Net-Zero Energy Building Design and Economics
Introduction
In the U.S., the residential and commercial buildings consume about 38% of all primary
energy, about 84% of which comes from non-renewable fossil fuels (Annual Energy
Review 2008, Energy Information Agency, U.S. Department of Energy). The demand for
non-renewable fossil fuel energy could be significantly reduced by making buildings
more energy efficient and powering them with onsite renewable energy.
Net-zero energy buildings use a combination of energy efficiency and renewable energy
technologies so that the building sells back as much energy as it purchases over the
course of a year; hence on a net basis the building consumes zero off-site energy. The
concept of net-zero energy buildings in consistent with the larger concept of
sustainability because net-zero energy buildings function within natural steady-state
energy flows without borrowing energy resources from the future. In addition,
generating energy onsite eliminates energy transmission and distribution losses and
reduces the land required for renewable energy technologies. Many important
organizations have established goals for net-zero energy or net-zero carbon emission
buildings including:




American Institute of Architects (AIA) Sustainability 2030
o Renovate new buildings for 50% CO2 reduction
o 50% CO2 reduction in new buildings by 2010
o Additional 10% reduction every 5 years until net-zero C02 by 2030.
U.S. Green Building Council LEED Certification:
o 50% reduction in site energy use for base LEED
o 65% Silver
o 80% Gold
o 100% Platinum
ASHRAE
o Standard 90.1-2010: 30% less energy than 90.1-2004
o Standard 90.1-2020: guidance for net zero site energy use
U.S. Department of Energy
o All commercial buildings are net zero energy by 2025
The fundamental approach to designing net-zero energy buildings is to minimize energy
demand through energy efficiency, and then add sufficient on-site renewable energy
technologies (i.e. solar photovoltaic system, solar thermal system, wind energy system,
etc.) to satisfy that demand. To cost-effectively design net-zero energy buildings, the
costs of energy-efficiency and renewable-energy options can be compared to determine
the least-cost set of options for achieving net-zero energy. The levelized cost of energy
provides an accurate measure of the cost of an energy option, and hence is an excellent
1
vehicle for prioritizing energy options in pursuit of net-zero energy. This chapter
describes how to use solar energy simulation software and levelized cost of energy to
cost-effectively design net-zero energy buildings.
Levelized Cost of Energy
The levelized cost of energy (LCE) represents the total cost of an energy resource per
unit of energy. Key inputs to LCE include energy output, capital costs, fuel costs,
operations and maintenance costs, and financing costs. LCE enables the cost
effectiveness of different types of energy options, including energy efficiency,
renewable energy and purchased energy, to be compared. As such, it can be used as a
guide for prioritizing energy efficiency and renewable energy options in net-zero energy
buildings.
Fundamentally, LCE is the annualized total cost (ATC) of an energy project divided by the
annual energy output (AEO) of the project over the project lifetime.
Levelized Cost of Energy = Annualized Total Cost / Annual Energy Output
LCE = ATC / AEO
Calculation of LCE begins by determining the expected annual energy output (AEO) of a
project and the expected project lifetime (n). Next, the annualized total cost of the
project is determined by calculating the present value of all costs (including capital
costs, fuel costs, operations and maintenance costs, and financing costs), then
annualizing these costs over the expected project lifetime. In practice, some project
costs occur in the future; use time-value of money relations to calculate the present
values of these future costs, then sum the present values of all costs to calculate the
total present value of a project (Pt). To calculate the annualized total cost (ATC) of an
energy project, find the annualized value of Pt over the project life time using time value
of money relations. This method accurately calculates the levelized cost of energy even
when the financing period and project lifetime are different.
The two most important relations for calculating the present value (P) of a future
amount (F) or series of future annual amounts (A) are the present worth factor (PWF)
and the series present worth factor (SPWF). Both PWF and SPWF are functions of the
discount rate (i) and the number of years into the future (n) that F or A occur. The
discount rate (i) is the rate of return that could be generated by an alternative
investment; in many cases the best value to use for discount rate is the annual interest
rate of a loan to finance the project.
