This group brings together the best thinkers on energy and climate. Join us for smart, insightful posts and conversations about where the energy industry is and where it is going.


When the Wind Doesn't Blow

Robert Rapier's picture
Proteum Energy

Robert Rapier is a chemical engineer who works in the energy industry. Robert has over 20 years of international engineering experience in the chemicals, oil and gas, and renewable energy...

  • Member since 2018
  • 724 items added with 200,032 views
  • Jun 10, 2014

Hawi Wind Farm

Every morning after I wake up, I have a routine. The first thing I do, regardless of how sleepy I might still be, is slip on my shoes and run a mile. This erases the fog of sleep and gets me ready for the day. As an aside, I can highly recommend a quick run in the morning for just about everyone. The time commitment is minimal, it’s good for the heart, helps with stress, and it kicks the brain into high gear much faster than a cup of coffee can (which I still have later in the morning).

When I am traveling, I will often use a hotel treadmill, and catch up on the news for a few minutes as I run. But when I am in Hawaii, I run outdoors in all but the worst weather. The town I live in — near the north end of the Big Island — is known for the wind. In fact, the school mascot where my children have attended school for the past five years is “Ka Makani”, which means “the wind” in Hawaiian. There is a 10.6 megawatt (MW) wind farm — Hawi Renewable Development Wind Farm  (shown in the picture above) — 20 miles north of where I live.

While the wind there blows enough to support a wind farm, and more often than not I have to run against it during some part of my run, on some mornings everything is dead still. On those mornings, I know I can look to the west and see black smoke rising into the sky.

The average capacity factor — that is the output of an electricity-producing asset over a period of time divided by its maximum theoretical power output — was about 32 percent for wind power in the US over the past 3 years (Source). The Hawi Renewable Development Wind Farm is a little bit better than that at 45 percent, but for the 55 percent of the time that it isn’t producing power, backup is required. Often, intermittent renewable power power supplies are backed up by dirty and inefficient power.

The Waimea Generating Station is located only a few hundred yards from my house. It is owned and operated by Hawaii Electric Light Company, Inc. (HELCO). The plant consists of three 2.5 MW diesel engine generators that are fired on Number 2 fuel oil with a maximum sulfur content of 0.5 percent by weight. Every time I notice that its calm on my morning run, I can always find the smoke rising from these generators. They come on when the wind turbines aren’t spinning.

When people talk about the intermittent nature of resources like the wind and sun, they are referring to the fact that there are times — often unpredictable — when these resources aren’t producing. At 7 am, the world is waking up and demand for electricity is climbing. At that early hour, and with the sun perhaps not yet shining brightly enough for solar power to contribute appreciably, back-up power is needed in areas like my neighborhood that utilize wind power when it’s available.

That is the nature of intermittent resources. People don’t usually think about the fact that if the wind isn’t blowing that an electric utility — somewhere — brings on line backup power. When this happens, for the consumer it is transparent. Their toaster continues to function as it did when the wind was blowing. People don’t realize it’s happening, unless they see it happen (as I did several times this past week on my morning run when I saw the smoke rising).

Good backup or storage options are required for intermittent resources. At times these renewables can be backed up by hydropower, but more often than not they are backed up just like the Hawi Renewable Development Wind Farm — with fossil fuels.

Promising energy storage options are in development. These include batteries, compressed air, flywheels, and hydrogen production. Without economical backup and storage options, renewable power will be unable to reach its full potential. That’s why I have referred to this as The Most Important Problem in Renewable Energy.

Link to Original Article: When the Wind Doesn’t Blow

Robert Rapier's picture
Thank Robert for the Post!
Energy Central contributors share their experience and insights for the benefit of other Members (like you). Please show them your appreciation by leaving a comment, 'liking' this post, or following this Member.
More posts from this member
Spell checking: Press the CTRL or COMMAND key then click on the underlined misspelled word.
Hops Gegangen's picture
Hops Gegangen on Jun 10, 2014


I understand that some data centers are using excess solar and wind to make ice to use later for cooling the servers.

Myself, I sometimes manage my AC to take advantage of natural conditions, such as running it a bit in the morning when it is still cool around the heat exchanger. If I had excess solar during the day, I would over-chill the house a bit.

