Category: Electric utilities

Grids, Smart Grids and More Grids: What’s Coming

In an earlier blog post on energy storage I stated that there are two developments related to the widespread use of renewable energy that ‘I would fall on my sword for’, energy storage and smart grids. This post discusses the second of these in the context of large-scale smart grids and smaller minigrids. Both are critical to the future of renewable energy in both developed and developing countries.

Grids are collections of wires,switches,transformers,substations, and related equipment that enables the delivery of electrical energy from a generator to a consumer of that energy. A traditional grid structure today is shown below:

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The first grid, for delivery of alternating current (AC) electricity, was put into operation in 1886. Electrical energy can be delivered as either AC or DC (direct current) electricity, but for over a century AC has been the preferred delivery mechanism. A more complete discussion of AC vs. DC is a good topic for a future blog post.

The traditional grid is a one-way distribution network that delivers power from large centralized generating stations to customers via a radial network of wires. Regional grids, when integrated, constitute a national grid, something the historically balkanized U.S. electric utility system is still trying to achieve. Transmission lines are long distance carriers of electrical energy transmitted at high voltages and low currents to minimize electrical losses due to heating in wires. This high voltage energy is then reduced via transformers to lower voltage, usually 120 or 240 volts, to supply local distribution networks that bring the energy to our homes and businesses. The U.S. Energy Information Administration estimates that national electricity transmission and distribution (T&D) losses average about 6% of the electricity that is transmitted and distributed in the United States each year.

While the traditional grid has brought the benefits of electricity to billions of people for many decades, its shortcomings have become more visible in recent years. The problem is its vulnerability to disruption by extreme weather events (only a small fraction of T&D wires are underground), physical attack and accidents leading to widespread power outages, cyber attack in today’s world of increasing dependence on information technologies, and even large solar storms that strike the earth occasionally and interact with the T&D system acting as giant antennas.

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The utility industry has usually (but not always) resisted putting wires underground because of high costs, and increased effort is going into trimming trees that can fall on or otherwise disrupt power lines. Control of the grid has also been improved to minimize the possibility of disruption in one grid sector spreading to others, but this is a costly work in progress. What is looming as a major threat to the traditional grid is its increasing dependence on automated remote control via advanced computer/information technologies built into the grid system that are vulnerable to hacking and other malevolent interventions.

Grid systems with computer controls are referred to as smart grids. Through the gathering, communication, analysis, and application of analog or digital information on the behavior of suppliers and consumers, a smart grid can use automation “..to improve the efficiency, reliability, economics, and sustainability of the production and distribution of electricity.” The issue of cyber vulnerability has only begun to receive careful attention in recent years as the hacking phenomenon has surged and the ability to interrupt remote industrial activities via computer viruses such as Stuxnet have been demonstrated.

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What can be done to protect against this vulnerability? Considerable effort is going into developing software that is resistant to hacking, but this is proving extremely difficult to achieve. As has become all too obvious, there are lots of talented hackers out there and some of them are supported by national governments. Nevertheless, this is a path that has to be pursued, and is becoming a priority in the training of new IT programmers and specialists.

Another approach is to move away from the historic centralized grid and move to a grid system where disturbances can be isolated (islanded) once detected and thus unable to affect other parts of the grid. This will require distributed generation sources that supply unaffected parts of the grid, and could be other centralized generators that can be tapped or local renewable energy sources (wind, solar) that are not in the disturbed grid sector.

Traditional grids are expensive, and extending these grids from urban to remote areas often can not be justified economically. This is particularly true in developing countries where most of the world’s 1.5 billion people without access to electricity reside. Improving access to modern energy services in rural areas is a major development priority, and there is increasing attention to decentralized generation and distribution through mini-grids. “A ‘mini-grid’ is an isolated, low-voltage distribution grid, providing electricity to a community – typically a village or very small town. It is normally supplied by one source of electricity, e.g. diesel generators, a solar PV installation, a micro-hydro station, etc., or a combination of the above.” It includes control capability, which means it can disconnect from a traditional grid and operate autonomously.

A recent workshop organized by the Africa-EU Renewable Energy Cooperation Programme (RECP), held in Tanzania in September 2013, focused on this rapidly emerging option – ‘Mini-Grids: Opportunities for Rural development in Africa’. The workshop background was described as follows: “Given Africa’s abundance of renewable energy resources, the widespread existence of isolated, expensive, highly-subsidized fossil-fuel based mini-grids on the continent, very low grid connection rates, the often low levels of electricity demand from households, the high costs associated with grid extension, the lack of reliable, centralized generation capacity and increasing levels of densification as a result of ongoing urbanization, renewable energy and hybrid-based mini-grids provide a practical, efficient energy access solution.” It should also be noted that the use of renewables can reduce fossil-fuel use, reduce carbon emissions, and create local jobs and economic development.

