The Ergosphere
Tuesday, December 21, 2004

Tide turning II

New Scientist reports an ultra-thin "polymorphous" (polycrystalline?) silicon solar cell coming in at one micrometer thick and potentially as cheap as 1 euro per peak watt.  On top of this, it's flexible and can be rolled.  (Hat tip: Slashdot.)

This leapfrogs the current contender for price/performance leadership, the titanium-dioxide technology used by NanoSolar (though NanoSolar appears to have a greater margin for price cuts).  The extreme reduction in material required should cut the energy-payback time by a large fraction, probably to less than a year.  The efficiency is not great at 7%, but cost more than makes up for this; the creators hope they can reach 10%.  If they can do this without increasing the cost/area, the cost will fall to less than $1/Wpeak.

Insolation over much of the continental US runs between 120 and 200 kcal/cm2/yr, so selecting values in that range:

Energy yield,
Energy cost,
120 1394.67 97.63 $123.80
7% 25 10.8
1859.56 130.17
7% 25 8.1
2324.44 162.71
7% 25 6.4

This appears to be competitive with flat-rate grid power, and extremely competitive with daytime afternoon peak rates.  Panels at this price could begin replacing peaking generation in the Southwest as soon as they went into production.  For the USA, tax considerations make solar even more favorable for homeowners.  Mortgage interest is tax-deductible, while utility costs are after-tax.  If the full added cost of the solar system is mortgaged and the buyer's marginal tax rate is 28%, the cost of the homeowner's own energy consumption falls to less than 8 cents per kWH.

Economic analysis:  At 7% efficiency and $1.34/Wpeak at a solar flux of 1000 W/m2, the new cells would cost $93.80/m2.  If we assume that encapsulation and other costs run to $30/m2, covering the roof of a 2000 sf, 2-story house (~90 m2) with such cells would cost roughly $11,000; this roof would generate 6300 watts in peak sunlight, of which perhaps 6 kW could be converted to AC for use locally or on the grid.

What could this do?

The impervious area of the United States (roughly the area of Ohio) receives on the order of 500 quads of solar energy per year.  If this could all be captured and 7% converted to electricity, that is 35 quads of electricity.  In contrast, all coal- and nuclear-produced electricity amounts to less than 10 quads per year, and the petroleum-derived power delivered to the wheels of all US vehicles is approximately 5.5 quads/year (15.04 TBTU/day * 0.365).  Energy from solar would be cheaper than petroleum, and plug-in hybrids could turn it into a direct replacement for imported oil.  An investment of $100 billion per year would purchase ~800 million m2 of panels, which would produce ~100 billion KWH (0.34 quads) of electricity every year.  In fifteen years solar electricity could replace all petroleum-derived energy used by motor vehicles; adding another $100 billion/year would generate enough to replace all coal and nuclear electricity over roughly 30 years.

Let's get moving. We have no time to waste. 
Very nice. Just wish this was available today, instead of 3 years from now. The other company, Nanosolar, looks like it has a good product for the time being.

The current Energy User News has a picture of these rolls as well, but they didn't give the name of the company. They also stated that the current installed cost of PV is $10/watt. So your post is timely as well.
Ten dollars a watt?  I've been following the field (mostly via Home Power and Solar Today) and the figures I've been seeing are closer to $5-6 per peak watt, installed.  (That's for a grid-tied system with no storage.)

PV is falling steadily in price and, given the bounds of physics and the way technology relentlessly pushes toward them, is all but certain to become highly efficient and dirt cheap at the limit.  The same is true of inverters, which are just another application of the same power electronic devices which have had such massive economies of scale brought to bear on them; the marginal cost of inverters and other control & conversion gear is bound to drop steeply as the volume increases.  The one thing which may remain expensive is storage.

I don't think it will matter.  We'll add capacity to feed our daytime loads and discard the power we don't need, then demand-managed uses will be found for the discarded watts.  Lather, rinse, repeat.  This cycle doesn't end until anyone with sunlight can generate all the power they need to have decent creature comforts and be part of the information society.

I'd like it today too, but I can wait 3 years.
The author used an NREL estimator and included storage in the cost. Other quotes I've seen at that rate include storage as well.
I think it's a big mistake to specify storage costs for systems which don't need it.  So long as the value of the energy stored is less than the cost of storage, all it does is make it needlessly costly (and less attractive).

There are different types of storage, too.  A hybrid car must have storage, so this can be charged from external power (if the connection is available) at no additional cost.  An air conditioner can be constructed to make ice with off-peak power; this optional storage is relatively cheap and can take advantage of inexpensive power.  Stationary batteries are quite expensive and even free energy for charging them isn't cheap enough to pay back the costs of storage.

