River’s Gonna Rise* - Hydro Power in New Hampshire – Part 3: PSNH Hydro Operations and River Flows

In my last few posts, Down by the Water  and Take Me to the River, I mentioned that my office looks onto the Merrimack River and the upstream Amoskeag hydroelectric operation that has been producing electricity for the past ninety years.  From this view, I often take note of river flows and whether the water is spilling over the top of the dam wall, as in the photograph below. In this post, I discuss the variability of river flows and how hydro plant electricity outputs are very dependent on these. I also look at the capacity factors of the Merrimack River hydro operations and compare them to national averages.

Photo: PSNH Flckr Photostream

Weather and precipitation are the most important variables in hydro electricity operations because these determine river flow. I dug up some relevant information about Merrimack River flows near my office from the United States Geological Services (USGS). The chart below shows the river flows at the Goffs Falls monitoring point, which is just downstream of the Amoskeag Dam. The jagged blue line shows the data for 2013 and it is surprising how variable the flow is from day to day. The orange dots show the average flowrates over the past 76 years. This historical data shows that river flows generally rise during April to June due to snow melt, reaching flows that are four times the average value, and then drop off considerably during the dry August to October period, to about one quarter of the average. Interestingly, the summer of 2013 was a wet one, as indicated by the higher-than-average river flows during this period.

Source: USGS

A simple relationship dictates the generating capacity of a hydro operation:

Power = Constant x Flow x Height

In an operation such as Amoskeag, the height (or head) is essentially fixed because this is a constant-level run-of-river operation. However, since Merrimack River flows do vary, I took a look at the 2013 monthly river flows and compared them to monthly electricity production (measured in MWh) for the two larger operations on the Merrimack River. These are plotted in the figure below on the left, with river flows in the green bars, and Amoskeag and Garvin Falls electricity generation in blue and red, respectively.

Data Source: USGS and EIA

As expected, high river flows, particularly during the April snowmelt or the wet July of last year, generated higher amounts of electricity.  Low river flows, such as in the dry months of August to October, were associated with lower generation rates. 

The chart on the right plots energy generation against river flows for the Amoskeag plant. I was somewhat expecting a 1:1 linear relationship and was initially surprised to note how generation tended to start leveling off at high flowrates. However, the PSNH hydro folks pointed out that the maximum flowrate through the Amoskeag turbines is 5000 cubic feet per second (cu. ft/sec), so one would expect to see generation level off above this flowrate. Moreover, an average monthly flowrate of greater than 5000 cu. ft/sec does not necessarily mean that flow rates are higher than 5000 cu. ft/sec for 24 hours a day – there may be periods when it is substantially higher and then there are periods of lower flows.

In one of my recent posts, Down by the Water, we noted the simple mathematical relationship between energy and power:

 Energy = Power x time.

Applying this relationship to the Amoskeag operation, which has a nameplate capacity of 16 MW, and assuming 30 days per month and 24 hours per day of operation, the maximum monthly generation from the Amoskeag Dam can be calculated as

Energy = 16 MW x 30 days x 24 hr/day = 11,520 MWh

This is pretty close to the maximum monthly generation output on the chart above.

I was also surprised to note that the power generation of Garvin Falls was half that of Amoskeag although its generation capacity (12 MW) is 75% that of Amoskeag (16 MW). Calculating the total generation for both operations for 2013, I noted that Amoskeag produced 66% of its maximum electricity output (also termed its capacity factor), whereas Garvin Falls produced only 44%. It turns out that Garvin Falls is a more troublesome operation because it has a gatehouse and a narrow channel for a head race that is used to direct water into the power houses. River-borne debris, such as leaves, branches, trees, etc., build up behind the gatehouse and restrict flow to the channel, which significantly compromises the steady generation of electricity from this operation. Regular maintenance, involving the removal of debris from the screens where the water enters the power house, is required.

The Energy Information Agency, EIA, produces an average annual capacity factor for all hydro operations across the US. In 2013 it was 38.1%, which is much lower than I would have anticipated. I was expecting capacity factors for hydro operation to be of the order of 80% or so but the annual data from 2008 to 2013 shows US capacity factors ranging from 37.2% to 45.9%. The national data does indicate that the Garvin Falls and particularly the Amoskeag operation have capacity factors greater than the average US hydro operation.

There are several reasons for these lower-than-expected capacity factors for hydro operation:

• Precipitation and river flows are variable and the maximum flow of water that the generators can handle is not always available.
• River-borne debris and winter ice can at times significantly compromise water flows into the generating units.
• The generating units need to be slowed or shutdown for periodic maintenance.
• Even though hydro plants are generally the lowest cost producers of electricity when selling into the wholesale markets, they can be underbid by other generators, particularly heavily subsidized wind operations which will sometimes even pay to produce electricity. At times like these, there might not be any call for hydro power and the units are shutdown.

