Is Waste the Answer to a Renewables Deficit?
The U.S. has made major strides in increasing the reuse and recycling of large quantities of municipal solid wastes. Rick Brandes and Nickolas Themelis look at whether waste to energy (WtE) can plug a hole in the renewables sector and ask the question: can power from WtE facilities be classed as renewable?
The largest consumer of goods in the world would seem naturally to be the largest generator of waste. Such is the case of the United States, the world’s largest single consumer of energy and materials and the world’s largest single municipal waste generator. Efforts to bring this dynamic into a more sustainable equilibrium have been somewhat successful over the past fifty years. Considerable progress has been made in both increasing efficiency of production and in increasing the reuse and recycling of the municipal solid wastes (MSW) associated with a high level of consumption.
Waste to Energy (WtE) is an essential component of the U.S. materials management strategy that could supply up to 4% of the nation’s electricity needs. However, by comparison to its use in other developed nations, WtE is grossly underused in the U.S. While ‘zero waste’ as a strategy for handling materials flowing through society may seem a commendable goal, its impracticality, particularly in the near term, results in the freezing of the status quo, i.e., landfilling. The U.S. needs to convert its waste management problem into a renewable energy solution by expanding its WtE capacity significantly.
The role of WtE in sustainable waste management
According to the Hierarchy of Waste Management, the preferred order of managing MSW is reduction, recycling, waste to energy, and then landfilling. Of course, as in any rule, there can be exceptions. For example, a Columbia University study showed that the Californian practice of using green wastes as daily cover in sanitary landfills, in place of soil, is environmentally preferable to windrow composting of this material.
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| Montgomery County Resource Recovery Facility. Maryland could generate up to 200 GWh of electricity for the grid by diverting waste to WtE from landfill |
The United States generates a massive amount of MSW - an estimated 390 million tons (353 million tonnes) per year. Over 60% of the MSW generated is buried in landfills, less than 30% is recycled and composted, and only 7% is converted into energy. Attention focused on materials recovery from MSW in the last 20 years has doubled the rate of recycling plus composting to the 30% level and MSW generation has stabilised at about 1.3 tons (1.18 tonnes) per capita. Further increases in materials recovery will occur but will be progressively more difficult. This is because the successes of the past 20 years have come from collecting the ‘low hanging fruit’ of the more valuable commodities, such as paper fibre, metals, and some types of marketable plastics. The only practical alternative to the landfilling of post-recycling wastes is energy recovery by means of controlled combustion. Over the next several decades, the primary means for reducing landfilling will be to increase WtE capacity. The reasons for expanding WtE capacity in the U.S. include:
Taken all together, the above reasons provide an overwhelming argument for building WtE capacity in the U.S.. However, the development of renewable energy portfolios in many states in the U.S. has created a renewable energy mandate that is currently not filled by the available renewable energy sources. It is an immediate problem as many RPSs are about to reach legally imposed deadlines. Therefore, building up the existing WtE capacity can help fill the void and meet these legal requirements.
Energy consumption and renewable energy mandates
The U.S. is a huge consumer of electricity. The U.S. Energy Information Agency (EIA) data for 2010 shows that the U.S. consumed 4.12 billion MWh of electricity. Of this amount, only 4% was generated by what the EIA defines as renewable energy sources. The mandate for increased renewable electric power has made any source of such power extremely valuable.
EIA data from 2009 shows that 33 states in the U.S. have established mandated RPSs. Most require a specific percentage of power of the state electricity grid to come from defined renewable energy sources by a certain date. Wind, solar, and some biomass energy are considered renewable by all of these states. Some of them also include combustion of MSW as a renewable energy. U.S. power companies are thus under legal obligation to add renewable energy to their generating capacity within an established deadline. In most states, however, achievement of the mandatory RPS by that deadline is problematic. There is simply not sufficient renewable energy to go around. The following case of the State of Maryland illustrates this problem.
The State’s Renewable Energy portfolio Maryland law requires 20% of the power on the grid in the state come from renewable energy sources by 2022. The state published a plan and a strategy for achieving this goal that shows required levels and increases over time. Figure 2 shows the plan’s targets by year.
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Figure 2. Maryland’s RPS plan for 20% renewable energy by 2022 (in GWh) |
To achieve this mandate, purchases of power for the grid must come from ‘Tier 1’ energy sources in the form of Renewable Energy Credits or RECs.
