Made For Each Other: A National Electricity Grid And Renewable Energy  

Grist has a post on why building a national electricity grid makes switching to renewable energy cheaper ("A purely local approach would double or triple costs") - A national grid will make renewable electricity work.

This is one more attempt to kill a zombie myth: the notion that local generation of renewable electricity can substitute for long-distance transmission. I can see where this comes from -- the sun shines almost everywhere, and the wind blows strong within a few hundred miles of most places where it doesn't, right? If we are going to use renewable electricity at all, it's hard to understand why we wouldn't get it from rooftops, parking lots, or at worst surrounding rural areas.

But if we generate renewable electricity locally (locally being anything from your own rooftop to a wind farm a few hundred miles away), we end up with a huge monthly variation. Even in one of the nation's best solar sites [PDF] you end up with slightly over half the power available in the worst months compared to the best. Wind sites can be worse. For example, the Northfield, Minn. school district recorded a more than a 3 to 1 ratio between best and worst months.

In contrast, if you connected all existing U.S. wind farms [Excel] in a national transmission grid, in 2007 the ratio between best and worst months would vary by no more that 1.7 to 1. Add solar electricity (which tends to be high in months wind is low) and that ratio would be reduced to a 30 or 40 percent difference between best and worst production months. Long-distance transmission can reduce daily variation as well.

In short, a mostly renewable grid without long-distance transmission will cost at least double one that includes such transmission. Note that this applies to rooftop generation and giant solar or wind farms alike.

Q&A

Aren't long-distance transmission lines even more expensive?

Not than doubling or tripling generation. Also very high prices quoted for transmission installation and maintenance conflate transmission and distribution. In the U.S., long-distance transmission costs are about half of distribution. Maintenance is even a smaller percentage. For example, a few years ago Western Washington suffered a major outage where wind storms took down both transmission and distribution. Long-distance transmission was mostly up within 24 hours, whereas distribution was fixed over the course of almost two weeks. Even though transmission is much more expensive to build and repair per mile, distribution requires many times the line miles. Transmission is point to point, or perhaps a few points to a few points. Distribution has to branch out to ever county, municipality, unincorporated area, and ultimately to every home.

Don't long-distance lines reduce reliability?

Not if they are modern High Voltage Direct Current lines. The most common HVDC type installed today actually can help guard against spikes and improve power quality. ...

Won't demand shifting in a smart grid make long-distance transmission unnecessary?

Demand shifting for a few hours or even a day won't compensate for monthly variations in production. Even on a day-to-day basis, long-distance transmission is probably needed to produce a smooth enough production curve for smart-grid demand shifting and electricity storage (including vehicle to grid) to match.

Don't most such variations match local seasonal peaks? That is, isn't wind strongest in winter in cold climates, and sun strongest in summer in hot ones?

If we were just changing electricity supply this would be valid. But climate control has huge potential for both efficiency improvements and non-electrical renewable supplies. Improved insulation, weather sealing, air circulation, along with ground source heat pumps can reduce demand. Direct solar heating (in commercial buildings and multi-unit residences cooling) also has significant potential. Dollar for dollar, these save or provide more energy than renewable electricity. This does not mean we don't need renewable electricity. By the laws of physics, doing more with less won't ever extend to the point where we can get something for nothing. ... These efficiency techniques will reduce seasonal variation in electricity demand.

Tom Konrad has a guest post at The Oil Drum comparing power demand with wind availability and looking at the benefits of using a combination of wind power and heat pumps - Wind and Heat Pumps: A Winning Combination.

Last month, I posted some nice maps showing when and where good wind resources are found in the US. Now I've found something better: a visual comparison of electrical load with wind farm production, published by the Western Area Power Administration in 2006. The study compared electricity production from five wind farms in Northern Colorado, Southwestern Nebraska, and Central Wyoming in 2004, 2005, and the start of 2006, compared with electricity consumption in the same area over the same time period.

Comparison of Wind Production to Electricity Demand

I've copied four of the most representative graphs below.

The first and third heat graphs below show electricity production at the five wind farms studied in 2004 and 2005, respectively. The second and fourth show electricity demand in the surrounding territory. Red(blue) denotes areas of high(low) production or demand.

