From: gary@ke4zv.uucp (Gary Coffman)
Newsgroups: sci.environment
Subject: Re: Solar Power?
Date: 6 Apr 92 15:15:59 GMT
Reply-To: gary@ke4zv.UUCP (Gary Coffman)
Organization: Gannett Technologies Group

In article <m0lWSoT-00036sC@piglet.uucp> dmocsny@piglet.UUCP (Daniel Mocsny) writes:
>In article <1992Apr1.111654.26352@ke4zv.uucp> G.C. writes:
>>A turbine trip at a major central plant is common, when it does
>>happen, there are work around procedures in place and on site 
>>repair personel. That's why large blackouts are so uncommon. On
>>any given day, say 1 in 100 large turbine units are down through
>>either failure or planned maintenance. That usually causes no
>>hardship to grid users.
>
>Sure, because the system has an overdesign factor capable of absorbing
>about as many failures as will happen, say, 99% (or more) of the time.
>
>Nothing prevents a distributed system from having the same safety
>margin.

Not if the system is grid dependent. The problem with most distributed
system approaches is that no customer wants to install the excess equipment
necessary to export power to the grid. Because of economies of scale,
small producers face an inordinately poor return on capital for small
power sales. Therefore there is a strong disincentive to have enough
installed capacity to meet peak needs, much less have export capabilites.
Therefore the grid has no excess capacity to supply the total needs of
customers with breakdowns, so a 1% failure rate leaves 2 million customers
without power.

>On-site repair personnel are not necessary in the distributed system,
>because a site failure has much lower consequences for the grid as a
>whole, and thus a leisurely approach to repair is possible.

A failure has less consequence in general, but it has total consequence
to the customer without power. In central systems, responses to failures
are very rapid and no one customer is without power for long periods. In
a purely distributed system, repair response is much slower, about like
your local CATV installer. Care to make an appointment for a week from
Thrusday, and oh by the way, be sure to be home between 8am and 5pm so
our repairman will have access to the equipment. Meanwhile sit in the 
dark.

>> In a distributed system, a 1 in a 100
>>failure rate of customer maintained generation means 2,000,000 
>>customers are without power at any given time.
>
>No it doesn't. It means 2,000,000 customers are drawing power from
>the grid.
>
>Today, of course, 200,000,000 customers are drawing power from the
>grid, with not much problem. I suspect a grid capable of serving
>200,000,000 customers can probably handle 2,000,000.

Oh it could, if the central plants are operating, and if the central
plants' line crews are out every day maintaining the system. But in
a purely distributed system, the central plants are gone, and so are
the line crews paid by the central plant owners. As noted above, excess 
installed capacity is a bad investment for individual consumers, so 
where's the excess power going to come from? 

>Also, local site failures happen routinely even when every customer
>draws power passively from the grid. That is why we have mobile
>electricians.

Backfeed systems are at least an order of magnitude more complex
than circuit breakers. Failures could leave the customer detached
from the grid. No real harm done, I'll call the repairman next week.
That attitude, when multiplied 200 million times, leads to grid
collapse. Or, the failure could be in the local power conditioning
system. Then the customer has no power to deliver to the grid, and
no means to tap grid power. Call repairman immediately and make an
appointment. Sit in dark. Or the failure could be to local power
producing equipment. Customer switches to grid power and calls
repairman when he thinks he has enough money to pay for repairs.
This attitude, when spread over 200 million customers, leads to
grid collapse.

>>Since they don't 
>>have on site repair people, and no work around backups, they suffer. 
>
>No, their power management computers flip a switch.

Unless of course the failure is *in* the power management computer or
power conditioning equipment. In which case, they sit in the dark.

>>*Every day*. In addition, very complex backfed grids tend to 
>>uncontrolled oscillations in their output leading to *grid* failures.
>>Such grids tend to be chaotic systems for which we have no good
>>control strategy other than rapid disconnects to localize the
>>oscillations. That usually leads to brownout or grid collapse.
>
>This scenario contradicts your earlier claim that customers
>with failed equipment will go without power. If sites with failing
>equipment do not draw power from the grid, there is no feedback, and 
>therefore no oscillation.

The oscillation occurs when the equipment *is* functioning and *is*
contected to the grid. No contradiction. Each site is delivering *to*
the grid a variable amount of power depending on sun or clouds, wind or
calm, whichever "green" generating system they are using. Each site is
demanding power *from* the grid depending on arbitrary choices of demand
applicances at any given instant. With no central regulation, the grid
develops local peaks and sags that oscillate through the grid. Since
the causes of these variations are manifold and random, the oscillations
are randomly started. Once started, they feed on each other in complex
ways through the myriad cross connections of the grid. Nasty standing
waves can form and collapse, blowing grid breakers, wrecking customer
equipment, etc. Avoiding chaotic behavior in the grid is one of the 
nastiest problems in grid management. Distributing generation makes
it worse at a log rate.

>>Since power and control signals *both* travel at the speed of
>>light, it's unlikely that control systems can damp the oscillations
>>without disrupting the grid.
>
>Assuming the grid *does* have feedback, then it will be necessary to
>(effectively) slow down the power signals relative to control signals.
>Local storage combined with local intelligent power management does 
>this nicely. I.e., if a site has a primary equipment failure, it
>switches to stored power, begins shutting down non-essential power
>drains, and communicates its impending need for power to other sites.
>Ideally, all the local control computers should communicate on a 
>network where they would create a commodity market for power. The
>price of power should vary dynamically, reflecting the power available
>on the grid. Each consumer could tell his/her power management computer
>how much power to buy at each price level. Consumers with high-priority
>needs could tell their computers to bid aggressively for power, and
>consumers who could do without would drop out of the market when the
>price got too high.
>
>If the peak prices of power became too burdensome, it would then be
>economical for many sites to invest in increased local storage. This
>would tend to reduce the peak demand for power, and hence the peak
>price.

Chaotic behavior in the grid spreads at the speed of light. It's not
a matter of just dealing with failed equipment. Your market never has
time to develop. Due to the diseconomies of small scale storage and
management, customers would be reluctant to invest more capital than
absolutely necessary to meet *average* demand. If they could afford
peaking capability, they'd have no incentive to be connected to the
grid at all. The grid is there to spread the cost of peak demand among
many users since it's too expensive for each customer to provide the
reserve necessary to meet all his peak demands. Central systems exist
because the economies of scale and the semi-random nature of demand
allow a central supplier to size his plant to meet varying demand at 
a cost less than the cost of each customer providing his own power plant.

Gary
Newsgroups: sci.environment