At even 11 cents/KWH, solar PV is cheaper than afternoon peak electric rates.  It would pay to displace peaking generation (and charge hybrids' batteries to displace petroleum) long before it would pay to store power for nighttime use.
I see what you mean about storage and the $5-6 per watt quotes work for me too ;)

I am curious about thermal storage, though, and if you see it fitting in with the solar scenario. I thought that it could since the chiller, without thermal storage, works on partial loads most of the time anyway. If the chillers were running at full capacity on sunny days, they could take care of the building load and be making ice at the same time. As a bonus, the chillers would be running at their highest efficiencies almost all the time and would not necessarily have to be sized at the full building capacity.

The main difference between unloading schemes of today's grid and the solar grid could be that the ice could be used on cloudy days instead of at peak electricity times.
That is exactly what I had in mind.  (Short-term storage of ice is a proven technology; seasonal storage of ice has been tested and found to work during post energy-crisis tests.)

Cloudy days tend to need less cooling, which is a really good match of supply to load. ;-)

I think the most interesting feature is the daily load curve.  Solar generation follows the sun, while A/C loads peak in the late afternoon.  A solar system built for peak-shaving of A/C loads is going to have a lot of excess capacity in the morning.  What to do with this power?  I like the idea of charging plug-in hybrids out in the parking lot; it yields a two-fer.  Ice storage can be used to balance short-term differences between production and demand without the expense of batteries.  A ton of water costs what, a few dollars?  As ice, it will store 288,000 BTU of cooling or ~84 KWh of cooling; at a coefficient of performance (CoP) of 3.0, this replaces the need to store 28 KWh of electricity.  Even lead-acid batteries cost tens of dollars per KWh of capacity, and perhaps $0.15/KWh to cycle.  Compared to a mass of water worth the change in your pocket and which never wears out, the decision of which to use is a no-brainer.
This is a really cool (sorry about the pun) idea. Wish I thought of it first ;)

How about a district chilled water plant based on this idea? I helped with a feasibility study for one a long time ago, but of course, it wasn't based on a solar grid.

Any ideas for heating storage, maybe rock beds? If so, maybe the heating and cooling plants could work in tandom, with the heating based on solar thermal.
Thanks for mentioning it. I heard about either that or something similar a couple of years ago and then heard nothing more. Glad to know it's still coming along.
Actually, you don't have to wait three years - Citizenre - has already achieved production costs low enough to be competitive with or cheaper than retail electric utility rates in 40 US States. They released the following press release today on Business Wire:

Citizenre Introduces its REnU 25 Year Fixed Rate Home Solar Rental Program Making Solar Competitive with Utility Electric Rates in 40 States

WILMINGTON, Del.--(BUSINESS WIRE)--Citizenre’s new REnU 25-year fixed rate residential solar electric
system rental program is the first to allow homeowners in forty states to choose green energy while
eliminating the large upfront investment costs and premiums over power purchased from electric utilities.
The REnU program offers the most attractive terms in the solar industry.
Citizenre Corporation manufactures, pays for, installs, permits, owns, maintains, and operates the solar
photovoltaic system installation. All homeowners are required to do is to pay for the electricity generated
from these panels, at a fixed rate that is at or below their current electricity price, for up to twenty-five
years. REnU customer benefits include:
1) No upfront investment.
2) No waiting for rebates.
3) No headaches with the city and the utility - Citizenre handles the engineering, procurement, and
4) Performance-based contract means homeowners only pay for what is delivered and their total electricity
cost should be less than or equal to their current electricity bill.
5) Actual hedge against future utility price increases. Homeowners “lock-in” their electricity rate for 25
years. Most electric utilities are increasing their rates 5% to 30+% every year.

Citizenre is running a special introductory promotion waiving the normal $500 security deposit requirement
for customers who sign up for the service in December. This makes the move to solar power risk-free and
allowing them to cancel their contract at any time at no cost to them. Orders placed in December will be
installed in September 2007.
The REnU program is very appealing to customers who want to help clean the environment, stem global
warming, strengthen our energy grid, and become energy independent while also saving money. The
program is the single most cost effective method for homeowners to reduce their environmental impact,
reduce their carbon dioxide emissions, and increase their sustainability.
The REnU program is expected to have a significant impact on the Leadership in Energy and
Environmental Design (LEED) green building program for homes.

The six LEED for Homes certification
points for renewable energy are now the six easiest points to achieve, instead of being the six most
expensive and least commonly scored points.
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