From: gary@ke4zv.uucp (Gary Coffman)
Newsgroups: sci.energy
Subject: Re: SOLAR efficiency
Date: 30 Sep 92 10:27:38 GMT
Reply-To: gary@ke4zv.UUCP (Gary Coffman)
Organization: Gannett Technologies Group

In article <1992Sep28.213033.1123@michael.apple.com> ems@michael.apple.com (E. Michael Smith) writes:
>In article <1992Sep24.005801.12643@ke4zv.uucp> gary@ke4zv.UUCP (Gary Coffman) writes:
>>
>>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....

Well, on the flip side, my central unit, with a SEER of 10.6 can
bring my brick house with white roof and tree shading back down to
68 degrees after a 90 degree day in about 10 minutes, using about
2 kWh in the process. Meanwhile your window unit has used about
7 kWh keeping the house cool all day. 

>>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...).

Keep then in the fridge. That's where I store film. It's a lot cheaper
to cool a little box than an entire house.

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

Of course it does..that's the whole point of this exercise, cost 
minimization with utility maximization. Right now solar electric
doesn't fit. Passive solar does in many cases. That's why my house
is surrounded by oaks and maples, why I have a white roof, and why
I use lots of good insulation including storm windows year round.


>>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...

But not a very good one.

>>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.

While I'm not a power systems control expert (no kidding) I've read enough
to be dangerous. It appears that conventional generation has inherent
feedback that helps with dynamic stabilization of the grid. When several
generators are connected together *across* the grid, the dynamics get
confused because of the speed of light delays in the phase feedback.
This can result in huge spikes and sags in the voltages propagating 
across the grid. Electric current flow is not instantaneous and grids
are large. The control systems have to be designed to compensate for
this. With an unknown number of generators supplying power in unknown
quantity at unknown times, grid behavior becomes chaotic and unpredictable.
By contrast, load demands all propagate to a single central source with
inherent damping, making for a nice stable system. 

When grids are interconnected, the preferred method is through an EHV
*DC* circuit that isolates the phase response from one grid to another.
This keeps the two generation systems from getting into a contention
war and simplifies the control problem to one of managing the inverters
on each end. That's still not simple, but it's managable.

>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

Yes I'm presuming exactly that. While intra-regional interties exist,
inter-regional ties aren't practical on the scale required. The losses
are too great for transcontinental tie lines without superconductors,
and the grid management problem would be incredible.

>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 ...

Daytime temperatures do moderate a bit, but humidity reaches, you guessed
it, 100% when it's raining. At night, the temperatures don't fall as much
due to the trapping effects of the clouds and it becomes oppressively hot
and sticky. AC is mandatory precisely at the time of the evening residential
peak. Georgia Power says they reach their peak demand at 7pm. That's when 
folks get home and fire up their electrical loads. Office lighting and cooling 
loads don't drop significantly until the cleaning people leave at around 
midnight, and industry runs all night. The major variable load is residential 
and that's tied to the times people occupy their homes. Note that the summer 
peak *used* to be around 2 pm, but that's changed with the near universal use 
of home air conditioning and energy conserving setback thermostats. The winter 
peak is between 5-11 pm as electric heating systems add to lighting loads.

>>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...)

Most utilities maintain a modest *emergency* reserve, about 1000 MW,
for plant trips and the like, but they normally *schedule* plant
outages for maintenance and use their normal peak capacity in the
off peak time to make up the difference. Plant that sits idle waiting
to serve emergency trips is not producing revenue. Plant that shaves
peak and responds to scheduled off peak maintenance needs is generating
billable revenue. Utilities don't like to tie capital up in non-revenue
producing emergency plant, but it's no problem to build revenue producing
peak capacity. With a large shift from central peaking to distributed
solar peaking, the amount of non-revenue producing plant must increase
to take care of non-peak maintenance needs. This can be partially addressed
by the Public Service Commission allowing idle plant to be counted in the
base rate, but that means higher utility bills for the consumer. So far
the Ga PSC hasn't allowed idle plant to be counted in base rates.

Gary
Newsgroups: sci.energy