ello class.  Please read the homework 2 assignment and then consider the following suggestions……

Essentially your only choice for each scenario is the size of the solar array.  Once you make that choice, you need to make sure it meets all the constraints listed in the homework description.  Then, if it meets the constraints, you can perform the calculations needed to determine the overall cost under 15 years of operation.  That’s the big picture.  Consider a specific example:

Scenario 1

You pick a solar array of 25kW.  Does it meet the constraints for this scenario (i.e. with battery system)?  Yes, because it’s at least 8kW and no more than 40kW.  What are the initial costs?  

$4,000 – battery

25,000 * $3/Watt = $75,000 – solar array

Total = $79,000

How much power do I need?  1,388.9 Watts continuous + 8kW to keep the battery charged

During 30% of each 24 hour period, my array produces 25,000 Watts.  That is 7.2 hours of each day.  So each day my array produces (25,000 * 7.2 = 180kWh).  The rest of the time my array produces nothing.  My demand is 9,388.90 Watts all the time so I use (9,388.90 * 24 = 225.3336 kWh) each day.  The difference is (180-225.3336 = -45.3336 kWh).  This is how much I can sell back to the grid each day.  It’s negative so this solution is not feasible since this scenario is off-grid.  If I increase the solar array size to 35,000 Watts then each day my array will produce (35,000 * 7.2 = 252 kWh).  Now the difference is 26.6664 kWh which is greater than zero so this solution works although I have excess energy that I cannot sell.  

My cost for the 35kW array with battery is $105k + $4k = $109k.  This cost is the same regardless of the number of years given this is an off-grid scenario.

In a grid-connected scenario I can sell excess energy to the grid or buy needed energy depending on the size of my solar array.  Say I have a 25kW array and I need to buy 45.3336 kWh each day from the grid.  My buying price is $0.14/kWh so my total cost is (0.14 * 45.3336 = $6.35).  So each day with this configuration I spend $6.35.  

Now calculate how much I spend over 15 years.  

$6.35/day * 30 days/month * 12 months/year * 15 years = $34,290

What is my overall profit (cost) with a 25kW array?

$34,290 + $75,000 = ($113,290)

Now this is overly simplified as a problem since the amount of production from a solar array varies a lot day to day and season to season and there are other costs that are associated with a realistic system, however it’s a way to compare options (scenarios).  You can try many different solar array sizes to find what seems to provide the best investment (i.e. highest profit or lowest cost).  Similar computations can be done for the other scenarios.  Hopefully this helps you with the homework.