Case Studies - Off-grid Solar for Small Office

Client Profile

The client operates a small tax accounting practice in a predominantly residential area of Johannesburg.

Business Problem Statement

Essentially, there are two problems to be solved.
The first is continuity of electricity supply, since a power cut causes loss of supply to computing equipment, rendering staff unable to work for the duration of a power cut. The resulting delay forces pressure on deadlines which could compromise the business. The other problem is the need to save electricity costs as far as possible

Technical Situation
Building

  Storeys
  1
  Number of Computers
  4
  Persons
  4
Analysis of Energy Requirements

At present desktop computers are being used.. Each computer system is consuming 220 Watts of power. In addition, there is a small amount of power consumed by networking devices, such as routers, modems etc. The office would also like to run a portable radio, however the power consumption of this device is negligible.
Each computer has two LCD screens this is included in the overall figure of 220 Watts per computer.
If laptop computers were to be used, the energy consumption could be reduced to less than 50 Watts per workstation. For example, this is being written on a dual screen computer system drawing just 40 watts and costing less than R 4 000.00 for the entire system, excluding the modem. Laptops have a further advantage in that they operate for several hours without mains electricity.

The Problem of Computer Printers
If possible, an inkjet printer should be used, as the power consumed is negligible. On test, my small laser printer draws 600 Watts (peak) and between zero and 250 watts on standby.

Solution

The first thing to examine is the viability of using laptop computers vs desktops. It is only fair to compare a laptop solution with a desktop plus battery and inverter. This is only fair, since a laptop will provide at least two hours of operation in the event of a power failure.
Comparison of laptop vs Desktop Computer including 2 hours backup

Desktop
Laptop
  Computer
  R 3,800.00
  R 6,000.00
  Monitors
  R 2,200.00
  R 1,100.00
  Keyboard
  R 200.00
  R 200.00
  Inverter (half of a 1kVa inverter)
  R 700.00

  Battery (Half of a 100A-H deep cycle)
  R 800.00

  Totals
  R 7,700.00
  R 7,300.00


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Costs are based on those obtained from an on-line computer retailer for desktop computers having similar specifications. Laptop has slightly higher specification (more RAM). If we take into account the provision of back up power, there is almost no difference in cost between a desktop computer and a mid-range laptop. Since the laptop computer based solution is the least expensive in terms of first cost and energy consumption.

If the office converts to laptop computers the annual electricity consumption is very low only about R 300 per year for 4 computers. The peak kW consumed would be about 200 watts, or 1.6 kWh per 8 hour day.

Benefits of the Proposed Solution
Year
Yield
Cum Yield
Cost
Maintenance
    Cum Cost
Cum Saving
1
R 23,040.00
R 23,040.00
2638.4

2638.4
R-20,401.60
2
R 2,304.00
R 25,344.00
3034.16

5672.56
R-18,716.56
3
R 2,534.40
R 27,878.40
3489.28

9161.84
R-26,251.03
4
R 2,787.84
R 30,666.24
4012.68

13174.52
R-21,925.39
5
R 3,066.62
R 33,732.86
4614.58
R 10,307.26
R 7,481.83
R-18,988.87
6
R 3,373.29
R 37,106.15
5306.76

R 12,788.60
R-15,407.78
7
R 3,710.62
R 40,816.77
6102.78

R 18,891.38
R-44,264.95
8
R 4,081.68
R 44,898.44
7018.2

    R 25,909.58
R-22,423.91