Question E7D11:
What is the purpose of an inverter connected to a solar panel output?  

Choices:  
A: Reduce AC ripple on the output  
B: Maintain voltage with varying illumination levels  
C: Prevent discharge when panel is not illuminated  
D: Convert the panel’s output from DC to AC    

Correct Answer is  D: Convert the panel’s output from DC to AC  

Correct answer: D — Convert the panel’s output from DC to AC

Why D is correct:
- A solar panel produces DC. Many household loads and grid-tie systems require AC. An inverter’s primary job is to convert the panel’s DC into usable AC at the correct voltage and frequency.

Why the other choices are incorrect:
- A: Reduce AC ripple on the output  
  Ripple reduction applies to DC power supplies after rectification; it’s done with filters/regulators, not by an inverter. An inverter actually creates AC, not smooth DC.
- B: Maintain voltage with varying illumination levels  
  That’s the job of a DC-DC regulator or an MPPT charge controller, which adjusts operating point to regulate or maximize power. The inverter’s main purpose is DC-to-AC conversion (though some inverters include MPPT upstream).
- C: Prevent discharge when panel is not illuminated  
  That’s done with a blocking diode or a charge controller to stop backflow into the panel at night.

Useful formulas and rules of thumb:
- Inverter efficiency:
  $$\eta = \frac{P_{AC}}{P_{DC}}, \quad P_{AC} = \eta \, V_{DC} I_{DC}$$
  Typical $\eta \approx 0.85$–$0.98$.
- MPPT context (not the inverter’s primary purpose):
  $$P = V I, \quad V_{mp} \approx 0.7\text{–}0.8 \, V_{oc}$$
- Blocking diode drop (for discharge prevention):
  $$V_{out} \approx V_{in} - V_D, \quad V_D \approx 0.3\ \text{to}\ 0.7\ \text{V}$$
- Ripple (for rectified DC supplies, not an inverter’s role):
  $$V_r \approx \frac{I_{load}}{f C}$$