I’ve also read about using heat and biomass to create methane for later use in power generation.

Smart appliances would also be useful — when the wind blows, run the washer.




John NIchols's picture
John NIchols on Jun 11, 2014

What is the capacity factor for wind during peak demand in Hawaii?

Robert Rapier's picture
Robert Rapier on Jun 11, 2014

I don’t know if I have seen it broken out like that, so I don’t know for sure.

Nathan Wilson's picture
Nathan Wilson on Jun 11, 2014

Wow, I’d love to live on a water-front lot.  Where I live, there is not enough water-front land for parks, much less residential use.  It looks like Hawaii has enough to allocate some from agriculture!

So Robert, do you have any insight into the aversion to (baseload) geothermal energy that Eric reported in this article?

Robert Rapier's picture
Robert Rapier on Jun 11, 2014

double posted

Robert Rapier's picture
Robert Rapier on Jun 11, 2014

There is a very vocal minority that objects to it on religious grounds. They get pretty passionate about it. I used to have a link to a video of a guy explaining his opposition. From a scientific/technical point it makes no sense, but for him and those who follow those beliefs it is a matter of utmost importance.

Robert Rapier's picture
Robert Rapier on Jun 11, 2014

I understand that some data centers are using excess solar and wind to make ice to use later for cooling the servers.”

We actually looked into that for subcooling food during the day.

Nathan Wilson's picture
Nathan Wilson on Jun 11, 2014

Oh well.  Maybe someday reversible fuel cells will be affordable for long-term energy storage.


John NIchols's picture
John NIchols on Jun 11, 2014



    If Hawaii is like other states, peak demand occurs late in the day.  The greatest energy use probably occurs on exceptionally warm days, when high pressure systems settle over the islands and the wind doesn’t blow. In a state the size of Texas, ERCOT reports about a 5% capacity factor during these high pressure events.  The weather patterns and energy demand may be different on islands in the Pacfic.    The grid operator should be able to answer the questions.

Marijan Pollak's picture
Marijan Pollak on Jun 14, 2014

¹Honoured sir, what you write is true, however I have invented combined Power Station that use both intermitent resources and can produce electricity 24\365, giving even double quantity in “Peak Consumption Periods” too. It is called WindSolar P.S.

It can do this by storing energy as heat in Thermal Storage of its CSP Solar, so this way all of available Wind energy can be utilized, not just that much that is required at moment it is. generated…

That covers electricity produced in ” Low Consumption Periods” and enable production of electricity from Wind at full lnstalled capacity. In addition, my new and much more effective wind turbines can produce at least FOUR times more electricity at same turbine diameter and same wind speed, which is tested so far only at 5m/sec. wind speed, but I am quite certain (because CFD simulations show this is so) that my turbine would work same at all speeds of Wind, including 25m\sec. and faster winds, too.  Since I can place 18 times more turbines at space where just ONE high capacity standard  WPS can be situated, that means ot is possible to produce 72 times more  electricity from same Wind, and as I explained, it can be used when required. 

In addition, wind speed of 5m/sec. cannot be used by contemporary model WPSs economically justifiable, since they can produce just 10 to 15% of their rated capacity, and places with such wind is much more common than standardly required 10m/sec. so use of my turbines would open at least 20 times greater resources of Wind than presently known and not yet exploited in full, too!

Regards from Croatia, the Homeland of Engineer Nikola Tesla!

Bentham Paulos's picture
Bentham Paulos on Jun 15, 2014

Mr. Rapier,

I don’t think it is nit-picking to point out that your definition of capacity factor is not correct.

Capacity factor is not a measurement of time. It measures the total output of a generator compared to the maximum theoretical output. Or as the IEEE puts it “The gross energy that was produced by a generating unit in a given period as a fraction of the gross maximum generation.”

A 1 MW wind turbine with a CF of 33% does not produce 1 MW of power 1/3 of the time. Instead it produces 1/3 of the power that it is theoretically capable of producing (333 kW on average) over a time period. It may in fact produce some power 50 or 80% of the time. It may in fact never produce the maximum output of the generator.