The present value P of a future amount F is:
P = F PWF (i,n)
where PWF = (1 + i)-n
2
The present value P of a series of annual amounts A is:
 1  (1  i) n 
P = A SPWF (i,n) where SPWF = 

i


The total present value of a project (Pt) is the sum of all present costs:
Pt =  Pi
The annualized total cost (ATC) over the project life time is:
ATC = Pt / SPWF (i,n)
Example: Calculate the levelized cost of energy for the following project. The project is
expected to save 2,000 kWh/yr over a 10 year period. The initial cost of the project is
$1,000 to be financed with loan with 5% annual interest. Recycling the equipment at
the end of the project lifetime will cost $200.
Solution: The annual energy output is given as AEO = 2,000 kWh/yr and project lifetime
is given as n = 10 years. Assume the discount rate is the annual interest rate i = 5%. The
initial cost is given as IC = $1,000 and the recycling cost after n years is given as RC=
$200. The present value of the recycling cost, Pr, is the recycling cost, RC, multiplied by
the present worth factor, PWF. The present value of all costs, Pt, is the sum of the
initial cost, IC, and the present value of the recycling cost, Pr. The annualized total cost,
ATC, is Pt annualize over the project lifetime using the series present worth factor
(SPWF). The levelized cost of energy, LCE, is annual total cost, ATC, divided by annual
energy output, AEO.
Input Data
Annual energy output: AEO (kWh/yr)
Project life: n (years)
Initial Cost: IC ($)
Discount rate: i
Recycle Cost: RC ($)
2,000
10
1,000
0.05
200
Calculations
PWF = (1+i)^(-n)
Present value of recycle cost: Pr ($) = RC PWF
Pt ($) = IC + Pr
SPWF(i,n) = (1-(1+i)^(-n))/i
ATC ($/yr) = Pt / SPWF
LCE ($/kWh) = ATC / AEO
0.614
123
1,123
7.722
145
0.073
The use of the levelized cost of energy for evaluating options for net-zero energy
building design is demonstrated in the sections that follow.
3
Levelized Cost of Energy Efficiency
The first step in net-zero energy building design is to make the building as energy
efficient as is economically feasible. This typically involves choosing between multiple
energy-efficiency measures. Calculating the LCE of energy-efficiency measures enables
the cost effectiveness of these measures to be compared and prioritized.
Example: Consider a building heated by an electric heat pump and in Dayton, Ohio
whose energy use is well described by the following ESim building energy simulation
model. Calculate the levelized cost of energy saved from increasing ceiling insulation
from R = 27 to R = 52 (hr-ft2-F/Btu) if the cost of the additional insulation is $1,000.
Assume a project lifetime of 30 years and a loan rate of 5%.
Solution: Energy savings can be estimated by comparing simulated whole building
electricity use from the baseline building with R = 27 (hr-ft2-F/Btu) insulation to a
building with R = 52 (hr-ft2-F/Btu) insulation using the ESim software. ESim simulations
from the baseline building and the building with additional ceiling insulation are shown
below.
4
Based on these simulations, the annual energy output (savings) are:
AEO = Esav = E,sim,baseline – E,sim,energyefficient
AEO = Esav = 18,131 kWh/yr – 17,646 kWh/yr = 485 kWh/yr
The series present worth factor is:
 1  (1  i) n   1  (1  0.05) 30 
SPWF = 
 = 15.372
=
0.05
i


 
The annualized total cost of the additional insulation is:
ATC = Pt / SPWF = $1,000 / 15.372 = $65 /yr
Thus, the levelized cost of the energy saved by adding insulation is:
LCE = AEO / ATC = ($65 /yr) / (485 kWh/yr) = $0.134 /kWh
This approach can be used to quantify the levelized cost of energy efficiency for multiple
measures and to compare the relative cost effectiveness of each measure. For
example, the table below shows a list of energy efficiency options with the levelized cost
5
of each option determined using this method. Note that each measure should be
evaluated using the appropriate lifetime. For example, if the expected lifetime of an
Energy Star refrigerator is 12 years, then the SPWF should be computed with n = 12
years. The list is then sorted from lowest to highest levelized cost, and can be used to
select the most cost-effective measures.
