Question

if you are designing a photovoltaic solar system for a university building, estimate the total load for the building. please show the different loads for each component ( projector, computer, lights, printers,etc...) in watts? how many of these are in the building and whats the total load? assume the building area?

Answer 1

Design Solar power system for university building:

Step 1:

Calculate total power and energy consumption of all load which will be connected to the solar power system. In the given example, we need to design solar power system for the university building. In the university building let’s assume following loads will be connected to the power supply:

• Lights
• Projectors
• Fans
• Computer
• Printers

Calculate total Watt-hours per day for each appliance used.
Add the Watt-hours needed for all appliances together to get the total Watt-hours per day which must be delivered to the appliances.

Let’s assume power consumption of following units as:

• Lights (6 Hours per day)                      :              15 watts (240 Nos.)
• Projectors (2 Hours per day)                :              300 watts (4 Nos)
• Fans (10 Hours per day)                      :              80 watts (120 Nos)
• Computer (4 Hours per day)                :              200 watts (300)
• Printers (1 Hours per day)                   :              40 watts (20 Nos)

Let’s assume that all these devices / appliances working on AC 230V / 50 Hz power supply only.

Total power required in watt-hours per day is:

P(AC) = (No. of lights X 15 X 6) + (No. of Projectors X 300 X 2) + (No. of Fans X 80 X 10) + (No. of Computer X 200 X 4)

+ (No. of Printers X 40 X 1)

P(AC) = (240 X 15 X 6) + (4 X 300 X 2) + (120 X 80 X 10) + (300 X 200 X 4) + (20 X 40 X 1)

P(AC) = 21600 + 2400 + 96000 + 240000 + 800

P(AC) = 360800 watthours per day

P(AC) = 360.8 kWhr per day

Considering power lost in the system, we will multiply total power needed by 1.3 to get approximate power needed per day in terms or Whr

P(AC) = 360.8 X 1.3

P(AC) = 469.04 kWhr

Step 2) Determine total no. of PV modules needed

Total Wp of PV panel needed = (469.04 / 3.4) X 1000 = 137952.9 Wp

Let’s assume that, the system will be powered by 12 Vdc, 110 Wp PV module.

Total no. of PV panels needed = (137952.9 / 110) = 1254.11 Nos.

Actual requirement = 1255 modules
So this system should be powered by at least 1255 modules of 110 Wp PV module.

Step 3) Determine Inverter sizing

Total watt of all devices        = (240 X 15) + (4 X 300) + (120 X 80) + (300 X 200) + (20 X 40)

                                             = 3600 + 1200 + 9600 + 60000 + 800

                                             = 75200 watts

For safety we will consider requirement of inverter 25% more than actual watts needed.

So, Inverter shall be of 94000 watts.

Step 3) Determine Battery size

Battery Capacity (Ah) = [(Total Watt-hours per day used by all devices) / (0.85 x 0.6 x nominal battery voltage)] x Days of autonomy

Where, factor 0.85 is for Battery loss and factor 0.6 for depth of discharge

Consider days of autonomy as 3 days

Battery capacity (Amp-Hours)              = [469040 / (0.85 X 0.6)] X 3

                                                            = 2759058.8235 Ahr (approx. 2760000 Ah)

So, the battery bank should be rated 12 V 2760000 Ah for 3-day autonomy.