PSNH owns and operates several hydro operations in NH. Those listed below are owned and operated by Northeast Utilities, the parent corporation of PSNH.

Source:PSNH

Based on recent documentation submitted to the NH Public Utilities Commission, hydro operations will be responsible for about 11% of  the ~3,016,000 MWh of electricity that PSNH is planning to generate from its own facilities in 2014. These are PSNH’s lowest cost electricity generators and are thus an important asset to keep in operation and perhaps even consider expanding, even though the impacts of new or expanded hydro operations could be considerable and permitting could be extremely difficult. We have to recognize that there is a price to be paid for every energy source we use but, unlike fossil fuels where every ton of carbon dioxide we dump into the atmosphere intensifies the green-house effect, hydro plants will be still generating electricity one hundred years from now and will still not be pumping carbon dioxide into the atmosphere.

An important debate regarding these facilities is presently underway in NH (discussed in Should I Stay or Should I Go). In order to complete the electricity deregulation process in New Hampshire, it has been proposed that PSNH should be compelled to sell these hydro generating operations, along with their wood- and gas-fired operations and the large coal-burning plant on the Merrimack River in Bow. However, with electricity prices shooting up this winter and with PSNH customers, for the time being at least, somewhat shielded from these increases, this does give one pause for thought and to consider that ownership of generating operations may perhaps have some benefits. This is certainly a topic I will return to in a future post.

Until next time, remember to turn off the lights when you leave the room and, if it is raining, contemplate that the river’s gonna rise* and the hydroelectricity output will increase.

Mike Mooiman

Franklin Pierce University

mooimanm@franklinpierce.edu

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(*River’s Gonna Rise – An instrumental tune by Patrick O’ Hearn, a LA bass player and electronic musician who has had a long and varied career, including stints playing bass in Frank Zappa’s band, the New Wave group, Missing Persons, as well as releasing over a dozen solo albums featuring electronic and ambient music. He is well known for his film scores and in the past few years has been playing bass in John Hiatt’s band. Here is the title track from Patrick O’ Hearn’s 1988 album River’s Gonna Rise.)

Take Me to the River* - Hydro Power in New Hampshire – Part 2: Touring the PSNH Hydro Operations

In my last post, Down by the Water, I noted that my office looks onto the Merrimack River and the upstream Amoskeag dam and the hydroelectricity power plant that has been in operation for ninety years. In this post, I take a closer look at this power plant, which I had an opportunity to tour, as well as its sister upstream plants in Hooksett and at Garvin Falls. 

In the process of learning more about the operation of the Amoskeag Dam and the hydro plant, I was fortunate enough to be given a tour of the operations by the experienced hydro team at PSNH. The photographs below were taken during this tour. My tour of the facility was fascinating. I got a great view of the dam from the powerhouse side and was able to view the power plant from the inside.

The power plant is home to three 1920s vintage turbine and generator sets, which continue to work perfectly today and are so well designed and maintained that replacement is not warranted. As an engineer, I was very impressed to see these 90+-year old units still operating and generating electricity. The hydro industry is rather unique in the electricity generation business, in that many of the operations rely on old, well-designed equipment, which, in some cases, are 100 years old. This is a testament to past engineers who designed these units without the use of calculators, spreadsheets, or computer-aided design and drawing tools.

Photo: PSNH Flckr Photostream

The Amoskeag Power Plant has a long history. The project was started by the Amoskeag Manufacturing Company, the textile manufacturing company established on the banks of the Merrimack River and which led to the founding of Manchester. The Amoskeag Mill was at one time the largest cotton textile plant in the world. At its peak, the mill was powered by thirty water turbines, twelve steam engines, and five steam turbines.  In 1918, a decision was made to completely dam the Merrimack at the Amoskeag Falls and to install a hydroelectric generating station. This was placed into operation in 1924.

During my research I was excited to uncover the photograph below from the PSNH Shoebox website, which is a collection of old PSNH-related photographs. This  shows one of the turbines being readied for installation in the Amoskeag powerhouse in the 1920s. It is still in operation today.

Photo: PSNH Shoebox

After World War I, business became difficult for the Amoskeag Manufacturing Company because the US was in recession. Furthermore, the proliferation of electrical generating operations throughout the US, and especially down south, meant that cotton did not need to be transported north to be milled and woven. High costs, aging equipment, and labor unrest eventually led to the bankruptcy of the Amoskeag Manufacturing Company and the sale of the hydro operations to PSNH in 1936.

The Amoskeag Dam spans the Merrimack River so that the river flow can be harnessed and fed through the three turbines at the Amoskeag Powerhouse (see photograph below). The average annual river flow is some 4000 cubic feet per second (cu. ft/sec) (equivalent to 1.8 million gallons per hour). At full power, the maximum combined water flow through the turbines is 5000 cu. ft/sec. This means during average river flows of 4000 cu. ft/sec, all the water, except for a 280 cu. ft/sec habitat bypass,  is directed through the turbines and there is no overflow over the top of the dam. My photographs of the water overtopping of the Amoskeag Dam were taken during the tour. Because the river flow that day was very low (~ 2000 cu. ft/sec), I was surprised to see overtopping. It turned out that the Amoskeag power house was down for maintenance because the transformers were being replaced so there was no river flow going through turbines and the full river flow, except for the bypass, was consequently all spilling over the top of the dam.