EE (sorted by LCE)
HW: T140 to T120
Nightsetback 22-7, 72to80sum, 72to64win
Comp Fluor
HW: ef.86 to ef.92
Infiltration: n.5 to n.25
Energy Star Refigerator
Infiltration+AtoAHXe.7: n=.25 effhx=.7
HP: SEER12 to 18, HSPF 8.3 to 10.5
Ceiling+Roof Insul: 27 to 52
slab: r5 to r15 floor: r2 to r7
Windows: 3ftover + (N40to10, S40to90, EW24to14)
Walls: 15 to 30
Windows: r2 to r4
Total EE
Base
kWh/yr
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
Engy Eff
kWh/yr
16,889
17,279
17,218
17,772
17,007
18,008
16,290
16,783
17,646
17,823
17,950
17,410
17,686
Esav
kWh/yr
1,242
852
913
359
1,124
123
1,841
1,348
485
308
181
721
445
9,942
InitCost
$
0
100
80
200
1,000
108
2,000
2,000
1,000
800
500
2,000
2,000
11,788
AnnCost
$/yr
0
7
16
20
65
7
130
133
65
52
33
130
130
LevCostEngy
$/kWh
0.00
0.01
0.02
0.06
0.06
0.06
0.07
0.10
0.13
0.17
0.18
0.18
0.29
Including Interaction Effects
The method described above is useful for prioritizing energy efficiency options.
However, interaction effects between options can cause the overall energy savings from
multiple options to be different than the sum of the savings from each option evaluated
individually. For example, increasing the thermal resistance of the envelope reduces the
heating load and heating energy use. Similarly, improving the efficiency of the heating
system reduces heating energy use. However, when both measures are implemented
simultaneously, the reduced heating load decreases the savings from improving heating
system efficiency. Thus, the overall savings, including interaction effects, is less than the
sum of the savings evaluated independently. To quantify interaction effects, include all
of the selected energy efficiency measures in a single building energy simulation.
Example: To illustrate the importance of including interaction effects, recall that the
total expected savings from each energy efficiency measure evaluated individually is
9,942 kWh/yr. In comparison, the ESim output below shows that building electricity use
with all energy efficiency measures evaluated simultaneously would be 10,992 kWh/yr.
6
The total energy savings including interaction effects would be:
Esav = E,sim,baseline – E,sim,energyefficient
Esav = 18,131 kWh/yr – 10,992 kWh/yr = 7,139 kWh/yr
Thus, in this example, interaction effects reduced the total expected savings by about
28%. When all energy efficiency options are combined and interaction effects included,
the overall levelized cost of energy efficiency is about $0.11 /kWh.
EE with interaction
Base
kWh/yr
18,131
Engy Eff
kWh/yr
10,992
Esav
kWh/yr
7,139
InitCost
$
11,788
AnnCost
$/yr
767
LevCostEngy
$/kWh
0.11
Levelized Cost of Solar Hot Water Systems
In many buildings, hot water is required year round and the energy required to heat the
water can be substantial. In many cases, solar hot water systems can preheat water at a
lower levelized cost than heating the water with electricity. To determine whether
solar hot water is cost effective, the solar hot water system must first be sized to meet
hot water demand. This is typically done using a solar simulation program that
7
calculates savings from solar hot water systems based on system performance and
design parameters and meteorological data. After the system is appropriately sized, the
levelized cost of energy from system can be computed to evaluate the system’s cost
effectiveness.
Sizing and Performance of Solar Hot Water Systems
The thermal energy delivered by solar hot water systems varies throughout the year
with incident solar radiation. Thus, sizing a solar hot water system to meet the entire
hot water heating load, even during winter, means that the system will be oversized
during summer. To improve cost-effectiveness, many solar hot water systems are sized
to deliver 100% of the hot water heating requirements during the summer, and some
fraction of the annual hot water heating requirements. The performance of solar hot
water systems can be simulated using solar simulation programs such as SolarSim. The
use of SolarSim to size a solar hot water system to deliver 100% of hot water
requirements during the summer is shown below.
Example: Use the SolarSim software to size a solar hot water system for a house in
Dayton, Ohio so that the solar system delivers about 100% of the energy needed for hot
water during the summer. The collectors face south with a slope of 39.9 degrees. The
system has a 227 gallon storage tank. Average hot water use is 2.5 gal/hr (60 gal/day),
the hot water set point temperature is 120 F, and the backup electric hot water heater
has an energy factor of 0.92. Once the system is sized, determine the annual water
heating energy savings.
When these values are loaded into SolarSim, the output screen below shows that a solar
hot water system with 6 m2 of collector area would supply 100% of the energy needed
during July and August.