A Maryland-eligible Renewable Energy Credit (REC) is equal to the attributes associated with 1 MWh generated by a Tier 1 Renewable Energy Facility. This includes solar, wind, qualifying biomass, methane from a landfill or wastewater treatment plant, geothermal, and ocean, including energy from waves, tides, currents, and thermal differences. Hydroelectric power plants less than 30 MW in capacity are also Tier 1. Recent legislative action (Maryland Senate Bill 690) included WtE in the Tier 1 renewable energy sources, thus eligible for RECs under the mandate.
To meet the targets of the ambitious plan, the state will have to ramp up current Tier 1 sources thirteen-fold within 11 years, from less than 1000 GWh currently generated by renewable energy sources to over 13,000 GWh in 2022. The sources for this capacity, as called for in the plan, are 1300 GWh solar, 1700 GWh biomass, 1300 GWh on-shore wind, and 7700 GWh off-shore wind. The rest presumably would come from out-of-State sources, as allowed by the RPS.
The 2009 EIA figures for Maryland show that the state generated only 551 GWh of existing Tier 1 electricity, nearly all of it from biomass combustion. The amount has not increased recently. Also, Governor of Maryland, Martin O’Malley, recently cancelled a large off-shore wind power project due to the potential high cost to Maryland ratepayers. Thus, the State’s RPS mandate requires power that hasn’t yet been created in a period of time that surpasses the ramp up times for planning, funding, and construction of projects.
To this looming dilemma, the authors suggest one partial, but proven, solution: to increase the WtE capacity of Maryland from its present level of 850,000 tons (771,000 tonnes). Maryland also recycles and composts another 2.2 million tons (2 million tonnes) of MSW - about 30% of the total. However, the state still landfills 3.9 million tons (3.5 million tonnes) of MSW. Diverting this material from landfills to new WtE power plants would generate between 1800 GWh and 2000 GWh of Tier 1 electricity for the grid, or about 15% of the required renewable energy, according to Maryland’s plan.
Maryland’s Plan states unequivocally: "It is important for Maryland to monitor and support all sectors that help meet the State’s renewable portfolio standard." Here in a nutshell is the argument for WtE as part of an integrated, more sustainable materials management system. Without it, most U.S. states can forget even coming close to meeting their ambitious RPSs. It will not happen in any reasonable time frame. The above case for Maryland can be applied to all fifty states of the Union.
Is WtE renewable energy?
There is no formal definition of the generic term ‘renewable energy’. The foundation of the concept of renewable energy requires energy replenishment equal to or greater than the consumption rate. Thus, to be renewable in a strict sense, energy should come from a source that is constantly available and continuously replenished. Embellishments of the concept get into the sources of the energy. Some definitions would require that the sources be ‘natural’ or ‘organic’ i.e., from physical realities like the wind or from living materials like plants (biogenic). Others merely require that the sources be essentially limitless, like solar radiation or gravity.
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Frederick and Carroll counties will use 45 MW of electricity generated from the new facility |
What is renewable energy depends on whether or not the person defining it is a purist or a pragmatist. A purist would say renewable energy can only come from the sun (solar energy and wind energy) or from gravity. They are the only eternal, replenishing sources. A pragmatist would expand the term to embrace energy from processes that are replenished, available, and simply better than the non-renewable alternatives (fossil fuels). This expansion of the term is the basis for what happened in Maryland this year when O’Malley explained his approval of the legislation raising WtE to a Tier 1 renewable in this way:
"The question is not whether waste to energy facilities are better for the environment than coal-fired generation, or better for the environment than the landfilling of trash, but rather whether waste to energy facilities are better than the combination of coal and landfilling, based on the best available science. The answer to that question is a qualified yes."
Recovering energy from MSW has a very desirable carbon emissions impact because the positive carbon balance of WtE is significant. The EPA’s models for calculating GHG emissions reductions from the various MSW management techniques show that 0.5 to 1.0 tons of carbon equivalents are avoided per ton of MSW incinerated for energy recovery. The carbon emissions savings accrue from a combination of avoiding GHG generation in landfills, energy offsets from the replacement of more carbon-intensive electricity, and recycling benefits of metals recovery from incinerator ash.
Under any practical definition, energy recovered from MSW is renewable energy and should be legally defined as such by States seeking to fill their renewable energy portfolios. It is part of our materials management system whether we like it or not. Waste is replenished mostly by natural sources (plants and trees) at a rate equal to or greater than it is consumed, and it has a positive carbon balance when compared to the alternative energy sources of coal, oil, or natural gas.
Rick Brandes, retired, was chief of the Energy Recovery and Waste Management Branch at the U.S. Environmental Protection Agency (EPA), Office of Resource Conservation and Recovery.
email: brandes.william@gmail.com
Nickolas J. Themelis, is the director of the Earth Engineering Center, Columbia University
email: nickolas.themelis@gmail.com
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