Photo: PSNH Flckr Photostream 

I was also fortunate to be taken down to the lower levels of the powerhouse, where I walked to the other side of the dam through a service tunnel inside the dam wall that runs along its entire length. On emerging on the other side, I got a closer look at the inflatable gate that is used to control the height of the water in the dam.

Photo: PSNH Flckr Photostream

The Amoskeag dam is just one of three hydro plants operated by PSNH on a fairly short stretch of the Merrimack river, so I decided to take myself to the river* and drive upstream to visit the other two. About 7 miles above the Amoskeag dam, there is a small single turbine 1.6 MW hydro plant on the Hooksett dam;  a further 5 miles upstream is the much larger Garvin Falls Dam, which hosts four turbines in two powerhouses which have a combined capacity of 12.1 MW. The PSNH Merrimack coal-fired power plant, which uses the Merrimack River as a cooling water source, lies between these two dams. It is clear that, even today, the mighty Merrimack has an enormously important role to play in energy generation in New Hampshire. Below are some photographs from my upstream excursion.

Much of this post has been touristy in nature with descriptions of power plants, tours and lots of pictures but in the next post I will dig deeper into the technical information, such as river flows and electricity generation, associated with these hydro operations. My visits and research for these posts has given me a better understanding of the operation and importance of these hydroelectric facilities as well as a much better appreciation for the engineering design and construction skills of those old time engineers.

Until next time, remember to turn off the lights when you leave the room.

Mike Mooiman

Franklin Pierce University

mooimanm@franklinpierce.edu

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(*Take Me to the River – The fabulous and heavily covered Al Green tune. The definitive cover is by the Talking Heads. Here it is from one the best concert movies ever made – “Stop Making Sense”. Turn up the volume and enjoy Take Me to River.)

Down by the Water* - Hydro Power in New Hampshire – Part 1

My office is in Manchester, in Franklin Pierce University’s graduate school which is located in one of the renovated mill buildings located on the Merrimack River. From the conference room there is a great view of the river and the upstream Amoskeag dam. This is a 30-foot high, 710-foot long concrete dam that holds back the Merrimack River at this point so that the water can be directed through the turbines at the Amoskeag Power House located on the western bank of the Merrimack.  These turbines have a combined generating capacity of 16 MW. The photos below show my view of the dam wall and a Google Map satellite image for an overhead view. This dam was originally commissioned in 1924 to service the Manchester mills. While gazing at the river this week during a meeting, I decided it was time to turn my attention to the topic of hydro power in New Hampshire. This post is the first in a multi-part series on this topic.

Man has utilized the power of water (hydro power) for centuries. In the late 1700s and into the 1800s, advances in technology, powered by running water (and eventually by steam) is what lead to the industrial revolution. Throughout New England, textile mills were established along the main rivers, most notably the Blackstone River that runs down through Worchester, Massachusetts into Rhode Island and the Merrimack River that follows a route through New Hampshire into Massachusetts. The river flow turned water wheels and turbines which, through a system of gears, shafts, and belts, were used to drive machinery inside the mills.

In the 1880s, water-driven turbines were combined with electric generators to generate the first hydroelectricity, and in 1882 the world's first hydroelectric power plant started operation on the Fox River in Appleton, Wisconsin. From that point on, the use of hydroelectricity grew phenomenally and, in 1940, hydro generated 40% of all electricity in the US. Since then, demand for electricity has increased ten-fold, but natural gas-, coal-, and nuclear-fired operations were established to fill the need. Hydro power output grew, but its share of electricity production has dropped off to about 6 to 8% of the electricity generated in the US today.

Hydro operations range in size from the very large 6809 MW Grand Coulee Dam in Washington state, the 2515 MW of the Robert Moses Niagara Power Plant and the 2080 MW of the Hoover dam on the Colorado River to “hobby” projects less than 1 kW in capacity. (Remember there are 1000 kW in a MW.) There are about 1750 hydropower operations in the US: most of them are much smaller than in size than the very large Hoover Dam operation which we usually associate with hydropower.  In fact, most hydroelectric operations in the US are much smaller - almost 90%  are less than 30 MW in size.

