Solar Basics

Panels, batteries and what a small system really runs

6 minIntermediateUpdated 2026-10-23 Solar Basics

You will learn

Explain what each part of a solar system does
Estimate what a small panel and battery can power
Know where DIY stops and a licensed installer starts

⚠️ Never connect solar to household wiring or the grid yourself; that requires a licensed electrician and registration.

⚠️ Fuse every battery positive lead close to the battery; a DC short can start a fire.

⚠️ Panels produce voltage whenever light hits them. Cover them before working on connections.

The four parts

Every solar setup has the same pieces. Panels turn sunlight into DC electricity: a typical residential panel is about 1.7 by 1 metre and rated around 400 watts. A charge controller sits between panels and battery and stops the battery overcharging; an MPPT controller squeezes 20 to 30 percent more from the panels than a cheap PWM one. The battery stores energy for night and cloud; lithium iron phosphate (LiFePO4) is now the standard because it lasts thousands of cycles and can be drained deeply. An inverter converts battery DC to 230 V AC for normal appliances. Skip the inverter and run 12 V devices directly if you can: it is more efficient.

💡 Panel watts are peak lab figures. Real output on a good day is 70 to 80 percent of that.

Watts, watt-hours and the maths

Watts measure power right now; watt-hours measure energy over time. A 10 W bulb on for 5 hours uses 50 Wh. To size a system, list what you want to run, multiply each item’s watts by daily hours, and add them up. A 400 W panel in Portugal produces roughly 4 to 5 peak sun hours a day in summer and 2 to 3 in winter, so about 1,600 to 2,000 Wh on a summer day and 800 to 1,200 Wh in winter. Batteries are rated in amp-hours: multiply by voltage for watt-hours. A 12 V 100 Ah LiFePO4 battery holds 1,200 Wh, of which you can safely use about 1,000.

💡 Design for winter output, not summer. A system that works in December works all year.

What a small system can actually run

Reality check. One 400 W panel with a 1,200 Wh battery comfortably runs LED lighting (5 to 10 W per bulb), phone and laptop charging (10 to 60 W), a Wi-Fi router (10 W), a 12 V water pump for the garden, and a small 12 V fridge (40 W running, about 500 Wh a day). It will not run an electric kettle (2,000 W), a washing machine, an oven or air conditioning. Those need a grid connection or a system of 3 to 5 kW with a large battery bank costing thousands. A small system’s real job is lights, communication, water and refrigeration: the things that matter when the power is out.

💡 A 2,000 W kettle for 3 minutes uses 100 Wh, the same as a laptop for two hours. Heat is the enemy of small solar.

Placing panels

Panels want to face the equator, so south in Portugal, tilted at roughly your latitude (about 38 degrees in Lisbon) for year-round output, or steeper in winter and flatter in summer if you can adjust them. Shade is a system killer: a shadow across 10 percent of a panel can cut its output by half, because cells are wired in series. Watch the spot through the day before mounting anything. Keep panels cool with air flow behind them; output drops as they heat up. Rinse dust and pollen off a few times a year with plain water, early morning, never when the glass is hot.

💡 A portable panel you can carry into the sun beats a fixed one in a bad spot.

Where DIY stops

A 12 V or 24 V off-grid kit for a shed, van, boat or garden pump is a reasonable beginner project: low voltage, fused, isolated from the house. Anything that connects to your home’s mains wiring, feeds the grid, or exceeds extra-low voltage is licensed work. In Portugal, a grid-tied or self-consumption system (UPAC) must be registered with the DGEG and installed by a certified technician, and the inverter must be approved; the same is true across the EU. Even off-grid, a DC arc from a battery bank can start a fire, so fuse every positive lead close to the battery, size cables correctly, and use proper connectors, never twisted wires.

💡 Buy a complete matched kit for your first system. Mismatched parts are where beginners get hurt.

Check yourself

What does a charge controller do?

The charge controller regulates power from panels to the battery. An MPPT type also harvests more from the panels than a basic PWM one.

A 12 V 100 Ah battery holds roughly how much energy?

Amp-hours times volts gives watt-hours: 100 × 12 = 1,200 Wh. Use about 80 percent of that on a LiFePO4 battery.

Which appliance is realistic on one 400 W panel and a small battery?

Small solar handles lights, charging, a router, a pump and a small 12 V fridge. Heating appliances draw far too much.

Which job must go to a certified installer?

Any connection to household mains wiring or the grid is licensed work and must be registered with the energy authority.

Try it for real: Size a mini system

List five devices you would want in a power cut and find their watts on the label
Multiply by daily hours to get watt-hours per day
Work out how many 400 W panels and 100 Ah batteries you would need for a winter day
Watch your sunniest outdoor spot at 9, 12 and 15h and note any shade