Living here in the Portland Metro area—from the West Hills to the neighborhoods across the Willamette—we love our tree canopy. Those towering Douglas Firs and leafy Maples define our city, but for a homeowner thinking about energy independence, they pose a big question: Is my roof too shady for solar?
If you’ve been researching solar in Oregon, you’ve likely stumbled across the acronym TSRF. It sounds technical, but it’s actually the most important number for determining if solar makes financial sense for your home.
Here is everything you need to know about TSRF solar meaning, how we calculate it, and what is a good TSRF for homes in Portland.
What Does TSRF Stand For?
TSRF stands for Total Solar Resource Fraction.
So, what is TSRF in plain English? It is the amount of sunlight your specific roof area will receive over the course of a year, expressed as a percentage.
In more scientific terms, the TSRF solar definition is the ratio of insolation (sunlight energy) available, accounting for both shading and the Tilt and Orientation Factor (TOF), compared to the total insolation available at a given location at the optimal tilt and orientation with absolutely no shading.
Think of it this way: A 100% TSRF represents a roof that gets every single drop of possible sunlight. In the real world, 100% is very rare due to trees, chimneys, and other shading factors. TSRF in solar calculations helps us figure out exactly how much power you’ll lose to those real-world obstructions.
TSRF vs. Solar Access vs. TOF: What’s the Difference?
To really understand the TSRF meaning, you have to distinguish it from two other common terms you might hear solar installers throw around.
- Solar Access: This measures only shade. It tells you what percentage of the day the sun hits your roof, ignoring the angle of your roof.
- TOF (Tilt and Orientation Factor): This measures only the angle and direction. A steep, south-facing roof in Portland has a perfect TOF. A flat, north-facing roof has a poor TOF.
- TSRF: This is the “Grand Unified Number.” It combines both Solar Access and TOF.
For example, you might have a roof with zero shade (100% Solar Access), but if it faces due North, your annual TSRF will still be low because the panels aren’t catching the sun at the right angle. TSRF tells the whole story.
What is a Good TSRF? (Minimal Qualifications)
Homeowners often ask us, “What is tsrf solar qualification going to look like for my home?” or “What is a good TSRF?”
While we can install solar on many roofs, there are specific thresholds you need to meet to qualify for state-level incentives. Crucially, these specific percentage requirements apply only to customers of Portland General Electric (PGE) or Pacific Power. Because these two utilities fund the Energy Trust of Oregon (ETO) programs, they have strict performance standards. To qualify for 2026 ETO incentives, your proposed system generally needs a solar TSRF greater than or equal to:
- 75% if we do a Physical (On-Site) Assessment.
- 80% if we do a Remote Assessment.
Remote TSRF Analysis (>80% TSRF)
We use advanced remote assessment software to analyze your project site. This isn’t just a map; we use the latest satellite imagery and aerial 3D height scans (LiDAR) to model your roof and the surrounding Portland tree canopy. The remote software we use is Energy Trust of Oregon approved because of its high level of accuracy. If this software shows your annual TSRF is equal to or greater than 80%, you are good to go!
On-Site TSRF Analysis (>75% TSRF)
If the remote data is borderline, or if you have complex shading from neighboring buildings or trees, we come to you. This is our most common type of assessment for tricky Portland roofs. We perform physical assessments when we want more detail about your roof structure and specific shading obstacles. On average, the physical assessment will take no more than 30 minutes. In this scenario, equal to or greater than 75% is the minimum TSRF meaning you are qualified for incentives.
Improving Your Score in the “City of Trees”
In Portland, our urban forest is one of our best assets, but it can be a challenge for solar. If your initial tsrf solar score comes back low (say, 65%), you still have options:
- Selective Pruning: You don’t always need to cut down a tree. Often, hiring a certified arborist to “window” a specific canopy or trim back branches can bump your Solar Access enough to get your TSRF into the qualifying zone for PGE or Pacific Power rebates.
- Technology Solutions: We utilize modern technology like microinverters or optimizers. While these don’t change the raw TSRF number, they mitigate the impact of partial shade. In older systems, one shaded panel would drop the production of the whole string. With our systems, if one panel is shaded by a chimney or a branch, the rest keep producing at 100%.
Why Generic Solar Estimates Fail in Portland
You might find a generic TSRF calculator online, but be careful. Automated tools often miss the nuances of our local geography and neighborhood-specific tree coverage.
If a national solar company gives you a quote without verifying your annual TSRF through a local lens, they are guessing. And in Portland, guessing leads to under-producing systems and missed incentives. That is why Sunbridge Solar relies on Energy Trust of Oregon verified software to ensure your system meets the 2026 standards for PGE and Pacific Power.
Does a Low TSRF Mean No Solar?
Not necessarily. While the Energy Trust of Oregon requirements for PGE and Pacific Power customers are strict (the 75% cutoff), solar can still make sense at lower numbers.
If your TSRF is 60-70%, your system is still generating clean energy, though your Return on Investment (ROI) may take a little longer. However, many Portlanders prioritize energy resilience. If your goal is to pair solar with a battery backup—like the PGE Smart Battery Reward program—to keep the lights on during the next winter storm, a lower TSRF system is still a powerful investment in your home’s security.
Get A Free Portland Roof Analysis
Calculating angles, TOF, and determining the optimal location for a solar electric system requires local expertise and professional equipment.
Don’t guess with a basic online tsrf calculator. Let us provide you with the accurate information you need to make the right decision for your Portland home.
Ready to find out your home’s solar score?
Call Sunbridge Solar today at 360-313-7190 or contact us online for a free consultation. We serve the entire Portland Metro area, including Gresham, Beaverton, and Lake Oswego.
