From: ems@michael.apple.com (E. Michael Smith)
Newsgroups: sci.energy
Subject: Re: SOLAR efficiency
Date: 28 Sep 92 21:30:33 GMT
Organization: Apple Computer Inc, Cupertino, CA

In article <1992Sep24.005801.12643@ke4zv.uucp> gary@ke4zv.UUCP (Gary Coffman) writes:
>In article <1992Sep22.032733.18172@michael.apple.com> ems@michael.apple.com (E. Michael Smith) writes:
>>In article <1992Sep18.152316.18452@ke4zv.uucp> gary@ke4zv.UUCP (Gary Coffman) writes:
>>
>>>Without
>>>large improvements in the cost and efficiency of residential solar
>>>electric storage, or drastic changes in lifestyle, individual solar
>>>electric systems make little sense for most people. The Sun doesn't
>>>shine at night when most residential energy use occurs.
>>
>>This I completely disagree with.  If I had solar A/C available to me
>>it would be on in exact co-relation with solar incidence and would be
>>used to keep the house cool all day SO THAT there would NOT be a PEAK
>>at 7PM when I got home and turned the A/C on ...
>
>Unless your home is very unusual there isn't enough thermal inertia
>in the structure to make cooling while the building is unocupied
>worthwhile. 

My home is a VERY ordinary stucco (boy, can you get stucco! ;-) house.
It has boring drywall interior walls.
It has boring bath & kitchen tile.
It has ALOT of heat storage capacity...

Never underestimate the heat storage capacity of several tons of 
stucco, drywall, insulation, wood, tile, composite shingles, ...

If we don't turn the A/C on until 7pm, we will still be sweltering
at 10pm (and sometimes later...).  If we turn it on at about noon,
the house stays comfortable all day long.  Admittedly, this is with
a little wall unit, but then again, it is accurate testimony to the
expected behaviour of a smallish solar powered system....

>That's the whole reasoning behind setback thermostats.
>In the daytime, when no one is home, there's no reason for a house
>to consume power. 

Unless you have NO photographic materials you care about, there
is more than ample reason to keep your house at 74 or less all day long.
At temps over 85 F, photos degrade at an alarming rate...  Ditto for
some other household archives...  I'd rather keep the house cool,
while not sucking down a huge peak pulse of kW-hrs when I get home,
and have my 'stuff' age well (my old cabernet, especially...).

Solar exactly matches the best way to run my household.  It just costs
too much.

>Only if you have a *storage* system does it make
>sense to pump heat while the structure is empty.

The house IS a storage system...

>>Also,  a home system could sell power at peak times to the commercial
>>users and buy it back in the evening when the residential customer
>>wanted it.  Peak happens at mid day, even if residential peak doesn't
>>(a postulate I've seen no evidence for, BTW) so home solar with grid
>>exchange would make sense anyway.
>
>For anything other than trival amounts of power, such a grid is
>dynamically unstable. 

I'd expect that some simple intelegence in the design would prevent this.
For example, if the home systems were set to stop feeding into the grid
at some (stochastic) point between 118 and 121 VAC, there would be an
inherent sheding of supply when an excess was starting to show.  Adding
a trivial communications capability and a trivial microprocessor would
let the utility tell the local systems if there power was desired right
now or not.  The fact that the power is generated when peak demand 
exists also argues for inherent stability, since there were be little
doubt that demand for the power existed...

>Large scale residential power sell backs
>would be a control systems nightmare. 

The biggest problem I see is that the systems today look to the power
line to decide if the line is live and if they are in phase or not.
With a large number of 'independents' the control feature provided
by a central big generator could be 'lost in the crowd'.  Given that
we are talking about a 20% of load (max) scenario, I'd expect this
to be managable (though it is likely to take something more than the
present designs in terms of communications with the central authority).

>Not to mention the extra
>cost of the conditioning systems that are required for matching 
>of frequency, phase, and voltage to the grid. 

These are part of the home system and are required for grid connect.
They are paid for by the home system owner.  They are part of the cost
of the solar plant.  If the plant isn't cost effective with these factored
in, then the home system owner won't grid connect and the question is moot.

>On a scale of hundreds
>of suppliers the grid would be controllable, on a scale of thousands 
>the grid would be squirrelly, on a scale of millions, grid disconnects 
>would be very frequent as dynamic loads and generation distributed over
>the grid kicked in and out. 

Interesting speculation.  Do you have a scenario in mind that supports
this?  I'd expect the control theory folks to be able to handle this
with only a moderate increase in information flow over that used today.
Heck, something like 60%+ of houses have cable TV feeds already.  How 
much control info could be sent to the local ($10-$100) microprocessor
over just 1 TV channel of bandwidth?  

>It's hard enough to control a grid with
>only two generating stations feeding it. With many the situation grows
>out of hand rapidly as standing waves shift rapidly on the transmission
>lines.