Hoover Dam Hydroelectric Plan

All hydropower operations, whether private, municipal, or state-owned, are licensed by the Federal Energy Electricity Commission  (FERC) – the  federal “godfather” of the electricity business. There are 41 FERC-licensed hydro operations in NH, ranging in size from 136 MW to 58 kW.  Small projects, such as those less than 10 MW installed on an existing dam or those of less than 40 MW installed on a waterway used for another purpose (such as an irrigation canal), are exempt from FERC licensing. There are 43 such exempt facilities in NH, ranging from the 3.5 MW Gregg’s Falls operation on the Piscataquog River in Goffstown to a 5 kW operation on Marden Brook. FERC licenses often involve combinations of hydro operations run by a single operator on a stretch of water:  for example, the three PSNH operations on the Merrimack River are combined into one license. I also noted that the very large Moore and Commerford hydro plants on the Connecticut River are listed by FERC as Vermont operations. These licensing/classification artifacts can cause confusion, especially when data on generation, as provided by the Energy Information Agency (EIA) and used later in this post, is reviewed.

There are many different ways of classifying hydro operations. The first is by size. Large hydro plants in the US are generally considered to be those above 25 MW in capacity but international standards consider those above 10 MW to be large. Most of the hydro plants in New Hampshire are small operations: within this class there are subclasses which typically have the following size ranges:

·                                Mini                <1 MW

·                                Micro              <100 kW

·                                Pico                <10 kW

·                                Family             <1 kW

To give you a sense of what these capacities mean, it is important to remind ourselves of the difference between power and energy.  I discussed this topic in the I’ve Got the Power! blog a while ago. As a reminder, remember that electrical energy is the ability of an electric current to do work − such as producing motion, heat, or light. The units of electrical energy are kilowatt hours (kWh) or megawatt hours (MWh). There are 1000 kWh in one MWh. Electrical power, on the other hand, measured in kilowatts (kW) or megawatts (MW), is a capacity, i.e., the rate at which energy can be produced from a generator. Large generators, which can produce more energy per unit of time, naturally have larger capacity or power ratings.

The confusion between power and energy often stems from the similarity of the units: kilowatt hours or megawatt hours are energy units, and kilowatts or megawatts are power units. However, it is important to understand that even though the units seem similar, there is a world of difference between them. This difference stems from the simple mathematical relationship between energy and power;

Energy = Power x time.

I find it is always useful to understand these relationships from a homeowner’s point of view. Consider that an average US household uses 11,000 kWh per year of electricity (~900 kWh per month). If you had to generate that electricity yourself and you were going to do it over 24 hours a day for 365 days per year, you would need generator with a power rating of 1.3 kW.

The calculation would be done as follows:

Energy = Power x time

Power = Energy / time

Power = 11,000 kWh/(365 days x 24 hours/day) = 1.3 kW.

Of course, this calculation is based on a daily average, but our daily electricity use is actually rather “lumpy”:  there is a first peak in the morning as we turn on the lights, make coffee, heat up the house, and take hot showers, followed by a second and larger peak in the late afternoon/evening when we are making dinner, watching TV, doing the laundry, turning on the electric blanket, reading this blog, etc. If you were to actually buy a generator, you would want a unit that has a capacity of more than the average 1.3 kW so that it could handle the peaks in usage. This is why backup generators for homes often have sizes of the order of 5 kW to 15 kW. But I digress somewhat (I may come back to the topic of home generators in a future post)….

The second classification of hydro plants is by type of operation. The three main types are:

• Reservoir or Pond-and-Release Operations: We most commonly associate these with hydropower and they involve large concrete dams holding back enormous reservoirs of water with the power plant at the base, as shown in the Hoover Dam picture above. The reservoir provides for a great deal of storage and steady power generation even during the dry season. These operations usually involve the upstream flooding of large tracts of land and significantly impact downstream water flows. The water level in the reservoir can also fluctuate greatly, depending on the incoming water flows and the discharges through the power station.
• Run-of-River Operations: These hydroelectric plants depend on the natural drop in the river elevation. A portion of the upstream river flow is sometimes diverted through a large pipe (called a penstock) to a downstream generator plant, after which the water flow is reintroduced into the river (see the figure below). These operations often have dams at the upstream location to provide the water diversion point but their storage capacity, called pondage, is limited and, as such, these operations are more subject to the vagaries of seasonal precipitation and natural river flows. With limited storage, the reservoir level tends to remain fairly constant – excess river flow simply spills over the top of the dam. Electricity production can therefore vary substantially over time. Because these operations don’t involve large amounts of storage or flooding of large acreages of land, they tend to viewed as more environmentally friendly or “greener” than the larger reservoir operations.
• Pumped Storage: These operations involve pumping water from a river uphill to a reservoir at a higher elevation during low electricity demand and low cost periods. When electricity demand increases and prices are high, these operations then run in reverse and the water in the reservoir is drained through a turbine back into the river, generating electricity in the process. There are a three of these operations in New England with a combined capacity of 1696 MW.

