A battery solar system is five parts in a chain: the panel makes electricity, the charge controller tames it, the battery stores it, the inverter translates it for household equipment, and the loads spend it. Each part exists because the parts on either side of it speak different electrical languages. Know the five names and what each one is for, and every kit listing, video, and forum thread starts making sense.
The chain.
Current flows left to right when the sun is out and right to left from the battery at night. The controller sits in the middle of everything for a reason: it is the only part that understands both the panel's moods and the battery's limits.
The panel.
A panel is a sandwich of photovoltaic cells in series, and it behaves less like a steady power supply and more like a moody spring: its pressure changes with light and temperature. Two numbers on its label matter. Open-circuit voltage (Voc) is the pressure with nothing connected, the highest voltage the panel will ever produce, and the number your controller and fuses must be rated above. Maximum power voltage (Vmp) is where it actually works. A "12 volt" panel runs near 18 volts at Vmp and over 21 at Voc; the name is a family label, not a measurement.
Panels wire together like batteries do: in series (a string), voltages add; in parallel, currents add. Series strings are why an array can sit at several hundred volts of DC, and why a panel is treated as always live whenever light hits it. Cold weather raises voltage, so string math is done for your coldest morning, not a summer afternoon.
The charge controller.
Connect a panel straight to a battery and the panel will overcharge it, quietly and then dramatically. The charge controller exists to prevent that: it takes whatever the panel offers and feeds the battery what the battery can accept, tapering as it fills.
The two kinds are worth knowing by name. PWM controllers are simple switches: cheap, reliable, and they work by dragging the panel down to battery voltage, wasting the difference. MPPT controllers (maximum power point tracking) are small power converters: they let the panel run at its happy Vmp and convert the extra voltage into extra charging current. MPPT earns its higher price on bigger panels, higher-voltage strings, and cold weather, which is exactly when a panel has the most extra voltage to harvest. For a small sensor-node panel, PWM is usually the appropriate choice; for anything running a pump, price out MPPT.
The battery.
The battery is the reservoir that makes solar useful after sunset, and it is the part with the most ways to be treated badly. It gets its own page: Batteries and Storage covers chemistries, depth of discharge, and the electronics inside lithium packs. For the chain, know this much: the battery sets the system voltage everything else must match, and it is the part that makes fusing non-negotiable, because it can deliver hundreds of amps into a fault.
The inverter, and skipping it.
Batteries and panels speak DC; wall-plug equipment speaks AC. The inverter is the translator, and two of its habits matter. First, quality: a pure sine wave inverter produces power like the grid's, which motors, pumps, and anything with electronics want; the cheaper modified-sine kind runs some equipment badly or hotly. Second, appetite: an inverter draws power just by being on (standby draw), often several watts around the clock, which can be more than a small system's actual loads.
Which points at the quiet trick of farm solar: skip the inverter where you can. Pumps, gate openers, lights, fence energizers, and every sensor node this site describes come in DC-direct versions that run straight off the battery circuit. No translation, no standby tax, one less box to buy and fuse.
The shortest version
Panel makes DC, controller tames it, battery stores it, inverter translates it for AC equipment, loads spend it. The controller exists so the panel cannot cook the battery; MPPT harvests high panel voltage, PWM throws it away. Buy pure sine if you need AC at all, and prefer DC-direct equipment so you often do not.
Words to work from
Take these terms with you. They are what the spec sheets and the videos assume you know.
- Open-circuit voltage (Voc)
- The panel's voltage with nothing connected; the ceiling your controller and DC parts must be rated above.
- Maximum power voltage (Vmp)
- The voltage where the panel actually does its best work, well above its family label.
- String
- Panels wired in series. Voltages add, and cold mornings raise them further.
- Array
- All the panels together, however they are wired.
- Charge controller
- The device between panel and battery that prevents overcharge. The one part that talks to both sides.
- PWM
- The simple controller type: a fast switch that drags the panel to battery voltage and wastes the difference.
- MPPT
- The converter type: runs the panel at Vmp and turns extra voltage into extra charging current. Earns its price on big arrays and cold days.
- Pure sine wave
- Inverter output shaped like grid power. Motors and electronics want it.
- Standby draw
- What an inverter eats just being switched on. Can exceed a small system's real load.
- DC-direct
- Equipment that runs straight off the battery circuit, skipping the inverter and its losses.
Frequently asked questions.
Can I connect a solar panel directly to a battery?
Briefly, yes; wisely, no. Nothing stops the current at first, but nothing stops it later either: the panel will push the battery past full and keep pushing, which ruins lead-acid and can make lithium dangerous. A charge controller costs less than any battery it protects. The only exception is tiny trickle panels sold specifically as unregulated maintainers, and even those deserve scrutiny.
What is the difference between PWM and MPPT?
A PWM controller is a fast switch: it connects the panel to the battery and the panel's voltage collapses to the battery's, wasting the difference. An MPPT controller is a power converter: it lets the panel run at its best voltage and converts the surplus into extra charging current, commonly 10 to 30 percent more harvest. MPPT costs more and earns it on larger panels, higher-voltage strings, and cold weather.
Why does my 12 volt panel measure 21 volts?
Because "12 volt" is a family label, not a measurement. A panel built for 12 volt systems runs near 18 volts at its maximum power point and over 21 volts open-circuit, so it can still charge a battery through real-world losses and heat. The controller manages the difference. Rate your wiring, fuses, and controller for the open-circuit number, not the label.
Do I need an inverter?
Only if something in the system genuinely needs AC. Pumps, lights, gate openers, fence energizers, and sensor electronics all come in DC versions that run straight off the battery, and skipping the inverter also skips its standby draw, which around the clock can outweigh a small system's real work. If you do need AC for motors or electronics, buy pure sine wave.