Waste Heat to Power

There is a lot of interest in recovering waste heat. Combined Heat and Power (CHP) is at the heart of a large part of the distributed generation business. The heat can be used to heat water, provide process heat, and even cooling. Converting waste heat to electric power is getting attention as well.

On the bleeding edge, there are a number of efforts underway to do it without moving parts–solid state conversion (of course not limited to waste heat). There are programs, for example to put thermoelectric converters on the exhaust manifold of diesel trucks, with the goal of replacing the alternator. Thermoelectrics, thermionics, thermophotovoltaics — all are being pursued with renewed vigor, in the hope that new physics can overcome the longstanding problem of high cost and very low efficiency…a subject for another day.

Waste heat gets wasted only because it tends to be hard to use. A diesel engine converts about 1/3 of the fuel energy to useful work (electric power, in the case of a genset) — the rest goes off as waste heat in cooling water and exhaust — unless a cost-effective means can be found to use it, as in CHP.

Making more electric power with the waste heat is another matter. The age-old Rankine cycle, the basis of all steam power plants, can be made to work at lower temperatures by using something other than water as the working fluid ("refrigerant"), typically an organic compound, thus the term "organic rankine cycle" (ORC). In effect, this is a heat pump or refrigerator running backwards. Instead of using mechanical energy to create a temperature difference, mechanical energy is produced by a temperature difference.

The main challenge isn’t the theory, it’s the practical difficulty of doing it. Factors such as temperatures (inlet and outlet), flow rates, size and type of heat exchangers, type of expander, materials, controls, etc. must be considered in the trade-offs of cost, performance, reliability and longevity.

It’s a lot harder than it looks. Despite many attempts, and the obviousness of the basic idea, there are actually not very many commercial providers of such systems, particularly in smaller sizes which can operate effectively at lower waste heat temperatures.

UTC, for example, announced it’s new "PureCycle" 200 kW unit only last Fall. It requires inlet temperatures above 500 deg F.

Ormat, (ORA-NYSE) long established ORC maker for geothermal plants, is moving into the industrial waste heat market. They too need relatively high temperature, for units in the 250kw – MW range. They also sell small standalone ORC-based generators which burn a fuel as the external heat source.

In Europe, one can find Turboden (Italy), Triogen (Netherlands) and FreePower (UK). All require high temperature, with the possible exception of FreePower, who say they can operate as low as 230 deg F.

High temperature means industrial processes that put out high temperature waste heat. Ormat, for example, has a 1.5 MW showcase unit that takes air at 520 deg F from a cement plant in Germany.

The water jacket of the lowly diesel engine, however, can only be allowed to go to around 230 deg F (and the water must be returned no cooler than around 215 deg F). While such temperatures can be readily adapted to CHP uses, power conversion is more difficult.

Cooler Power, Inc, a startup in California, has successfully built units that work in this range. The engine’s cooling water is taken (before it goes to the engine’s own radiator), and is fed to a heat exchanger where it is heated further by the engine exhaust. In another heat exchanger, the hot water heats and vaporizes the organic working fluid, which then drives the expander which turns the generator. The expander is key. In principle, any compressor technology can work backwards to act as an expander: scroll, screw, turbine, or piston. All have been used at one time or another. Cooler Power initially used a scroll, but then developed its own proprietary modification to a commercially available screw compressor, as the heart of the system. They have a patent in final review stages covering the modification and use of the screw expander, as well as the control system and choice of working fluid.

Cooler Power has proprietary software to develop process flow diagrams to size and specify components or installations. The proprietary Program Logic Control (PLC) circuits are designed for optimal failsafe performance and contain algorithms that are protected from reverse engineering. Each of the key components (heat exchangers, expanders, condensers, generators) are designed to last 20+ years and come from one or more sub-sectors of the existing industrial equipment industry.

The system can be scaled to fit applications ranging from 50 kW – 1 MW. Installed costs are in the range of $1500-1800/kW. Depending on the sales price for power, payback can happen in 2 years or less. It’s important to emphasize that this is green power, which usually enjoys premium pricing. There is no fuel cost; operating costs are very low; and there are also (monetizable) environmental benefits.

