You paid for a system that sits on your roof every day. The sun comes up, the panels face it, and somehow your electricity bill drops. But what’s actually going on up there?
It’s not a mystery, but most explanations skip the parts that actually matter to a homeowner: why panels underperform in the heat, how shade from one tree can cut your output more than you’d expect, and why that efficiency rating on the spec sheet rarely matches what you see on your monitoring app.
This guide breaks down the real process, from sunlight hitting a cell to AC power running your appliances, including the factors that quietly reduce what your system delivers. At AWS Solar, we’ve been installing residential and commercial systems across Los Angeles County, Ventura County, and Orange County since 2007. Understanding this process helps you make a smarter decision before and after going solar.
If you’re considering solar installation in Los Angeles, getting clear on how the technology actually works under real-world conditions is a great first step.
The Core Process: How Sunlight Becomes Electricity
Solar panels don’t have any moving parts. There’s no combustion, no turbine, no steam. The conversion from sunlight to electricity happens at the atomic level inside each cell.
Here’s a straightforward breakdown of the process:
Step 1: Photons hit the cell Sunlight is made up of photons, which are tiny packets of energy. When they strike a photovoltaic (PV) cell, some photons are absorbed by the semiconductor material inside the cell. Roughly 95% of today’s solar panels use crystalline silicon as that semiconductor, according to the U.S. Department of Energy.
Step 2: Electrons get knocked loose When silicon absorbs a photon, the energy transfers to an electron. That electron breaks free from its atom and starts to move.
Step 3: The internal electric field directs the current Each solar cell is made with two layers of silicon treated differently: one with extra electrons (n-type) and one with fewer (p-type). Where those layers meet, a built-in electric field forms. It acts like a one-way street, pushing the freed electrons in a single direction.
As the U.S. Department of Energy explains it: “When the sun shines onto a solar panel, energy from the sunlight is absorbed by the PV cells in the panel. This energy creates electrical charges that move in response to an internal electrical field in the cell, causing electricity to flow.”
Step 4: DC electricity flows out The moving electrons create a direct current (DC). That current exits through thin metal grid lines printed on the surface of each cell.
Step 5: The inverter converts DC to AC Your home runs on alternating current (AC). An inverter converts the DC electricity from your panels into the AC electricity that powers your appliances. String inverters and microinverters both do this job, with peak efficiencies ranging from 96% to 98.5% according to industry testing data.
What the Spec Sheet Doesn’t Tell You
Panels are tested under “standard test conditions” (STC): 25°C (77°F) and no shade, in a controlled lab. Your roof is not a lab.
Here are the real-world factors that affect how much electricity you actually get:
Heat: The Biggest Performance Reducer
More sun does not always mean more output. Panels produce less electricity as they get hotter, not more.
Standard panels are rated to lose roughly 0.3 to 0.5% of their output for every degree Celsius above 25°C (77°F). In Southern California, rooftop panels can easily reach 60°C or higher on a clear summer day. At that temperature, output can drop 10 to 20% below the lab rating.
Modern n-type panels (technologies like TOPCon and HJT) handle heat better, with temperature coefficients of just -0.25% to -0.35% per degree. That’s a meaningful difference over time in a warm climate like Los Angeles.
Shading: One Shadow Affects the Whole String
Here’s something a lot of homeowners don’t realize: in a traditional string inverter setup, one shaded cell can reduce output across the entire string of panels.
A nearby tree, a chimney, or even an antenna can create partial shade on just one panel. Without module-level power electronics (microinverters or DC optimizers), that shadow pulls down production across multiple panels, not just the one it’s covering.
Depending on the site, residential systems can lose 5 to 25% of annual production from shading, according to field data. Proper shading analysis during the design phase matters.
Dust and Dirt: A Bigger Deal in California Than You’d Think
California’s dry season creates real soiling problems. Research specific to California (including Los Angeles County) shows average daily energy losses of 0.051% from soiling alone. During a drought period of 145 days, efficiency can drop from 15% to as low as 13.9%, roughly a 7.4% drop, with low-tilt roofs (under 5 degrees) showing losses up to five times higher than steeper roofs.
The good news: regular panel cleaning can recover up to 9.8% of annual energy, according to field data. That’s not a small number.
Panel Degradation Over Time
All panels lose a small amount of output each year. According to decades of field data from the National Renewable Energy Laboratory (NREL), the median degradation rate is about 0.5% per year.
Premium panels, particularly modern n-type designs, can degrade as slowly as 0.3% per year.
