tandard Calculation Recommendations
Final: September 10, 2008
Evaluation Contractor: PA Consulting Group
Prepared by: Bobbi Tannenbaum, KEMA

Doug Kneale, KEMA

Brian Dunn, KEMA

This report is the property of the state of Wisconsin, Public Service Commission of Wisconsin,
and was funded through the Wisconsin Focus on Energy Program.

State of Wisconsin
Public Service Commission of
Wisconsin
Focus on Energy Evaluation
Renewable Energy Program
Standard Calculation Recommendations
Final: September 10, 2008

� PA Knowledge Limited 2008

Liaison Contact: Dr. David Sumi
PA Consulting Group
6410 Enterprise Lane, Suite 300
Madison, WI 53719
Tel: +1 608 443 2700
Fax: +1 608 661 5181
E-mail: David.Sumi@paconsulting.com
Prepared by:
Bobbi Tannenbaum, KEMA
Doug Kneale, KEMA
Brian Dunn, KEMA

Contributions by: Focus on Energy, Renewable Energy Program Leads
Acknowledgment: Ralph Prahl, Prahl & Associates, contributed critical review and analysis.


iii

Focus on Energy Evaluation, Renewable Energy Program, Standard Calculation Recommendations, Final: September 10, 2008
TABLE OF CONTENTS
1.

Introduction
11

2.

Standard Calculations
21

2.1

Biogas Systems
21

2.2

Biomass Systems
29

2.3

Photovoltaic (Solar Electric)
213

2.4

Solar Water Heating
217

2.5

Wind Systems
222




11

Focus on Energy Evaluation, Renewable Energy Program, Standard Calculation Recommendations, Final: September 10, 2008
1.
INTRODUCTION
The purpose of this document is to provide a set of recommended standard calculations for
estimating kWh, kW, and therms associated with renewable energy systems installed through
the Focus on Energy program. The purpose of developing standard calculations and
documentation for renewable energy systems is to ensure that the Focus Renewables
Program estimation approach is transparent, consistent, and accurate. Biomass and solar
water heating calculations estimate therms displaced by renewable energy sources (savings).
Biogas, PV (Solar Electric), and wind estimates are for annual kWh and average system peak
kW generation.
KWh is estimated on an annual basis. KW is calculated based on the average kW savings
over the period from 1 pm to 4 pm, Monday through Friday, during the months of June
through August. Average kW is the kWh savings realized over the three-hour peak period (1
pm to 4 pm), divided by these same three hours per day.
1

KEMA established these standard calculations in conjunction with the Focus on Energy
program. First, we reviewed the calculation approach used by the program to calculate
tracked savings (generation) for a randomly selected subset of FY07 projects. Next, we
developed and discussed with the program leads recommendations for calculating savings
(generation). The discussions with the program leads resulted in a set of improved Standard
Calculation recommendations. Finally, we presented this report in draft format for review and
comment by the program administrator and the Public Service Commission of Wisconsin
(PSCW). We present our final recommendations in this report.
The Standard Calculation recommendations are provided in the following section. We discuss
energy savings, demand savings (where applicable), and information required on the
application or in program documents for each of the five measures installed through the
program. The renewable energy technologies are presented in the following order: Biomass Biogas Photovoltaic (Solar Electric) Solar Water Heating Wind Energy

1
See BP OPS Manual, Revised Peak KW Reduction Description, p. 57, April 1, 2008. 1. Introduction

12

Focus on Energy Evaluation, Renewable Energy Program, Standard Calculation Recommendations, Final: September 10, 2008
We are providing these recommendations to the PSCW, who may adopt them as policy as is
or suggest changes before doing so. This revised document includes substantial changes
from the draft version based on comments from the program implementers and the PSCW.
We provide recommendations for standard calculation approaches that are both reasonable
(in terms of the amount of effort and data required to complete them) and accurate. Since we
cannot anticipate all situations, we expect the program implementers may occasionally
deviate from the recommended approach. In these situations the program files should include
full documentation of the calculation approach used (input values and equations), as well as
an explanation for the deviation from the recommended approach
2
.

2
KEMA will review and revise this document in the next program year, subject to approval by the
PSCW of this activity in the Detailed Evaluation Plan for 2009. We intend to make the revisions based
on program staff experience and evaluation review of projects using the recommended approach.

