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In solar, we have to deal with both AC, and DC power, because our solar panels, and batteries work with DC power, but most home appliances use AC power.

DC = Direct current
Direct current just means the flow of electrons, and the voltage stays one direction.

AC = Alternating current
With alternating current the flow of electrons, and the voltage alternate directions.

Almost everything we use today requires DC power: appliances, TV’s, computers, LED lights, ect.  Anything that uses any electronic part requires DC power.  So that brings up the question, why do our homes, and all of our appliances run off of AC power from the electrical grid rather than DC power?

To answer that question we have to look back to when the power grid was developed.  Initially, the only electricity we knew of was DC power. However, we didn’t know how to easily convert the voltage of DC power (this is not the case now), and as a result, this the DC power could not be transported over large distances.  So the plan was to build power plants on every block (within 1 mile of the end user).

Nikola Tesla invented AC power, which was very easy to convert the voltages up and back down.  This made it possible to increase the voltage, to transport large amounts of energy long distances over wires, then drop the voltage down to a safe level to supply each home its power.

There was lot of debate over the choice to use AC or DC power, but in the end AC won, and we all use AC power now.  At the time it was a logical choice because they did not have computer or electronics that needed DC power, and AC power was much easier to transport over long distances.  And now we are stuck with the AC power grid, and every appliance that has an electronic circuit has to convert the AC power to DC power (wasting energy) to make it usable.  To make it even worse, if you use solar, we need to convert the DC power to AC, so the appliance uses it, then the appliance converts it back to DC power.  Each step wasting power.

Types of waveforms:

The power grid uses a type of waveform knows as a sine wave (sometimes called pure sine wave).  This is also what appliances are designed to use.  With this wave form, the voltage gradually goes from positive to negative, and back to positive.

Pure sine wave:

Pure sine wave is the most efficient form of AC power, and will work for any ac appliance.  However because the electronics to convert DC power to pure sine wave AC power (pure sine wave inverter), they are not always used, and instead a less expensive modified sine wave inverter is used.  A modified sine wave inverter approximates the sine wave by doing it it steps.

Modified sine wave:

The Problem with the modified sine wave is that your appliances will be less efficient, run hotter, and may not even run at all.  It’s comparable to driving a car with square tires.   Even if they are cheaper I would not use them.