Also, your assertion that a wind farm needs a fossil fuel backup is not entirely accurate. In a networked grid, all generators back up all other generators. Since any generator can fail at any time, utilities keep reserves equivalent to at least the largest single failure. So in a regular utility system there is no generation dedicated to “backing up” a wind farm. Instead generators are dedicated to backing up everything, in an “operating reserve.”

Of course, Hawaii is unique, and has many fewer options in maintaining reliability. Fortunately, the growth of distributed generation, demand response, smart grid controls, and storage are improving reliability, lowering costs, lowering pollution, lowering oil imports, and enabling more wind and solar on the Hawaiian system.

– Ben Paulos

Marijan Pollak's picture
Marijan Pollak on Jun 15, 2014

Honored Mr.Paulos, please do not consider it a “Nit picking” or Hair splitting, but there is misstep in Your thinking, assurely nobody would install 1MW generator unless WPS turbine can produce so much electricity from prevailing Wind on location, that is in expected conditions.

It is true that Wind energy required to be available for such results is actually in range close to 7MW, due to low efficiency of contemporary turbine models, but I would say that nobody would buy WPS declared for 1MW at required Wind speed, that would not deliver it, as they would feel cheated for money paid.

Therefore, if Hawai have required Wind 45% of time, they should be able to produce electricity at full installed generator capacity.

In other case You are right, there is no “backup” capacity, as this is normal PS producing electricity, but problem is that they cannot start producing electricity on moment notice, so they are burning fuels even when Wind blows or Sun shines and most of electricity is provided using those resources.

In case of my WindSolar PS, Solar is converting thermal energy to electricity, and it can be stopped when the Wind start supplying electricity and also restarted at once when Wind stops, because its thermal Storage have heat for steam production allways ready. Storing of Sun heat of course can go unimpeded whenever there is Sunshine available, regardless of current electricity production, and so Solar can work 24/365 guaranteed, without need for backup, as it is designed to be fault tolerant.

Regards from Croatia, the Homeland of Engineer Nikola Tesla!



Robert Rapier's picture
Robert Rapier on Jun 15, 2014

“I don’t think it is nit-picking to point out that your definition of capacity factor is not correct.”

I was about to take exception to your characterization of my definition, but I looked at it and I agree that the way I worded it was poor. I will change it to make it clear. 

Bob Bingham's picture
Bob Bingham on Jun 27, 2014

Not a very bright analysis. Most people would pump water uphill while the wind blows and takethe hyrdo energy back when the wind drops.

Mark Heslep's picture
Mark Heslep on Oct 14, 2014

Also, your assertion that a wind farm needs a fossil fuel backup is not entirely accurate. In a networked grid, all generators back up all other generators.”

The two, wind generation and traditional generators are not comparable in that sense.  Cover Hawaii with diesel generators here and there and yes at any given time one may trip, a line may go down, requiring every, say, twenty generators to have one or two spares.  

But with wind generation, the entire island can suffer a wind lull, taking every wind turbine down all at once, regardless of how many are built.  The larger the wind penetration into the grid the larger the problem.  The same thing can and has happened over regions as large as the entire Pacific coast of the US (CAISO and Bonneville all at once), where wind generation falls to 1 or 2% of average for days at a time when a large Pacfic high pressure system moves ashore. 

Mark Heslep's picture
Mark Heslep on Oct 14, 2014

In a state the size of Texas, ERCOT reports about a 5% capacity factor during these high pressure events.  “

Yes, and over longer time periods of measurement, say decades, much lower cap factor events would be expected, say, 1%, and for days at a time.  Therefore, absent the development of some kind of cheap storage, the only alternative is to keep the entire traditional generation fleet inplace as backup, regardless of how much wind or solar is built out.  The result must be enormously expensive: see, e.g. Germany.

Get Published - Build a Following

The Energy Central Power Industry Network is based on one core idea - power industry professionals helping each other and advancing the industry by sharing and learning from each other.

If you have an experience or insight to share or have learned something from a conference or seminar, your peers and colleagues on Energy Central want to hear about it. It's also easy to share a link to an article you've liked or an industry resource that you think would be helpful.

                 Learn more about posting on Energy Central »