Evaluate Greenhouse Gas Reduction Strategies Using Renewable Energy in Buildings
Once Federal sites have been screened for viability of different renewable energy resources to evaluate emissions profile, the next step is to establish what renewable energy resources developed at which particular sites would have the greatest impact on the agency's overall greenhouse gas (GHG) emissions goals. It is important to consider that some types of renewable energy generation could impact not only Scope 1 and 2 GHG goals, but also Scope 3 goals through avoided transmission and distribution losses.
Estimate Greenhouse Gas Reduction Potential
It is important to note that solar systems can have the greatest reduction during peak electric generation times, but this not necessarily true for all renewable energy systems. For example, photovoltaic (PV) systems are typically at peak production in the middle of the day when electric demand, such as air conditioning, is the highest.
In order to respond to this demand, electric utilities use different fuel mixes than for baseload generation. So, agencies can use the non-baseload GHG emission factors when calculating emissions reductions for PV and possibly other electric generation systems if the energy production is known to coincide with the utility's peak demand. Table 1 below shows the difference in baseload and non-baseload emissions using data from the eGRID website.
Table 1: Baseload and Non-Baseload GHG Emissions
|Site||eGRID Region||Baseload CO2e Emissions (MT/MWh)||Non-baseload CO2e Emissions (MT/MWh)|
To calculate the total emissions reductions per megawatt-hour (MWh), calculate the total carbon dioxide equivalent (CO2e) using the non-baseload emissions. The calculation for CO2e can be found on pg. B-3, equation B-2 in the Federal Greenhouse Gas Accounting and Reporting Guidance: Technical Support Document.
Different types of energy generation will reduce emissions in different scopes.
On-Site Electric Generation (Scope 2 and Scope 3)
Electricity generated on-site reduces Scope 2 emissions directly through the reduction of purchased electricity. On-site generation also reduces Scope 3 emissions because the electricity is not subject to line losses in transmission and distribution.
On-Site Thermal Generation (Scope 1)
Non-electric generation is typically used to meet thermal energy demands such as space heat and hot water. Natural gas, heating oil and other fossil fuels are burned in boilers and furnaces to supply the thermal energy, contributing to Scope 1 emissions. Technologies such as solar ventilation pre-heat and solar hot water systems can be used to reduce emissions from thermal energy generation, and can be quite cost-effective.
Biomass/Biogas (Scope 1/Scope 1 - Biomass)
Biomass and biogas are fuel sources made from organic materials such as forest thinning, municipal solid waste (MSW), and natural gas recovered from landfill sites. These fuels can replace fossil fuels to help meet the thermal demand for a site. The fuels are still burned on-site, but because the CO2 emitted during combustion was removed from the atmosphere relatively recently, they are considered to be carbon neutral. This CO2 is counted in a separate "biomass" category. The other GHGs, methane and nitrous oxide, are still counted in the Scope 1 category.
Purchasing electricity generated from burning MSW in a waste-to-energy (WTE) facility is an exception to this. Agencies interested in purchasing electricity from a WTE facility must ensure that the electricity is created from the renewable portion of the waste stream. WTE facilities reporting their biogenic CO2 emissions and anthropogenic GHG emissions under the U.S. Environmental Protection Agency Mandatory Reporting rule should be able to provide this information.
Renewable Energy Certificate Purchases (Scope 2)
Renewable energy certificates (RECs) certify that 1megawatt of electricity has been generated from a renewable resource. They also have an associated environmental attribute from offsetting electricity from fossil fuel combustion. Depending on the region, electricity is generated from differing fuel mixes and some regions of the electric grid are cleaner in terms of emissions than others. For instance, the grid regions in the northwest are cleaner than regions in the southeast because they use more hydropower as opposed to coal. RECs can have varying environmental attributes due to the fact that they offset electricity produced using different mixes of fossil fuels.
Table 2. illustrates the difference in avoided emissions due to differences in fuel mixes in the eGRID regions. Agencies should consider these differences when considering the purchase of RECs from outside their eGRID region in order to make sure that each REC purchased accounts for the appropriate quantity of avoided emissions for a given site.
Table 2. Environmental Attributes for 100 MWh of Electricity
|Site||eGRID Region||Avoided Emissions (MT/MWh)|
For more information about RECs, see Purchasing Renewable Power.
After evaluating GHG reduction strategies, the next step when planning to use renewable energy in buildings for GHG mitigation is to estimate the cost of implementing the strategies.
- Step 1
Assess Agency Size Changes
- Step 2
Evaluate Emissions Profile
- Step 3
Evaluate Reduction Strategies
- Step 4
Estimate Implementation Costs
- Step 5
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