For wind advocates, these are probably rather scary graphs. The first thing you probably noticed was the big blue patches of wind production during summer peak demand, roughly 10am to 10pm in June, July, and August. This is why wind is referred to as an "energy resource" not a "capacity resource." Right when demand is often highest, the wind is least likely to be blowing, namely hot summer afternoons.

On Second Thought - How Much Backup Do You Need?

That is just the first impression, and while it is a true impression, it's also an oversimplification. If you look at the scale, you will notice that the blues on the wind production graphs actually represent wind generating at 10% to 15% of nameplate capacity. If you factor in the fact that a normal capacity factor for wind is about 25-40%, that means that even on these hot summer afternoons, the farms are generating at one-third to one-half of their "normal" output. This means that, contrary to popular misconception, wind does not require a "100% back-up with natural gas." It is true that wind is less reliable than baseload power plants such as coal and nuclear, which typically run about 90% of the time, but in an apples-to-apples comparison, a 100 MW coal or nuclear plant will produce as much energy over the course of a year as a 270 MW wind farm. During the peak summer months, the coal plant will need some backup power in case of an unscheduled shut down due to lack available coal (this happened in Colorado in 2005 due to problems with dust in rail tracks) or lack of available cooling water during a heatwave, and when a coal or nuclear plant goes down, it goes all the way down, so the 100 MW baseload plant has a small chance of needing 90 MW of backup to produce at its "normal" rate of power production. On the other hand, the wind farm will be operating at (a conservative) third of its "normal" capacity, producing about 30MW. To bring that up to its normal capacity for the year, it will need 60MW of back-up power.

In other words, because some part of a large distributed group of wind farms is always producing some power, it will never go completely down. A large baseload power plant, on the other hand, is completely down about 10% of the time (although less during peak summer months, because utilities schedule maintenance in off seasons.)

Pick Farms to Match Your Load

Another point worth noting, is that the wind has different annual patterns in different locations. The smallest (8.4 MW out of 139MW) of the five farms in the study was "Wind Farm B" in central Wyoming. If you look at the following two heat maps below for 2004 and 2005, which show the production of just this wind farm, you will note that during the peak summer demand, this farm was producing at over 50% of "normal" capacity for much of the summer peak.

Since we know what electricity demand looks like, if we plan new wind farms (and adequate transmission), we can choose to build wind farms that produce more power when we most need it. If all the farms in the example in the last section had more favorable production patterns like Farm B, even less back-up generation would be needed to bring them up to "normal" capacity.

For instance, in the Texas Competitive Renewable Energy Zones study wind in the coastal area (along Texas's southern gulf coast) was found to be a much better match for the ERCOT load shape than wind in other areas, although the average capacity factor was considerably lower than panhandle wind. ...

Hence, careful selection of wind farms can lead to wind production with higher capacity during peak loads, and correspondingly less need for dispactchable power. Although Texas is currently focusing on developing wind farms in West Texas and the Panhandle because of their high capacity factors and correspondingly high annual energy output, the power from coastal wind farms is likely to become increasingly valuable as wind reaches higher penetration. ...

How Heat Pumps Fit In

Which brings me to the title of this article: why heat pumps are an excellent fit with wind generation. In my article on how to invest in the Pickens Plan, I mentioned that ground-source heat pumps (GHP) can displace gas used for heating with a smaller amount of electricity from wind. Since a GHP is both an efficient air conditioner as well as an efficient heat source, it not only reduces natural gas used for heating, but also reduces electricity used for cooling in hot summer months, which in turn reduces summer peak loads.

Deployment of GHPs does three things to make energy supplies fit energy demand:

1. Winter electricity usage is increased just when wind capacities are highest.
2. Summer electricity consumption is decreased when wind capacities are lowest.
3. Use of natural gas for heating is reduced during times of peak gas demand.

GHPs, because of their extreme efficiency, also have the benefit of saving users a lot of money. ...

Electricity Demand Can Shift

Heat pumps are just one option for changing the shape of the electricity demand curve. Many such efficiency measures can do so. Other examples are improved home sealing and insulation, which typically pay for themselves in a couple years or less, and, because air conditioners work less hard in the summer, reduce summer peak loads. Wind is undoubtedly a tricky sort of electricity to use in the existing grid, but the fallacy that demand is fixed makes the problem seem much harder than it needs to be.

