Avoid Low Export Credits: San Antonio Solar by Month for a 6 kW System

A typical 6 kW residential solar system in San Antonio produces about 8,981 kWh per year, based on NREL PVWatts modeling. That works out to roughly 748 kWh a month on average, but the real story lives in the swings between June and December. Below, you’ll find the full month-by-month breakdown and what drives those seasonal ups and downs.

TL;DR:

• Solar output in San Antonio peaks from March to June, with June reaching about 1,080 kWh for a 6 kW system and dropping to approximately 646 kWh in December.
• Weather factors like panel temperature, shading, soiling, and inverter performance can cause seasonal and monthly production deviations of 10% or more from modeled estimates.
• Surplus energy exported during summer months is worth less under CPS Energy’s rate structure, emphasizing size based on household consumption rather than raw production.
• Actual system performance should be monitored over at least three months to identify persistent issues, especially if output falls more than 10% below models consistently.
• Site-specific assessments and maintenance, including cleaning and shading control, can significantly optimize monthly production and overall system efficiency.

Table of Contents

• San Antonio Solar Production by Month for 4 kW, 6 kW, and 8 kW Systems
• Why Your Monthly Output Swings So Much
• How CPS Energy Billing Changes the Value of Each Month’s Output
• How to Estimate Your Own Home’s Monthly Production
• What Utility-Scale Solar in San Antonio Tells Rooftop Owners
• Solar Panel Degradation and What It Does to Your Monthly Numbers
• Actual vs. Modeled Production: Why the Numbers Never Match Perfectly
• Maintenance and Its Effect on Monthly Output
• What Homeowners Get Wrong About Their Monthly Numbers
• How Alpha Solar Solutions Turns These Numbers Into a Real Plan for Your Home
• Sources
• FAQ

San Antonio Solar Production by Month for 4 kW, 6 kW, and 8 kW Systems

San Antonio’s solar output follows a predictable curve: it climbs from January through June, holds relatively strong through August despite brutal heat, and tapers off from October through December. The table below scales PVWatts-style modeling across three common residential system sizes, anchored to the 8,981 kWh/year figure for a 6 kW system.

The peak sun hour figures reflect San Antonio’s average solar resource, which runs around 5.2 hours a day annually but ranges from roughly 3.8 in December to 6.5 in June.

A few assumptions sit behind this table, and they matter if your roof doesn’t match them:

• Fixed-tilt rooftop mount at roughly 25 to 30 degrees, facing true south
• Standard system losses of about 14% (wiring, inverter efficiency, soiling, and shading combined)
• Standard crystalline silicon modules with typical residential inverters, not microinverters or optimizers
• Modeling centered on San Antonio zip codes near the geographic center of Bexar County
• No snow losses, since San Antonio essentially never needs that adjustment

If your panels face west or east instead of south, or sit at a steeper or flatter pitch than 25 to 30 degrees, your monthly numbers will shift by a few percentage points in either direction. That’s normal, and it’s exactly what a personalized model corrects for.

Why Your Monthly Output Swings So Much

Day length and sun angle explain most of the seasonal curve, but they’re not the whole story. Panel temperature actually works against you in summer: solar cells lose efficiency as they heat up, so a 100-degree August afternoon can produce less energy per hour of sunlight than a milder April day, even though August gets more total daylight. This is why July and August often plateau instead of setting the year’s peak, even with San Antonio’s brutal summer sun.

Orientation and tilt shift the entire monthly curve, not just the annual total. A west-facing array shifts more production into afternoon hours and slightly favors summer months, since the sun tracks farther northwest in June. A true south array, by contrast, produces more evenly across spring and fall. Neither is wrong. It depends on whether you want production to match your afternoon air-conditioning load or spread it more evenly.

System losses eat into every month equally, but a few are worth checking yourself:

• Soiling (dust, pollen, bird droppings) can cut output by 2% to 6% between cleanings, worse after Texas dust storms
• Shading from a single overhanging branch can knock out an entire string’s output for hours a day
• Inverter clipping on oversized systems can shave a few percent off peak summer days

Walk your roofline once a season and note any new shade from tree growth. A phone compass app will confirm your true azimuth in about thirty seconds, and most inverter apps show daily and monthly production history you can compare against the table above.

Pro Tip: If your production consistently runs more than 10% below the modeled numbers for your system size across three consecutive months, that’s a strong signal something changed, not just normal weather variation.

