Lesson 2 of 7

Solar PV

7 min read

Solar photovoltaics went from a niche, expensive technology to the cheapest source of new electricity generation in much of the world within about two decades — and it did so while working on a fundamentally different principle from every generation technology covered earlier on this platform: no combustion, no turbine, no moving parts at all.

The photovoltaic effect, briefly

A solar cell is a semiconductor (almost always silicon) engineered so that photons hitting it knock electrons loose and push them in a consistent direction, producing a DC voltage and current directly from light — with no intermediate mechanical step. This is why solar is one of the few generation technologies genuinely without moving parts, which is also a major reason for its very low maintenance requirements compared to almost anything else in this curriculum.

From a single cell to a power plant

Cell: The basic semiconductor unit, producing on the order of half a volt.
Module (panel): Many cells wired in series and parallel, packaged together — the physical panel you'd recognize on a roof.
String / array: Multiple modules wired together to reach the voltage and power level needed for a given installation, from a single rooftop to a utility-scale solar farm covering hundreds of hectares.

Because output is DC, and the grid runs on AC, every solar installation — from a single rooftop to a utility-scale farm — needs an inverter to connect to the grid. That's important enough to be its own lesson next in this track.

What actually determines output

Solar output depends primarily on irradiance (how much sunlight is hitting the panel), the angle between the panels and the sun, temperature (counterintuitively, panels lose some efficiency as they get hotter), and simple geometry — output tracks a predictable daily and seasonal curve, rising from sunrise, peaking around midday, and falling to zero every night, modulated unpredictably by cloud cover.

Capacity factor: rated power isn't average power

A solar farm's nameplate capacity describes its peak output in ideal sunlight, but its average output over a full year — its capacity factor — is typically only around 15-25% for fixed-tilt utility-scale solar (higher with sun-tracking mounts), simply because the sun isn't shining at full strength most of the time. This gap between nameplate and average output is central to how much generation capacity actually needs to be built to meet a given amount of average demand.

Utility-scale vs. distributed rooftop solar

Utility-scale solar farms connect directly to the transmission or sub-transmission network, behave (from a grid-planning point of view) somewhat like a conventional but variable power plant, and are relatively easy for an operator to monitor and, if necessary, curtail. Rooftop solar is the opposite case: thousands of small, independently-owned systems connected at the distribution level, individually invisible to transmission operators, which is exactly the distributed-resource visibility challenge covered in the Smart Grids track.

Key takeaways

Solar PV converts light directly to DC electricity via the photovoltaic effect, with no moving parts.
Cells combine into modules, modules into strings/arrays, scaling from rooftop to utility-scale.
Output follows a predictable daily/seasonal solar curve, modulated unpredictably by cloud cover.
Capacity factor (typically ~15-25% for fixed utility-scale solar) is why nameplate capacity overstates average output.