How a PV system works

Chapter 3 separated kW from kWh. Now: how a PV system actually generates those kWh — from sunlight to socket, in four steps.

The chain: modules → strings → inverter → house/grid

1. Modules convert sunlight directly into direct current (DC). This happens inside the solar cell itself — no moving parts, no combustion.

2. Strings. Modules are wired in series into "strings" to produce a usable voltage. A roof usually has several strings — often split by roof orientation.

3. Inverter (with MPPT). The inverter does two things at once: it converts the modules' DC into the AC that your house and the grid use — and it continuously hunts for the point where the modules are currently producing the most power (MPPT — Maximum Power Point Tracking). Because sunlight and temperature keep changing, that optimal point keeps shifting; MPPT follows it automatically. A hybrid inverter also manages the battery.

4. House and grid. The AC produced feeds household loads first; any surplus goes to the battery (if you have one) or out to the public grid.

What actually drives yield: roof orientation

Module technology matters less to annual yield than people expect — roof orientation dominates:

• South-facing produces the most total energy over a year.
• East/west split spreads generation across the day — a lower midday peak, but more power in the morning and evening, which is often more useful for self-consumption.
• A southeast-facing roof (azimuth around −30°) shifts production toward the morning and noticeably underperforms in the late afternoon — an effect to plan for in the yield estimate, not discover afterward.
• Shading costs disproportionately more yield than you'd expect — even a chimney or tree shadow on a few cells can drag down a whole string. Multiple MPP trackers or module-level power optimizers soften that.
• Temperature: hot modules produce somewhat less power. The more realistic NOCT behaviour (Normal Operating Cell Temperature) tells you more about real-world field yield than the STC lab figure on the datasheet.

Remember: before you get deep into module technology or inverter brands, nail down the roof orientation. It often affects annual yield more than the choice of module does.

Where the battery and heat pump plug in

With a hybrid inverter, a battery usually hangs off the same device and charges DC-coupled — efficient, and the usual choice when PV and storage are planned together. The heat pump, by contrast, is a large, controllable load: run it while the sun is shining and you use your own power instead of exporting it cheaply and buying it back later at a premium. How to actually coordinate that is a later chapter.

What this means for you

If an offer quotes you an annual yield, ask what orientation and shading assumptions it's based on — and whether multiple strings (e.g. for different roof faces) were modelled separately. The next chapter goes deeper into the modules themselves: bifacial vs. monofacial, cell quality, and how to read part numbers.