How CPS Energy Billing Changes the Value of Each Month’s Output

Not every kilowatt-hour you produce is worth the same amount, and this is the part most rooftop calculators skip entirely. Under CPS Energy’s net billing structure, your solar production offsets your usage in real time up to your monthly consumption. Anything you produce beyond what your house uses that month gets exported and credited at a far lower avoided-cost rate, not your retail rate.

CPS Energy’s published billing facts show sample avoided-cost credits of roughly $0.0165 per kWh from October through May and $0.0202 per kWh from June through September. Compare that to a retail rate several times higher, and the math gets clear fast: exported surplus is worth a fraction of the power you use yourself.

Rates change over time, so always confirm current avoided-cost figures directly with CPS Energy before running your own numbers.

That pricing gap has real seasonal consequences worth planning around:

• Summer kWh production is worth more because summer air-conditioning load usually absorbs most of what your panels generate on-site
• Winter surplus is worth less, since lower household usage means more of your solar output gets exported at that lower avoided-cost rate
• Oversizing a system to “cover everything” often backfires financially if the surplus mostly gets exported instead of consumed

The practical takeaway: size your system around your annual and monthly consumption pattern, not around maximizing raw kWh output. If you want to actually capture more of that winter surplus value instead of exporting it for pennies, a battery backup system lets you store daytime production and use it during evening hours, when your panels aren’t producing anyway.

How to Estimate Your Own Home’s Monthly Production

You don’t need to hire anyone to get a rough monthly forecast for your specific roof. Here’s the process professionals actually use:

1. Start with the rule of thumb. South Texas systems typically generate 1,500 to 1,700 kWh per kW per year, depending on tilt and losses. Multiply your system’s kW size by that range to get a rough annual estimate, then apply the monthly percentages from the table above to split it out.
2. Validate against real data. After installation, pull at least three months of inverter or utility meter readings, though a full 12 months gives you a true seasonal picture. Compare those actual numbers to your PVWatts model month by month.
3. Call for a site visit if the gap is large. If actual output consistently trails the model by double digits, especially in months where shading or a tricky roof pitch could be a factor, a local installer can run an on-site shading analysis instead of relying on satellite modeling alone.

Pro Tip: Screenshot your PVWatts monthly table before you finalize your system design. It becomes your baseline for judging whether your actual production is on track once panels go live.

What Utility-Scale Solar in San Antonio Tells Rooftop Owners

CPS Energy’s utility-scale solar plants, including Blue Wing and Somerset%20MW%20Hrs.pdf?ver=2021-06-06-103637-410), show the same seasonal shape as rooftop models: monthly MWh output climbs through spring, peaks around early-to-mid summer, and drops off by year’s end.

• Utility-scale plants confirm the seasonal pattern isn’t a rooftop modeling quirk. It’s a regional solar resource fact.
• Fixed-tilt utility arrays track closely with rooftop fixed-tilt systems, while tracking arrays can flatten the curve slightly by following the sun.
• Utility curtailment (grid operators reducing output during low-demand periods) can create dips that don’t apply to your home system.

Solar Panel Degradation and What It Does to Your Monthly Numbers

Every solar panel loses a small amount of output capacity every year, and this shows up as a gradual, predictable decline layered on top of the seasonal pattern you already see month to month. Most manufacturer warranties assume a degradation rate of around 0.5% per year, meaning a system producing 748 kWh a month in year one might produce closer to 730 kWh in that same month a decade later, all else being equal.

This decline is linear and gradual, not a sudden cliff. You won’t notice it month to month. You’ll notice it when you compare year five’s July production against year one’s July production and see a modest gap that has nothing to do with weather or shading.

The practical implication for monthly tracking: don’t panic if your tenth summer produces slightly less than your first. That’s expected aging, not a system failure. What should concern you is a sudden month-over-month drop that’s larger than a percent or two, since that points to something specific: a failing panel, a loose connection, or a shading change, rather than the slow, steady decline every panel experiences.

When you’re comparing your actual production against a PVWatts model years after installation, build in that small annual degradation factor before assuming something’s wrong.

Actual vs. Modeled Production: Why the Numbers Never Match Perfectly

PVWatts and similar tools give you a modeled estimate built from typical weather year data, not a forecast of this specific year’s weather. Real production will always deviate from the model in both directions, sometimes by a meaningful margin in any single month.

Over a full year, these deviations tend to average out, which is why annual totals track closer to the model than any individual month does. If you’re only checking one month against the table above, you’re looking at the noisiest possible comparison.

The more useful comparison is trailing twelve months against modeled annual output, rather than July against July. That smooths out the day-to-day weather variance and shows you the actual trend, whether your system is performing at, above, or below what the model predicted.

