Solar panels produce direct current, or DC, because their photovoltaic cells push charge in one direction when light hits them. Most homes, schools, businesses, and power grids use alternating current, or AC, where the current reverses direction many times per second. A solar inverter is the machine that makes solar electricity usable by converting panel DC into grid-compatible AC.
It also helps the solar system operate safely and efficiently.
Key Facts
- Solar panels produce DC power, while most electrical grids use AC power.
- Power is the rate of energy transfer: P = VI.
- Inverter efficiency can be estimated by efficiency = Pout / Pin x 100%.
- A grid-tied inverter must match grid voltage, frequency, and phase before sending power out.
- Maximum power point tracking adjusts the panel operating voltage and current to increase solar power output.
- String inverters serve groups of panels, while central inverters serve large solar arrays with much higher total power.
Vocabulary
- Direct current
- Direct current is electric current that flows in one direction, such as the output from a solar panel.
- Alternating current
- Alternating current is electric current that repeatedly changes direction, such as grid electricity in homes and buildings.
- Solar inverter
- A solar inverter is a power electronics device that converts DC electricity from solar panels into AC electricity for loads or the grid.
- Maximum power point tracking
- Maximum power point tracking is a control method that finds the voltage and current where a solar panel produces the most power.
- Grid synchronization
- Grid synchronization is the process of matching an inverter's AC output to the grid's voltage, frequency, and phase.
Common Mistakes to Avoid
- Thinking the inverter creates energy, which is wrong because it only converts electrical energy from one form to another and loses a small amount as heat.
- Confusing DC and AC, which is wrong because DC flows in one direction while AC reverses direction at a set frequency such as 50 Hz or 60 Hz.
- Ignoring inverter efficiency, which is wrong because the AC output power is usually slightly less than the DC input power due to heating and switching losses.
- Assuming any inverter can connect to any grid, which is wrong because grid-tied inverters must match voltage, frequency, phase, and safety standards.
Practice Questions
- 1 A solar array sends 320 V DC at 12 A into an inverter. What is the DC input power in watts?
- 2 An inverter receives 5000 W of DC power and delivers 4750 W of AC power. What is its efficiency as a percent?
- 3 A shaded panel reduces the current in one string of panels. Explain why maximum power point tracking helps the inverter extract more useful power from the solar array.