Source: IPCC

In NH, we do not have any pumped storage operations but we have reservoir and run-of-river operations.  Data from the EIA indicates that there are 92 hydro generators in NH with a combined name-plate capacity of 446 MW and a total winter capacity of 511 MW. The ten largest NH hydroelectric operations are listed below.  The Moore and Comerford dams, located on the Connecticut River which runs between New Hampshire and Vermont, are the largest hydro operations in all of New England. All operations listed are individual dams, except for the Great Lake Hydro-owned operation on the Androscoggin River in the Berlin area which is a series of different dams and 21 generating facilities. The largest PSNH-owned operation in NH (and the one that distracts me during meetings)  is the Amoskeag dam on the Merrimack River.

Source: EIA

As a wrap-up for this post, I thought a comparison with other New England states would be interesting. The table below lists total electricity production capacity (the power of the generator) and hydro capacity by state for 2012, as well as total production of electricity and hydroelectricity. The data include conventional hydro only and excludes pumped storage operations. We can see that Maine is the “hydro powerhouse” of the New England region, with the largest capacity, followed by NH. The upper New England states, New Hampshire, Vermont, and Maine  provide the bulk of the region’s hydro generation capacity.

I note with interest that, even though Maine total hydro capacity was only 17% of its total generating capacity, 26% of their electricity output for 2012 was generated from hydro. This means that their hydro plants worked very hard in 2012, which is indicated by the highest capacity factor for their combined hydro plants. (Recall from I’ve Got the Power! that capacity factor is the ratio, expressed as a percentage, of the actual electricity output from a generator over a year compared to the theoretical output if the unit operated 24 hours/day 365 days per year.) The comparative numbers for NH are quite different. In orange I have highlighted that hydro represented 10% of NH generating capacity but, in 2012, it was, surprisingly, only responsible for 7% of the NH total electricity output. The capacity factor of all NH’s hydro plants, in yellow, was therefore an extraordinary low 33%.

Source: EIA

This anomaly is quite striking and some follow-up research is warranted. It is clear that hydro power is intriguing topic and I plan to continue my explorations in future posts. Now, when I gaze out the windows at the Merrimack River and the upstream Amoskeag dam during faculty meetings, my colleagues can be assured that my distraction is not idle daydreaming; instead I will be thinking of river flows, generating plants, and capacity factors!

Until next time, remember to turn off the lights when you leave the room.

Mike Mooiman

Franklin Pierce University

mooimanm@franklinpierce.edu


Click on this link to receive email notifications for Energy in New Hampshire updates

(*Down by the Water – A great tune by one of my favorite indie groups, The Decemberists. These guys are great song writers and I always look forward to their new releases. Here they are from Austin City Limits – the best music show on TV. Enjoy Down by the Water.)

Not So Classical Gas* - Energy Conversion Efficiency and Improvements in Natural Gas Technology

Last week I covered a ratio called capacity factor which some folks confuse with energy conversion efficiency. While the topic is still fresh, I thought I would cover energy efficiency this week to make sure there is a clear understanding of the two concepts. In my last post I noted that a great deal of energy technology is about converting energy from one form to another. For example, in a nuclear power operation we convert the nuclear energy holding the uranium nuclei together into heat which is then used to boil water to produce steam which drives a generator that produces electrical energy. The key to energy technology is to make these conversions as efficiently as possible.

The example I provided was my Prius versus a Maserati. I noted that the higher powered and larger engine of the Maserati could more rapidly convert the chemical energy in the gasoline into mechanical energy, i.e., rotation of the crankshaft, which is then converted into forward motion, or kinetic energy. However, I also noted that the Maserati does so less efficiently and that was cause for some smugness on my part.
 

  (Picture source: Maserati)

Let's be sure we understand the term conversion efficiency. Energy conversion efficiency is the ratio of useful energy produced to the input energy of the fuel used to drive an engine. It is typically calculated as a percentage: 

 

Energy Conversion Efficiency = (Output Energy/Input Energy) x 100
 

In automobile engines, energy conversion efficiencies are measures of how effectively the engine converts the chemical energy in gasoline into the mechanical energy of a turning crankshaft. The efficiencies are typically 25 to 35% for gasoline engines such as those found in a Maserati, 37% for my Prius and over 40% for turbocharged diesel engines. In fact, some turbocharged diesel engines can reach 47% conversion efficiencies. The rest of the energy is lost as waste heat. The useful mechanical energy that is produced is then used to overcome friction, turn the wheels and move me and the hunk of metal that constitutes my Prius from Concord to Manchester. Indeed, if we were to calculate the energy required to move one 200 lb man from Concord to Boston, we would determine, on that basis, that efficiencies are only of the order of 1%. The rest of the energy is lost as waste heat, waste energy during idling, overcoming friction, powering the devices in the car and moving the bulky metal can around me. That low overall efficiency is, for me, always pause for reflection.

 

The challenge with conversion efficiency is that one needs to be sure what one is comparing and recognize that there are many measures of efficiency. For example, when discussing automobile engines, we must not confuse fuel economy with energy conversion efficiency. Even though the fuel economy of a Prius is three times that of Maserati, it does not mean that the Maserati has a conversion efficiency one third of my Prius. The Prius owes most of its higher fuel economy to a lower vehicle weight plus its regenerative braking technology. In other words, the three-fold better fuel economy is more a vehicle issue than an engine issue.

