When sourcing 'cheap' solar panels, you must prioritize Photovoltaic (PV) Efficiency and Cell Type. Look for Monocrystalline silicon cells, which offer higher efficiency (19-22%) compared to polycrystalline. For 'automatic' features, ensure the panels are compatible with MPPT (Maximum Power Point Tracking) controllers to optimize energy harvest. Key specs include Rated Power (Wp), Open Circuit Voltage (Voc), and a Positive Power Tolerance (e.g., 0 to +5W) to ensure you receive the full wattage paid for.