Green Means
Solar?
By Shannon Scott
Elko receives enough sun, more than
130 days annually, to heat and power a home. We’ve
got sun, so let’s use it. After doing
some research and talking with Lonnie A. from Rockin’ A Electric, this is what
I learned.
The difference between passive and
active solar
Passive solar design integrates building
site, climate, and materials to minimize heating and cooling demands without mechanical
systems – no moving parts. Greatly
simplified, sun enters south facing windows absorbing into dense materials such
as concrete or tiled floors, then radiates back into a room after sun has set. Passive solar homes require smaller and less
costly heating systems of any type or fuel source.
Active solar uses solar collectors
combined with mechanical systems to heat fluids or generate electricity. Photovoltaic (PV) systems generate
electricity. Solar thermal collectors heat fluids.
Differences among solar collectors
Consider three factors when choosing
either PV panels or solar thermal collectors: their performance in all light
conditions; how much area they take; their intended purpose; and cost. Better PV panels generate more watts per
square foot, last for decades, and don’t lose more than 1% efficiency per year.
Hybrid PV panels offer good return
on investment as they produce more energy per area. Named hybrid, they combine amorphous and crystalline
silicon cells to provide good performance in all sun conditions.
Monocrystalline
silicon panels are economical, durable, and reliable. A single or “mono” silicon crystal makes up
each module on the panel for greater efficiency.
Polychrystalline
panels absorb slightly less solar energy than monocrystalline or hybrid, so you
need a few more of them to generate the same watts as monocrystalline or hybrid
panels. However, the process to
manufacture these panels is simpler so they cost less.
Amorphous
panels flex. These thin-film panels have
silicon laid as thin composites, simple to manufacture and cheapest to buy. However, they provide less electric output
and may not be prove durable.
Evacuated Tube
Collectors
Evacuated tube collectors do not
generate electricity, but surpass flat panels for most fluid heating needs like
radiant heat and domestic water. Glass
tubes collect and transfer heat via heat absorbers and metal pipes to a header filled
with a mixture most often of propylene glycol (food safe antifreeze) and
water. The heated fluid flows within
copper pipes (closed system) into a heat exchanger tank, often placed in a
utility room or basement. The hot copper
pipes heat potable water within the tank and often fluid for radiant heat
zones.
How
collectors are used
Grid
tie-in: Sun shines on PV collectors
that convert sunlight to direct current electricity (DC). An inverter changes DC to common household
alternating current (AC). Inverter AC
output connects to the utility grid via a breaker in the homes service
panel. These are very easy for DIYers to
install as they often just have male and female connectors from panels to
inverters. A home still has grid power
for periods of insufficient solar gain, or when household demands exceed solar
system capacity.
PV
systems with battery back-up: These also push excess electricity produced
back to the utility grid, but can power loads when there’s no sun and the grid
is down. A more complex and higher
maintenance system, DC current from PV panels enters into a charge controller
then goes to battery bank, dual purpose inverter, service panel, electric
meter, and ultimately the grid. Like a
tie-in system electricity can flow from and to grid.
Off-grid
PV systems: Off-grid requires deep
cycle battery storage. These systems
prove costly, yet provide power day and night when sun is not available. Solar panels must provide enough electricity
for household demands while recharging batteries at the same time –meaning
larger arrays. Most off-grid systems
incorporate a back-up generator. Instead of going to a service panel, energy goes
to AC circuits not tied to any grid source.
The largest off-grid problems include replacing expensive batteries
every 6-12 years, and often not having enough juice to power household needs.
Direct-tie:
The simplest PV set-up directly ties panels to a pump or fan. The pump only runs when the sun is out. This works great for attic fans and to pump
water at remote livestock troughs.
Solar
Thermal: These systems transfer heat from solar
collectors, often evacuated tubes, to heat transfer fluids or water. Pumps circulate cool fluids to solar panels
or evacuated tubes, where it picks up heat, then moves it to radiant heat
systems, hot water taps, or a swimming pool.
Flow control or mixing valves keep water from overheating beyond demand
or for personal safety.
Cost Effectiveness
A typical Nevada residence uses
about 30 Kwh/day of electricity (2011 statewide average). Materials costs for a grid tie-in system vary
depending upon solar panel type. A
friend told us that his tie-in system to power a 5,000 square foot home, cost
more than $60,000. Another bid for a
2,200 sq. ft. home came in at just over $30,000. These costs reflect solar PV system only – no
back-up heating system, ducts, radiant, or other mechanics.
For radiant heat and domestic hot
water, thermal solar systems appear the most cost efficient. They can meet 80% or more of 1,000 sq. ft
home’s heating needs for about $13,000; a
3,000 sq. ft. home just under $20,000 (Floor Radiant Company, VT).
If you’re interested in learning
more about how solar can work for you contact Lonnie Anderson at Rockin’ A
Electric here in Elko. He’s energetic
and does solar with a passion for quality and customer satisfaction.
Interested
in participating in green building and development discussions? The USGBC (US Green Building Council) of
Nevada would love to have an active Elko branch. If you’re interested in green development,
building, or are a LEED professional please e-mail me to discuss what we can
do.
Shannon Scott is
a green home owner, builder, and LEED Green Associate. If you’re interested in upcoming DIY hands-on
straw bale home building workshops, she can be reached at: greenmeansnv@gmail.com
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