AC (alternating current) is the type of electricity supplied by the mains grid, where current flows back and forth rapidly. DC (direct current) is the type stored in batteries, where current flows in one direction. Most household appliances use AC, whilst solar panels and batteries produce DC, which is why an inverter is needed to convert between the two.
AC and DC are terms you will encounter constantly in off-grid solar, van builds and portable power. Understanding the difference helps you choose the right equipment, avoid compatibility problems and make smarter decisions about energy efficiency.
What Is AC Power?
Alternating current changes direction many times per second. In the UK, mains electricity is AC at 230 volts and 50Hz, meaning the current reverses direction 50 times per second. This frequency is what allows transformers to work efficiently, making it practical to transmit electricity over long distances through the national grid.
Your standard wall sockets deliver AC power. Most household appliances (ovens, washing machines, kettles, televisions, standard power tools) are designed to run on AC.
What Is DC Power?
Direct current flows in one direction only. Batteries produce DC power, as do solar panels and fuel cells. DC is stable and predictable, making it ideal for electronics and energy storage.
Many devices that plug into the mains actually convert AC to DC internally. Your laptop charger, phone charger and most consumer electronics contain an internal power supply that performs this conversion, which is why they feel warm during use.
Why Does Solar Produce DC?
Solar cells work through the photovoltaic effect: photons from sunlight knock electrons free in a semiconductor material, creating a flow of electrons in one direction. This is inherently a DC process. The DC output from panels is then either stored in batteries (which are also DC) or converted to AC by an inverter for use with standard appliances.
The Role of Inverters
An inverter converts DC battery power to AC mains power. This is what allows you to run a standard kettle, television or power tool from a battery. Modern inverters are efficient (90 to 95% for quality units), but the conversion process does involve some energy loss as heat.
Where possible, running devices directly from DC outputs (USB, 12V) rather than routing through the inverter saves energy. A 12V compressor fridge running from a 12V DC output is meaningfully more efficient than the same fridge running via an AC inverter.
Common DC Voltages in Off-Grid Systems
- 5V: USB charging for phones, tablets and small devices
- 12V: Standard vehicle and leisure battery voltage. Used for 12V fridges, lights, fans and accessories
- 24V: Common in larger van or marine systems for reduced cable losses
- 48V: Standard for home battery storage systems. Higher voltage means less current and thinner cables for the same power
- USB-C PD (up to 140W): A higher-power USB standard for laptops and larger devices
AC vs DC Efficiency in Practice
For off-grid and battery-powered systems, minimising AC conversion losses is a worthwhile goal. Consider:
- Using USB or 12V outputs for devices that support them
- Choosing a 12V compressor fridge over an AC-powered domestic fridge
- Using LED 12V lighting rather than AC-powered bulbs
- Running laptops via USB-C rather than through a standard AC socket
Each of these removes one conversion step and reduces overall system losses.
Portable Power Stations and AC/DC
Modern portable power stations like those in the EcoFlow DELTA range provide both AC and DC outputs simultaneously. They include a built-in inverter for the AC sockets and direct DC outputs (USB, 12V, USB-C) for more efficient device charging. This flexibility means you can power virtually any device from a single unit, whether it requires AC or DC.
Safety Considerations
AC power at mains voltage (230V in the UK) is dangerous and can cause fatal electric shocks. DC power at low voltages (5V, 12V) is generally safe to handle, but high-current DC systems (such as large battery banks) can cause severe burns and fire from short circuits. Always fuse DC circuits appropriately and treat any battery bank with respect regardless of voltage.