Tom also had a column looking at various related topics at Alt Energy Stocks recently - Investment Ideas From the One-House Grid.

In June, I wrote how intermittent power sources such as photovoltaics and wind would have to compete with baseload technologies such as IGCC "Clean Coal" and nuclear for capacity on the grid. The key problem is that neither baseload technologies nor intermittent technologies are able to match themselves to the fluctuations of demand. This creates a need for technologies which can fill the varying gaps between supply from these sources, and normal energy use. From the comments, it seems like I was not completely clear how intermittent and baseload power cause problems for each other, so I will start with a simplified example, which I will use to illustrate the various strategies for dealing with the problem. I see investment potential in all of these strategies.

The One-House Grid: An Illustration

Suppose that the entire grid were just one house, and it was the utility's job to make sure that there was always enough power to run all the gadgets that anyone in the house was using. Even in the middle of the night when everyone is asleep, there will still be some power usage: running clocks, the VCR, charging cell phones for use the next day, and maybe the porch light. That is the minimum load of the house, and traditionally utilities have met this demand with baseload power. In contrast, there will probably also be a moment on hot summer afternoon when the air conditioner is running full blast, the refrigerator kicks on, dad is watching football on his 60" plasma TV, dinner is cooking in the electric oven, and 15 other appliances are on somewhere or other. This is peak load, and the difference between the minimum load and peak would traditionally be met with dispatchable generation, which, until recently, mostly means gas turbines.

In addition, some dispatchable generation will always be kept running below full capacity in order to maintain power quality and availability as appliances are turned on and off throughout the day. These ancillary services [pdf] are called load-following reserves (maintaining availability) and voltage and frequency regulation (power quality,) and both require fuel, even if the actual energy provided is negligible. Ancillary services are like your car's engine idling at a stop light so that you can start quickly when the light changes. They're necessary to keep the system running, and they use fuel, but they don't actually get you anywhere. Also like idling engines, options like hybrids exist which can save much of the energy cost (see below.)

Add a Solar Panel

Suppose we now add a photovoltaic system and a wind turbine on the roof. Most people with solar systems know, that if you want to spin your meter backwards (i.e. produce more energy than you are using) the best time to do it will be in the late morning, while it is still cool, but it's bright enough that the panels (which actually produce more power from the same amount of light when they are cool) are producing near their peak output.

With grid-connected solar, spinning your meter backwards may be fun, or at least get you bragging rights. However, in my fictional one-house grid, we now have a new minimum demand: demand will be negative (we're going to have to find something to do with the excess electricity) because there is no other grid to sell it back to. Peak demand will also be reduced, because on the hot summer day, the PV will also be producing power. The result is that the one-house gird with a PV system will no longer need any baseload generation (since minimum demand is now negative), and it will probably also need less dispatchable generation, because peak demand will also have been reduced, most likely by more than minimum load. Not only will peak demand have been reduced, but it will also have shifted to the early evening when the PV is producing little electricity, but cooling, cooking, and football watching needs are still high.

Adding a wind turbine to the roof has a similar effect. Now, the meter will also be spinning backwards on windy nights, and demand is reduced whenever it's windy, which will in turn save fuel and reduce the need to run the remaining dispatchable generation.. However, if the climate is similar to that here in Denver, on the hottest days of the year, the wind will typically be minimal, so there will be little further reduction in peak load, so nearly the same total amount of dispatchable generation will be needed, although it will not be in use as often.

Consequences

As the above illustration shows, the oft-repeated shibboleth that we "need" baseload generation is not only misleading, but also counter-productive. Adding baseload generation will simply increase the number of hours per year that intermittent sources of power exceed net demand. I too, formerly believed we needed baseload. I no longer do, although some level of baseload power in the grid is no doubt inevitable, at the very least produced by renewable sources such as geothermal and electricity generation from industrial waste heat.

Solutions

Returning to our one-house grid thought experiment, a number of options present themselves.

1. Storage. In the real world, if you build a house off the grid, you will add batteries so that you can still run your lights when the sun isn't shining and the wind isn't blowing.

