Solar power

Solar energy

Uganda Climate graph contributed by

As would be expected Uganda has plenty of sunshine. On average 2408 hrs. per year, 6.6 hrs per day. Sun hours per day range from 6.0-7.5 depending on time of year. The amount of energy delivered by the sun is between 4.5-5.2 KWh/m2 (average peak sun hrs.). The average amount is 5.1 KWh/m2. This provides excellent circumstances for the use of solar power.

A common solar installation looks like this:

Two components in this setup are optional. The backup generator can be omitted if backup power generation is not necessary. The Inverter can be omitted if there is no need for 230/110V AC power.

Solar panels are produced in a huge variety of types and power rating. This is not the place to get into the details of solar panels. What is important here is that the current price for a solar panel seems to be around 4 $/W. Common sizes (for solar arrays) are between 75-250W total power. These prices are based mainly on the US market prices. Ugandan prices will probably be higher.

Batteries are used as an intermediate energy storage to buffer both demand of current and fluctuations in delivery of energy by the solar panels. Batteries are a contentious issue in solar energy systems for developing countries because batteries well suited for solar energy applications are expensive, and it is tempting to try and use low-cost batteries (car batteries for example). This might make sense in the short term, but does, however, not make sense in the long run. The price for good quality solar batteries is about $4/Ah.

To get an estimate of the needed battery capacity we need some calculations. Assumptions are
  • We want to be able to keep the power running for one day with no sunshine (or considerable less than normal).
  • We do not discharge batteries below 50% of their capacity (in order to extend their life).
  • We also assume a loss factor of 0.55.
  • Calculations are based on the average mount of available solar energy (5.1KWh/m2).
  • We only take in to account the power consumption of the computers. Other electric appliances will also need power.
  • Battery prices are based on battteries suited for solar power use.
The results are shown here:

 # Scenario  Power used
 W/Day used
 Ah Wpeak Solar panels
 $ Batteries
 $ solar panels
 1 Low Power
 300W  2400 400 855 1.600 3.420
 2 Standard  930W  7440 1240 2650 4.960 10.600
 3 Refurbished  2250W  18000 3000 6417 12.000 25.668

The cost for solar panels and the batteries are not the only costs but the constitute the most expensive parts of the system.

One thing that stands out from these calculations is that for the refurbished PC's any savings made on the low price of these machines is completely swamped by the additional costs of the energy supply. Looking at these numbers the only sensible way to go is use low-power hardware, or standard, very cheap hardware selected for low power consumption.

Check out this page for a further discussion of low-power hardware.

"The table below is a pure mathematical calculation. It illustrates the calculated total cost in US cents per kilowatt-hour of electricity generated by a photovoltaic system as function of the investment cost and the efficiency, assuming some accounting parameters such as cost of capital and depreciation period. The row headings on the left show the total cost, per peak kilowatt (kWp), of a photovoltaic installation. The column headings across the top refer to the annual energy output in kilowatt-hours expected from each installed peak kilowatt. The calculated values in the table reflect the total cost in cents per kilowatt-hour produced. They assume a 10% total capital cost (for instance 4% interest rate, 1% operating and maintenance cost, and depreciation  of the capital outlay over 20 years)."

Source: Wikipedia

The column that fits the Ugandan circumstances is between 1800-2000.