 

While we are on the topic of engines, let's take a closer look at those extremely large engines in New Hampshire that are used to produce electricity. These engines can be coal-, oil-, wood- or natural gas-fired or even powered by wind or water. In this case we will measure efficiency by dividing the produced electrical energy by the input energy in the fuel which is used to drive the generator.

 

The table below shows the calculated aggregated conversion efficiencies for the various forms of electricity generation in New Hampshire. (Unlike last week, we have to resort to 2010 data as a full set of 2011 data is not yet available from the Energy Information Agency.) In this table, I have compared electricity output with the input energy consumption for each form of electricity production.

 

The conversion efficiencies are presented in the last column and are ranked from lowest to highest. The conversion efficiencies are generally low, and if we were to consider all the energy in NH produced from a single enormous generator – the Megarac 4500 from last week – the conversion efficiency for this device would only be 34%. The rest of the energy, 66%, is lost as waste heat.

 

Biomass has the lowest conversion efficiency, only 23%, partly because some of the energy is expended in driving off the water in the wood chips which can contain as much as 50% moisture. Coal-, nuclear- and oil-based fuels have conversion efficiencies in the low 30s. The conversion efficiencies for the State's hydroelectric operations are only 35%, which I found somewhat surprising: large hydroelectric operations are reported to have efficiencies of close to 90%, which means they can harness 90% of the energy in channeled water flow; even smaller operations are reported to operate with efficiencies of the order of 50% so the 35% figure for NH is a little puzzling. Modern three-blade wind turbines typically harvest about 40% of the available wind blowing over the turbine area so the 37% figure for wind is as expected. Natural gas, at 45%, has the highest conversion efficiency.

 

Natural gas is particularly intriguing as we are presently witnessing the large-scale switchover from coal- to natural gas-fired electricity generation. The driver for this switch has been low natural gas prices, but there has also has been a lot of research and development into gas fired turbines used for electricity generation which has significantly improved the conversion efficiencies of these devices. With modern gas-fired units, we have moved away from the classical way of generating electricity - burning fossil fuels to boil water to make steam to turn a generator which produces electricity. Instead, gas-fired generators are now of the gas turbine variety, where the turbine is propelled not by steam, but directly by the hot expanded gas that results from the combustion of natural gas. Moreover, because of new advanced turbine materials, we can run them at higher temperatures of operation which also improves engine efficiencies. With higher operating temperatures, we then have exit gases leaving at elevated temperatures. We are then able to harness these high temperature off-gases in a secondary operation to boil water to create steam to drive a secondary steam-powered generator. These units are known as combined cycle units and they can operate at very high efficiencies. A basic schematic of a combined cycle unit is shown in the figure below.

 

(Picture Source: Wikipedia)

 

The chart below, which is from an MIT report that reviewed advances in gas turbine technologies, shows how gas turbine technical advances have led to increased efficiencies for both simple(those without a secondary steam boiler) and combined cycle units (those with a secondary steam boiler). At the time of the report, units with 60% efficiencies were foreseen and today commercial units from both GE and Siemens are available that can achieve 60% or even slightly higher. These advances come as a result of years of turbine research for aircraft engines and energy generation as well as advances in materials that can withstand even higher temperatures.

 

 

It is these increased conversion efficiencies that are part of the attraction of natural gas. Not only does natural gas release less carbon dioxide per unit of input energy, but the energy conversion efficiencies are substantially greater than those of coal-burning operations: this further serves to reduce carbon dioxide emission per megawatt hour of electricity produced. In fact, per unit of electricity produced, carbon dioxide emissions from natural gas operations can be less than one half of that of equivalent coal operations. Over time, as equipment is improved, new investments are made and older, less efficient equipment is retired, I would expect the conversion efficiency of natural gas-based electricity generation in NH to creep up from the 45% noted in the table above. There clearly is a lot we can do to improve the existing efficiency of natural gas combustion in New Hampshire.

 

Returning to the conversion efficiency table above, we note that conversion efficiencies for technologies other than natural gas are surprisingly low. Technological advances over time should improve these. However, breakthrough advances, like those we have seen for natural gas, are unlikely. Instead, we will see small incremental improvements over time and, in my mind, continual improvement in efficiencies should be part of the operating philosophy of every electrical generator and should perhaps even be part of the permit to operate. Small incremental improvements in conversion efficiency can result in large bottom-line benefits for both generating companies and for the planet, as this will reduce the amount of carbon dioxide released per megawatt hour of energy produced.

 

But, instead of waiting for breakthrough energy efficiency technologies, there is something we could do right away. We should be focusing on that 66% of waste heat. We should be investigating applications where we harness that unused heat and find ways to distribute it to the community, such as you would find in district heating applications that are in common use in many of the northern European countries. If we did this, then we would certainly be getting away from the classical way of doing things - simply burning fossil fuels to produce steam to turn turbines which only generate electricity and a lot of wasted heat.

