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Step 1 Power demand

The first, most logical, but also the most difficult question concerns the power demand. Related to this is the purpose of the power: Lighting, domestic appliances, education, medical equipment? This survey needs to be executed.

What is your reference?

The investigation of the power need can result in high numbers if your reference is power from a diesel generator. Just as the fuel consumption of a car is not really dependent to the number of passengers, it does not really matter the generator if a light is switched on or off. For this reason, we found electrical installations at orphanages without any switch! The switching on and off of the generator simply was the switch. Between 6 and 10 pm there is power, and there is light everywhere. After 10 pm, it is pitch-dark. In other words: There has never been an urgent need for saving electricity.

Stroom uitwringen

◄ Wringing out the power consumption is part of the standard procedure to make the solar system viable.

With a solar power system this is different. A kWh from the system is in the range of $1,00 (see price of a kWh). So energy efficiency is important. The replacement of all 36W TL tubes with 13W energy savers will both reduce the investment in solar energy as exploitation costs with (36-13)/36 = 64%. To halve the switch-on time will contribute for another 50% saving.

The following table will help you with the survey. Note that the most energy efficient equipment is always the best way of action.

▼ Survey of power demand. The last column is the multiplication of the middle three columns, corrected by the partial factor in the last but one column (the fridge is switched on one third of the time).

Power demand
This table is also available as Excel-sheet:

AC or DC?

Electricity is not by definition 230V AC. There are many reasons to plead for using only direct current (DC). This will prevent the expensive and inefficient conversion step via the DC-AC-inverter.

The battery system will be based on 12V of 24V direct current (sometimes 48V). For 12V many appliances are available. For 24V it is a little more difficult, and for 48V there is hardly anything.

  • The big disadvantages of the low voltage (12 or 24V) is the need for expensive thick cables for the longer distances.
  • The big disadvantage of the inverter is that this device will help the end-user to waste energy after some time. If the point of departure is ‘no electricity’, the user will discover the advantages of electricity in the course of time. He will realise that many luxurious items from the big city will come within reach of his situation in the rural areas. It will be quite a temptation to buy the energy wasting ceiling fans, televisions, fridges, freezers, you name it. The laborious inventoried power need will not meet the reality after some time.

For a further deepening of the AC-DC discussion, Website Sundaya (klik op animations -> general -> 7 reasons for DC)