8
In addition, the output screen shows that the annual amount of electrical heating
energy displaced by the solar hot water system would be 3,103 kWh/yr, which would
account for 85% of the total how water heating requirement.
Levelized Cost of Energy from Solar Hot Water Systems
The levelized cost of energy from solar hot water systems can be calculated from
performance and cost data.
Example: Calculate the levelized cost of energy from the solar hot water system in the
previous example. The solar hot water system reduced electricity use by 3,103 kWh/yr.
The solar hot water system costs $2,000 plus $500 per m2 of collector area, has a
lifetime of 20 years, and negligible maintenance costs. The solar system can be financed
with a loan interest rate of 5% per year
Solution: The annual energy output AEO is 3,103 kWh/yr over a lifetime of n = 20 years.
Assuming negligible maintenance costs, the present value of the total system is:
Pt = $2,000 + (6 m2 x $500 /m2) = $5,000
Assuming a loan interest rate of 5% per year, the series present worth factor, SPWF, is:
9
 1  (1  i) n   1  (1  0.05) 20 
SPWF = 
 = 12.462
=
0.05
i


 
The annualized total cost of the solar hot water system is:
ATC = Pt / SPWF = $5,000 / 12.462 = $401 /yr
The levelized cost of the energy from the solar hot water system is:
LCE = AEO / ACT = $401 /yr / 3,103 kWh/yr = $0.129 /kWh
Levelized Cost of Photovoltaic Systems
For a net-zero energy building, energy saved from energy-efficiency measures and
energy produced by a solar hot water system reduces the energy that must be provided
by a photovoltaic (PV) or other renewable energy system. After energy demand has
been minimized by energy efficiency and solar thermal hot water systems, a
photovoltaic system can be sized to meet the remaining energy demand. This is
typically done using a solar photovoltaic system simulation program that calculates solar
PV electrical output based on system and design parameters and meteorological data.
After the system is appropriately sized, the levelized cost can be computed to evaluate
the systems cost effectiveness.
Sizing and Performance of Solar Photovoltaic Systems
The performance of solar photovoltaic systems can be simulated using solar simulation
programs such as SolarSim.
Example: Use the SolarSim software to size a solar photovoltaic system for the house in
Dayton, Ohio considered in previous examples so that the solar system delivers 100% of
the electricity needs after energy efficiency and solar heating options have been
implemented. The collectors face south with a slope of 39.9 degrees.
Solution: The building’s baseline energy use is 18,131 kWh/yr, the total expected savings
from energy efficiency measures is 7,139 kWh/yr and the electrical heating energy
displaced by the solar hot water system is 3,103 kWh/yr. Thus, for the building to be
net-zero energy, the electrical energy required from a photovoltaic system is:
Esolar,pv = 18,131 kWh/yr – 7,139 kWh/yr - 3,103 kWh/yr = 7,889 kWh/yr
To size a solar photovoltaic system to deliver this much electrical energy, the
performance specifications of the solar system and the energy requirements of the
building were loaded into the solar energy simulation program SolarSim. The
performance of the system in Dayton, OH was then simulated, and the size of the
10
system was then modified until the system delivered the required amount of electricity.
According to SolarSim, the annual amount of electrical energy generated by a solar
photovoltaic system rated at 5.4 kW with 52 m2 of collector area would be 7,891
kWh/yr.
Levelized Cost of Energy from Solar Photovoltaic Systems
The levelized cost of energy from solar photovoltaic systems can be calculated from
performance and cost data.
Example: Calculate the levelized cost of energy from the solar photovoltaic system in
the previous example with PV output of 7,891 kWh/yr. The solar PV system costs
$5,000 /kW, has a lifetime of 20 years, and incurs negligible maintenance costs. The
solar system can be financed with a loan interest rate of 5% per year
Solution: The annual energy output AEO is 7,891 kWh/yr over a lifetime of n = 20 years.
Assuming negligible maintenance costs, the present value of the total system is:
Pt = 5.4 kW x $5,000 /kW = $27,000
The series present worth factor, SPWF, is:
11
 1  (1  i) n   1  (1  0.05) 20 
SPWF = 
 = 12.462
=
0.05
i


 
The annualized total cost of the solar hot water system is:
ATC = Pt / SPWF = $27,000 / 12.462 = $2,167 /yr
The levelized cost of the energy from the solar system is:
LCE = AEO / ATC = $2,167 /yr / 7,891 kWh/yr = $0.275 /kWh
Levelized Cost of Purchased Energy
In many cases it is useful to compare the costs of energy-efficiency and renewable
energy options to the cost of commercially-purchased energy. To do so, the cost of
commercially-purchased energy over the lifetime of the energy efficiency and
renewable energy technologies must be determined.