 

Hopefully this week I have left you with an appreciation of how low our energy conversion efficiencies are for electricity generation and that there are opportunities for improvement. You should also have a good understanding of the difference between energy conversion efficiency and capacity factor. Remember, energy conversion efficiency is the ratio of useful energy output to the input energy and capacity factor is the ratio of a generator's actual output compared to what theoretically could be achieved if the generator could be run 24 hours, 365 days per year.

 

Until next time, remember to turn off the lights when you leave the room.

 

Mike Mooiman
Franklin Pierce University
mooimanm@franklinpierce.edu
3/25/13

(*Classical Gas is the name of a guitar instrumental tune, written and performed by Mason Williams in 1968 who, at the time, was a writer on the Smothers Brothers Show. For an instrumental, it was a big hit, reaching #2 on the charts. Forty five years later I still think it has a lot of appeal. Take a listen to the acoustic version without all the orchestral filigree.)

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I’ve Got the Power!* – Electricity Production in New Hampshire

My post this week is part informative and part instructional. When we debate and discuss energy issues, a couple of key concepts come up time after time and to be a contributor to an energy discussion, we have to know, or familiarize ourselves with, some technology and terminology. This week I want to explain two fundamental energy concepts. The first is the difference between energy and power, and the second is capacity factor. I will then show how they can be applied to electricity production in New Hampshire.  

Let's start with the difference between energy and power. The terms energy and power are often used interchangeably. This is OK in a general conversation, but in an energy related discussion it can lead to confusion, misunderstanding and bad decisions. It is essential to be specific about which term you are discussing so let's take a crack at distinguishing between the two.

 

The standard scientific definition is that Energy is the ability of a system to do work. It is a quantity which we need to get something to move, heat up, light up, burn, explode, etc. Energy also comes in different forms, for example, electrical energy, chemical energy, nuclear energy, kinetic energy etc. and much of energy technology is about converting one form of energy to another in the most efficient manner. Some of the more common units of measurement for energy are kilowatt hours (kWh), megawatt hours (MWh), BTUs, among others.

 

Power, on the other hand, is the rate at which energy is produced from a fuel source or is converted from one energy source to another. Units of measure for power include kilowatts (kW), megawatts (MW), BTU/hour or horsepower.

 

The confusion between these two often stems from the similarity of the units like kilowatt hours, which is an energy unit, and kilowatts, which is a power unit. However, it is necessary to understand that even though the units seem similar, there is a world of difference between them. This difference stems from the simple mathematical relationship between energy and power;

 

Energy = Power x time.

 

One my students in the Energy and Sustainability program at Franklin Pierce University recently noted that energy and power are analogous to distance and speed. Energy, like distance, is a quantity, whereas power is a rate like speed. Like the relationship between energy and power, the relation between distance and speed is written as;

 

Distance = Speed x time.

 

Let's consider a simple backup generator that I have been eyeing at Lowe's – the Generac 5500 Watt Portable Generator.

 

  (Picture source: Lowes)

 

This unit is rated at 5500 Watts or 5.5 kilowatts (kW), so the power of the unit is 5.5 kilowatts. If I were to run this unit for 1 hour, I would produce,

 

5.5kilowatts (kW) x 1 hour = 5.5 kilowatt hours (kWh)

 

of electrical energy that I could use to run my home. Running it for 24 hours would produce 5.5 kW x 24h = 132 kWh of electrical energy. The power rating of 5.5 kW is a measure of the rate at which the backup generator can take the chemical energy in the gasoline and convert it to electrical energy that I can use to keep my home running during a blackout. The larger the motor on the generator, i.e., the greater the power, the faster is the rate of energy conversion. In automobiles we are looking to convert the chemical energy in gasoline into forward kinetic motion to get us from point A to B. Again, the greater the power of the engine, the faster will be the rate of energy conversion. The pictures below illustrate this point.

 

(Picture source: Maserati)

 

The Maserati with its higher power, and larger, 700HP motor has the ability to more rapidly convert the energy in the gasoline tank into forward kinetic motion than my trusty and somewhat dusty blue Prius with its 80 HP motor. These two automobile engines, under specific circumstances, can produce the same amount of energy, however, the Maserati can do so in substantially less time. The Maserati will do so a lot less efficiently than the Prius but with a whole lot more fun. Even if I can't barrel down the highway at very high speeds, at least I will have my energy efficiency smugness to compensate me for the lack of admiring or envious glances for my ride. We will come back to the topic of energy conversion efficiency in a future blog post.

 

Let's go back to the Generac 5500 generator unit so we can discuss the second fundamental concept for this post – capacity factor. If I could run the generator solidly for 24 hours a day the whole year, I theoretically could produce;

 

5.5kW x 24h/day x 365 day/year = 48,180 kW of electrical energy.