2. Transmission. Suppose our one-house grid has a neighbor, running his own one-house grid. While generation from their PV and wind systems will be similar (but not identical), demand at the two houses is likely to be different. By diversifying the electric demand, average demand will double, but peak load will increase by somewhat less, and minimum load will more than double. This reduced volatility of electrical load brought by connecting two homes is analogous to the reduced volatility of a portfolio of two securities, rather than just one. Unless the electrical load of the two homes is perfectly correlated, there will be benefits in terms of a reduction in the overall amount of dispatchable generation needed to service the same total load. Our knowledge of the principles of diversification will correctly lead us to the intuition that connecting dissimilar users of electricity will lead to greater diversification benefits than similar users. If residential, commercial, and industrial users are all on the same grid, the same average electric demand will be easier to serve than if only residential or only industrial customers were connected, because a residential user will have lower correlation of demand with most industrial users than with other residential users.

3. Demand-Response. My sister lives in an old house, and the kitchen is on an old, low amperage circuit breaker. If she ran both the microwave and the toaster at the same time, it would trip the breaker and she would have to trudge outside to turn it back on. Needless to say, she quickly stopped using the toaster and the microwave at the same time, and thereby reduced the peak load in her kitchen. Demand response involves getting electric customers to agree ahead of time to refrain from using high-wattage appliances during times of high electric demand. In the one-house grid example above, dad might choose to record the football game and watch it later in that evening.

4. Energy Efficiency. Another way to reduce volatility of demand is simply to reduce overall demand. If dad had decided to buy an LCD TV rather than a Plasma TV, the demand from his 60" TV might have been reduced by as much as 200-300 watts, depending on the models, and this in turn would have reduced peak load. ...

EWnergy Tech STocks has a story on a variant of the "distributed power station" theme that I've mentioned here a few times (both for Californian solar projects and German renewable energy projects centred around biogas) - Duke Energy’s New Solar Concept Has Potential to Supercharge Solar & Smart Grid Companies.

Duke Energy just said it plans to test a concept which, in EnergyTechStocks.com’s opinion, has the potential to revolutionize the solar power industry even before it has taken root. Duke’s plan envisions turning rooftops into solar power collectors. Nothing new about that, right?

Wrong. Duke is going to test the idea of linking hundreds of solar-power-collecting rooftops into a unique kind of power plant, one that’s the opposite of today’s power plants. Today’s plants generate electricity from a central location and transmit it over lines into millions of homes, offices and factories. Duke’s idea is for a completely de-centralized power plant, one that generates electricity remotely and then feeds that power into the grid at the same point where power from a central plant is being delivered.

Duke’s test will involve rooftops at some 850 locations in North Carolina. Not just homeowners but schools and other buildings will be involved. Public support could be strong, given that Duke plans to pay a rental fee to participants. (Every school board in America might warm to that idea.)

If Duke’s test works – and it’s still very much an “if” – just imagine the increase in business that might come the way of companies that make solar chips and panels, as well as inverter manufacturers and more. Imagine also the companies that could benefit from making the computer chips and other software that would be needed to make the power grid “smart,” essentially enabling a simultaneous two-way flow of electricity into and out of your home.

Duke’s test calls for generating 16 megawatts of electricity from those 850 locations. Think about how many rooftops there are – and how anxious people might be to rent their roofs to their local utility – and it’s easy see how, within a decade or less, not just the solar power industry but the entire electric utility industry could be radically transformed. To be sure, solar power will continue to grow, which no doubt is why Duke is conducting its test. Either Duke and other electric utilities figure out a way to keep their customers in the fold, or they risk losing them to suppliers of solar systems that promise to take homes “off the grid.”

Renewable Energy World has an excellent survey of the US wind power industry from a pair of authors at Lawrence Berkeley National Laboratory - Surpassing expectations: State of the US wind power market.

The wind power industry in the US has been growing dramatically in recent years, and the rapid pace of development has made it difficult to keep up with trends in the marketplace. Yet the need for timely, objective information on the wind industry and its progress has never been greater. As Figure 1 shows, the country added roughly 5300 MW of new wind power capacity in 2007 – more than twice the previous record set in 2006 – bringing the cumulative total to more than 16,900 MW. This growth translates into roughly US$9 billion (real 2007 dollars) invested in wind project installation in 2007. No other country, in any single year, has added the volume of wind capacity that was added to the US electrical grid in 2007. ...

