A do-it-yourself solar electric system is a chain of components that each play a specific role. The solar panel is the most visible part, but it cannot work alone. Understanding how the pieces fit together helps you plan a safe, efficient setup for off-grid cabins, backup power, or portable projects.
How a solar panel makes electricity
According to the U.S. Energy Information Administration, a photovoltaic (PV) cell converts sunlight directly into direct current (DC) electricity. Sunlight is made of photons. When photons strike the semiconductor material inside a PV cell, they can be absorbed and dislodge electrons from the material’s atoms. Special treatment of the cell’s surface makes the front more receptive to free electrons, creating an electrical imbalance between the front and back of the cell. This imbalance produces a voltage potential, much like the terminals of a battery. When conductors are connected to an external load, current flows through the circuit. The EIA notes that individual PV cells produce only 1 or 2 Watts, so manufacturers connect many cells together inside a weather-tight panel, or module. Panels can then be grouped into arrays to generate more power.
PV cells and panels produce the most electricity when they face the sun directly. The U.S. Department of Energy explains that mounting structures tilt the array at a fixed angle determined by local latitude, orientation, and electrical load requirements. In the northern hemisphere, modules are usually pointed due south and inclined at an angle equal to the local latitude to achieve the highest annual energy output.
The panel is only one part of the system
The Department of Energy states that solar photovoltaic modules are where electricity gets generated, but they are only one of many parts in a complete PV system. To make that electricity useful in a home or business, other technologies must be in place. A basic off-grid or backup system follows a predictable energy path: panel, solar charger, battery, inverter, and loads.
Victron Energy’s Wiring Unlimited guide is clear on one critical rule: solar panels are not allowed to be directly connected to a battery. A solar charger must sit between the panels and the batteries. The solar charger converts the higher solar panel voltage into a voltage suitable for battery charging. If a panel were connected straight to a battery, the battery would get damaged.
The solar charger, often called a charge controller, regulates the charging process so the battery receives the correct voltage and current. Once the battery is charged, the stored DC energy can be used directly by DC devices, or it can be sent to an inverter. The Department of Energy explains that inverters convert DC electricity into alternating current (AC), which is used for local transmission and by most household appliances. The EIA adds that nearly all electricity is supplied as AC in transmission and distribution systems, so an inverter is essential for running standard AC loads.
DC versus AC and why it matters
Direct current flows in one direction, while alternating current reverses direction periodically. PV panels naturally produce DC. The EIA notes that DC electricity can charge batteries and power devices that use DC. However, because the grid and most appliances run on AC, an inverter is needed to make the switch. The Department of Energy mentions that PV systems may have a single central inverter or microinverters attached to each module. A single inverter is generally less expensive and easier to service, while microinverters allow each panel to operate independently, which helps if some modules are shaded.
Battery storage is what makes solar energy available when the sun is not shining. The Department of Energy states that batteries allow for the storage of solar photovoltaic energy so it can be used at night or when weather keeps sunlight from reaching the panels. In a DIY system, the battery bank is sized to cover the loads during periods without solar production.
Watts, watthours, and the power formula
To size a system correctly, you need to understand the difference between power and energy. The EIA explains that electricity is measured in units of power called Watts. One kilowatt equals 1,000 Watts. Power at a specific moment is measured in Watts, but electricity use over time is measured in Watthours. One Watthour is the energy of one Watt used for one hour. Utility companies typically bill in kilowatthours (kWh). For example, a 40-Watt light bulb left on for five hours uses 200 Watthours, or 0.2 kWh.
Victron’s Wiring Unlimited guide introduces the power formula P = V x I, where P is power in Watts, V is voltage in Volts, and I is current in Amps. This relationship is fundamental because it shows that for a fixed power load, a lower voltage means a higher current. Victron gives an example: a 2,400-Watt load on a 12-Volt battery draws 200 Amps (2,400 / 12 = 200). The same load on a 24-Volt system draws only 100 Amps, and on a 48-Volt system it draws 50 Amps. This has a direct effect on wiring.
Why low-voltage DC needs thicker cable
All cables have some resistance. When current flows through a cable, the cable heats up and a voltage drop occurs. Victron’s guide calculates that with a 2,400-Watt inverter connected to a 12-Volt battery using two 1.5-meter-long, 16 mm² cables, each cable has a resistance of 1.6 milliohms. The voltage drop over one cable is 200 A x 0.0016 Ω = 0.32 Volts. Because there are two cables (positive and negative), the total voltage loss is 0.64 Volts. The inverter no longer receives 12 Volts but only 11.36 Volts, and the current rises to compensate, making the system less efficient. Victron points out that this represents a 5% energy loss turned into heat.