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Another type of mini-grid is the micro-grid, a term used to describe mini-grids that deliver DC electricity to its consumers. Still another variation is the skinny-grid, which emphasizes the use of energy efficiency technologies to reduce consumer demand and thus allow the use of thinner and less expensive connecting wires between generators and end users.

I will conclude this blog post by discussing the role of smart grids in facilitating the integration of renewable energy into the grid. Renewable energy is now growing rapidly as a share of the global energy mix and this trend will continue as we move further into the 21st century. We are also learning that, despite the variable nature of solar and wind energy, by using the control features of increasingly sophisticated smart grids and the use of energy storage, this integration can be done safely and cost effectively with high levels of renewables penetration.

IRENA, the International Renewable Energy Agency headquartered in Abu Dhabi, has addressed this issue in a comprehensive November 2013 report entitled ‘Smart Grids and Renewables’. As stated in the Executive Summary: “This report is intended as a pragmatic user’s guide on how to make optimal use of smart grid technologies for the integration of renewables into the grid. …The report also provides a detailed review of smart grid technologies for renewables, including their costs, technical status, applicability and market maturity for various uses.” It acknowledges that “Much of what is known or discussed about smart grids and renewables in the literature is still at the conceptual/visionary stage..” but includes “..several case studies that involve actual, real-world installation and use of smart-grid technologies that enable renewables.” The report also points to needed policy and regulatory changes for successful renewables integration. It is a valuable and forward-looking document.

Energy Storage: A Critical Link In the Renewable Energy Chain

An issue that has always grabbed my attention is the critical role I and others foresee for energy storage in the eventual widespread use of variable (intermittent) renewable energy sources such as wind and solar. In fact it was the focus of my first decision when I assumed responsibility for DOE’s renewable electricity programs in 1994. That decision was to establish a comprehensive storage program to complement the established generation programs – up until that point the only storage program was a small effort on underground hot water storage at a university in South Carolina (no doubt related to the fact that the Chairman of the relevant budget authorization subcommittee was from South Carolina). The new program, in addition to thermal storage, added battery storage and superconducting magnetic energy storage (SMES) – superconductivity was another of the programs I managed.

Energy storage is one of two critical renewable energy issues that I have always said I would ‘fall on my sword for’. The second is the need for a national smart grid that will allow renewable electricity generated in one part of the country to be shared with other parts. I have touched briefly on the energy storage topic in earlier blog posts; this post takes a much more detailed look at various storage options.

The need for storage to steady the output from a variable energy source is not new. In fact, in December 1861 the following words and illustration appeared in an agrarian newsletter:
“A Mighty Wind One of the great forces nature furnished to man without any expense, and in limitless abundance, is the power of the wind. Many efforts have been made to obtain a steady power from the wind by storing the surplus from when the wind is strong. One of the latest and simplest of these is illustrated in the accompanying engraving. A windwheel is employed to raise a quantity of iron balls, and then these balls are allowed to fall one by one into buckets upon one side of a wheel, causing the wheel to rotate, and thus to drive the machine.”

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If one substitutes water for the iron balls and attaches a generator to the rotating machine you have today’s system of pumped water storage and generation. A modern version of the 1861 system, using gravel instead of iron balls, is shown in the following sketch:

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Since the discovery of electricity generation using rotating coils of wire in magnetic fields by the British scientist Michael Faraday in 1820, people have sought ways to store that energy for use on demand. Without such storage, or use in some other way (e.g., to electrolyze water to create and store hydrogen, heat water, bricks or phase change materials that store heat , or refrigerate water to create ice) surplus electricity generation is lost. With modern societies increasingly dependent on energy services provided via use of electricity, the need for electricity storage technologies has become critical. This is especially true as more and more variable renewable energy enters the grid, to avoid grid destabilization. This can occur because electric power supply systems must balance supply and demand, and because demand is highly variable and hard to control the balancing is routinely achieved by controlling the output of power plant generators. If these generators are variable solar and wind, and their grid contribution becomes significant, achieving the balance is that much more difficult, and a means of stabilizing these variable outputs is needed.

