1. Different Voltage Levels & Current Characteristics DC Side (Solar Array → Inverter):-
Operates at high voltage (e.g., 600V–1500V DC) but low current (since P=V×I P=V×I). Voltage drop is highly sensitive to cable length and resistance due to low current.
AC Side (Inverter → Grid/Load): Operates at lower voltage (e.g., 230V/400V AC) but higher current for the same power. Voltage drop depends on impedance (resistance + reactance), not just resistance. → Combining them would ignore these critical differences, leading to inaccurate calculations.
2. Separate Regulatory Standards DC Side:-
Follows IEC 62548, which mandates <1–3% voltage drop for efficiency. AC Side: Follows IEC 60364-5-52 , typically allowing <1–3% voltage drop. Mixing them would violate standards, as DC and AC systems are evaluated independently for safety and performance.
3. Impact on System Performance DC Voltage Drop:-
Affects MPPT (Maximum Power Point Tracking) efficiency. Even a small drop can significantly reduce energy harvest. AC Voltage Drop: Affects grid compliance Compensating one side for the other (e.g., allowing higher DC drop to reduce AC drop) would: Reduce PV array output. Risk inverter shutdown due to under voltage.
4. Design Flexibility & Practical Constraints DC Cables:-
Often long (from panels to inverter). Use larger cross-sections to minimize drop (since Vdrop=I×R). AC Cables: Shorter (inverter to grid). Can tolerate slightly higher drop due to higher current. Adjusting one side to fix the other is impractical: Increasing DC cable size is costly but necessary for efficiency. Reducing AC cable size could violate grid codes.
5. Safety & Protection Devices DC and AC systems use different protection devices (e.g., DC isolators vs. AC circuit breakers). Voltage drop calculations influence protection coordination. Combining them could lead to: Undersized DC fuses (if AC drop is overcompensated). Nuisance tripping of AC breakers.
Why Not Combine Them? A total voltage drop = DC + AC approach fails because: DC and AC drops have different impacts (efficiency vs. compliance). Standards enforce separate limits. Compensation is not linear (e.g., a 2% DC drop harms production more than a 2% AC drop).
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