Local factors matter too. San Antonio’s summer haze and occasional Saharan dust plumes can quietly reduce irradiance on days that look clear to the naked eye, something a satellite-based model can’t always fully capture at the neighborhood level. That’s one more reason your actual meter readings, not the model, are the final word on your system’s real performance.

Maintenance and Its Effect on Monthly Output

A system that’s technically installed correctly can still underperform its monthly targets if nobody’s paying attention to upkeep. Dust, pollen, and grime build up gradually on panel surfaces, and in a city that sees both dry spells and sudden dust events, that buildup can quietly shave several percents off your output before it’s visually obvious.

Panel cleaning has the biggest seasonal impact right before and during peak production months. A system that goes uncleaned from spring pollen season straight through summer is losing exactly the kWh that matter most, both because summer sun is strongest and because CPS Energy’s summer avoided-cost credit and your own summer AC load make that production more valuable.

Inverter health checks matter too. An inverter quietly underperforming or throwing intermittent faults can cause a production dip that looks like a weather problem but isn’t. Reviewing your inverter’s monitoring app monthly, not just when the power bill arrives, catches these issues faster than any modeled comparison will.

Tree growth is a slow-moving maintenance issue specific to established San Antonio neighborhoods. A branch that cleared your panels at installation can start casting a shadow three or four years later, and that shade shows up as an unexplained dip in one specific month’s output, often worsening year over year until someone notices the pattern.

What Homeowners Get Wrong About Their Monthly Numbers

Most homeowners panic at the first month that underperforms, without checking whether that dip is normal seasonal variation or an actual problem. Give your system three months of monitoring before drawing conclusions, then compare that trend against your PVWatts model.

— Anthony

How Alpha Solar Solutions Turns These Numbers Into a Real Plan for Your Home

Reading a modeled table is one thing. Getting a system sized specifically for your roof, your shading, and your household’s actual monthly usage is another, and that’s the gap Alpha Solar Solutions closes for San Antonio homeowners. Instead of a generic estimate, you get an on-site assessment that accounts for your roof’s real tilt, orientation, and any shading the satellite models can’t see, paired with a month-by-month production forecast built for your address.

Alpha Solar Solutions handles Residential Solar Panel Installation from design through permitting and CPS Energy interconnection paperwork, so you’re not stuck deciphering utility forms on your own. Battery backup options are available to help capture surplus solar production for later use instead of exporting it at lower avoided-cost rates. Once your system is running, Solar Panel Cleaning & Maintenance keeps soiling losses from quietly eating into your summer output, and if you ever need panels removed for a roof repair, reinstallation service gets you back up and producing without starting from scratch.

Ready to see what your actual roof could produce month by month? Request a quote through the residential solar page and get a site-specific forecast instead of a rough estimate.

Sources

• Catalog
• CPS Energy solar billing facts (PDF)

FAQ

What Is the 33% Rule in Solar Panels?

In San Antonio specifically, the more reliable guidance is sizing around your actual monthly consumption, since CPS Energy credits exported surplus at a much lower avoided-cost rate than retail.

Does Texas Have More Solar Power Than California?

Texas has surpassed California in total installed solar capacity in recent years, driven largely by massive utility-scale solar farms across the state rather than rooftop installations. California still leads in rooftop residential solar adoption per capita, but Texas’s flat, sunny land and grid demand have made it the larger overall solar producer.

How Much Money Does a 20 Acre Solar Farm Make?

Revenue from a 20-acre solar farm depends heavily on the power purchase agreement rate, system efficiency, and local interconnection costs, and no single figure applies universally across markets. Utility-scale projects like the ones reflected in CPS Energy’s monthly generation data operate under long-term contracts rather than spot pricing, so residential rooftop economics don’t scale directly from farm-level numbers.

What Is the 20% Rule for Solar?

Anything beyond that gap is worth investigating with a local site check.

How Much Does Residential Solar Installation Cost in San Antonio?

Alpha Solar Solutions prices Residential Solar Panel Installation from $12,000 to $25,000, depending on system size, roof complexity, and equipment selected. A custom quote based on your specific monthly usage and roof gives you the most accurate number.

Why Does My Solar Production Drop in Winter?

Shorter days and a lower sun angle reduce peak sun hours from around 6.5 hours a day in June to roughly 3.8 hours in December, which is the main driver behind winter’s lower output. This pattern shows up consistently in both rooftop models and utility-scale generation data across San Antonio.