There is also strong economic and social incentive for storing electricity in a localized, distributed manner. Today’s 100-year-old centralized utility business model, in which large central power plants deliver electricity to customers via transmission and distribution lines, includes the imposition of peak demand charges that can account for a significant fraction of a business’ or an individuals’ electricity bill. With the use of localized generation (e.g., PV panels on your roof), combined with storage at your site, these demand and peak charges can be reduced if not eliminated, and independence from the utility, to some degree, can be achieved. This reality is taking place in Germany (and coming to the U.S.) and threatening the utility business model in Germany to the extent that German utilities have gone into the solar-energy storage business. They now sell or lease or maintain roof-mounted PV and battery storage systems.

Today’s menu of devices that allow storage of surplus electricity for use at other times includes: solid state batteries and supercapacitors, flow batteries, flywheels, compressed air energy storage (CAES), and pumped hydropower. Hydrogen generated from any electricity source via electrolysis of water, and combusted or used in fuel cells, is, in many ways, the ultimate storage technology for surplus electricity. Flywheels, pumped storage, and fuel cells are discussed in earlier blog posts ; other storage technologies are discussed below.

Historically, electricity has been stored in lead-acid batteries, and this is still the dominant battery storage technology today in cars and elsewhere because of low cost, high power density, and high reliability. Disadvantages are low specific energy storage capacity, large size, high weight, and the need for an acid electrolyte. Lead is also a toxic material. Research to improve batteries has been underway for more than a century, and considerable progress has been made (e.g., improved lead-acid batteries that require no maintenance and recycling of used batteries to recover the lead), with considerable promise for further developments in the future.

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Most battery attention today is focused on lithium-ion batteries where cost and safety are prime concerns. Research into post lithium-ion batteries is also being actively pursued.
Lithium-ion batteries are widely used today because! “pound for pound they’re some of the most energetic rechargeable batteries available.” For example, it takes six kilograms of a lead-acid battery to store the same energy as one kilogram of a lithium-ion battery. Lithium-ion batteries (there is a variety of battery chemistries) also hold their charge well (losing about 5% per month), have no memory effect (therefore no need to fully discharge before recharging), can handle many hundreds of charge/discharge cycles, and have good ’round trip efficiency’. The story does have a negative side – lithium-ion batteries are sensitive to heat, can’t be fully discharged (thus requiring a computerized battery management system), are still costly (although costs are coming down), and certain chemical formulations can occasionally burst into flame if damaged or otherwise overstressed. One person making a big bet on lithium-ion batteries is Elon Musk, who has announced plans for a $5 billion battery factory, to provide lithium-ion batteries for his Tesla electric vehicles and other applications. Through such large scale production Musk hopes to reduce the cost of the batteries by 30 percent (to about $10,000 for a 60 kWh battery pack).

Supercapacitors store energy in electric fields and fill a gap between ordinary capacitors and rechargeable batteries. Their claim to fame is that they can be charged/discharged much more rapidly than batteries and can tolerate many more charge/discharge cycles. They are widely used as low current power sources for computer memories and in cars, buses, trains, cranes and elevators, including energy recovery from braking.

Redox (reduction/oxidation) flow batteries are large scale rechargeable energy storage systems that are on the verge of wide application in the electric utility sector. They are particularly well suited to storing large amounts of energy, e.g., the surplus energy created by hours of solar or wind power generation. The energy storage materials are liquids that are stored in separate tanks, and when energy is needed the liquids are pumped through a ‘stack’ where they interact to generate electricity. Many different chemical liquids have been tested for flow battery operation, with most current attention being focused on vanadium compounds which are expensive. Flow batteries also have relatively low round-trip efficiencies and response times. Because of the vanadium cost concern many other chemical possibilities are being evaluated.

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CAES (compressed air energy storage) utilizes surplus electricity to compress air to high pressures in large caverns, which can then be heated and released as needed to power expansion turbines that generate electricity. Such a CAES system has been operating successfully in Alabama since 1991, and gases other than air (e.g., carbon dioxide) can be used as well.

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SMES stores energy in the magnetic field of a circulating dc electrical current in a superconducting coil. The superconductor has no electrical resistance and the current continues indefinitely unless its energy is tapped by discharging the coil. A typical SMES device has two parts, a cryogenic cooler that cools the superconducting wire below its transition temperature at which it loses its electrical resistance, and power conditioning circuitry that allows for charging and discharging of the coil. Its advantages are ultra fast charge and discharge times, no moving parts, nearly unlimited cycling capability, and an energy recovery rate close to 100 percent. Disadvantages are cost of the wire, the need for continuous cooling, large area coils needed for appreciable energy storage, and the possibility of a sudden, large energy release if the wire’s superconducting state is lost. SMES devices are often used to provide grid stability in distribution systems and for power quality at manufacturing plants requiring ultra-clean power (e.g., microchip production lines). One MWh SMES units are now common and a twenty MWh engineering test model is being evaluated.

