Some particular house uses 15 kW-hr in a day. The owner would like to unhook fro

Question

Some particular house uses 15 kW-hr in a day. The owner would like to unhook from the electric
company and use only solar cell modules to generate electricity along with batteries to store enough
energy for night-time use. Assume that the sun shines reliably for 4.5 hours each day on average. If each
solar module generates 275 W of power when the sun is shining and each battery can store 2.25 kWhours
of energy, how many solar modules and how many batteries would be required to allow the
building to operate entirely on the solar cell/battery system? If each solar cell modules costs $200 and
each battery costs $225, what is the material cost of the system? If the power company charges $0.14/
kW-hour, how long would it take to achieve “pay-back”?
(Hint: Start by determining how much energy one solar panel will provide in typical day.)
solar panels = _______________________________
batteries = __________________________________
cost = ______________________________________
pay back time = ___________________________________

Explanation / Answer

Particular House power usage = 15 KWhr per day

Each solar module generation capacity = 275 W

Hence for an average of 4.5 hr sunshine in a day the total capacity of each solar module = 275 x 4.5 /(1000) = 1.2375 KWhr

(Note : 275 W is equal to 275/1000 KW)

To get required house usage of 15KWhr we need --> 15/1.2375 = 12 (Approx.) solar modules.

Now each battery stores 2.25 KWhr power then for storing 15KWhr we need --> 15/ 2.25 = 7 (Approx.) Batteries.

Each solar cell module cost is $200 and for such 12 solar cell module costs (12x200) = $2,400

Each Battery costs $225 and hence for 7 batteries cost will be (7x225) = $1,575

Total Material cost = $2,400 + $1,575 = $3,975

Calculation for Pay back period ;

Power company charges $0.14/KWhr then the total cost per day will be 15 x 0.14 = $2.1 per day

hence to compensate $3,975 (total material cost) payback period is --> 3,975/2.1 =1892.8 days or 5.2 years (Approx.)

So answers are;

Solar panels = 12

batteries = 7

cost = $3,975

Pay back time =1892.8 days or 5.2 years

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