[RE-wrenches] Apparent power

[Ray Walters]

I was just wondering about this same issue: of inverters being used to 
support the grid.  Just as charge controllers reduce their output 
current as the voltage reaches absorption voltage, I was thinking that 
GT inverters could do the same thing, instead of just shutting off, and 
not reconnecting for at least 5 minutes.
In Hawaii, with PV penetration on the grid as high as 15%, the utility 
asks us to widen the voltage operating window beyond IEEE specs, as 
they've found that when they have a low voltage line condition, the PV 
systems actually help, and they don't want them to shut off too soon and 
add to the problem.
I could see a new generation of inverter specs beyond UL1741,  that was 
part of a smart grid controlled by the utility.  They could extend the 
operating window when needed to keep the grid more stable.  As subsidies 
dry up, this could be a future selling point, especially if it offered 
the customer a more stable conditioned power supply.  Also be nice for 
the customer to get paid extra for this emergency peaking capabilities, 
just like the big generating facilities.  It might even make GT w/ 
battery backup more cost effective, if you could sell some battery 
amp-hrs at $1/ kwh every once in a while.

Ray Walters

On 2/4/2012 7:05 PM, boB at midnitesolar.com wrote:
>
>
> Sounds like a voltage source (and sinking) inverter to me.
>
> These types can cause current distortion which the UL1741 / IEEE 1547 
> specs try to prevent.
>
> Apparent must be able to  turn that mode on and off I would imagine.  
> It's not too difficult to do.  No wonder
> they talk about micro-grids.
>
> The old Trace SW series was a voltage source inverter, even when grid 
> tied and is basically why they had
> to add that extra inductor box between SW and the grid when selling.  
> It could actually help the grid wave-
> form voltage if it was distorted because of non-linear loads.
>
> boB
>
>
>
>
>
> On 2/4/2012 5:26 PM, Comet Systems wrote:
>> As I understand the issue they claim to be able to address, the 
>> utilities often need a source of reactive power close at the system 
>> delivery points, the customer sites, because reactive power does not 
>> transmit well through the lines and transformers and uses up 
>> transmission resources better used for real power. The reactive power 
>> is used as a method of voltage control.
>> Therefore, it is reasonable that the utilities would pay a premium 
>> for a reactive power source which would be close to the customers and 
>> under their control. The idea has some merit and could be a 
>> significant direction for solar pv, but whether an electronic 
>> inverter can adequately generate reactive power at will, to act as a 
>> compensation device and whether that is the highest and best use for 
>> that power source is to be demonstrated. Interesting idea, though.
>> -- 
>> Chris Mason
>> President, Comet Systems Ltd
>>
>>
>>
>
>
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