Investigating Solar Power

Recently BESCOM increased their tariff. But there is no improvement in reliability. This forced me to look for alternatives. Inverter was the obvious choice. But the engineer in me is worried about the electricity wastage. Inverter has around 90% cycle efficiency. There is wastage in charging the battery and converting it into AC power. What if the power supplied was free? That's where Solar power comes in.

Components of a Solar system

  • Photo-voltaic (PV) cells
  • Charge controller/ Conditioning Unit/ CCU
  • Battery
  • Inverter
There are numerous articles talking in depth about each of these. So I'll just list down the most important things to keep in mind.
  • PV cells are available in mono and poly crystalline models. Mono crystalline is more efficient and hence costs a premium. One can start with a single panel and add more over time as necessary. Less number of panels or less power panel will only increase the charging time.
  • Latest in CCU is Maximum Peak Power Tracking algorithm (MPPT). This is an improvement of about 20% over older technologies like Pulse Width Modulation (PWM).
  • Chargers that follow three/four (bulk-absorption-float-equalization (optional)) step charging increase the battery life while reducing the charging time.
  • Always look for a pure-sine wave inverter. Square wave or variations thereof are not good for modern electronic equipment. Also make sure this is bought keeping in view your future energy requirements. The only way to go from 1kW to 2kW is by inverter replacement.
Now Solar power charges a battery and an inverter converts this DC power to AC power. Can the normal inverter available in market be used here? Yes. But this configuration raises couple of problems:

  • One needs to switch off AC supply to inverter during daytime to avoid charging using grid supply
  • One needs to switch on AC supply during cloudy days and night time
This seems tedious. With advancement in technology, can't this be done automatically? The answer is Solar hybrid inverter. The problem is their availability is quite limited and they are highly priced. Worse, there is no information about the internal working of the system. Guess I still need to keep looking or develop my own!!!

Grid-tie inverter

To promote solar power, Government is proposing to buy electricity from individuals generated via Solar panels. This requires special type of inverter to ensure that the phase fed by solar power is in sync with utility power. It also needs to ensure that it doesn't supply power to grid when grid is off for maintenance (island protection). Grid-tie inverter allows one to do exactly this. There are two configurations available:
  • Gross metering: All the generated energy is fed into the grid. These don't require batteries.
  • Net metering: Only the surplus energy (energy not consumed in the home) is fed into the grid.

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