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To summarize, there are many energy storage options that work and tradeoffs are often required – e.g., among storage capacity, power capacity, round-trip efficiency, and most importantly cost. Lots of research is underway to reduce costs, given the large potential markets and the need to safely integrate variable renewable energy generation from solar and wind into the utility grid system. I have no doubt that cost-effective storage systems will soon be available, facilitating the needed rapid transition to a renewable electricity future.

Human Wastes: Another Energy Resource Waiting to Be Tapped

Recently I posted a blog entitled ‘Animal Wastes: An Energy Resource That Is Win-Win’. The Washington Post article reproduced below may be considered a follow-up to that blog but focused on using human wastes to generate energy. It usefully points out the several beneficial uses to which human wastes can be put and the economic benefits of doing so. It is worth reading!

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WASTE, NOT WASTED
By Ashley Halsey III
Washington Post (April 6, 2014)

This is a topic that one must approach delicately so as not to offend the reader’s sensibilities, but since it is a matter of importance for which you may receive a bill for some portion of $470 million, we start out with an analogy.

You need energy, so you eat. Through the miracle of digestion, your body sorts what you have eaten, say, a pastrami on rye with a glob of coleslaw and a dill pickle, and plucks out the nutrients — proteins, carbohydrates and sugars it needs to generate power. Then it jettisons the rest.

What your body jettisons disappears forever, carried along in a huge network of sewers to a plant in the southeastern corner of Washington.

Just like you, that plant needs energy. Through a miracle called thermal hydrolysis, it soon will be able to sort through what you have jettisoned and use it to generate electricity.

Yes, from poop will come power — 13 megawatts of it. Enough electricity to light about 10,500 homes.

Ben Franklin never dreamed of this one.

While Ben may have denounced the scheme as impossible sorcery, he also noted that a penny saved is a penny earned, so he might have been at least intrigued by this notion.

More than a few pennies may be saved for the citizens of the District and for some Virginians and Marylanders. Those people — 2.2 million of them — get a monthly bill for the privilege of sending their thoroughly digested nutritional intake to the plant in Southeast Washington operated by D.C. Water.

A chunk of that monthly bill is passed on to another local utility — Pepco. D.C. Water is the electricity company’s No. 1 customer. By converting poop to power, the water company will cut its Pepco bill by about one third and reduce by half the cost of trucking treated waste elsewhere.

But enough about poop, a subject that makes many a reader a bit squeamish. Because we’d rather not drive you away from the description of a wholly remarkable plan that is very likely to affect your pocketbook, henceforth we will refer to the matter that flows through the sewage plant as “the product.”

In fact, you soon will learn, it is going to be turned into a genuine product. One with a price tag. One that you may buy back.

Think about it.

The product has shed the label “wastewater” to morph into something called “enriched water,” a term laden with many more intriguing possibilities.

“It could be a game changer for energy,” said George Hawkins, an environmentalist who became general manager of D.C. Water. “If we could turn every enriched-water facility in the United States into a power plant, it would become one of the largest sectors of clean energy that, at the moment, is relatively untapped.”

What’s nearing completion outside Hawkins’s office window, however, is something never built on this scale anywhere in the world. A decade of study came first, and to see whether the system would work here, D.C. Water paid smaller European utilities that use the same process to modify their product so it more closely matched that which Washington produces.

“We’re confident that this model will work,” Hawkins said.

Something called the Cambi, for the Norwegian company that builds it, sits at the heart of it.

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When the product flows into the more than 150-acre plant known as Blue Plains, it goes through a couple of mesh filters to shed the debris swept up in the sewer system. Then it goes through a treatment process that turns it into what the Environmental Protection Agency categorizes as class B waste, enough to fill 60 big dump trucks with 1,600 tons of product every day.

And out the gate it goes, at a cost of $16 million a year.

That will change in May and June, as D.C. Water begins a phase-in intended to get the new system into full service by January.

