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:

• The heating season is 180 days long;
• The average household consumes 50 million BTU of natural gas per year for space heat, of which 80% (40 million BTU) is captured and 20% lost;
• Another 7.5 million BTU is consumed during the heating season for domestic hot water, also at 80% efficiency;
• The available wind power per household is either 3 kW or 5 kW, and the capacity factor of the wind turbines is 25%, 30% or 35%;
• The efficiency of transmission and distribution is 90%, and there are no grid-capacity limitations (cold weather and winter gales holding little prospect for overheating of lines or transformers); and
• The excess wind energy is used in resistance heaters to displace natural gas, with 100% efficiency for space heat and 80% for water.

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:

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:

• Extremely precise shedding of space heat loads in winter, and DHW heating loads in any season;
• Ability to maintain the entire electric-heating load as "spinning reserve" (available for redirection as fast as control systems permit) when excess generation requires it as a power dump, with positive consequences for grid reliability.

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:

• the wind supply is either at 100% or 0 (pessimal supply curve),
• the entire 26.8 kWh (41%, 91,500 BTU/day) is surplus and must go to heat,
• all the heat can be used,
• the DHW heat is supplied by a burner rather than the cogenerator,
• DHW heat losses are unchanged, and
• the new energy displaces fuel oil:

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.

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:

• eliminate petroleum consumption during the heating season
• reduce gas demand by 12%
• reduce total carbon emissions by more than 75%.

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. ;-)  ¶ 3/31/2005 10:15:00 PM