Historically, the cost of most commercially-purchased energy has increased over time as
fuel, equipment and maintenance costs increase. Residential natural gas and electricity
price escalation rates, e, over various periods are shown in the tables below (Annual
Energy Review 2006, Energy Information Agency, U.S. Department of Energy).
12
Natural Gas
Residential
Nominal
1967-2006
Input
n
P
F
39
1.04
13.76
Calculations
e
0.068461
Residential
Nominal
1996-2006
Input
N
P
F
10
6.34
13.76
Residential
Nominal
2001-2006
Input
n
P
F
5
9.63
13.76
Calculations
E
0.08057
Calculations
e
0.073986
Residential
1996-2006
Input
N
10
P
8.36
F
10.4
Calculations
E
0.022075
Residential
2001-2006
Input
n
5
P
8.58
F
10.4
Calculations
e
0.039224
Electricity
Residential
1967-2006
Input
N
39
P
2.3
F
10.4
Calculations
E
0.039448
Over any period of n years, the annualized (levelized) cost of energy can be calculated
by:
1) Defining the current cost of energy as A, then finding the present value P of
future costs escalating at rate e with discount rate i over n years as:
P = A ESPWF(i, e, n)
2) Finding the annualized (levelized) cost, A’, of the present value as:
A’ = P / SPFW(i, n).
Where:
 1  (1  i)n 
SPWF(i,n) = series present worth factor = 

i


ESPWF(i,e,n) = escalating series present worth factor =
n
1  1 e 
n
if i = e
  if i  e =
1  
(i  e)   1  i  
(1  e)
Example:
Determine the annualized (levelized) cost of electricity if
the initial cost of electricity is $0.13 /kWh and the
13
projected electricity cost escalation rate is 4% per year.
The system lifetime is 20 years and the discount rate is 5%
per year.
Annualized Cost of Purchased Electricity
Inputs
i=
n=
e=
A = Init cost elec ($/kWh)
Outputs
ESPWF(i,e,n)
P = A ESPWF
SPWF(i,n) =
LCE ($/kWh) = A' = P / SPWF
0.05
20
0.04
0.13
17.419
2.264
12.462
0.182
Thus, in this example, investments in energy efficiency or
renewable energy that have marginal costs of less than
$0.182 /kWh are cost effective.
Summary: Evaluating Energy Options for Net-Zero Energy Buildings
Net-zero energy buildings rely on both energy efficiency and renewable energy
technologies to achieve net-zero energy use, and the cost-effectiveness of these
measures is often assessed by comparisons with purchased energy. The levelized cost
of energy method described above provides a consistent basis for evaluating the
economics of both types of technologies. It also makes it possible to evaluate the
overall cost effectiveness of a net-zero buildings by comparing levelized costs of energy
efficiency and renewable energy to purchased energy.
Example: Sort the energy-efficiency, solar hot water and solar photovoltaic options from
the previous examples according to levelized cost to prioritize measures to achieve netzero energy according to cost.
Solution:
14
EE + SHW + PV (sorted by LCE)
HW: T140 to T120
Nightsetback 22-7, 72to80sum, 72to64win
Comp Fluor
HW: ef.86 to ef.92
Infiltration: n.5 to n.25
Energy Star Refigerator
Infiltration+AtoAHXe.7: n=.25 effhx=.7
HP: SEER12 to 18, HSPF 8.3 to 10.5
Solar hot water
Ceiling+Roof Insul: 27 to 52
slab: r5 to r15 floor: r2 to r7
Windows: 3ftover + (N40to10, S40to90, EW24to14)
Walls: 15 to 30
Solar photovolaic electricity
Windows: r2 to r4
Total
Base
kWh/yr
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
18,131
Engy Eff
kWh/yr
16,889
17,279
17,218
17,772
17,007
18,008
16,290
16,783
15,028
17,646
17,823
17,950
17,410
10,240
17,686
Esav
kWh/yr
1,242
852
913
359
1,124
123
1,841
1,348
3,103
485
308
181
721
7,891
445
20,936
InitCost
$
0
100
80
200
1,000
108
2,000
2,000
5,000
1,000
800
500
2,000
27,000
2,000
AnnCost
$/yr
0
7
16
20
65
7
130
133
325
65
52
33
130
2,167
130
LevCostEngy
$/kWh
0.000
0.008
0.018
0.056
0.058
0.059
0.071
0.099
0.105
0.134
0.169
0.180
0.180
0.275
0.292
Plotting the data makes it easier to visualize the relationship between levelized cost and
energy output.