Here’s how it works:

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A centrifuge drains off the liquid, and then the screened product will flow into four pulpers, tall stainless steel vats that look like Gulliver’s soda cans. Steam recycled from farther down the process is used to preheat it, and then it flows into one of the two dozen Cambis. They sit like a row of gleaming, blunt-nosed rockets, but they serve as pressure cookers.

The product is heated to more than 320 degrees under as much as 138 pounds of pressure for 22 minutes. Then it moves to a flash tank, where the temperature and pressure drop dramatically and a critical change takes place.

“Because of that pressure difference, the cells burst,” said Chris Peot, director of resource recovery at D.C. Water.

When the cells burst, the methanogens can have their way with them.

That happens in the digesters. They are four huge concrete vats, 80 feet tall and 100 feet in diameter. Right now, their interiors are like vast cathedrals, with domed ceilings and a shaft of light glancing through a hole in the top.

When the whole operation gets rolling, inside them is not a place you would want to be. The product will flow in from the four flash tanks, mixing with the methanogen microorganisms. Methanogens create marsh gases. In the digestive tracts of animals and humans, they also create gas, to the particular delight and fascination of middle-school boys.

That’s what this is all about — creating methane to generate electric power.

The temperature inside the digesters is kept at about that of the human body: 98.6 degrees Fahrenheit. Each digester chamber has five vertical blue tubes, as big around as manhole covers, that suck the product from the bottom and recycle it to near the top. After the product stews there for about two weeks, the methane produced by the process will vent out a 12-inch diameter pipe in the crown.

After a bit more purification, the methane will be used to fire three jet turbine engines that create electricity. A byproduct of that process: steam, which is funneled back to the pulper.

The power portion of the plant will be operated under contract by Pepco. The deal doesn’t allow D.C. Water to sell the power it generates, a moot point since the process of creating it eats up 3 megawatts and the remaining 10 megawatts will be sucked up by operations at Blue Plains.

Once the digester’s work is done, the remaining product will be drained out into dump trucks, but their total load will be cut in half to about 600 tons a day.

Remember that we told you earlier that what you jettison disappears forever? Let’s reconsider that, because there’s actually a chance you’ll see it again. In a strikingly different form. Right back where you saw it first: on your dinner table.

The product that has been trucked from Blue Plains is rated class B. But the product that comes out of the digester will be rated class A.

The difference?

Class B still has some bad stuff in it. Most of it is shipped to farmers, some in Maryland but most of them in Virginia. They get it free, but unless they let it sit for at least a month, and sometimes up to 18 months, the only things they can use it to fertilize are trees and sod used by landscapers.

Class A product can be used right away on anything, including fields that grow the fruits and vegetables you buy at the grocery store and serve for dinner.

That’s because, Peot says, in the Cambi, “All the pathogens are completely obliterated.”

“Our product has these super-elevated levels of these naturally occurring, extremely important plant hormones,” Peot said.

It is a more environmentally sound choice than the chemical fertilizer alternatives. In the raw, the class A product is so potent it needs to be cut with other materials before it is used to fertilize crops.

“We can blend this with sawdust and sand and make a topsoil substitute for use in green infrastructure projects,” Peot said. “We’re still going to go to farms while we try to build the market for this product.”

Hawkins, D.C. Water’s general manager, chimed in: “It’s clean, organic fertilizer. Conceivably, we could sell this product at Home Depot. ”

Unlike most innovations in waste treatment locally and nationwide, this project was not mandated by a federal court order. D.C. Water’s board decided it was a worthwhile investment of ratepayers’ money.

“This was one of the easier $500 million decisions that we’ll ever ask the board to make,” Hawkins said, ticking off the value: a savings in electrical costs of about $10 million a year; lowering the cost of hauling away treated waste; the potential to generate a profit by selling the product; a reduction by one third in the plant’s carbon footprint; and one more critical virtue.

For about three days a month ago, residents of part of Northwest Washington were told to boil their drinking water for fear it might be contaminated. That scare was caused by a power problem that shut down a pumping station.

“It wasn’t Pepco’s problem. It was internal to us,” Hawkins said. “We have great fears here about what would happen if there was a catastrophic power failure and Blue Plains stopped.”

Generating power internally will provide enough juice to keep the basics running, were that to happen, he said.

“This is the rare combination of both environmentally and economically positive,” Peot said.

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A Cambi installation in the UK

Zero Energy Buildings: They May Be Coming Sooner Than You Think

Buildings account for approximately 40 percent of the energy (electrical, thermal) used in the U.S. and Europe, and an increasing share of energy used in other parts of the world. Most of this energy today is fossil-fuel based. As a result, this energy use also accounts for a significant share of global emissions of carbon dioxide.