Higher system voltages dramatically reduce voltage drop. Victron shows that the same 2,400-Watt load at 24 Volts produces a total voltage drop of 0.32 Volts (1.3%), and at 48 Volts the drop is only 0.16 Volts (0.3%). The guide advises aiming for a voltage drop no larger than 2.5%. For a 12-Volt system that means no more than 0.3 Volts, for 24 Volts it is 0.6 Volts, and for 48 Volts it is 1.2 Volts. These numbers are targets, not code requirements.
Resistance does not come from the cable alone. Victron lists fuses, shunts, switches, circuit breakers, cable terminals, and even loose or corroded connections as items that add resistance. Keeping cables short, using sufficient thickness, making clean tight connections, and reducing the number of connections in a cable run all help prevent excessive voltage drop. High voltage drop can cause batteries to be undercharged, trigger low-voltage alarms, overheat cables, and reduce equipment lifetime.
System types: off-grid and grid-connected
The EIA describes two broad categories. Stand-alone, or off-grid, PV systems supply electricity in locations where power lines do not exist. These systems often charge a battery to provide electricity when the sun is not shining. Grid-connected systems, on the other hand, are tied to the electric power grid. The EIA notes that beginning in the late 1970s, PV panels were used in remote off-grid locations, and since 2004 most PV systems in the United States have been grid-connected. Small-scale grid-connected systems, sometimes called rooftop PV systems, have less than 1,000 kilowatts of generation capacity.
For a DIY builder, off-grid and backup systems are common starting points. A portable solar setup or a small cabin system typically operates independently of the grid. Any project that connects to household wiring or the utility grid must follow local electrical codes and be reviewed by a qualified electrician.
Estimating production with PVWatts
The PVWatts Calculator, now run by the National Laboratory of the Rockies, estimates the energy production of grid-connected photovoltaic systems. The tool allows homeowners, small building owners, installers, and manufacturers to develop estimates of potential PV installation performance. Its Version 8 uses weather data from the National Solar Radiation Database and says Version 8 provides production estimates based on its latest models. The page also notes that PVWatts does not distinguish better-performing modules from lesser ones except through its inputs, so its results are estimates. The expected range is based on 30 years of actual weather data at the chosen location, giving an indication of the variation you might see.
How the main components work together
The table below summarizes each key component, its function, and the source of the information.
| Component | What it does | Source |
|---|---|---|
| PV module (solar panel) | Converts sunlight directly into DC electricity. | EIA |
| Solar charger (charge controller) | Converts higher panel voltage to a voltage suitable for battery charging; prevents direct panel-to-battery connection. | Victron Wiring Unlimited |
| Battery | Stores solar energy for use when the sun is not shining. | DOE |
| Inverter | Converts DC electricity from the battery or panels into AC electricity for household appliances. | DOE, EIA |
| Mounting structure | Supports the array and tilts it at an angle that optimizes energy output. | DOE |
| Wiring and connectors | Carry current between components; must be sized to limit voltage drop and handle the system current. | Victron Wiring Unlimited |
Every part must be matched to the others. A solar charger has voltage and current limits listed in its manual, and the array must stay within them. Wiring must be thick enough to keep voltage drop within the 2.5% target Victron recommends. Fuses and circuit breakers protect the wiring, and their ratings come from the product manuals and local electrical code, not from a one-size-fits-all table. When in doubt, especially for anything connected to a building’s electrical system, consult a qualified electrician.
Frequently asked questions
Can I connect a solar panel directly to a battery?
No. Victron’s Wiring Unlimited guide states that solar panels are not allowed to be directly connected to a battery. A solar charger must be placed between the panels and the battery to convert the higher panel voltage into a suitable charging voltage. Connecting a panel directly will damage the battery.
Why does a 12-Volt system need thicker cables than a 24-Volt system?
For the same power load, a lower voltage means higher current. Higher current flowing through a cable creates a larger voltage drop and more heat. Victron’s guide shows that a 2,400-Watt load on 12 Volts draws 200 Amps and loses 0.64 Volts over two 1.5-meter 16 mm² cables, while the same load on 24 Volts draws only 100 Amps and loses 0.32 Volts. To keep voltage drop within the recommended 2.5%, low-voltage systems need thicker conductors.
Do I need an inverter for a small off-grid system?
Only if you want to run standard AC appliances. Many DC devices can be powered directly from a battery. The Department of Energy explains that inverters convert DC to AC, which is what most household equipment requires. If all your loads are DC, you can skip the inverter, but you will still need a solar charger and battery.
For more foundational concepts, visit the DIY Solar Fundamentals category page, where you will find articles on solar electricity basics, system types, and energy production. When you are ready to choose hardware, explore solar system components and the DIY solar planning section for step-by-step sizing guides.
