🚀 go-pugleaf

AES <siegman@stanford.edu> wrote in news:siegman-5AF1F3.09005231072010
@bmedcfsc-srv02.tufts.ad.tufts.edu:

> OT question for any posters or readers of the exchange on emergency 
> power generators appended below:
> 
> I have a 10 kW standard residential solar photovoltaic system on my 
roof 
> (no batteries or other added complexities).  I understand that if PG&E 
> goes down it stops functioning, and more or less why this is.
> 
> Suppose I acquired a small generator and had professionals install the 
> necessary (manual) switching to disconnect my house and the solar 
setup 
> from PG&E and connect them to the generator.
> 
> Once this switch was thrown and the generator fired up, would the 
solar 
> system function normally while the generator was running?  If so, what 
> size generator might be required?
> 
> 

I don't understand your system, to begin with.  If you have no batteries 
to store what the panels make, you have no power on days with no sun.  
Is that correct??  I've never seen a solar system without storage, 
before.  What would you do for lighting at night when the power goes 
down.  Both your systems would be dead, not just the solar.  That 
doesn't make sense to me.

I'd keep the panels loaded charging massive battery banks if I had that 
much money invested in solar panels.  10KW is a MASSIVE array!  There'd 
be a serious 48 or 96 or 144VDC battery house on the property with a few 
KW of 115/230 inverters that would autoswitch the mains from the utility 
to the inverters when utility fails.  You'd never even see the lights 
blink!  With so much solar energy simply going to waste because you're 
NOT storing all its potential just leaving the panels cooking in the sun 
on the immediate load, then going dark when the sun gets low in the sky, 
that's a terrible waste of potential useful energy, unless you're 
selling it to the utility through a reversible meter, which I suspect 
you will tell us is what you're doing.  There'd be no point in the 
investment, otherwise.

I wouldn't buy a generator with so much available power for free.  I'd 
build a battery house with some massive stationary batteries also used 
to power large electric fork lift trucks and quit selling it back to the 
utility for peanuts.  10KW for 6 hours a day, 60KWH on a good day in 
California is plenty to run a fairly good energy efficient home.  If it 
proved to be enough, I'd simply tell PG&E to stuff it!  60 x 20 days 
(guessing an average in sunny California month) = 1200 KWH.  With a 
little conservation and energy efficiency I'd be power company free!

But, if you are determined to put in a genset that will power the house, 
a 20KW propane would be appropriate, I'd think.  Automatic start and 
switchgear for it isn't a huge investment.  It cranks when the power 
blinks, even if it doesn't fail, and puts the load on the genset until 
the power system settles, then shuts itself off after X minutes and puts 
you back on the grid.  I like propane for two reasons.  Natural gas 
would be great, but you live in an earthquake zone where natural gas 
disruptions are an issue as the fault line breaks the gas lines.  A big 
propane tank isn't pretty....well, not until the neighborhood is in 
total darkness and you're house sticks out like a sore thumb with all 
the lights on half the night.  Then, propane tanks are downright 
BEAUTIFUL!  The propane company will automatically keep them topped up 
and you will do nothing to keep them topped up, unlike gasoline you'd be 
hauling yourself.  Diesel is a great fuel IF YOU USE IT OFTEN.  Diesel 
fuel grows black algae and is hygroscopic, collecting water right out of 
the vented air.  When you need it most, if it's been sitting in a 
standby condition, it may not be ready for use loaded with algae that 
required constant maintenance.  Propane can sit in a tank until your 
kids are grandparents and crank the genset immediately.  It doesn't "go 
bad" like gasoline or diesel and if the gas lines downtown rupture and 
the neighborhood has no natural gas pressure, you STILL ARE RUNNING on 
propane.  A 15-25KW propane genset with autostart and switchgear would 
be great for your system.  Compared to 10KW in solar panels, it's 
downright cheap!  Your electrical contractor can do a power use survey 
and recommend a suitable system.  Mine is just a guess.  Electrical 
Engineers don't, usually, bite and most are housebroken.  I'd guess 
there are plenty of them at Stanford that have some knowledge of 
PRACTICAL systems that could plan it.  If the EE department can be 
persuaded to make your electrical system a "student project", you may 
even get the Federal Government to fund it through the school.  I used 
to teach electronics technicians in a technical college on a much lower 
level than Stanford.  The Air Conditioning and Refridgeration School 
made a student project of our house and I ended up with a steal on 7 
tons of overkill for the price of 2 tons, neatly installed by the 
students.  Check the school.  Plenty of grants going around.  Make it 
say something about "Global Warming" and "Saving the Planet" and it's 
sure to be approved, even if it's a new toilet.



-- 
iPhone 4 is to cellular technology what the Titanic is to cruise ships.

Larry