Information and explanation of calculations for
evaluating your project:
Outputs
Energy offset (kWh/year)
The calculators provided (links) should
provide either annual or lifetime savings.
If the calculator provides lifetime energy savings (EPA Purchase and
Procurement calculators for Appliance Swap projects, etc.), determine
lifetime in years and divide lifetime energy savings by the years. In some cases, the years might be under the
second tab of the spreadsheet, “Assumptions”.

kWh energy saved per lifetime
Years lifetime
= kWh energy saved/year

Emissions offset (lbs CO2/year)
Same concept as with energy offset, but
with CO2 emissions. If emissions are
given in carbon instead of carbon dioxide (C not CO2), see Conversions
section below for appropriate conversion.

lbs CO2 saved per lifetime
Years lifetime
= lbs CO2 energy saved/year

Payback
period (years)
Some calculators will do this for you. If it is not provided, please use a simple
payback calculation. You may have to
calculate the next item on the worksheet to complete this calculation.

Capital Cost
Annual Cost Savings
= Simple Payback Period in year

Anticipated
Savings/Costs per year
This should be financial savings apart
from capital costs. For example,
yearly savings from lower energy bills minus operation and maintenance costs
of alternative energy supply. One way
to calculate these savings is to take the amount of energy saved or offset
and multiply by the cost of that energy.

Energy saved per year * Cost per energy
unit
= Energy savings per year
1,000 kWh energy saved per year * $0.085/kWh = $85.00 energy savings
per year

Assumed Project Lifetime (years)
If you know the lifetime of your project,
such as expected life of the technology or how long the project will be
implemented, state that here. If the
lifetime is unknown, refer to the Estimated Lifetimes section below. Note: For planning purposes, you may want
to run calculations for 23 different lifetime estimates. The final output results are very sensitive
to this input.

Project
Lifetime energy offset
Take the annual energy offset, recorded
above, and multiply by estimated project lifetime.

Annual Energy Offset * Lifetime in Years
= Lifetime Energy Offset

Project
Lifetime emissions offset
Take the annual emissions offset, recorded
above, and multiply by estimated project lifetime.

Annual CO2 Emissions Offset * Lifetime in
Years
= Lifetime Emissions Offset

Project Lifetime (net) savings
While calculating the net present value,
internal rate of return, and benefitcost ratio for your project is a crucial
part of the planning stage (see Finance Calculations section if interested),
the undiscounted net value of the project can also be useful. It takes into consideration all anticipated
savings and subtracts anticipated and current costs.

Savings (lifetime energy offset * energy
rate avoided, other savings)
– Costs (capital, operation, etc.)
= Net Savings/Cost of project

Note: Since there are a
variety of things that one could include or exclude, it's important to be as detailed as possible in
explaining what is being considered or left out. Use your own judgment as to what costs and
savings are relevant for evaluating the economic outcomes of your project.

Cost
per energy unit offset (project total cost/energy unit offset)
Project Total Cost is the upfront cost of
the project. Divide by lifetime energy
offset.
Note: This result should not be considered the "price" of energy produced by the project. Rather it is an underestimate of the price of producing energy, without including maintenance costs, and fully accounting for inefficiencies.

Project Total Cost or Capital Cost
Lifetime Energy Offset
= Cost per kWh offset
1,200 kWh energy saved per lifetime
$12,000 Project capital costs
= $0.10/kWh offset

Cost
per emissions reduction (project total cost/emissions reduced)
Project Total Cost is the upfront cost of
the project. Divide by lifetime energy
offset.
Note: This result should not be considered the "price" of
the emission reduced by the project. Rather it is an underestimate of the
price of producing energy, without including maintenance costs, and
fully accounting for inefficiencies.

Project Total Cost or Capital Cost
Lifetime CO2 Offset
= Cost per lb CO2 offset
1,200 lbs CO2 saved per lifetime
$12,000 Project capital costs
= $0.10/lb CO2 offset

Solar Projects
The
list below is to assist you in your calculations.
Explanation of inputs:
·
Size: Choose the size of system that
closely represents your system.
·
Cost: Take the total cost of system
(not including installation or infrastructure) and divide by the watts
provided. (Wattage of system should be
included in the specifications.)
·
Tilt: Can leave at default unless
you are aware that you are using a different tilt. If you are changing your tilt with the
seasons, choose which ever angle you prefer to use for calculations and make
a note if it is either over or underestimating energy production.
·
Orientation: Leave
facing South since we are in the
Northern Hemisphere
·
Electric Bill: Useful
for planning.
·
Escalation: General
estimations are 3.0% escalation rate.
·
Payment: If you are financing the
system through a loan and want greater accuracy, complete the form
accordingly.

