In Governor Cuomo’s 2018 state of the state address he announced a plan to create new energy efficiency targets and appliance standards and on Earth Day new energy efficiency targets were announced. This is all part of the effort needed to meet the Reforming the Energy Vision (REV) 80 by 50 goal. The study New Efficiency New York describes the new efficiency target, the “utility-leveraged action” to drive energy efficiency, market enabling actions and other aspects of the program. This post addresses one aspect of the program that I consider a fatal flaw: widespread implementation of air-source heat pumps at the same time the state is pushing renewable energy, particularly solar.
Air-Source Heat Pumps
In order to meet the REV reduction goal carbon dioxide emissions from the home heating sector need to be reduced by replacing oil and natural gas furnaces with electricity. Heat pumps are the recommended choice for home heating electrification in no small part because they can be used for both heating and cooling. According to the Department of Energy (DOE):
An air-source heat pump can provide efficient heating and cooling for your home. When properly installed, an air-source heat pump can deliver one-and-a-half to three times more heat energy to a home than the electrical energy it consumes. This is possible because a heat pump moves heat rather than converting it from a fuel like combustion heating systems do.
Air-source heat pumps have been used for many years in nearly all parts of the United States, but until recently they have not been used in areas that experienced extended periods of subfreezing temperatures. However, in recent years, air-source heat pump technology has advanced so that it now offers a legitimate space heating alternative in colder regions.
Note that there are two types of heat pumps: air source and ground source. Both extract heat from outside the building to warm the inside. Air-source heat pumps extract it from the atmosphere where the efficiency is affected by air temperature but it is relatively easy to duct the pump to the source. On the other hand ground-source heat pumps use stable ground temperature so are uniformly more efficient. The tradeoff is that developing the ground system is much more complicated. As a result, an air-source heat pump can be retrofitted into an existing structure much more easily than a ground-source heat pump.
The reason that heating electrification is included in the energy efficiency policy is related to peak loads. Section 7.2 of New Efficiency New York is entitled “Support Heat Pump Adoption to Decarbonize Heating and Cooling”. The rationale for advocating heat pumps is based on the observation that the value of energy efficiency is higher when it reduces demand during a utility system’s peak load hours. The report notes that a Lawrence Berkeley National Laboratory study of the time-varying value of electric efficiency concluded “that of five common measures modeled, residential central air conditioning in summer-peaking systems has the most significant added value”.
Peak loads are a problem that are a primary driver of political agenda of REV. Electricity demand varies with time. In the middle of the night the residential use drops when people sleep but it peaks in the later afternoon when everyone is awake and using electricity. The electrical grid uses power from different sources at different rates to cover this normal variation. The peak problem is that when there is abnormally warm and cold weather energy use increases a lot. The existing system is designed to provide power for these abnormal periods but that requires the use of additional facilities that only run during peak load periods. The problem is that those additional sources are expensive so prices peak too. The theory is that if the peak load could be shaved then you would not need those expensive sources and the prices would be reduced.
The New York Independent System Operator (NYISO) provides peak load data for New York State (NYS) for the hour in the summer and winter when electricity usage was highest. The following data are for coincident peak demand which refers to simultaneous load peaks between different sectors. For example, residential and commercial heating will peak at the same time during cold weather. There are two significant electric load peaks during the year: summer when air conditioning use is highest and winter when heating demand is highest (Figure 1: NYISO Gold Book Actual and Project Coincident Peak Demand Generation. Over the last 20 years (1998-2017) the summer peak averaged 6,760 MW larger than the winter peak. Figure 1 also includes forecasts from the 2008 Gold Book and 2018 Gold Book. The discontinuity between 2017 and 2018 represents the changeover between the two forecasts.
