The Ergosphere
Thursday, March 31, 2005
 

Forty-two

To get the right answer, you've got to ask the right question.

I think that people have been asking the wrong questions about wind power.  As Randall Parker notes, wind is not a power source which can be turned up or down according to the desires of the users; you either grab and make use of it when it's blowing, or you do without.

People have been asking how much other grid generation could be replaced by wind.  The answer is "as things are now, not much of the total", but I think this is the wrong question.  A better question is, "What uses can wind power serve, and what else might we need to make it serve them?"

Uses of wind-electric power

Offhand, I can think of three major categories of uses for intermittent, non-schedulable electric power sources like wind (which are not mutually exclusive):

  1. Produce power to allow other generation to be turned down, to reduce fuel consumption and save wear and tear.
  2. Produce energy for storage.
  3. Produce energy for uses which currently do not use much electricity, but can take advantage of the underutilized supply and idle grid capacity.

Storing electricity is one of the most expensive things which can be done with it.  One strategy for storage is to convert the electricity into the desired product and store that instead.  Consumers and electric utilities have used this system to good effect for years:  some consumers who use electric water heaters have them on timers which switch them off during peak periods, and some larger users of air conditioning purchase off-peak electricity at night to make ice which is then used for cooling when electric costs are higher.

The applicability of these possibilities to wind power is questionable.  Across the cold north, winds blow strongest in the winter rather than during the air-conditioning season and a great many users heat water with gas rather than electricity.  After motor fuel, the greatest consumer of fuel in the average northern household is space heat.  What could wind power do to help with that?

This, of course, means Back Of The Envelope time....

What can you do with it?

Assuming the following:

At the low end, the total wind energy delivered per heating season is 2916 kWh (9.96 million BTU); at the high end, it is 6804 kWh (23.2 million BTU).  Here's a grid of the per-household heat production for various figures:


Capacity factor
Rated power 25% 30% 35%
3 kW  9.96 mmBTU/yr   11.9 mmBTU/yr   13.9 mmBTU/yr 
5 kW  16.6 mmBTU/yr   19.9 mmBTU/yr   23.2 mmBTU/yr 

Here's a table of the fractional heating fuel displacement possible using wind electricity in simple (cheap) resistance heaters:


Capacity factor
Rated power 25% 30% 35%
3 kW  21% savings   25% savings   29% savings 
5 kW  35% savings   42% savings   49% savings 

These figures are encouraging.  Even a 21% reduction is quite a bit compared to current gas needs; slashing requirements by 49% would be phenomenal, and eliminate the prospect of gas shortages for some years to come.

Someone's bound to ask if 5 kW of wind power is too much of a good thing, supplying more energy during gales than could be used.  Well, maybe... but after you subtract 1 kW/household average for other electricity, and recognize that the periods of highest wind are also the periods of greatest heat loss through drafts, it doesn't look as if overheating is a serious threat during the winter.  The bulk of that 49% savings would likely be realizable either in saved fuel at generating plants or saved gas at homes and businesses.

Would we actually dump that much electricity as heat?  Probably not; it would make more sense to turn down other powerplants and use the wind-generated electricity to run lights and motors (or charge cars) before running it to resistance heat.  But not all powerplants can follow rapidly varying loads or compensate for fast ramps in other capacity, like wind farms; this would require having enough generation on-line to carry the system through the short-term lulls.  If any overage can be used to make space heat or hot water that we'd be using anyway and avoid the need to burn fuel for that purpose, every bit of wind power can be used productively even if it cannot be scheduled or accurately predicted; the only abilities we need are to transmit it and make the load follow the gusting wind.

The control systems required to perform such load management would be useful for other purposes as well:

What happens if you combine this wind-power system with widespread home cogeneration systems and plug-in hybrids?  I'm going to re-do the scenario from cogeneration@home using the 3 kW/25% and 5 kW/30% wind power figures from the above list, and with DHW heat requirements added.

If the house requires the same 4320 kWh for its own consumption and the car consumes 2520 kWh, total electric requirements are 6840 kWh for the season or 38 kWh/day.  The 3 kW wind system at 100% capacity supplies 2.7 kW (64.8 kWh/day) or 26.8 kWh in excess of electric needs.  Further assuming that:

Fuel

Old
 consumption 
New
 consumption 
Δ consumption  Cost/unit
Δ cost
CO2 emission
 per unit
Old emission New emission Δ emission
Wind
(3 kW, 25%
capacity)
0
2916 kWh
+2916 kWh


0


0
As electricity
0
1710 kWh
+1710 kWh
$0.05/kWh
+$85.50
0


0
As heat
0
41.2 mmBTU
(41.2 therms)
+41.2 therms
$0.02/kWh
(off peak)
+$24.12
0


0
Electricity,
coal-fired
4320 kWh
0
-4320 kWh
$0.08/kWh
-$345.60
3.4 lb/kWh
7.34 tons
0
-7.34 tons
Natural gas
575 therms
575 therms
0
$0.60/therm
0
11.52 lb/therm
3.31 tons
3.31 tons
0
Gasoline
288 gallons
0
-288 gallons
$2.00/gallon
-$576.00
19.4 lb/gallon
2.79 tons
e
0
-2.79 tons
Fuel oil
0
43.6 gallons +43.6 gallons
$2.00/gallon
+$87.20
19.4 lb/gallon
0
0.42 tons +0.42 tons
TOTAL



-$724.78

13.44 tons
3.73 tons
-9.71 tons

Fuel oil consumption in this case is reduced to less than 40% of the original, and total petroleum consumption is cut by almost 80%.

