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” systemIt 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 panelsB- DC to AC inverterC- Electrical distributionD – AC loads

E – Electric meterF – Main power grid

How many solar panels do you need for a net zero system?

Sun Hours - Expected output from solar panels

CharlotteExpect 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/KW-Hr. 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