What does that mean in practice?
| Years in Use | Expected Output | |
| Year 1 | ~100% | |
| Year 10 | ~95% | |
| Year 25 | ~87–88% |
Most manufacturers now back this with warranties guaranteeing 85 to 90% output at year 25. Older panel types had a one-time efficiency drop (called light-induced degradation, or LID) of 1 to 3% in the first few weeks.
How Southern California’s Climate Affects All of This
Los Angeles County, Ventura County, and Orange County average roughly 5.5 to 6.0 peak sun hours per day with 284 or more sunny days per year. That’s genuinely excellent for solar production.
But it also means the heat and soiling factors above apply here more than in most parts of the country. A system designed with generic assumptions, rather than a site-specific analysis, can underperform by 10 to 30% compared to a properly modeled design.
Orientation and tilt matter too. South-facing panels at an optimal tilt angle capture the most sunlight over the year. East or west-facing panels can still work well, especially if your utility offers time-of-use rates that reward afternoon or morning generation. Every roof is different, which is why a site-specific assessment from a licensed contractor makes a difference.
At AWS Solar, we’ve completed numerous installations across Southern California, and the site conditions vary more than most people expect, even within the same neighborhood.
The Full System: It’s More Than Just Panels
A rooftop solar system is made up of several components working together:
- PV modules (the panels): Where electricity is generated
- Inverter: Converts DC to AC; string inverters serve the whole array, while microinverters work at the panel level
- Racking and mounting: Secures panels to your roof at the right angle
- Monitoring system: Tracks production in real time so you can spot drops early
- Battery storage (optional): Stores excess generation for use at night or during outages
Each component affects total system performance. An efficient panel paired with an undersized or poorly placed inverter won’t perform as well as a balanced system.
Efficiency Numbers: What’s Realistic in 2025?
Efficiency refers to how much of the sunlight hitting a panel actually becomes electricity.
- Weighted average for crystalline silicon modules: 22.7% as of Q4 2024 (up from 21.6% the prior year), according to industry tracking data
- Top commercial products: Up to 24.8%
- Lab record for mono-Si cells: 27.8%
- Practical residential range: 20 to 24% for high-quality panels
Higher efficiency means more watts per square foot of roof. On a smaller or partially shaded roof, this can make a real difference in how many panels you need and how much you generate.
Common Questions About How Solar Panels Work
Do solar panels work on cloudy days? Yes. Panels still generate electricity from diffuse light, typically producing 10 to 25% of their clear-sky output on overcast days. Consistent cloud cover will reduce overall annual production, but it won’t stop the system from generating.
Does heat make solar panels work better? No. This is a common misunderstanding. More sunlight means more energy, but higher temperatures reduce efficiency. The photovoltaic process works on light, not heat. Warmer climates benefit from more sun hours but need to account for temperature-related losses.
How long do solar panels last? Most quality panels are rated for 25 to 30 years and carry performance warranties to match. NREL field data shows median degradation of 0.5% per year, meaning a panel can still produce around 87% of its original output at year 25.
Why is my system producing less than the spec sheet says? Temperature, shading, soiling, and inverter losses all contribute. A 450-watt panel produces 450 watts under perfect lab conditions. On a real roof on a hot, dusty afternoon, it’s producing less. That’s normal, but the gap can be narrowed with the right system design.
Do solar panels need a lot of maintenance? Generally, panels require minimal maintenance. In California’s dry climate, periodic cleaning matters more than it does in rainier regions, given the soiling data above. Monitoring your system output regularly helps catch issues early.
What’s the difference between a string inverter and a microinverter? A string inverter connects all panels in a series and converts the total DC output to AC in one unit. A microinverter is attached to each individual panel and converts DC to AC at the panel level. Microinverters reduce shading losses and make monitoring easier, but they cost more upfront. For roofs with shading or complex angles, the production gains often justify the cost. A licensed solar contractor can run the numbers for your specific roof.
Ready to See What Your Roof Can Actually Produce?
Understanding how solar works is the first step. The next is finding out what’s realistic for your specific home or business, given your roof’s orientation, shading, and local utility rates.
AWS Solar has been helping homeowners and businesses across Los Angeles County, Ventura County, and Orange County do exactly that since 2007. All work is done by our in-house crews, not subcontractors. We handle residential solar panels, battery storage, EV chargers, and commercial solar systems.
If you want a clear picture of what your roof can generate and what the numbers actually look like for your situation, reach out to the AWS Solar team for a site-specific assessment. No pressure, just real answers.
AWS Solar is a licensed solar and electrical contractor serving Southern California since 2007.