AC vs. DC and Solar Power
Creating free electrical power from the sun’s rays requires more than just solar panels. Devices called inverters are necessary to convert the DC current produced by your panels into the AC current your home runs on. But a very small quantity of energy is lost in the process. So, when shopping for a solar system, make sure the energy production estimates you’re getting from different providers are all based on the same kind of current.
For comparison purposes it doesn’t matter which. But it makes sense to look at estimates based on the AC power the inverters are sending into your home rather than the DC power initially generated by your solar panels. That way, you get a more accurate idea of your electric bill offset.
But why don’t solar panels themselves automatically produce the kind of power you need?
Electricity Isn’t Really Electrons
AC stands for Alternating Current.
DC stands for Direct Current.
Strictly speaking, mentioning AC or DC “current” is redundant since it’s already meant by the “C”. But like “SAT test” and “PIN number,” acronyms sometimes become so common that we stop thinking of them as such. It then seems funny not to redundantly throw in that already included last word when it helps to explain the concept being abbreviated.
Just like a current of water, an electrical current is something that flows in a certain direction. But the kind of current that flows through wires is composed of an electrical charge carried by electrons in motion. You’ve probably heard people say that electricity is composed of the electrons themselves. That common explanation does make it easy to visualize electric current. But, in reality, alternating current actually prevents the electrons themselves from flowing.
Alternating Current gets its name because the direction in which it flows is constantly alternating back and forth. The AC powering your appliances changes directions an amazing 60 times every second. That rapid oscillation never even gives the electrons a chance to start flowing and they wind up vibrating instead. But the vibrations do, nonetheless, cause current or electrical charge to flow in alternating directions.
Direct Current, by contrast, continually flows in one direction. Its name can be a little misleading since DC isn’t really any more direct than AC. But, in direct current, the electrons themselves do flow with the electrical charge.
Why AC Became Standard
Around 200 years ago, scientists discovered an efficient way to generate electricity using a spinning magnet. But, instead of direct current, it produced current that alternated direction with the magnet’s rotation. Since there wasn’t any practical use for alternating current, early alternators usually had devices which converted their output to DC. Automobiles today still use an alternator to efficiently generate AC power, which is then converted to DC for battery storage.
When the invention of the electric light bulb created a demand for electric lines running into our homes, however, alternating current turned out to have one very big safety advantage. Transmitting electricity over distances much more than a mile requires dangerously high voltage to minimize the amount lost from electrical resistance. But lowering the voltage of direct current so it was safe to run into people’s homes was technologically unfeasible. As a result, DC power plants had to be very close to their customers. Besides all the inconvenience and inefficiency, generating DC power at a reasonable cost for sparsely populated regions was impossible since each plant could only serve a few homes at most.
Around 1886, however, William Stanley* invented a commercially viable device for transforming high voltage alternating current into a safer lower voltage. That meant that large scale power plants could provide high voltage AC power to customers many miles away and Stanley’s transformers could then be used to lower the voltage to a safe level before bringing it into their homes. AC power pretty quickly became the norm and manufacturers stopped producing DC appliances.
The way solar panels generate energy from sunshine produces DC power. Nowadays, we actually have the technology to easily transform DC power to low voltage too. If it had existed 200 years ago, all the appliances in your home would run on direct current and we wouldn’t need to use inverters or accept the very small lose in energy production.
Thankfully, since solar power is a completely clean and 100% renewable resource, there’s always more sun to make up the small difference. And we don’t have to worry about damaging the environment by doing so.
*Though Nikola Tesla invented the AC motor and helped refine other technology important to making alternating current the dominant technology, he did not invent the transformer as is commonly claimed.