21

Focus on Energy Evaluation, Renewable Energy Program, Standard Calculation Recommendations, Final: September 10, 2008
2.
STANDARD CALCULATIONS
2.1
BIOGAS SYSTEMS
We recommend calculating methane production from anaerobic digestion using the chemical
oxidative destruction (COD) method. The COD method uses a standard rate of methane
production per COD destroyed, which allows for a standard calculation of methane production
regardless of digester inputs. This makes the COD method applicable for industrial
processes, such as food waste processing, landfill gas, and wastewater treatment, in addition
to manure.
Peak kW in the current contract period (and going forward) is based upon average kWh
during system peak in the summer.
The calculations for biogas systems have been broken into four sections. Section 2.1.1
defines the calculation to estimate methane gas production from the digestion process given
certain operational parameters. Section 2.1.2 defines the calculation to estimate the kWh
production of the engine-generator (genset) given operational values for the genset. Section
2.1.3 defines the calculation to estimate kW savings. Finally, Section 2.1.4 defines the
calculations to estimate therm savings.
2.1.1
Methane Gas Production
To estimate methane gas production from the digestion process, the bio-digester design
consultant typically provides the values for the calculation variables based on farm type or
industrial process as well as experience with a particular design and operation. For any
particular site, the Program must thoroughly document the values used in the equations, their
units, and their sources. This information should become part of the applicants folder.
Calculate biogas (methane) production from the following variables and equations:
A = Number of animals (farm) or gallons of influent/day (industrial)
B = Animal Unit (AU) = average lb of animal/1000 lb, assumed to be 1.4 for dairy
cow, 0.16 for pig, 0.03 for poultry (not used for industrial digester)
C = lb COD/AU/day or lb COD/gal/day (industrial)
D = Manure collected in influent (percent expressed as a decimal), 0.951.0 range
(not used for industrial digester)
E = Digester efficiency (percent expressed as a decimal), 0.10.7 range based on
manure type and digester efficiency
F = COD converted (ft
3
biogas/lb COD), 6.3ft
3
/lb @ 95 degrees F and 760 mm Hg,
at other temperatures and pressures adjustment is made using the General
Gas Law
3


3
The General Gas Law is expressed by the equation: V
2
= V
1
x (T
2
/T
1
) x (P
1
/P
2
)
Where: V
1
= gas volume (m
3
) at temperature T
1
(�K) and pressure P
1
(mm Hg)
V
2
= gas volume (m
3
) at temperature T
2
(�K) and pressure P
2
(mm Hg). 2. Standard Calculations

22

Focus on Energy Evaluation, Renewable Energy Program, Standard Calculation Recommendations, Final: September 10, 2008
G = Percent methane in biogas (percent expressed as a decimal), 0.55 to 0.80
range depending on digester type and influent source
days
G
F
E
D
C
B
A
ft
Methane
Annual
365
)
(
3
�
�
�
�
�
�
�
=
(farms)
days
G
F
E
C
A
ft
Methane
Annual
365
)
(
3
�
�
�
�
�
=
(industrial)
Where possible, the applicant or bio-digester design consultant should determine the COD
content of the manure through laboratory analysis. Where this analysis is not available, the
applicant or bio-digester design consultant may approximate the COD content based on the
volatile solids (VS) content of the manure
4
but must document the values used and
approximations made.
2.1.2
kWh Savings Estimate
Based on the quantity of methane produced, the applicant or bio-digester design consultant
can select a generator and calculate the potential annual electrical energy production. The
applicant must document the operating parameters of the generator. This information should
become part of the applicants folder.
The actual quantity of electrical energy generated is a function of the quantity of methane
delivered to the engine, heating value, capacity factor and the thermal conversion efficiency.
5

413
,
3
)
(
3
J
I
H
ft
Methane
Annual
kWh
Annual
�
�
�
=

H = Thermal conversion efficiency (percent expressed as a decimal), 2225% for
older, naturally aspirated gensets, 2931% for lean-burn gensets, and 38%
for larger (>1 MW) lean-burn gensets
I
= Lower heating value
6
(LHV) of methane (BTU/ft
3
) (corrected for temperature
and pressure of methane production); approximately 1,000 BTU/