Explanation of outputs:
·
Net System Cost After Incentives: If you are in the planning
stages and estimating your system, use this number. If you are in the evaluative stages, please
use information from purchasing receipts.
·
System Savings From Incentives:
·
PV System Electricity Production: Again,
this is a useful estimation for planning, and can be used for evaluation if no other information is available.
·
Electricity Supplied by System: Useful
for planning.
·
First Year Electric Bill Savings: Useful
for planning.
·
Carbon Dioxide Emission Reductions: This
is annual reductions; can use to calculate lifetime emission reductions.

Adjusting Assumptions in MS Excel Calculators
In any of the calculations that
use MS Excel, the creators have provided ways to adjust the
assumptions that underlie all the calculations.
If you are unfamiliar with the basics of MS Excel,
there are a variety of tutorials online (Google Search: MS Excel
Tutorials).
·
The
basic concept is that there are input cells where you are asked to enter the
quantity, size, energy demand of an appliance or other project.
·
There
are output cells which are determined by formulas or calculations behind
them.
·
In
many equations, there are more variables than those you entered as
inputs. These other variables are
assumed values, such as price of product, price of energy, amount of product
usage and energy demanded.
·
If
your product is similar enough to the energy star products and generic
products, it is unnecessary to change any of the assumptions.
·
If
your product is dissimilar enough, for greater accuracy, you may want to
alter some assumptions.

To alter assumptions:
·
You
need to locate the assumptions that are affecting the output cell.
o
To do
this, if you select/click the output cell, the formula will appear in the
formula bar above. These list
cells. Seek the Help file if you have
difficulty understanding their coordinate system.
o
In
many cases, the assumptions are listed in cells that are either hidden or on
another worksheet within the Excel workbook.
Worksheets are listed as tabs at the bottom. The EPA calculators call their assumptions
worksheet, “Assumptions”.
o
In
most cases, their assumptions are documented and labeled, so they should be
easy to identify and alter as necessary.

Conversions
Conversions helpful in
calculating your project’s energy, emissions, and economics.
Miles per hour > Meters per second
1 mph = 0.44704
meters per second
1 meter per
second = 2.23693629 mph

Converting Carbon to CO2
To convert carbon
dioxide (CO2) to carbon (C), multiply the lbs CO2 times (12/44) (or
.27273). (This is the ratio of the atomic weight of C over CO2.) Or to convert carbon to carbon dioxide,
multiply the lbs of C by (44/12) (or 3.66667).

lbs CO2 * .27273 =
lbs C
lbs C * 3.66667 =
lbs CO2

Converting Pounds (lbs) to
Tonnes (ton)
To convert CO2 or C
lbs to tonnes, you can use one of the following conversions (depending on
your preferred conversion)

1 metric tonne =
1,000kg = 2,205lb
1 US short ton =
907kg = 2,000lb

Converting kWh to CO2
If you already know
the kWh used by the lighting and appliances, then you can actually multiply
the amount of kWh by the carbon intensity of our electricity in Minnesota,
which is 1.810 lbs CO2/kWh. (EPA EGrid)

kWh * 1.810 lbs
CO2/kWh = CO2 output

Fuel Emissions Factors Can be used to estimate CO2 offset by another system. From MPCA, except Electricity is from EPA eGrid 2005. 
Natural Gas

11.07 lbs CO2/therm


Fuel Oil

22.13 lbs CO2/gallon


Electricity

1.810 lbs
CO2/kWh


Gasoline

19.56 lbs CO2/gallon


Propane

12.67 lbs CO2/gallon

Converting kWh to CO2
If you already know
the kWh used by the lighting and appliances, then you can actually multiply
the amount of kWh by the carbon intensity of our electricity in Minnesota,
which is 1.810 lbs CO2/kWh. (EPA EGrid)

kWh * 1.810 lbs
CO2/kWh = CO2 output

*Putting all three Carbon
conversions together (C à CO2, lbs à tons, kWh àCO2)
These calculations
together can help you take either electrical output, carbon or carbon dioxide
emissions and understand them in various forms.

___ kWh * 1.810 lbs
CO2 per kWh * (12/44) C per CO2 / tonnes conversion = C output
750 kWh * 1.810 lbs CO2/kWh = 1,357.5
lbs CO2
452.2 lbs CO2 * (12/44) = 370.23 lbs C
370.23 lbs C / 2,205 lbs per metric ton = .1679 metric tons C

There is a
calculator available for national averages (http://www.epa.gov/cleanenergy/energyresources/calculator.html),
but in the case of Minnesota, which sources its electricity on a significant
amount of coal, our carbon intensity is much higher.

Estimated Lifetime
If you already know the expected lifetime of your product or system,
please indicate and use that
as your parameter. If you do not have a
way of estimating lifetime for your specific project,
you may use the estimated/average parameters listed below.
Solar Projects
Average solar panel lifespan
is 25 years. (Average from data
collected from Google searches and studies.)
Note: With solar panels lifespan is largely determined by quality of
materials and other components of the system.
Ask the manufacturer or retailer if they can provide an estimate.

Helpful Assumptions
Minnesota Energy Profile: EIA Energy State Profile  MN 
