking only at raw production numbers.

Strong analysis considers:

•    Weather normalization
•    System age
•    Utility tariff structure
•    Equipment availability
•    Seasonal operating patterns
•    Recent maintenance history

Without context, it is easy to misdiagnose normal variability as a system issue — or worse, overlook meaningful underperformance entirely.

The Bottom Line

Some solar production loss is inevitable. But substantial avoidable loss is far more common than many portfolio owners realize. The difference between a high-performing solar portfolio and an underperforming one is often not the equipment itself. It is the consistency of monitoring, investigation, and operational follow-through. Owners who actively track performance trends, benchmark sites appropriately, and investigate anomalies early are typically able to preserve significantly more long-term financial value from their solar investments. Because in solar asset management, small production losses rarely stay small for long.