brianbruggeman · March 6, 2015 01:43 · Mar 6, 2015
diff --git a/gistfile1.txt b/gistfile1.txt
@@ -0,0 +1,152 @@
+#!/usr/bin/env python
+"""
+Calculates return on investment over time.
+
+Usage:
+    calc_roi [options]
+
+Options:
+    -h, --help                    This message
+    -u, --unit-cost <uc>          Cost per panel (USD) [Default: 750]
+    -i, --initial <ic>            Initial investment cost (USD) [Default: 9000]
+    -i, --units <units>           Initial units purchased [Default: 15]
+    -d, --degradation <deg>       Efficiency degradation per year % [Default: 0.007]
+    -y, --years <years>           Years to calculate [Default: 25]
+    -r, --return <return>         Annual return per unit (USD) [Default: 90]
+    -p, --purchase                Purchase new units with profit [Default: True]
+    -s, --sunset <year>           When to sunset a panel [Default: 100]
+    -m, --margin <margin>         Percentage of revenue kept [Default: 80%]
+    -c, --cease <year>            Year to cease purchasing new units [Default: 100]
+"""
+
+
+class Panel(object):
+
+    """
+    Solar Panel used for calculating roi per unit
+    """
+
+    @property
+    def break_even(self):
+        """ Year when this panel will break even """
+        investment_return = 0
+        for year in xrange(100):
+            coeff = 1.0 - (self.degradation)
+            margin = self.profit_margin
+            revenue = self.annual_revenue
+            investment_return += coeff * revenue * margin
+            if investment_return >= self.investment:
+                return year
+
+    @property
+    def age(self):
+        """ age of panel """
+        return self.start + self.year
+
+    @property
+    def roi(self):
+        """ return on investment (%) """
+        return self.investment / self.generated_revenue
+
+    @property
+    def degraded_revenue(self):
+        """ degradation of panel in revenue """
+        value = 0
+        if self.age < self.sunset:
+            coefficient = (1.0 - self.degradation * self.age)
+            value = coefficient * self.annual_revenue * self.profit_margin
+        return value
+
+    def __init__(self, cost=750, year=0, revenue=2250 / 25, degradation=0.007, margin=0.8, sunset=100):
+        """ Creates a unit which can be updated """
+        self.investment = cost
+        self.start = year
+        self.year = 0
+        self.profit_margin = 0.8
+        self.degradation = degradation
+        self.annual_revenue = revenue
+        self.generated_revenue = 0
+        self.sunset = sunset
+
+    def update(self):
+        """ Increments unit for this year """
+        self.generated_revenue += self.degraded_revenue
+        self.year += 1
+
+    def __repr__(self):
+        """ Panel at any point in time """
+        args = {
+            "years": self.years,
+            "capital": self.investment,
+            "return": self.generated_revenue,
+            "roi": self.roi,
+        }
+        string = "<Panel age:{years}, capital:{investment}, "\
+                 "return:{revenue}, roi:{roi}>"
+        return string.format(args)
+
+
+def calculate(args):
+    unit_cost = args.get("--unit-cost")
+    initial_cost = args.get("--initial")
+    units_purchased = args.get("--units")
+    degradation = args.get("--degradation")
+    years = args.get("--years")
+    annual_return = args.get("--return")
+    purchase_new_units = args.get("--purchase", False)
+    sunset = args.get("--sunset")
+    margin = args.get("--margin")
+    cease = args.get("--cease")
+
+    cpu = initial_cost / units_purchased
+    units = [Panel(cost=cpu,
+                   revenue=annual_return,
+                   degradation=degradation,
+                   margin=margin,
+                   sunset=sunset)
+             for unit in xrange(units_purchased)]
+    titles = ["year", "units", "monthly", "roi", "investment", "return"]
+    print "{0:>4}: {1:>10} | {2:>16} | {3:<15} | ({4:>19}/{5:>19})".format(*titles)
+    cumulative = 0
+    for year in xrange(years):
+        profit = sum(u.degraded_revenue for u in units)
+        cumulative += profit
+        if purchase_new_units and year < cease:
+            while cumulative > unit_cost:
+                panel = Panel(cost=unit_cost,
+                              year=year,
+                              revenue=annual_return,
+                              degradation=degradation,
+                              margin=margin,
+                              sunset=sunset)
+                units.append(panel)
+                cumulative = cumulative - unit_cost
+        data = {
+            "units": sum(1 for u in units),
+            "year": year,
+            "cost": sum(u.investment for u in units),
+            "profit": sum(u.generated_revenue for u in units),
+            "monthly": sum(u.degraded_revenue/12.0 for u in units),
+        }
+        data["roi"] = data["profit"] / data["cost"]
+        print("{year:>4}: {units:>10} | ${monthly:>15,} | {roi:<15} | (${cost:>18,}/${profit:>18,})".format(**data))
+        for unit in units:
+            unit.update()
+
+
+if __name__ == "__main__":
+    import docopt
+
+    args = docopt.docopt(__doc__)
+    for k, v in args.iteritems():
+        try:
+            if "." not in v:
+                v = int(v)
+                args[k] = v
+            else:
+                v = float(v)
+                args[k] = v
+        except:
+            pass
+
+    calculate(args)