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Source: U.S. Department of Energy, Buildings Energy Data Book

These simple facts make it imperative that buildings, along with transportation fleets and power generation, be primary targets of reduced global energy and fossil fuel demand. This blog post discusses one approach in buildings that is gaining increasing visibility and viability, the introduction of net zero energy buildings and the retrofit of existing buildings to approach net zero energy operation. A net zero energy building (NZEB or ZEB) is most often defined as a building that, over the course of a year, uses as much energy as is produced by renewable energy sources on the building site. This is the definition I will focus on. Other ZEB definitions take into account source energy losses in generation and transmission, emissions (aka zero carbon buildings), total cost (cost of purchased energy is offset by income from sales of electricity generated on-site to the grid), and off-site ZEB’s where the offsetting renewable energy is delivered to the building from off-site generating facilities. Details on these other definitions can be found in the 2006 NREL report CP-550-39833 entitled “Zero Energy Buildings: A Critical Look at the Definition”.

The keys to achieving net zero energy buildings are straight forward in principle: first focus on reducing the building’s energy demand through energy efficiency, and then focus on meeting this energy demand, on an annual basis, with onsite renewable energy – e.g., use of localized solar and wind energy generation. This allows for a wide range of approaches due to the many options now available for improved energy efficiency in buildings and the rapidly growing use of solar photovoltaics on building roofs, covered parking areas, and nearby open areas. Most ZEB’s use the electrical grid for energy storage, but some are grid-independent and use on-site battery or other storage (e.g., heat and coolth).

A primary example of what can be done to achieve ZEB status is NREL’s operational RSF (Research Support Facility) at its campus in Golden, Colorado, shown below.

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It incorporates demand reduction features that are widely applicable to many other new buildings, and some that make sense for residential buildings and retrofits as well (cost issues are discussed below). These include:
– optimal building orientation and office layout, to maximize heat capture from the sun in winter, solar PV generation throughout the year, and use of natural daylight when available
– high performance electrical lighting
– continuous insulation precast wall panels with thermal mass
– windows that can be opened for natural ventilation
– radiant heating and cooling
– outdoor air preheating, using waste heat recovery, transpired solar collectors, and crawl space thermal storage
– aggressive control of plug loads from appliances and other building equipment
– advanced data center efficiency measures
– roof top and parking lot PV arrays

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U.S. ZEB research is supported by DOE’s Building America Program, a joint effort with NREL, Lawrence Berkeley National Laboratory, Oak Ridge National Laboratory, and several industry-based consortia – e.g., the National Institute of Building Sciences and the American Institute of Architects. Many other countries are exploring ZEB’s as well, including jointly through the International Energy Agency’s “Towards Net Zero Energy Solar Buildings” Implementing Agreement (Solar Heating and Cooling Program/Task 40). This IEA program has now documented and analyzed more than 300 net zero energy and energy-plus buildings worldwide (an energy-plus building generates more energy than it consumes).

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An interesting example of ZEB technology applied to a residential home is NREL’s Habitat for Humanity zero energy home (ZEH), a 1,280 square foot, 3-bedroom Denver area home built for low income occupants. NREL report TP-550-431888 details the design of the home and includes performance data from its first two years of operation (“The NREL/Habitat for Humanity Zero Energy Home: a Cold Climate Case Study for Affordable Zero Energy Homes”). The home exceeded its goal of zero net source energy and was a net energy producer for these two years (24% more in year one and 12% more in year two). The report concluded that “Efficient, affordable ZEH’s can be built with standard construction techniques and off-the-shelf equipment.”

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The legislative environment for ZEB’s is interesting as well. To quote from the Whole Building Design Guide of the National Institute of Building Sciences:
“Federal Net Zero Energy Building Goals
Executive Order 13514, signed in October 2009, requires all new Federal buildings that are entering the planning process in 2020 or thereafter be “designed to achieve zero-net-energy by 2030”. “In addition, the Executive Order requires at least 15% of existing buildings (over 5,000 gross square feet) meet the Guiding Principles for Federal Leadership in High Performance and Sustainable Buildings by 2015, with annual progress towards 100% conformance”.
Two milestones for NZEB have also been defined by the Department of Energy (DOE) for residential and commercial buildings. The priority is to create systems integration solutions that will enable:
Marketable Net Zero Energy Homes by the year 2020
Commercial Net Zero Energy Buildings at low incremental cost by the year 2025.
These objectives align with the Energy Independence and Security Act of 2007 (EISA), which calls for a 100% reduction in fossil-fuel energy use (relative to 2003 levels) for new Federal buildings and major renovations by 2030.”