What would happen if you could get 4.5 kW/household at 30% capacity factor?  On the days with wind the excess electricity creates 280,000 BTU/day of heat, or about 6% more than the average combined space heat and DHW demand.  It's likely that windy days are also days of high heat demand, so I will assume that all of this heat can be used and counted against total annual heating requirements.

Fuel

Old
 consumption 
New
 consumption 
Δ consumption  Cost/unit
Δ cost
CO2 emission
 per unit
Old emission New emission Δ emission
Wind
(5 kW, 30%
capacity)
0
5832  kWh
+5832 kWh


0
0
0
0
As electricity
0
2052 kWh
+2052 kWh
$0.05/kWh
+$102.60
0
0
0
0
As heat
0
15.1 mmBTU
(151 therms)
+151 therms
$0.02/kWh
(off peak)
+$75.60
0
0
0
0
Electricity,
coal-fired
4320 kWh
150 kWh
-4170 kWh
$0.08/kWh
-$336.60 3.4 lb/kWh
7.34 tons
.26 tons
-7.09 tons
Natural gas
575 therms
505 therms
-70 therms
$0.60/therm
-$42.00
11.52 lb/therm
3.31 tons
2.91 tons
-.40 tons
Gasoline
288 gallons
0
-288 gallons
$2.00/gallon
-$576.00
19.4 lb/gallon
2.79 tons
0
-2.79 tons
TOTAL



-$776.40
13.45 tons
3.17 tons
-10.28 tons

In this case the remaining electric demand cannot be quite satisfied by the cogenerator without discarding heat, so a small amount of electricity is generated from coal again.  Annual cost is down slightly,  carbon emissions are down more than 75% despite the renewed reliance on coal, and petroleum consumption hits zero.  Gas consumption drops 12%.  If the DHW supply was heated by the cogenerator, coal use would be eliminated at the cost of somewhat greater gas consumption.

Conclusions

Despite being unreliable and unschedulable, it appears that wind could be used to offset fossil fuel consumption quite easily.  In the context of current systems it can be used to reduce fuel demand at gas-turbine plants until they shut down; beyond this point it could be used for space heat and domestic hot water, offsetting gas consumption there as well.  In a near-future system using cogeneration for all space heat needs and grid-charged hybrid vehicles for transport, the availability of wind could:

  Is it worth using?  Looks like it to me.

UPDATE 5/23/05:  Corrected typo in third table.  Had to catch that one myself.  So much for the eyeballs of the web as fact-checkers. ;-) 

Comments:
Where did you get this: "The available wind power per household is either 3 kW or 5 kW, "?

Can you think of another way of stating what you meant where it might make more sense or be more precise? As it stands, it makes a shaky premise for an argument.
 
I disagree.

In Europe the costs are:

0.11 €/kWh for Wind energy

0.06 €/kWh for electricity produced from coal and combined cycle gas powered units, whose efficiency is far better

0.03 €/kWh for Nuclear Power Stations

(and around 0.60 €/kWh for Solar Electric Power)

The figure for wind energy is a regulated fixed price. The two following come from rough spot prices in the Energy market. How can compete that expensive energy? The government, on grounds of environment protection, forces the electricity distributors to buy as much as it is available and the grid is able to handle without becoming unstable, thus, the EPCO's and partners that have built all those windfarms have their production subsidized. Is it fair?

In a free market, only a few locations would be able to produce competitive wind power, and even then, it would be a risky business.
 
Anonymous #1: Those are what are known as an "assumptions", which is why I ran through with two different ones.  If you think they are unrealistic, try re-doing the calculations with something you like better.

Anonymous #2: Wind power in the USA is quite a bit cheaper. An AWEA page with a copyright date of 2000 lists figures from 6.56 cents/kWh down to 4.35 cents/kWh.  The assumptions appear to be that both money and construction are cheaper in the USA, and the absence of huge subsidies means that the high-cost sites will not be used.  This will keep the average down.

If you think the economics would be terribly different with non-surplus wind power going for a higher price, go ahead and post.  I laid out my assumptions, and it should be simple to plug my numbers into any spreadsheet and then twiddle to your heart's content.
 
The costs that have been quoted for wind power in Canada (I've talked with a few companies in the business) are close to $.08 /kWh. This is Canadian dollars so the U.S. price would be marginally less.
 
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