However, within the US some individual states are beginning to realize relatively high levels of wind penetration. Minnesota and Iowa lead the nation in terms of estimated wind power as a percentage of total in-state generation, at 7.5% each (Table 2, above). Four additional states – Colorado, South Dakota, Oregon, and New Mexico – surpass the 4% mark by this metric. Though not shown in Table 2, some individual utilities are achieving even higher levels of wind penetration – greater than 10% in some cases – into their individual electricity distribution systems.

Wind has also made great strides in terms of becoming a significant contributor to the nation’s resource mix. For the third consecutive year, wind power was the second-largest new resource added to the US electrical grid in terms of nameplate capacity, behind the 7500 MW of new natural gas plants, but ahead of the 1400 MW of new coal. New wind plants contributed roughly 35% of the new nameplate capacity added to the US electrical grid in 2007, compared to 19% in 2006, 12% in 2005, and less than 4% from 2000 through 2004, as shown in Figure 4, above. Based on the amount of wind power capacity currently working its way through eleven of the major transmission interconnection queues across the country, this trend is expected to continue (see Figure 5). At the end of 2007, there were 225 GW of wind power capacity within these interconnection queues – more than 13 times the installed wind capacity in the US. Moreover, this wind capacity represents roughly half of all generating capacity within these queues at that time, and is twice as much capacity as the next largest resource in these queues (natural gas). Although many of these planned projects are still early in the development process, and a large number are unlikely to achieve commercial operations any time soon (if ever), the 225 GW figure is nevertheless astounding, and indicates the increasingly important role that wind may play in the nation’s power mix. ...

Though transmission availability, siting and permitting conflicts, and other barriers remain, 2008 is, by all accounts, expected to be another banner year for the US wind industry. Another year of capacity growth in excess of 5 GW appears to be in the offing, and past installation records may again fall as developers rush to complete projects prior to the scheduled year-end expiration of the PTC. Local manufacturing of turbines and components is also anticipated to continue to grow, as previously announced manufacturing facilities come on line and existing facilities reach capacity and expand.

All of this is likely to occur despite the fact that wind power pricing is projected to continue its upwards climb in the near term, as increases in turbine prices make their way through to wind power purchasers. Supporting continued market expansion, despite unfavourable wind pricing trends, are the rising costs of fossil generation, the mounting possibility of carbon regulation, and the growing chorus of states interested in encouraging wind power through policy measures.

If the PTC is not extended, however, 2009 is likely to be a difficult year of industry retrenchment. The drivers noted above should be able to underpin some wind capacity additions even in the absence of the PTC, and some developers may continue to build under the assumption that the PTC will be extended and apply retroactively. Nonetheless, most developers are expected to ‘wait it out,’ restarting construction activity only once the fate of the PTC is clear.

Home scale wind power (micro-wind power) doesn't seem to be a particularly economical way of generating power, but for those in windy or off-grid areas (or those determined to be self-sufficient / energy independent) it is an interesting option. EcoGeek has a roundup of some of the products available - Want Your Own Wind Turbine? Here's Our Guide.

gigawatts of wind power are being proposed all over the globe, and new wind farms are regularly being proposed that outstrip one another to be the largest in their respective locations, or in the world. At the far end of the scale, the largest size wind turbines have a rotor diameter of 126 meters (413 feet), and are estimated to be capable of producing 20,000,000 kilowatt hours of electricity annually (enough to power as many as 5000 European homes). Since the power generated by a turbine increases exponentially as it gets larger, new turbines will continue to grow in size.

But small-scale turbines are perhaps a more exciting realm of development. The standard, propeller-style turbine is well established, and there are many suppliers for this kind of generator in a range of sizes. In 2007, Home Power Magazine had a roundup of more than a dozen small wind turbines ranging from 8 feet to 56 feet in diameter (the latter of which is far larger than even a large, inefficient household would need for their power requirements).

Besides the propeller turbine, there are a number of other options that are being developed and coming into availability that offer different features and performance that can make them appealing alternatives for some.