alt.energy.renewable

Sunny side down
Feb 15th 2008
From Economist.com

Going solar is a luxury few can afford


IT'S not easy being green-nor is it cheap. With the best will (and some of
the most generous handouts) in the world, solar power still makes little
sense for the average homeowner, even in sunny southern California. Under
pressure from his environmentally conscious ten-year-old daughter, your
correspondent has spent the past week talking to experts around the state
and running the numbers to see if he could reduce Mayhem Manor's carbon
footprint.

Solar power ought to be the answer. The house faces south-east, lacks trees
or other shadow-casting obstructions, and its flat roof offers ample space
for a sizable solar array. At 720 feet up the hillside, it is well above the
"marine layer" (the locals' fancy name for morning fog) and gets about 300
sunny days a year. So what's the problem?

It's not even as though the place gobbles electricity. When the house was
being rebuilt five years ago, the new roof came with over a foot of thermal
insulation. The floor-to-ceiling windows along two sides of the structure
were replaced with double-glazed "low-E" glass (the sort that blocks
infra-red radiation), and thermal linings were included in all the exterior
walls. Even during the summer, the air conditioner usually stays off.

Admittedly, the architect went overboard on lighting. Fully illuminated, the
house demanded seven kilowatts of raw lighting-power before fluorescent
lights replaced thirsty tungsten filaments. Overall electricity consumption
is now a reasonable 8,300 kilowatt-hours (kWh) a year.

Given the local utility's rate of 10.8 cents per kWh, that adds up to a
modest $900 for the year-or just $2.50 a day. At those prices, solar energy
simply cannot compete with juice from the local power-station, even with
California-level subsidies.

The problem is that solar-energy technology has been improving
incrementally, but its costs have been falling slowly.

If solar cells had abided by Moore's Law, they too would have halved in
price every 18 months or so-and we would all be running our homes on
sunshine. But getting photons from sunlight to dislodge more and more
electrons in semi-conducting materials like silicon, and so generate
electricity, is harder than building a better microchip.

The first solar cells-built more than a century ago-had conversion
efficiencies of around 1%. Since then, their efficiency has doubled once
only every 30 years-a veritable snail's pace compared with the speed of
microchip development.

It was not until the 1950s, for instance, that America's famed Bell Labs
stumbled on a way of boosting a solar cell's conversion efficiency by
"doping" its silicon with certain impurities. It then took another 50 years
to raise the efficiency to nearly 20%.

The performance of solar cells has picked up recently. But that's only for
the most exotic cells used in space. Today's satellites have solar panels
based on thin films of gallium arsenide that boast efficiencies of over 35%.
Meanwhile, in the laboratory, exotic "quantum wells" promise photovoltaic
conversion efficiencies of 45% or more.

But the solar panels used in space cost millions to make and last for a
decade at most. Back on earth, the only ones affordable enough to be used
commercially are early models based on crystalline and amorphous silicon
with efficiencies of around 15%.

And even these aren't exactly cheap. Sanyo's 200-watt module, one of the
better panels used by the industry, offers 17% efficiency and costs $1,500
retail.

As a rule of thumb, the industry reckons that a solar panel capable of
generating one kilowatt of power at peak times will average roughly 20% of
that over the whole day. In other words, every kilowatt of installed
capacity should be good for 4.8 kWh of daily consumption-or around 1,750 kWh
per year. By that reckoning, Mayhem Manor would need 4.8 kilowatts of solar
capacity to be able to generate the amount of electricity normally consumed
from the grid.

Unfortunately, that ignores all the losses that occur between the sun's rays
striking the solar array and that direct current being converted into
alternating current to run the house. Such losses can easily mop up 25% of
the solar panel's output. So, better install at least 6.4 kilowatts worth of
solar panels on the roof.

Here's where going green gets tough. At today's prices, your correspondent
would have to stump up $48,000 for the solar panels alone. Add the cost of
the switching modules, the power controller, the fault protector, the
DC-to-AC inverter and the service panel-not to mention the installation
charges and the contractor's profit-and the final bill could easily come to
$65,000.

What about incentives and tax credits? That depends on where precisely you
live and how effective an installation you have. To get anything like a full
grant in your correspondent's neck of the woods, the array would have to be
facing due south and tilted at an angle of 34 degrees to the sun. The first
might be possible; the second would definitely not. At best, Mayhem Manor
would qualify for about $12,000 worth of local assistance plus a $2,000
federal grant.

Borrowing the balance at today's interest rates would mean repayments of
roughly $600 a month for ten years, even after setting the interest charges
against tax. And all that just to feel good about saving $75 of electricity
a month. Better to buy a couple of tons worth of carbon offsets each year
for $70 and have done with it.


http://www.economist.com/research/articlesBySubject/displayStory.cfm?story_id=10709096&subjectID=348924&fsrc=nwl

--
Qolin

Email: my qname at domain dot com
Domain: qomputing