[ExI] Small scale solar payback time (was Re: Planetary defense)

[Keith Henson]

On Fri, May 13, 2011 at 12:01 AM, Eugen Leitl <eugen at leitl.org> wrote:
> On Thu, May 12, 2011 at 04:14:12PM -0700, Keith Henson wrote:
>> On Thu, May 12, 2011 at 3:29 PM, Kelly Anderson <kellycoinguy at gmail.com> wrote:
>> > On Thu, May 12, 2011 at 9:49 AM, Keith Henson <hkeithhenson at gmail.com> wrote:
>> >> Ground solar currently has an energy payback time of 2-4 years.
>> >
>> > Where does this come from? It is certainly not the case for small scale solar.
>>
>> ^ "What is the Energy Payback for PV?" (PDF). National Renewable
>> Energy Laboratory. http://www.nrel.gov/docs/fy05osti/37322.pdf.
>> Retrieved 2008-11-24.
>>
>> If you say that's not the energy payback time, what is?  I.e., how
>> much energy does it take to make and install PV vs the average power
>> production per day?
>
> "Life cycle assessment and energy pay-back time of advanced photovoltaic modules: CdTe and CIS compared to poly-Si", by Marco Raugei, Silvia Bargiglia and Sergio Ulgiati at Energy Volume 32, Issue 8, August 2007, Pages 1310-1318
>
> http://www.civil.uwaterloo.ca/beg/Downloads/NREL_PV_Embodied_Energy.pdf

See Figure 2 of the above cited paper.  .9 year is the bare PV, put a
frame on it and it goes up to just short of two years.

Payback time is significant because that's the time it takes to get
back the energy that you put into making and installing the PV.  In an
energy constrained situation (like Japan) it would take the whole
output of energy for two years to switch to this form of solar power.
(And Japan is worse than Europe for clouds.)

> EROEI of >40, energy payback time (which is not relevant,
> EROEI integrates over lifetime, energy payback doesn't
> contain total energy harvested over lifetime) of under a year.
>
> "Update of PV energy payback times and life-cycle greenhouse gas emissions" V. Fthenakis, H.C. Kim, M. Held, M. Raugei and J. Krones, 24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany

It's not on the web, but I bet you it's no better.  The frames alone
have a year payback.

> etc.
>
> I think SPS will have a pretty tough competitor, as in 10-20
> years both the ROI and EROEI will be untouchable.

It's about ten times as short a payback time, which is reflected in
the price, 2 cents/Wh vs at least 20 cents per kWh, and you don't need
storage for space based solar power.  (If it cost a small multiple
more more or has a substantially longer energy payback time, then I
don't think solar power from space is worth doing at all.)  This
really gets reflected in the cost of synthetic transport fuels, $50
per bbl vs $410 per bbl.  Long term, nobody except the very rich
travels on ground based solar.

StratoSolar might be even better than SBSP.  Based on materials
(Steel, aluminium  cost, it might get down to 1.5 cents per kWh.  The
front end demonstration cost are a lot lower too.  But the engineering
is really hard, mostly because of wind.  Wind forces go up as the
square of the velocity so the design of the main concentrator is
dominated by the fact it must be folded up into an aerodynamic shape
for a week out of two years.

StratoSolar gets 24 hour power for an incremental cost of 1/10 of a
cent per kWh.  It uses 35,000 cubic meters of firebrick for thermal
storage at 1400 C.  At that temperature a firebrick has more energy
per kg than a lithium ion battery.

I am not hung up on either of these, if someone has a ground solar
method that is less expensive an/or pays back faster I will support
that.

The US and Europe can probably get along on what they have till the
singularity.  But if Japan will freeze in the dark unless they go back
to nuclear or take a radical step like SBSP.

Full blown nanotechnology will certainly give us energy at any price
we want.  But it's not entirely obvious what kind of "economy" might
exist post singularity.

Keith

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