Should Your Next Home be a Net Zero Energy Home?

Should Your Next Home be a Net Zero Energy Home?
by Beth Shady
If you are in the planning stages of building a new home,
or a significant remodel to an existing one, you are most likely considering some form of
an energy efficient method to heat, cool and power your home. Net Zero Energy is the
simple concept of a home generating the same amount of energy that it consumes on
an annual basis.
Net Zero Energy is accomplished when the right combination of very efficient
mechanical, lighting, building materials and appliances are matched with properly
sized solar systems to achieve an annual Net Zero Energy balance.
Net Zero Energy Certified
David Knight of Monterey Energy Group, a mechanical engineering and energy
efficiency-consulting firm located in Pacific Grove, California started net Zero Energy
Certified (NZEC) in 2009. I sat down and talked with David to learn more about the mechanics, costs and benefits of Net Zero Energy.
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from the grid. The grid, not batteries, is
the storage medium. Most utilities in the
USA have net metering programs that
account for your energy production and
consumption on an annual basis. This is
one of the keys in making Zet Zero Energy
homes practical.
BS: What factors do you take into consideration when determining whether or not
a Net Zero Energy home is practical?
DK: There are several factors to consider. One is the local climate, which determines the heating and cooling loads, as
well as the solar production. Adequate
roof space and site orientation, ideally
unshaded south facing, are also very important. Local incentives for installing solar
electric systems play a key role, and the
grid rate of electricity is also a strong determination. For example in most of CA,
we have a mild climate, thus low heating and cooling systems, good solar incentives and very high grid electric rates.
That combination makes it very practical
to do a Net Zero Energy home.
By contrast, Omaha, Nebraska,
which has a harsh climate and no solar
incentives, and an inexpensive electric
rate, make a Net Zero Energy home not
as practical. In other words, mild, sunny
states with good solar incentives and high
grid electric costs benefit the most from
Net Zero Energy. While it is nice to have all
four variables, having at least two of the
four, can make building a net zero energy
home a sensible economic decision.
Knight’s Theory
These statistics support the Knight’s
Theory, which is: Homeowners would rather produce their own electricity from solar
than buy from the local utility company if
the after tax price is the same or less.
“Homeowners would
rather produce their own
electricity from solar than
buy from the local utility
company if the after tax
price is the same or less.“
- David Knight
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BS: One of the common concerns we
often hear with regard to solar power and
green building is that it is too expensive
and that the payback takes so long it
hardly seems worth it. Is building Net Zero
Energy affordable for the average homeowner?
DK: If you had asked me that question
two years I would have said that was absolutely true. Today, however, with the recent significant reductions in the cost of
grid tied solar electric systems, approximately 50% last year, combined with a 30%
uncapped federal tax credit have made
these systems very affordable compared
to the grid.
In addition, solar electric panels are
putting out more energy per square foot,
which makes them easier to integrate
into the building. Another factor is that
the overall efficiency of homes keeps improving. Better insulation, energy efficient
lights, windows and HVAC equipment, all
standard in today’s new homes, when
combined, reduce the demand for energy.
BS: What mechanical equipment innovations do you see that make all electric
DHW and space heating with solar power
more viable?
Daikin Altherma Air-to-Water Heat Pumps
The introduction of the air-to-water
heat pump to the U.S. market has been
a boon to the Net Zero Energy concept
for hydronic heating contractors. These
electric devices, for example, the Daikin
Altherma, use variable speed inverter
technology to efficiently produce hot
water for domestic and space heating.
These units are reversible and can also be
used for cooling, which opens up a huge
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untapped market for hydronic contractors who can now use chilled water for air
conditioning.
In colder climates, there is a 30%
federal tax credit for geo-exchange heat
pumps. These geo-exchange heat pump
systems not only convert electricity into
hot or cold water, but their capacity and
efficiency remain constant, regardless of
the outside temperature, due to the constant temperature of the surrounding the
earth.
Grid Tied Solar Electric
BS: How does a grid tied solar electric
system work?
DK: These are simple, very low maintenance systems that convert sunlight into
electricity. When the sun is out and your
home energy consumption is typically
low, the excess energy generated literally spins your electric meter backwards
and you are essentially selling electricity
back to the grid. Think of it like roll over
minutes on your cell phone bill. When the
sun goes away you buy electricity back
BS: What is the best way to determine
the rate of grid provided electricity versus
the cost of solar provided electricity?
DK: Table 1. represents the comparison
between the costs of solar provided electricity to the grid. I call this my SPER chart,
which stands for Solar Provided Electric
Rate. SPER is calculated by dividing the
annual after incentive cost by the KWH
produced. SPER is basically your fixed
electric rate for the life of the system, typically about 30 years, the same as your
mortgage.
To calculate the average after
tax equivalent cost of electrical power, I
made the conservative assumption that
the homeowner was in the 25% tax bracket and added any applicable state taxes.
For example, in Illinois, the average retail
electric rate is $0.113. Since mortgages
are tax deductible and an electric bill is
not, we added the cost of the 25% federal taxes and the 3% Illinois state taxes to
determine the after tax equivalent rate of
$0.16/KWH
BS: What overall conclusions can be
made from the SPER chart?
DK: In the last year, solar has become
cost effective in almost every major city
in the U.S. The simple way to use this chart
is to compare column 9, the SPER, to column 11, which is the after tax equivalent
rate of your electricity.