With many extremely small generators that act, by force of nature,
in unison and with long lead times (the sun only moves SO fast, and
even fast moving clouds take hours to cover a region) I'd be highly
surprised if standing waves were an issue ...  The 'control problem'
should in fact (due to the coincidence with peak demand) amount to
a simple reduction in apparent demand in the residential section of
the grid.  (A state I HOME the utilities can handle already!)  That 
some fraction of the houses were 'selling' power to their neighbors 
via the grid and that the displaced central generators would be able
to supply commercial users shouldn't even be a visible feature.  Or 
were you invisioning a scenario where the penentration of solar into
the residential market were so great that the ENTIRE residential demand
could be met mid-day by solar, with a net outflow from the residential
areas into the commercial areas?  That is a degree of adoption that
exceeds even MY wildest dreams ...

>>>Practical storage systems are the key to smoothing peak demand.

>>Yes, but it is also true that a solar electric generation plant
>>would reduce the need for PEAKing capacity in that it provides
>>power at exactly those times when AGGREGATE demand is highest.
>>Can you say fungible?  There, I knew you could ...
>
>No it would not reduce peak capacity requirements. There would still
>be cloudy days, like when Andrew crossed the South and left us all
>under thunderstorms for several days. 

Pardon me, but I was under the impression that Andrew, as big as it
was, didn't cause the entire SunBelt to be clouded over!  Are you
presuming that there will be NO sales of power from Calif., Ariz., Texas,
et.al. to the SouthEast when there is a hurricane?  Also, the last time
I was in the east in summer, there was a noticable decrease in AC needed
when it was raining.  Yup, still warm and humid, but not the same as
when the rain stopped, the sun came out, and it was REALLY HOT and REALLY
HUMID.  So even with the postulated storms, I'd assert that there is 
a reduction in demand during the clouded phase as compared with the
sunny phase that follows it.  Think a little bigger on the power 
sharing front ...

>So the same capital investment
        ^^^^
>in peaking capacity must be maintained. 

No, SOME, but not the SAME.  There would be a need for some small
residual completely dispatchable peaking plant to cover spikes and
disasters, but the quantity would be reduced.  Today we have enough
to cover the projected electricity consumption plus some margin for
random plant failures.  In the future the same would hold, but the
projected electricity consumption would appear lower to the extent
that solar chopped off the peak demand.  To the extent that solar
was less reliable than other plant, the required stand by power for
a plant outage would have to be a larger fraction that at present,
but it is still a fraction.  ( I would assert that on a continental
scale, solar would be a much more reliable power source than you 
give it credit for, though with a larger need to ship power between
regions due to local weather.  To the extent I'm right, that 'fraction'
could be rather small...)

>Peaking capacity is also used
>when baseload plants are down for maintenance. 

And it could still be so used.  If you need to have a nuke worth of
disaster coverage, you have a nuke worth of maintenance coverage or 
a nuke worth of 'loss of sun' coverage.  The 'loss of sun accident'
becomes just another term in your probability formula for determining
the level of standing reserve to plan.  At present power companies
have plans in place for what to do when they have one nuke down for
maintenance, it's high noon, and another 2 scram.  The same plans would
hold, but it would be 1 scram and 1 loss of sun ... and the sun loss would
have a more gradual onset ...

At high noon, all your peaking plant other than emergency reserve is
busy supplying demand and is not available for maintenance or disaster
use.  If you had solar covering that noon demand, you could have less
peaking plant, but would still need the same emergency reserve capacity.
That the emergency reserve would be used more often due to loss of sun
is a possible condition.  It is also possible that the utility would 
just by power from a neighboring state.

>What would be missing
>would be the routine peaking charge that makes peaking capacity profitable
>to build. 

No again.  What would happen is that as solar penetrated the market
for peak capacity, it would satisfy some of that demand and start a 
price reduction.  That price reduction would also stop the penetration
of new solar plant until the next round of price decreases for solar.
ONLY when solar was cheaper than ALL other peaking capacity would there
be no incentive to build ANY other peaking plant.  That would also be
the point when solar was starting to be cost competitive with baseload
plant (by definition, if solar is cost competitive with ALL peaking plant
it is only undersold by baseload).  At that time, the solar supply hump
would start to look like a mis-feature and the price for mid day power
would drop even further.  Another way of looking at this is that the 
mid day power price would approach baseload prices *and the nightime
rates would rise* to reflect the need to use peaking plant to supply
the non-solar nightime peak.  Think of solar as reduction demand rather
than contributing supply and I think you'll get the picture.

If demand were suddenly less mid-day and greater at night, we would
have peak pricing at night and low baseload pricing mid-day.  The 
present conventional peaking plant would be used to cover that evening
peak.  Now ask me how likely I think it is that solar is going to be
cheaper than Nukes or Coal in my lifetime ...

>So utilities would either have idle capacity costing them
>capital, 

As they do today.

>or they would take a chance, not build enough peaking capacity,
>and let the rolling blackouts begin. 

As they do today.

>Neither would be a happy choice for
>the ratepayers.

As it is today.

The only difference that solar makes to the problem is that it takes
the present mid day peak and chops it off.  It MAY add some degree of
lower reliability of supply, but I don't think so when looked at on a
continental (and likely on a regional) basis.

Bad planning would still be bad planning in either case.
-- 

E. Michael Smith  ems@apple.COM

'Whatever you can do, or dream you can, begin it.  Boldness has
 genius, power and magic in it.'  -  Goethe

I am not responsible nor is anyone else.  Everything is disclaimed.