The levelized cost of energy method makes it possible to combine all of the energy
efficiency and renewable energy options needed to achieve net-zero energy into a single
levelized cost. This cost can be comparted to the levelized cost of purchased energy to
evaluate the overall cost effectiveness of the energy measures.
Example: Calculate the levelized costs of energy efficiency combined, solar hot water
and solar photovoltaic electricity individually and as a group. Compare the overall
levelized cost to the levelized cost of purchased energy.
Solution: The list of energy efficiency, solar hot water and solar photovoltaic energy
options sorted by levelized cost is shown below.
15
EE(with interaction) + SHW + PV (sorted by LCE)
EE with interaction
Solar hot water
Solar photovolaic electricity
Total
Base
kWh/yr
18,131
18,131
18,131
Engy Eff
kWh/yr
10,992
15,028
10,240
Esav
kWh/yr
7,139
3,103
7,891
18,133
InitCost
$
11,788
5,000
27,000
43,788
AnnCost
$/yr
767
401
2,167
3,335
LevCostEngy
$/kWh
0.11
0.13
0.27
0.18
A plot of cumulative savings versus cumulative levelized cost is shown below.
In summary, in this example, the additional energy efficiency and renewable energy
measures considered here would increase the cost of the building by $43,788, which
would increase the annual mortgage cost by $3,335 per year. However, annual energy
costs would be negligible. The fraction of total energy demand met by energy efficiency
is 39%; 17% is met by solar hot water and 44% is met by solar photovoltaic system. The
overall cost of all energy efficiency, solar thermal and solar photovoltaic measures is
$0.18 /kWh. This is comparable to the average cost of purchased energy of $0.18 /kWh
when projected energy escalation costs are included. Thus, over a 30-year lifetime, the
owning and operating cost of this net-zero energy building is about the same as a
traditional building.
Leasing Solar Collectors
In many parts of the country, leasing provides a maintenance-free alternative to
purchasing a solar system. In most cases, the leasing company owns the system.
Systems are financed over 20 years and offer lower net monthly costs than purchasing
electricity from the utility. Total cost savings would be greater if the customer
purchased the PV system. However, the combination of guaranteed savings and
16
maintenance with no/low first cost is attractive. In some states, such as California,
leased systems account for the small PV system sales.
Annual deployment of residential scale (<10 kW) PV in California. (Rutberg, M., Bouza,
A., “Leasing Residential PV Systems”, ASHRAE Journal, December 2013)
For example, the pictures below show a solar photovoltaic system on a house in Agua
Dulce, California, about 45 minutes north of Los Angeles in the high desert mountains.
The system was installed in two half days.
A solar company owns the system and is responsible for its maintenance. In this
example, the homeowner used about 19,000 kWh/yr at an average unit cost of about
$0.174 /kWh for an annual cost of about $3,300 /yr. The PV system is guaranteed to
produce 11,639 kWh/yr. If the system doesn’t produce the expected electricity, the
company washes or replaces the panels. In this example, the homeowner would still
have to pay for 7,361 kWh per year, but at a reduced maximum rate of about $0.12
/kWh for a total cost of about $888 /yr. In addition, the homeowner would pay the
solar company $2,735 per year. Thus, the total cost for the home owner would be the
sum of $888 /yr and $2,735 /yr or about $3,623 /yr. This is only slightly more than the
$3,300 /yr the homeowner currently pays for electricity. But the homeowner has the
satisfaction of knowing that its electricity is carbon free and that the system may
actually reduce total costs in the future if purchased electricity rates increase.
17
Net-Zero Energy Buildings
U.D. partner Melink Corporation’s headquarters in Milford, Ohio is a net zero energy
facility.
18