Over a hundred years ago, Thomas Edison and Nikola Tesla were the generals in what was then called ‘The War of the Currents’. Tesla championed AC electricity, and Edison did the same for direct current (DC) electricity. When the dust settled on a battlefield that saw everything from intellectual property to political maneuvering, Tesla was left standing and safe, low-voltage AC power became the gold standard for homes and businesses. Yet, when homeowners are considering rooftop solar or home energy storage once again face the decision between AC and DC systems.
AC power’s historical advantage
AC power and DC power both move energy through a circuit. Not unlike water in a garden hose, when you disconnect the hose from the spigot, water stops flowing. In AC power systems, current cycles between positive and negative values; they alternate. In DC systems, current is fixed at a constant positive value, hence ‘direct’ current. So why are most modern homes served by AC power?
Thomas Edison, the DC power proponent, believed that neighborhoods would use energy from small generators located close to those neighborhoods. Nikola Tesla, the AC power proponent envisioned a system in which large, centralized generators would send out energy through long transmission lines. George Westinghouse, the father of the modern electric grid, opted for Tesla’s AC system, and the rest was history.
Why AC systems are safer
Homeowners use a different set of criteria than electric companies do when comparing the merits of AC and DC power systems. But if safety is the key consideration, AC power wins again. Here’s why.
DC power systems are higher voltage and have to be closely monitored for arc faults, which pose significant risk of fire and bodily injury. Even the smallest equipment failure, such as a damaged cable or a loose electrical connection, can generate an arc fault. Once an arc fault is triggered, it can be difficult to stop because voltage in DC systems is constant, and you have to be able to interrupt the circuit or the arcing will continue.
In an AC power system, voltage continually passes zero as current cycles between positive and negative values, making it possible to virtually eliminate the risk of an arc fault.
Rooftop solar systems using DC power also tend to rely on hazardous high voltage to move energy from a full array of solar panels to a centralized string inverter, while AC power systems like the Enphase Microinverter System always operate at low voltage. That is a safety feature from which solar installers, homeowners, first responders, and utility workers all benefit.
It’s important to be able to trust that friends and family will be safe around the products you bring into your home, including rooftop solar and energy storage systems. By choosing an AC system, you’re as safe as with any quality home appliance introduced in the last hundred years or so. In the War of the Currents, AC electricity won the day for households because of safety and reliability. There is no reason for homeowners to fight this war again on their rooftops, and introduce unnecessary risk. Our advice: Stay safe and keep it AC.