Sample Case solution

Requirements:

  • To operate 1.3kW – 1.4kW load 24/7 without utility.
  • To design a solar based solution that will run for 25 years max.

Assumptions:

Avg Temp of solar cell = 40 C (Lahore – PCSIR Study)
Avg Battery temp = 20 C (maintained through a refrigerator set at 20 C)

Max Load:

Below is provided the MAX load at one time in watts.

o1

Solution (Based on balance between quality and cost):

Solar Cells:

o2

We will use a total of 21 Solar panels, 6 parallel strings of solar cells having 3 solar cells each in series. Overall at NOCT,

  • Voc = 46.2 x 3 = 138.6 V
  • Vmp = 34.6 x 3 = 103.8 V
  • Imp = 4.35 x 7 Strings = 30.45 A
  • Wp = 103.8 x 30.45 = 3,161 Watts

o3

The solution will provide 1.5 kW to the Batteries for Night load and will provide 1.5kW in day from solar cells to appliances via inverter.

The Voc, Vmp, Imp, Wp are all within limits of Axpert MKS MPPT 5KVA- 48V.

Inverter (MPPT):

o4

Battery:

o5

o6

Cost of refrigerator to maintain system temp:

Assumption: 50,000

Cables/Stands/Installation Charges:

Assumption: 50,000

Final Analysis, Solution & Cost:

o7

This is an independent solar power generation for a small house with major load of 1300 to 1400 watts. Rs. 694k/- is the starting cost while around Rs. 63k/- per years is an average variable cost for remaining 24 years.

Assuming we are utilizing 1.3kW – 1.4kW load from the system throughout without any break. Monthly Utilization is 1000 kW or 20,000 PKR (assuming Rs. 20 per utility unit). Therefore it will take us 2 yrs 11 months (35 months) to cover the fixed cost.

For overall system, it will take around 9.5 years to cover the entire cost of 25 years of the solution. This will effectively save us 190,000 units of energy or in term of PKR it will save PKR 3,768,000/- with an assumption that unit price and other factors will remain same for 25 years. The ROI (Return on investment) is 1.65, for every rupee invested we get 2.65 back (1.65 is profit).

Another important thing to notice that 70+4% of the cost is related to Batteries and its temperature controller refrigerator. If we are ok with using energy from utility at night and from solar cells in morning, we can save more than 80% cost (with batteries eliminated, solar cells reduced to half, refrigerator gone)

o8

Assuming we are utilizing 1.3kW – 1.4kW load from system throughout without any break for 12 hrs at daytime. Monthly Utilization is 500 kW or 10,000 PKR (assuming Rs. 20 per utility unit). Therefore it will take us 2.5 yrs to cover the fixed cost.

For overall system, it will take 3.7 yrs to cover the entire cost of 25 years. This will effectively save us 131,000 units of energy or in term of PKR it will save PKR 2,616,768/- with an assumption that unit price & other factors will remain same for 25 years. ROI is 5.85, for every rupee invested we get 6.85 back (5.85 is profit).

Thus looking at ROI comparison, solar solution without batteries is 3.5 times better than the one with batteries backup.

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