Question

Environmental Engineering: Please answer the following question with details and clear hand writing.

Mention three main mitigation strategies for reducing fossil-fuel carbon dioxide emissions from a reference scenario to a stabilization path. Give an example for each strategy.

Answer 1

1.Biomass

Biomass fuel consists of organic material such as wood chips, oat hulls, corn husks, etc. Finding a long-term reliable supplier with enough biomass fuel to operate a campus heating or power plants can be a challenge. Ensuring that the biomass is produced sustainably is also a challenge. Other issues associated with biomass are biomass’ relatively low heat density (requiring greater volumes of fuel), the need for specialized handling equipment, and its air emissions and ash waste products. However, addressing the latter should be no more difficult than using coal.

Biomass is not only renewable but also theoretically carbon-neutral because the carbon that’s released into the atmosphere when biomass is burned can be captured and sequestered into new biomass fuel crops as that biomass grows. Sustainable biomass presumes that annual biomass production equals consumption and is accomplished without the environmental damage, e.g. cutting down forests. Since some fossil fuel inputs are generally involved in growing, harvesting, chipping, and transporting biomass fuel, it can be argued that biomass is not actually carbon neutral despite often being regarded as such. Calculating the life-cycle net carbon emissions of biomass-based heating or electricity production would be a great project for students and faculty.

Sustainable biomass can include waste products like wood waste from furniture plants, urban tree trimmings, or clean wood extracted from a municipal solid waste stream, and agricultural crop waste. While the waste-to-energy industry sometimes claims that general municipal solid waste is an acceptable biomass fuel, it is not regarded as such by environmentalists because of the dirty air emissions and toxic solid waste by-products its combustion produces and because burning municipal solid waste generally undermines municipal recycling programs.

Before proceeding with plans to convert to biomass campus heating or power generation it is essential that a fuel availability study is conducted. While a consultant can be hired to perform this study, it could be a great project for students with support from faculty and facilities management staff. Students could study the net availability of suitable biomass resources within a given distance from campus. This research would examine existing resources as well as the potential biomass resource if a market for biomass was created by demand from your proposed plant. Students could identify sustainable forestry or crop practices that your school could require for biomass purchases including consideration of the Forest Stewardship Council’s best practices. If you proceed with a biomass plant, once it is up and running students can study the supply chain to determine and evaluate what is actually happening on the ground.

While converting your heating or power plant from fossil fuels to biomass may be a long-range strategy due to the costs involved, in the meantime – depending on boiler type – it might be possible to co-fire biomass and thus reduce GHG greenhouse gas emissions. Co-firing generally involves displacing some fossil fuel combustion by burning biomass and fossil fuels together.

Ex.

Ironbridge, United Kingdom – 740MW

With 740MW capacity, the Ironbridge power plant located in the Severn Gorge, UK, is the world’s biggest biomass power plant. Ironbridge was previously a coal-fired power station with an installed capacity of 1,000MW. Two units of the plant were converted for biomass-based power generation in 2013.

The power plant is owned and operated by UK power and gas company E.ON. The Ironbridge power station is due to close in 2015 as part of the European Union’s Large Combustion Plant Directive (LCPD). E.ON has converted the plant to generate power from wood pellets until its scheduled closure.

2.Landfill Gas

Landfill gas is methane produced by the decomposition of garbage in landfills. Since methane is a powerful GHG gas which on a mass basis and a 100-year time horizon has over 20 times the global warming potential of carbon dioxide, it is important that it not be vented to the atmosphere. Collection systems can be installed in landfills to harvest methane. It is then scrubbed and often burned on-site to generate electricity or both heat and electricity. Landfill methane can also be delivered elsewhere via pipeline. While burning landfill gas produces carbon dioxide, it also prevents methane emissions – and thus produces a net reduction of GHG emissions. While not readily available to all college campuses, landfill gas can be a suitable fuel for campus power plants or any kind of natural gas-fired boiler or cogenerator.

Ex.

As a sprawling 725-acre operation, the F.R. Bowerman Landfill is one of the largest landfills in the United States. The landfill, located in Orange County, California, contains an estimated 31 million tons of waste.

When solid waste in a landfill decomposes, a natural by-product with high amounts of methane is released. This potent greenhouse gas can potentially affect global warming, climate change, ozone depletion, and sea-level rise, as well as having a negative impact on biodiversity. In order to better manage and reuse this onsite waste, Montauk Energy worked with Caterpillar Financial Services Corporation to develop and commission a $60 million, 113,000-square-foot, state-of-the-art renewable energy power plant to generate electrical power by capturing and conditioning the landfill gas.

3.Renewable Energy Technologies

Conservation and efficiency can take us far but not all the way. Even after we have reduced our energy load to a bare minimum, we will still have to meet that remaining load with some form of energy. In order to achieve climate neutrality or deep cuts in GHG emissions, campuses will need to transition as much as possible to carbon-free renewable energy technologies – solar, wind, biomass, geothermal, and hydro (though the latter is pretty much tapped out in most regions). We can either build renewable energy capacity on campus or buy green power. This section discusses on-campus renewable energy sources for non-heating or power plant applications.