 

However, if I were to use the generator only for 1 week during the year, say during a blackout, I would produce;

 

5.5kW x 24 h/day x 7 days = 924 kWh of electrical energy.

 

Dividing actual produced energy by the maximum that theoretically could have been generated in a 24/365 scenario produces a ratio called the capacity factor. In my case, it produces a figure of 0.019 which converts to a percentage of 1.9% and that would be the capacity factor of my generator for that year. In other words, my generator only ran at 1.9% of its maximum potential output. The capacity factor is a useful measure of how much of the capacity of an energy generating device was utilized over a time period, typically one year.

 

With these basic terms, energy, power and capacity factor under our belts, let's turn back to New Hampshire energy issues and particularly electricity generation. I have examined the 2011 electricity generation figures for New Hampshire that were published by the Energy Information Agency (EIA) and have combined, in one table, the number of generating units, their combined power, the energy produced from these units and the overall calculated capacity factors.

 

  

In 2011, there were 149 energy generating units in New Hampshire ranging from the large nuclear power at Seabrook, four coal fired plants, the wind farm in Lempster and 93 small hydroelectric operations, among others. The combined nameplate capacity of the generating units was 4,490 Megawatts or 4.5 Gigawatts, and they generated just over 20 million megawatts of electrical energy in 2011.

 

On examining the capacity factors, it is interesting to note how far they are from 100%. The only way a generating device can run at a capacity factor of 100% is by running 24 hours 365 days a year which is simply not practical or realistic. Equipment breaks down and has to be repaired or has to be shut down for maintenance. Moreover, power plants generating electricity make operating choices, based on prevailing wholesale electricity prices, fuel prices as well as demand to throttle back their units from their name plate capability. This reduces the amount of electricity produced which, in turn, reduces the capacity factor.

 

The units with the highest capacity factors are nuclear and wood fired operations which operated with capacity factors of 76% and 70%, respectively. These operations supply a great deal of the base load power to the electrical grid and therefore tend to run all the time except for maintenance shutdowns and reduced output during periods of low demand such as late evening and early morning hours.

 

Coal and natural gas ran at about 50% of their capacity and wind energy, which is very much dependent on wind speed and availability, has a capacity factor of 0.31 which is typical for wind projects. Oil and diesel based generators only have a capacity factor of 0.017 or 1.7%, which indicates these units are seldom used, due to the cost of producing electricity from oil. They function as back-up generators and are only used in an emergency. In many respects they are just like the small Generac 5500 unit, my present object of desire.

 

Even though the 149 New Hampshire based generating units are run by different operators with different technical and economic considerations, it is useful to consider their aggregated capacity. As noted above, the combined nameplate capacity of the generating units is 4,490 Megawatts or 4.5 Gigawatts. This combined capacity in a single unit would be one mammoth sized generator - we could call it the "New Hampshire Megarac 4500" – which is almost a million times larger than that unit I have my eyes on at Lowe's. 

 

 

 

(Generator Picture source: Lowes)

Based on 2011 data, this NH Megarac 4500 was operated at a capacity factor 0.51 which means the combined NH generating facilities only generated 51% of the energy that was theoretically possible. So, if we lose some of generating units in state, we have some excess capacity. However, we need to keep in mind that practical considerations such as cost and availability of fuel and maintenance requirements need to be taken into account when we shutdown generating units and expect others to operate at higher capacity factors. We also need to keep in mind that New Hampshire electricity generation is not an island unto itself. We feed into and draw electricity from the ISO-New England bulk power generation and transmission system which coordinates electricity supply and demand throughout New England. The six New England states have a combined capacity of about 35,000 MW of electrical capacity from 860 generating units.

 

Hopefully this has been an informative and instructional post and you now know the difference between energy and power and you have an appreciation for capacity factors. As you can see, we have a lot a capacity for generation in New Hampshire but it is crucial to appreciate that not all this capacity can be tapped at any one time. Running these generators depends on complex number of issues which include demand, cost of and availability of fuel, maintenance shutdowns and financial considerations and it all functions remarkably well most of the time due to the coordination of supply and demand that happens in the ISO-New England grid system.

 

In the meantime, if you see me in the parking lot at Lowe's trying to load a Generac 5500 into my dusty blue Prius, stop and give me a hand. Until next time, remember to turn off those lights when you leave the room.

Mike Mooiman
Franklin Pierce University   
mooimanm@franklinpierce.edu
3/18/13

 
(*The title of this week's blog comes from 1990's tune by Snap!, a German rap/pop group. Their song "The Power", features an incessant "I've Got the Power!" refrain. You do know the song, but as soon as I thought of it, the refrain became a relentless mind worm burrowing its way into my brain and I have not been able to get rid of it. Annoyingly, I now mentally hear it every time I flip a light switch. Here is the Youtube clip but be forewarned about that mind worm.)

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