A word about cost: ZEB’s cost more today to build than traditional office buildings and homes, but not much more (perhaps 20% for new construction). Of course, part of this extra cost is recovered via reduced energy bills. In the future, the zero energy building goal will become more practical as the costs of renewable energy technologies decrease (e.g., PV panel costs have decreased significantly in recent years) and the costs of traditional fossil fuels increase. The recent surge in availability of relatively low cost shale gas from fracking wells will slow this evolution but it will eventually occur. Additional research on cost-effective efficiency options is also required.

To sum up, the net zero energy building concept is receiving increasing global attention and should be a realistic, affordable option within a few decades, and perhaps sooner. ZEB’s offer many advantages, as listed by Wikipedia:
“- isolation for building owners from future energy price increases
– increased comfort due to more-uniform interior temperatures
– reduced total net monthly cost of living
– improved reliability – photovoltaic systems have 25-year warranties – seldom fail during weather problems
– extra cost is minimized for new construction compared to an afterthought retrofit
– higher resale value as potential owners demand more ZEBs than available supply
– the value of a ZEB building relative to similar conventional building should increase every time energy costs increase
– future legislative restrictions, and carbon emission taxes/penalties may force expensive retrofits to inefficient buildings”

ZEB’s also have their risk factors and disadvantages:

“- initial costs can be higher – effort required to understand, apply, and qualify for ZEB subsidies
– very few designers or builders today have the necessary skills or experience to build ZEBs
– possible declines in future utility company renewable energy costs may lessen the value of capital invested in energy efficiency
– new photovoltaic solar cells equipment technology price has been falling at roughly 17% per year – It will lessen the value of capital invested in a solar electric generating system. Current subsidies will be phased out as photovoltaic mass production lowers future price
– challenge to recover higher initial costs on resale of building – appraisers are uninformed – their models do not consider energy
– while the individual house may use an average of net zero energy over a year, it may demand energy at the time when peak demand for the grid occurs. In such a case, the capacity of the grid must still provide electricity to all loads. Therefore, a ZEB may not reduce the required power plant capacity.
– without an optimised thermal envelope the embodied energy, heating and cooling energy and resource usage is higher than needed. ZEB by definition do not mandate a minimum heating and cooling performance level thus allowing oversized renewable energy systems to fill the energy gap.
– solar energy capture using the house envelope only works in locations unobstructed from the South. The solar energy capture cannot be optimized in South (for northern hemisphere, or North for southern Hemisphere) facing shade or wooded surroundings.”

Finally, it is important to note that the energy consumption in an office building or home is not strictly a function of technology – it also reflects the behavior of the occupants. In one example two families on Martha’s Vineyard in Massachusetts lived in identical zero-energy-designed homes and one family used half as much electricity in a year as the other. In the latter case electricity for lighting and plug loads accounted for about half of total energy use. As energy consultant Andy Shapiro noted: “There are no zero-energy houses, only zero-energy families.”

Lighting: A Revolution In Progress

An energy revolution is underway before our very eyes – the replacement of traditional incandescent light bulbs with much more energy efficient and longer lasting light-emitting diodes (LEDs). It is a significant revolution because, according to NYSERDA, lighting accounts for 22% of electricity consumption in the U.S.. Other sources put this number at 19% on a global basis. It is estimated that LED use could cut the U.S. number in half by 2030.

At this point it may be fair to ask: What about CFLs (compact fluorescent lamps), which had been gaining market share for many years. A few words about lighting technology before we answer this question.

An incandescent light bulb, the most common type today in households and the least expensive to buy, produces visible light from a glowing filament wire (tungsten) heated to a high temperature (several thousand degrees) by an electric current passing through it. It was not invented by Thomas Edison, as is often stated (many earlier inventors had experimented with hot filament lamps), but he did invent the first commercially practical incandescent bulb. It was introduced into residential use more than 125 years ago. Its principal shortcoming is that more than 90% of the energy used by the traditional incandescent bulb escapes as heat and less than 10% goes into producing light. Filaments also burn out and are fragile, and a typical bulb lifetime is about 1,000 hours.

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Halogen lamps, also in common use today, are incandescent lamps with a bit of halogen gas (iodine or bromine) added to the bulb. The chemical reaction between the halogen and the tungsten wire allows the filament to operate at a higher temperature and increases the bulb’s efficiency and lifetime.