Solar Photovoltaic Electric Arrays

Many campuses are installing photovoltaic (PV) solar electric arrays. While rarely as cost-effective as energy conservation, PV becomes more cost-effective when conventional electric rates are high and ample incentives are offered by a state government or local utilities.

Obviously, the amount of available sunlight is another important factor though PV can work well in all regions. Where there is less sun, more solar panels are needed to meet a given load. This adds cost and stretches out payback but it works. Where snow may cover panels during winter months, panels can be tilted to shed snow or PV array output can be pro-rated downward to allow for a number of weeks or months when output is reduced. The performance of grid-interconnected PV is generally measured in terms of annual power production and most PV production occurs during the sunnier summer months when days are longer and there is less cloud cover. In areas where winter days are cold and clear, angling panels to take advantage of those conditions becomes more important. While winter output will be less, PV panels actually have a higher sunlight-to-electricity conversion efficiency when cold.

There are a variety of financial models for installing PV on campus. Your school can design, purchase and install its own system – typically with the technical assistance of a consultant or supplier. The relatively high cost and long payback of this kind of investment can be tempered by incentive dollars that reduce the initial or “first cost” of the system. Another financing strategy is to include the cost of the solar energy system in a larger self-financing energy conservation program and, in essence, allow the energy conservation measures (and the dollar savings they produce) to pay for the solar.

A solar energy system can be installed on campus through a power purchase agreement (PPA) with a renewable energy power provider who will install and own a PV system located on campus. A PPA will oblige a school to purchase power from the PV system for a number of years at rates established by the contract. The primary advantage of this arrangement is that the school is not responsible for the installation, operation, maintenance, or cost of the PV system. Also, this arrangement may allow the energy supplier to take advantage of tax credits which may not be available to the campus.

Maximum output from PV arrays occurs mid-day on hot summer days – precisely the time when regional grids in many areas are under strain because of high air conditioning loads. At these times, hourly rates for electricity may be much higher than average rates. This coincidence suggests that an analysis of PV cost-effectiveness should be sophisticated enough to factor in the additional dollar savings associated with avoiding that very expensive conventional electricity. PV arrays can also reduce peak demand and peak demand charges. PV project simple paybacks tend to be long though factoring in these additional savings will shorten it somewhat.

In order to claim a CO2 reduction from a campus-owned and operated PV system or from a PV PPA, you must own the renewable energy certificates or RECs associated with the output of your system. In the case of a PV system your campus owns, that means “retiring” and not selling them. In the case of a PV system installed under a power purchase agreement, to claim a CO2 emissions reduction your school must buy the RECs produced by the PV system. The REC purchase may be in addition to buying the actual power produced by the array.

Other Solar Options

Other on-site, on-campus solar options include:

• Passive solar
• Daylighting
• Solar hot water

Not only can all three of these technologies be considered for new construction, but all three can also be either made to work or installed in existing buildings. For example, you may already have buildings with rooms or corridors with ample south-facing glass that allows solar gain during the winter months. This gain may be a nuisance now, causing localized overheating. Building occupants may be fighting that sunlight with pulled down shades. Your maintenance staff may have solved the problem by installing a reflective window film to block the sunlight from entering the building. An alternate approach would be to let the sunlight pass through the windows and put that heat to work by installing thermal mass to store it for use later in the day or by modifying the HVAC system so the heat is captured, transported, and used in another part of the building. Engineering or architecture students may want to study passive or active solar heating options for that kind of campus building as a class or volunteer project.

Similarly, with daylighting, you may already have daylit spaces but are not taking advantage of their energy-saving opportunity because of inadequate controls on electric lighting. Installing photocells or sensors may be all it takes to keep electric lighting off when daylight from the sun is adequate to illuminate those spaces. Facilities staff or students can survey the campus to look for opportunities of this kind.

Solar hot water systems can be more cost-effective than PV solar electric systems yet are generally less common. Why is that? Maybe it is because piping is harder to install than wiring and there ends up being more maintenance with solar hot water systems. Maybe it’s because fewer incentives are available. Also, unlike PV (whose output can always be used by the building it’s mounted on or by the local power distribution grid it is connected to), solar hot water systems must closely match daily hot water production with daily hot water demand. And hot water needs may not coincide with those times when solar hot water systems readily produce hot water. On most campuses, hot water demand predominantly occurs in the fall, winter and early spring when the fall and spring semesters are in session. However, in many parts of the country solar gain is not ideal during much of that period: the sun is low in the sky, days are short, and there may be lots of cloud cover or snow. Also, while most campus buildings have hefty appetites for electricity, not all campus buildings have adequate hot water loads to justify a solar hot water system. Buildings with above-average hot water needs include athletic facilities, student residences, and foodservice facilities.

While solar hot water presents some challenges, it is a viable option for campuses interested in demonstrating solar energy. If the “first cost” of such a system is daunting, consider a power purchase agreement with a solar provider that would build, own, and operate “your” solar hot water system while selling you its hot water output. Students and faculty can even study the possibility of using solar hot water technology for seasonal solar storage – collecting and storing solar heat collected in the sunny summer for use in the cold cloudy winter.

Ex.

Chernobyl Solar Plant, The site of the world's most devastating nuclear disasters is now looking for a new image with a brand new solar farm. This one-megawatt solar plant isn't the biggest project in the world, but it's perhaps one of the most poignant.