The Table NYISO Gold Book Coincident Summer Peak and Winter Peak Average Demand by Zone – MWaverages load data for three periods: the last five years, a five year period 20 years ago and 2026 to 2030 at the first target date of REV. NYISO divides the state up into 11 load zones. Note that there is tremendous variation across the zones. Three downstate zones I, J and K accounted for 55% of the summer load and 48% of the winter zone in the most recent five years. Note that in zones D and E winter load is greater than summer load. I have been unable to track down older data but I believe that in the past that was the situation for more zones.
The latest state-wide report on NYS load, NYISO Power Trends 2018, states that:
Distributed energy resources — such as rooftop solar — are transforming historical patterns of consumption, and affecting consumer reliance on electricity provided by the bulk power system. For instance, energy usage from New York’s bulk power system is expected to decline over the next decade at a rate of 0.14% per year. Peak demand — a critical element to reliable system planning that establishes the total amount of capacity that must be procured to meet reliability standards — is projected to decline at a pace of 0.13% per year, through 2028.
However, nowhere in that document is there any mention of the plan to electrify residential home heating as a necessary component of the REV carbon reduction goal. To date all the NYS plans discuss summer peak demand reduction and have ignored the potential for an increase in winter demand.
I believe that overlooking the impact of electrifying the residential and commercial winter heating could be a fatal flaw. The Department of Energy claims that the preferred air source heat pump technology is a legitimate alternative and the Northeast Energy Efficiency Partnerships, an organization whose overview goal is “Assisting the Northeast/ Mid-Atlantic Region in reducing total carbon emissions 80% by 2050”, notes that the more efficient heat pumps provide cost savings. Unfortunately air-source heat pumps only work when they move heat and when it is cold enough there is no heat in the air to move.
The American Council for an Energy-Efficient Economy published a paper that documents the problem: Field Assessment of Cold Climate Air Source Heat Pumps (ccASHP) (https://aceee.org/files/proceedings/2016/data/papers/1_700.pdf). The report describes a Center for Energy and Environment field study in Minnesota where cold climate air source heat pumps were directly compared to propane and heating oil furnaces. The report notes that “During periods of very cold temperatures when ccASHPs do not have adequate capacity to meet heating load, a furnace or electric resistant heat can be used as backup.” For example, the figure Energy use versus outdoor air temperature method from ASHP Site 2 shows that as temperature decreases the energy use for an air-source heat pump goes up. Below 20 deg. F the efficiency of the air-source heat pump decreases to the point where the system cuts back and a backup system is needed. Below zero the air-source heat pump does not operate well enough to use.
The unanswered question is how these initiatives will be reconciled. Although air source heat pumps are more efficient, widespread implementation will exacerbate the winter peak load. If distributed rooftop solar is supposed to provide a significant portion of that load what happens when it snows for 66 straight hours and there is record cold? When the temperatures are that cold then home heating has to use something other than an air source heat pump. The fact is that either home owners will have to maintain their original furnace or invest in a radiant electric heating system. The economics of maintaining two furnaces does not seem likely to lead to widespread adoption. However a radiant heating system is far less efficient so the peak in electric use that cannot be covered by solar renewable energy will be exacerbated.
Several related issues have to be addressed. As more and more renewable energy is brought on to the system less and less energy is produced by fossil-fired generating facilities. The first issue is how much load will be required for the winter peak when the recommended alternative for heating electrification, air source heat pumps, must be supplanted with much less efficient radiant heating. Secondly, where is this energy going to come from? Depending upon rooftop solar for residential heating in the Upstate NY winter is clearly not viable so what is the renewable solution? Absent a magical solution the system is going to have to depend upon fossil-fired facilities to prevent people from freezing to death. However, widespread implementation of rooftop solar and other renewable energy alternatives has to negatively affect the economic viability of existing or new fossil-fired facilities. The final issue is to determine what will be necessary to incentivize the backup power needed when the subsidized energy from rooftop solar is unequal to the task of keeping the heat on. The potential fatal flaw is that identifying and reconciling all these issues takes time and it may not be possible to prevent a severe reliability problem before it occurs.