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A fluorescent lamp or fluorescent tube is a low pressure mercury-vapor gas-discharge lamp that uses UV-stimulated fluorescence of a phosphor to produce visible light. It is more energy efficient than an incandescent lamp but does require a ballast to regulate the current through the lamp, increasing its initial cost.

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Compact fluorescent lamps (CFLs) fold a fluorescent lamp tube into the space of an incandescent bulb with a ballast in the base. They use 3-5 times less energy than incandescent bulbs of the same light output and have much longer lifetimes. They do contain a small amount of mercury, creating a disposal problem.

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Light-emitting diodes (LEDs) are monochromatic, solid-state semiconductor point light sources. First appearing as practical electronic components in 1962, early LEDs emitted low-intensity red light, but modern versions are available at visible, ultraviolet, and infrared wavelengths with very high brightness. Today they are used in applications as diverse as aviation lighting, automotive lighting, advertising, general lighting and traffic signals. They are also used in the infrared remote control units of many commercial products including televisions, DVD players and other domestic appliances. Their high switching rates are useful in advanced communications technology.

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LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. However, LEDs powerful enough for room lighting are still relatively expensive (but costs are coming down) and require more precise current and heat management than compact fluorescent lamp sources of comparable output. Their advantages over CFLs are greater efficacy (i.e., more light output in lumens per watt), longer lifetimes, smaller size, directionality of the light produced, and very importantly they contain no mercury which has to be disposed of. These factors will limit CFLs’ time in the ‘limelight’ (I know, bad pun).

(Note: LEDs are based on inorganic (non-carbon-based) materials. OLEDs are organic (carbon-based) solid-state light emitters which are made in sheets that provide a diffuse-area light source. They are still in an early stage of development and several years away from broad commercial application. Interesting potential applications include TVs, computer and cell phone screens, wall coverings that allow changes in color, and automobile skins that allow you to change the color of your car.)

It is useful to compare these different lighting technologies, as white light emitters, in terms of their current efficiencies (efficacies), lifetimes, and color temperatures (measured in degrees Kelvin, as an indicator of the warmth or coolness of the light emitted). Efficacies for monochromatic LEDs are higher but are not listed here.

Technology Efficacy Lifetime Color Temperature
(lumens/watt) (hours) (K)
…………………………………………………….
Incandescent 12-18 750-1,500 2,400-2,900
CFL 60-70 6,000-10,000 2,700-6,500
Fluorescent tube 80-100+ 20,000 2,700-6,500
Halogen 16-29 2,000-4,000 2,850-3,200
White light LED 20-50. Up to 100,000 2,700-6,500

A quick calculation will help to demonstrate the cost effectiveness of lighting sources that may be more costly to buy but save energy and money over extended lifetimes (and don’t forget that not replacing bulbs as often also saves money by reducing labor costs). I will use CFLs as my example.

Assume we buy a 15 watt CFL bulb that today costs $6 and replaces a 65 watt incandescent bulb that costs $1. We further assume that the CFL will last 6,000 hours, the incandescent 1,500 hours (clearly a worst case for CFLs and a best case for incandescents), and that electricity costs 10 cents per kilowatt-hour. Over 6,000 hours the CFL will consume (0.015 kW)x(6,000h)=90 kWh for a total cost (purchase + energy use) of $15. The incancandescent will have been replaced four times in 6,000 hours and consumed (0.065kW)x(6,000h)=390 kWh for a total cost of $43. You save lots of money ($43-$15=$28) despite the higher initial cost for the CFL, and this is per bulb. In addition to this reduced cost the reduced energy consumption will be reflected in fewer carbon emissions from power plants supplying the needed electricity.

Finally, a word about the claim that the U.S. Congress has outlawed use of the incandescent bulb. This is not true, although other countries have done so. What the U.S. Congress has done is pass the Energy Independence and Security Act of 2007, which set performance standards for all general service incandescent lamps producing 310-2,600 lumens of light. The efficiency standard will start with 100-watt bulbs and end with 40-watt bulbs. Light bulbs outside of this wattage range are not covered, along with several classes of specialty bulbs (e.g., stage lighting). Thus, if bulb manufacturers can develop an incandescent bulb that meets the specified performance standard it can be marketed and sold in the U.S. Some are even beginning to appear. This is the same approach that is taken with respect to reducing the electricity consumption of many other household appliances such as refrigerators and dish washers.