power quality problems [RE-wrenches]

[Joel Davidson]

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December 26, 2006, I asked the members of 
distributed-generation at yahoogroups.com There is much discussion in the 
United States about the perceived difficulty managing wind and solar power's 
variable input to the electric utility grid. Yet Japan, Germany, Denmark, 
the Netherlands, etc. have very dense distributed wind and PV in some 
locations and seem to be managing variable grid input successfully. Are 
there any reports on how DG variability is managed?

The discussion went on until about 1/17/07 with several interesting links 
and can be reviewed at 
http://tech.groups.yahoo.com/group/distributed-generation/

In summary, 15% of Denmark's electricity comes from wind power generators. 
Germany has more wind generated electricity than any other country. Both 
countries integrate variable wind power smoothly into the electric grid. 
Japanese engineers report that locales with a lot of DG PV actually have 
more stable grid power.

This is not to say that the windfarm in HI is not a problem. A little data 
acquisition will identify the culprit.
---------

One person from Scotland replied:
A few anecdotal points about Denmark:

- Electrically, Denmark is managed in two halves: Eastern and Western.

- "Copenhagen is part of Sweden" said one Danish colleague!   In other 
words, interconnectors are an important part of energy balancing in Eastern 
Denmark.   Nordpool operates right across Scandinavia, and Norway 
contributes lots of balancing energy from hydro to the rest of the market.

- Western Denmark does have some grid constraints, and the huge presence of 
wind does take careful balancing.

- Denmark has 50% CHP penetration, with lots of plants of every conceivable 
size.   The population, and dispersion, of small generators is massive. 
The smaller generators participate in system balancing to a greater extent 
than in other countries.   Typically, Danish CHP (district heating variety) 
is equipped with large hot water stores, so the heat load and the 
electricity demand can be partially decoupled.   This allows the CHP to 
participate in energy balancing.

- As Denmark was an early adopter of wind energy, I expect they would have 
more reactive power problems than would be encountered in an area populated 
with modern machines.   I believe that Germany contributes reactive power to 
Western Denmark but I don't know how critical that support is.

About Germany, I have heard of two reasons why balancing of wind power is 
seen as problematic:

(1) wind is heavily concentrated around the north sea coast, so there is 
little geographical spread effect to smooth out the output changes.   Isn't 
Germany still the no.1 wind power producer worldwide?  So that would be a 
big effect.

(2) until a few years ago, the four transmission system operators (who also 
owned the large thermal stations) were not allowed to invest in wind energy. 
It's been suggested in the energy press that this made the TSOs dislike wind 
energy more than they might have done if it weren't a direct competitor.   I 
understand the rules have changed since then, so hopefully that isn't true 
any more, if it ever was.

All anecdotal and some hearsay; others will have more accurate information. 
But in short, despite the fact that Denmark and Germany lead the world in 
wind energy, neither country has fallen off a cliff.
--------------

One person working for the Danish TSO (that would be an ISO in the States). 
That is true that Denmark is challenging the variability of wind and 
dispersed generation every day. There are many controls which must be and 
are activated to operate such a complex power system as ours. Among these 
controls are the market mechanisms, an AGC (what we call an LFC in the UCTE 
system), strong grid connections for trading power with the neighbours, 
control of power plants etc. There is a challenge, yes, but so far it is 
working here and we expect more wind and dispersed generation in our and our 
neighbours' systems, so it has to work.
---------------

Email me off-list f you would like a copy of the papers written by the 
person working for the Danish TSO.

Joel Davidson

----- Original Message ----- 
From: "Todd Cory, Mt. Shasta Energy Services" <toddcory at finestplanet.com>
To: <RE-wrenches at topica.com>
Sent: Thursday, July 26, 2007 6:38 PM
Subject: Re: power quality problems [RE-wrenches]


>
> This brings up a question I have long held, namely at what percentage of 
> renewables being added to an electrical grid, will the ability of the 
> utility to regulate the grid become ineffective? This is probably what is 
> going on with the scenario in Hawaii.
>
> Todd
>
> Marco Mangelsdorf wrote:
>
>>We appear to be having power quality issues with our local utility.  I've
>>replaced the grid-tie 4 kW inverter twice now and my customer is still
>>seeing the bugger trip off-line frequently during the day.  There happens 
>>to
>>be an 11 MW windfarm not more than 10 miles from the site and I know that
>>frequency drift is an issue, so I have widened the frequency window of the
>>inverter (with the utility's knowledge and approval).


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