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Household Energy ConsumptionSolar Design DataFinancial Metrics
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Enter your average monthly energy consumption, which should be printed on your utility bill or found in your online account history. If you only have an annual consumption figure, divide by 12 and enter that result for each month.In this section you can define up to five solar arrays, each with a different number of panels and compass orientation (azimuth). Feel free to give each array a name in place of the 1-5 numbering, or check your solar proposal to see whether your installer named them. For example, if your proposal included 16 panels facing east, and 12 facing south-west, you would create the array #1 with 16 panels and an azimuth of 90. Array #2 would contain 12 panels and an azimuth of 225. Azimuths should be entered to the nearest whole number degree (no decimals) for the best accuracy. Your solar proposal almost surely includes exact azimuth numbers if a roof survey has been done.Simple ROI: [(Total return - Cost) / Cost]. This very simple ROI metric does not account for the time value of money. Money earned in 20 years is treated the same as money earned today.
Simple Rate of Return: [Simple ROI / duration of investment]. Compare this metric to other non-compounding, interest-bearing investments, such as long-term CDs or bonds.
Internal Rate of Return (IRR): A much better metric for evaluating an investment's attractiveness. This accounts for the time value of money, such that money earned in later years counts less than money earned today. Compare this metric to other compounding investment opportunities, such as a money market or brokerage account. Note that the stock market historically has an IRR of ~7.5%, however it also has higher risk and volatility than an investment in solar. Note that this can only be calculated for systems purchased without loans.
Levelized Cost of Energy (LCOE): [Cost / Lifetime energy production]. This metric quantifies the amount that installing a solar system 'locks-in' your future energy costs for as long as the system is operational. Compare this to the cost of continuing to purchase energy from OUC, which may change over time.
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1375January
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1375February
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1000MarchArray ID1+42+53+67+8+9Total All Arrays
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1500April# Panels101371040
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1500MayAzimuth16475255345
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1950JuneJanuary35730520315101015
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2000JulyFebruary36834822120001138
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1875AugustMarch45349328632001552
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2050SeptemberApril49659333242301844$30,270.81Net Cost
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1750OctoberMay4736113354700189088.96%Total energy consumption offset
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1750NovemberJune4355952964420176914years10monthsBreak even point
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1375DecemberJuly43859529043001753Program and License Information20-year financials25-year financials
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19500Annual household consumptionAugust45056629440001710Solar Calculator v1.0 | 2017-05-29$43,058.67Total return$56,891.06Total return
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NoWill you own an Electric Vehicle or Plug-in Hybrid and charge it at home?September40046324830201414Copyright (C) 2017 Marc Herndon42.24%Simple ROI87.94%Simple ROI
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400Miles driven per month on electric power (that you will recharge at home)October41241024924501315Direct questions to Herndon.MarcT@gmail.com2.11%Simple Rate of Return3.52%Simple Rate of Return
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99EPA MPG-e rating (choose city, highway or combined as appropriate)November35731220616201038This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details at <http://www.gnu.org/licenses/>.		3.81%Internal Rate of Return5.02%Internal Rate of Return
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0Monthly EV consumptionDecember3292681841260908$0.097LCOE (per kWh)$0.079LCOE (per kWh)
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0Annual EV consumptionAnnual Total4970555931453673017347$42,780.00 (LBNL)$36,999.20 (AI)Potential increase in home sale value
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Utility RatesEnergy Offset CalculationsLegend
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Typical solar proposals assume 4% - 5% annual increase in the cost of energy. This can make it appear like the system will pay for itself more rapidly. Historically, in Florida, the cost of energy rose ~45% in the nine years from Jan 2001 through Dec 2009, or approximately 5% per year. In the 6.5 years since January 2010, however, the cost of energy has increased less than 1% in total, alternating between small increases and decreases year over year. Combining those 15+ years, the average is ~3%/yr.This section calculates your expected pre- and post-solar monthly energy bills, and determines the amount of money you should expect to save in the first year after installing solar. If the loan option was selected, monthly and annual loan payments are displayed so you can understand whether the savings from solar is enough to fund the loan without going into a financial hole.Required user inputs
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Instructions / Supplemental information
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Important notes / Metadata
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Intermediate calculation results
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Important results
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$0.098Cost per kWh up to 1000 (OUC is currently 0.098)Before SolarAfter Solar
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$0.118Cost per kWh over 1000 (OUC is currently 0.118)Energy UsageEnergy BillEnergy UsageEnergy BillSavingsLoan Payments
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3.00%Estimated annual rate increaseJanuary1375$150.25360$43.23$107.02-$252.26
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February1375$150.25237$31.27$118.98-$252.26
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Solar Proposal DataMarch1000$106.00-552-$46.07$152.07-$252.26
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46How many panels will be installed?April1500$165.00-344-$25.71$190.71-$252.26
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310What is the STC rating of each panel? (Watts)May1500$165.00-390-$30.24$195.24-$252.26
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NoAre these "premium" high efficiency panels?
(Probably 'No' unless installing LG, Panasonic or SunPower)		June1950$218.10181$25.79$192.31-$252.26
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$33,626.25What is the proposed cost of the system? (before rebates/incentives)July2000$224.00247$32.21$191.79-$252.26
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14260Total system size (DC Watts)August1875$209.25165$24.15$185.10-$252.26
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$2.36Total $ / W (before rebates/incentives)September2050$229.90636$70.35$159.55-$252.26
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$8,742.83Federal tax rebate (down to 26% now)October1750$194.50435$50.58$143.92-$252.26
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$0.00State and local rebates or incentives (probably $0.00)November1750$194.50712$77.76$116.74-$252.26
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$24,883.43Net cost (after rebates/incentives)December1375$150.25467$53.72$96.53-$252.26
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$1.74Net $ / W (after rebates/incentives)Annual Total19,500$2,157.002,153$307.04$1,849.96-$3,027.08
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Purchase / Loan InformationImportant Notes
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If you will be taking a loan to pay for the solar installation, choose 'Yes' and input the loan terms. Note that over-borrowing and/or high interest rates can cause the loan payments to exceed the savings from solar production. In those situations you will be digging yourself into a hole until the loan is repaid and turning the rewards of your solar investment over to the bank.1.) This calculator is only valid within the city of Orlando, or other areas serviced by Orlando Utilities Commisson (OUC). The weather data and solar production model is valid for a much larger region of central Florida, however the net metering rules offered by OUC are uniquely advantageous for homeowners compared to other utility companies. Using this calculator to predict returns under a different utility company could drastically over-estimate your cost savings and ROI.
2.) A solar system should be expected to initially add value to your home at an almost dollar-for-dollar equivalent to its initial cost, and then depreciate over the useful life of the system. However, the real estate market is difficult to predict and not everyone will sell their home to captitalize on this extra value. As such, this value is ignored in the 'return' and ROI calculations on this sheet. For your consideration, two different values are calculated using formulas from the Lawrence Berkley National Lab and the Appraisal Institute, however these numbers are informational and not used for any other purpose. The formulas are based on comparative appraisal studies performed in 2015 and IMHO they significantly over-estimate the value of a solar installation in 2017. Regardless, this sheet assumes that the capital spent to install a solar system is gone forever, and nothing will be extracted from the sale of your home. The only 'returns' counted are the direct savings on your energy bill. For this reason, the financial metrics should be considered highly pessimistic.
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YesDo you intend to borrow some or all of the cost of this installation?
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$7,489.61Down payment (In most cases this should equal the tax rebate above)
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$26,136.65Total amount borrowed
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10Loan term (years)
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2.99%Loan interest rate
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-$252.26Loan monthly payment
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