Solar panels, step by step

1. The panel and its label

A good panel works for 25–30 years, with no moving parts and no fuel.

1. What it gives in a year — 1 kWp of panels gives roughly 850–1,100 kWh a year in the UK and Ireland and 1,200–1,700 kWh in most of the US.
2. The label on the back — Pmax is the maximum power, Vmp the voltage at maximum power and Voc the open-circuit voltage. Then the current and the temperature coefficient.
3. Size and weight — A 410–450 W panel measures roughly 1.7 × 1.1 m (5.6 × 3.6 ft), about 2 m², and weighs 20–24 kg (44–53 lb).
4. MC4 connectors — Connectors of the same make, crimped with the proper tool, with no home-made joints or insulating tape.

Why: Even so, many rural systems run at half power: the panels sit in shade, face whichever way the roof happened to face, or were sized on July sun. So first know what a panel really gives and what its label says.

• Wp is power in the lab. A 400 Wp panel at midday in July gives roughly 300–340 W, because the cells heat up.
• For an accurate estimate for your site use PVGIS, the free European Commission tool (it covers the UK and Ireland), or NREL PVWatts in the US.

2. Site and tilt

Best is south-facing at a 35–40° tilt (30–35° in most of the US).

1. South is best — South-east and south-west give 94–97 %, east or west 80–85 %. North isn't worth it.
2. Tilt 35–40° — The most electricity over the whole year, for a grid-tied system. In most of the US, 30–35°.
3. Winter 60–65° — Best for winter and for an off-grid system. In summer you lose roughly 10–15 %, and snow slides off faster.
4. Ground mount — Lower edge at least 60–80 cm (2–2.5 ft) above the ground. Gap between rows at least 3 times the panel height above the ground, 4 times in the UK, Ireland and Canada.

Why: Orientation and tilt decide how much electricity you get, and a steep tilt helps in winter. A ground mount gives you the ideal tilt, a south aspect and easy cleaning.

• Below 15° rain doesn't wash the panel well, and dust, pollen and bird droppings stay on.
• On a ground mount you can change the tilt twice a year: 60–65° from October to March, 30–35° from April to September.

3. Shade and December · Locked

Buy the Solar panels module and you get the PDF to download and print, plus lifetime access to this interactive lesson: all 6 chapters, 24 steps.

4. A small 12 V system · Locked

Buy the Solar panels module and you get the PDF to download and print, plus lifetime access to this interactive lesson: all 6 chapters, 24 steps.

5. Installation · Locked

Buy the Solar panels module and you get the PDF to download and print, plus lifetime access to this interactive lesson: all 6 chapters, 24 steps.

6. Maintenance · Locked

Buy the Solar panels module and you get the PDF to download and print, plus lifetime access to this interactive lesson: all 6 chapters, 24 steps.