Zero – Energy Building
What constitutes a zero energy
building?
A building that uses a “net” of zero energy – typically
producing excess energy via renewables with the excess
being sold into the grid and purchasing energy from the grid
when renewables are not available with a net cost of zero $
A zero “carbon” footprint building would be one that does
not use any high carbon (coal or oil) energy source and does
not add to carbon based air pollution
Renewable sources of electricity
What is a “grid-tie” system
It is an electrical generating system that ties into the
utility grid and can sell to the utility excess power
generated. Often called “net metering” where the
electric meter can move in both input and output
directions. Power generated at the home is used at
the home unless excess is generated. The excess is
returned to the power grid as a credit (meter runs
backwards). In periods of low generating output (low
sun or wind) the home receives power from the utility
and the meter runs forwards. In a well designed
system, the net cost to the homeowner would be $0
or possibly a small positive cash return.
Grid-tie solar system
•
•
•
•
•
Cost of installation can be reduced through
a federal tax incentive covering 30% of cost
Electric utilities must buy your excess
electricity
Current commercial solar panels near 15%
efficiency
Solar panels typically have a 25 year
warranty
Complete kits including all writing, solar
panels, mounting hardware, DC-AC inverters
are available
Components of a grid-tie solar system
A – solar panels
B- DC to AC inverter
C- Electrical distribution
D – AC loads
E – Electric meter
F – Main power grid
How many solar panels do you need
for a net zero system?
Sun Hours - Expected output from
solar panels
Charlotte
Expect only
4KW-hr/m2
per day
from a
solar panel
My home – average electrical usage was 1,567
KW-Hr per month for the last year. Peak usage
was 2,751 KW-Hr per month in summer
Average 1,567 KW-Hr/month =
50 KW-Hr/day
To meet average usage
• Expect – 4 KW-hr/m2 per day from
previous map
• 50 KW-Hr / 4KW-Hr/m2 = 12.5m2
of solar panels
• About 115 ft2 or about 10’ x 12’
Peak 2,751 KW-Hr/month =
92 KW-Hr/day
To meet peak usage
• Expected – 4 KW-hr/m2 per day
from previous map
• 92 KW-Hr / 4KW-Hr/m2 = 23.0 m2
of solar panels
• About 207 ft2 or about 10’ x 21’
Shown panel = 2’ x 4’. On the below
home, about 384 ft2 of solar panels (8
ft2 x 16 per row x 3 rows)
Complete kit for residential grid-tie solar
system
From previous slides
my home’s electrical
usage is 1,576 KW-Hr
per month average
and 2,751 KW-Hr per
month peak
This is equivalent to
1,400 KW-Hr per month in
Charlotte
But prices keep getting cheaper and
more competitive
Price on 7-11-2012
Price on 10-17-2012
Assume a cost of $20,000 for
a solar cell grid-tie system
• Current cost of Duke power is about $.10/KWHr. Using my average of 1,567 KW-Hr, my
average monthly cost is $156.70.
• For a $20,000 system to pay back $20,000/$156.70 = 127 months or 10.6 years
• But:
If the system cost is cut in half and Duke Power’s cost rises to
$.12/KW-Hr:
1,567 KW-HR @ $.12/KW-Hr = $188.04
$10,000/$188.04 = 53.1 months or 4.4 years
Assignment
• Assignment for lecture 10 – number of solar
panels need for a home in Charlotte
• Due next lecture