In 31 of the 40 cities shown, the SPER
is lower than the after tax grid electric
rate. Homeowners understand that their
mortgage is tax deductible, but their utility bill is not, that is why we compare the
SPER to the after tax equivalent electric
rate.
If you believe that grid prices will increase, another thing to note on this chart
is column 9, the SPER rate, compared to
column 12, which calculates the average
price per KWH if the grid rate increases
5% a year. As you can see, in all 40 cities
surveyed, the solar electric rate is significantly less than the grid rate over the 30
year period. So even in cities with harsh
climates, no solar incentives and low
electrics rates, you can make the case for
producing your own electricity and building a Net Zero Energy house.
“Even in cities with harsh
climates, no solar
incentives and low
electrics rates, you can
make the case for
producing your own
electricity and building a
Net Zero Energy house. “
- David Knight
BS: You have made a good case
for the homebuilder to use solar power for
the home’s lighting, air conditioning and
appliances. You obviously need electricity for those uses. For space heating and
domestic hot water, isn’t it more cost effective to use fossil fuels like natural gas,
propane and fuel oil?
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SPER Chart
DK: The introduction of the airto-water heat pump, which I mentioned
earlier, can make use of solar electric for
space heating and domestic hot water cost efficient and practical. To demonstrate my point, I developed Table 2,
which compares the use of an air-to-water heat pump with natural gas, fuel oil
and propane. For simplicity all units have
been converted to KWH/year.
As you can see, in the 40 cities surveyed, using solar in conjunction with an
air-to-water heat pump is significantly
more cost effective than using either fuel
oil or propane. This can be seen comparing column 4 with columns 7 through 10.
In 31 of the 40 cities surveyed the cost
of using solar with an air-to-water heat
pump is the same or less than the after
tax rate of using natural gas, shown in
column 6. However, in colder climates, a
geo exchange heat pump may be a better choice than an air source heat pump.
I think hydronic contractors can now offer their customers an alternative to fossil
fuels. BS:
What advancements, improvements and trends do you predict we will
see in the near future that will make building Net Zero Energy homes even more
feasible?
DK: The improvement in installation efficiency and lower material costs will contribute to lowering the overall installed
cost per KWH of solar electric systems. In
Germany, systems are routinely installed
for about $3.50 per watt as compared to
the $5.50 per watt rate I used in my SPER
chart. However, as prices decline, incentives will probably be lowered as well. Another improvement we are starting to see is solar electric panels incorporated into conventional building products
like roofing tiles and skylights, which makes
it easier for architects to integrate the solar
production into the design of the home.
Also a few products are just coming to
market in the USA that combine solar
electric and solar thermal production in
the same panel.
These panels not only produce hot water
for space and domestic uses, they also increase the electricity production on the
panels by cooling them on hot days.
As LED lights, which are about 5
times more efficient than incandescent,
become more reasonably priced, the energy required for cooling will be reduced
as well, since more efficient lighting creates less strain on an air conditioning system, which contributes to lowering cooling loads.
We will start to see higher COP’s for
air-to-water heat pumps at lower ambient temperatures. According to the California Energy Commission (CEC), about
50% of a household’s energy use goes
to space conditioning and domestic hot
water. The higher the COP, the smaller
and less expensive the solar electric system will have to be.
Another big trend is the connection
between home and transportation, as
more homeowners are installing enough
solar electric to provide sufficient electricity for at least one electric car.
Finally, real time monitoring for
both the energy consumption and solar
production. This will allow homeowners
to compare not only how much energy
they are using, but also how much they
are producing. This is just now available
and NZEC is slated to install our first system
at the end of this year.
All of these factors make building
Net Zero Energy homes even more feasible, practical and affordable.
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Air-to-Water Heat Pump vs. Fossil Fuels
Dan Chiles has been on the forefront
of the radiant heating business since 1975
and is a board member of The Radiant
Panel Association. Dan is the Mayor ProTem of Springfield, Missouri. He is currently
in the planning stages of building his Net
Zero Energy home.
BS: What were your reasons for deciding to build a Net Zero Energy home?
DC: I liked the idea of being energy independent. Here in Missouri, which is coal
country, electric rates may be low now,
but they are only going up. As a council
member, I myself just voted on a 16% rate
hike for residential homeowners and another 7% for commercial dwellings.
“I liked the idea of being
energy independent. As
an environmentalist,
I want to reduce my
carbon footprint.”
I like the assurance that NZEC locks in your
rate and that you are essentially becoming your own utility.
My home will also be a working farm and
I plan to put a solar electric array on the
barn and reserve space on the roof to
produce enough electricity to power an
electric car.
As an environmentalist, I want to reduce my carbon footprint. The Supreme
Court just ruled that coal is a pollutant,
and 85% or our energy in Missouri comes
from coal. We are part of the problem.
The rest of country is in the middle of the
PV revolution and the Midwest is in the
dark ages. I want to change the mindset
that solar electric is some kind of exotic
California technology that isn’t practical
anywhere else. David Knight
831-372-8328
netzeroenergycertified.com
- Dan Chiles
Architectural rendering of Dan Chiles’ home - Bois d’Arc, MO
Beth Shady is the President and Director of Marketing for Sustainable Design and Product Management.
Beth is a LEED Green Associate and holds an MS in Internet Marketing. She is a freelance writer and Internet
Marketing consultant to the renewable energy construction industry.
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