A showcase 50 KW beta unit was installed in 1992 at the Newby Island landfill site in Milpitas, CA, on a 1 MW engine. A new 150 kW system will come on line in March. The company anticipates installing 10 units in 2005, with rapid growth thereafter based on already-established customer and marketing relationships, selling both systems and power. They raising an equity investment round currently, and welcome both investor and customer interest.

Ray Smith, COO
Cooler Power Inc,
Redwood City, CA

DOE Distrib Power Review & IEEE Interconnection Working Group

** DOE Distributed Power Program Review and Planning Meeting
** IEEE SCC21 P1547 Interconnection Working Group
Arlington, VA, September 27-30, 1999


** DOE Distributed Power (DP) Program Review and Planning Meeting

— Welcome and Introduction
— Dan Adamson, Deputy Assistant Secretary, Office of Power Technologies
— Distributed Power in DOE’s Office of Energy Efficiency and Renewable Energy
— Dan Reicher, Assistant Secretary, EE

DP covers a wide gamut of topics, from village power and rural electrification to industrial power parks, partially self-powered office towers (incl. PV), combined heat and power (CHP) and all varieties of renewable energy. There are three “elements of success” that must be met — technologies, markets, and policies. A number of DOE programs involve DP, and there are several cross-cutting initiatives: CHP, Million Solar Roofs, Buildings for the 21st Century, Bioenergy, and Distributed Power (i.e. to address interconnection issues). A DP website is under construction.

— An Industry Perspective — Beverly Jones, Consolidated Natural Gas

Broad trends are setting the stage for DP: industry restructuring, gas/electric convergence, and the role of information technology in energy. All of these are changing the buyer seller relationship dramatically, as the distinct “one-point” of contact is replaced by myriad complex and overlapping interactions. As the slow process of policy change proceeds, the action is mostly at the state level, where there are many opportunities to bring up DR issues arise. States are competing for jobs, and see energy prices/markets as a key determinant. There is less urgency at the federal level, and the lack of standardization is a big problem. One area that’s particularly important–tax policy, especially depreciation rates for DR investments, which should be faster than for traditional generation and distribution facilities.

— Creating Value Streams for Distributed Resources — Dave Hoffman, Celerity Energy

Barriers to DP growth include 100 years with a regulated monopoly system, with it’s concerns about reliability, and the credibility, reliability and costs of DR. Market pressures and technology are driving change. Celerity’s business is acquiring options on peaking capacity from existing gensets, which will be linked via networks and bid into th e power market.

— Program Overview — Joe Galdo, DOE Program Manager

A workshop Dec 98 made recommendations for DOE program actions for DP:
-Interconnection (standards, documentation of the problem,
system integration modeling, and equipment certification)
– Outreach to state regulators
– Quantify benefits
– Model (building) codes and ordinances

The program is organized around three main topics:
– Strategic Research (concepts for advanced system control, etc.)
– Systems Integration (address safety, reliability, etc issues.
Analysis, modeling, hardware testing, interface hardware
and software)
– Regulatory and Institutional Barriers

FY99 Program — $1.2 Million funding — planning, support IEEE standards working group, document interconnection barriers, outreach to stat es.

— Documenting Barriers to Distributed Power — Brent Alderfer, Competitive Utility Strategies

[DP is not new. DOE commissioned a major study to examine what is currently being done.]

A report is due in the next 2 months, detailing 70 case studies of current interconnection experience and practices. Sizes ranged from 300 watt PV to 100 MW combined cycle.

DP “barriers” are seen differently by utilities–who are concerned with safety, reliability, risk, liabilities, and who don’t want “gadgets and gizmos” on the grid. Some utilities simply refuse any (non-QF) connection.

Standby tariffs range widely ($1 to $250/kw/yr). These are arbitrary now, often set to discourage DP. In the future, however, real markets may probably show as wide a range, but for entirely different reasons.

Uplift tariffs are usually based on entire radial system, even if transaction only uses a portion.

Restructuring by states generally has no impact on barriers. Some utilities have embraced DP (O&R 10 years experience using reciprocating gensets owned by 3rd parties to defer substation additions) Southern Co, while opposing FERC restructuring of G&T markets, is actively hooking up cogenerators.

— Interconnection Standard Development — Richard DeBlasio, NREL

[brief overview of SCC21 working group progress]

— Technical Assistance to States and Localities — Gary Nakarado, NREL

Assumed (interconnection) goals are uniform technical requirements, minimized cost, standardized contracts, and costs commensurate with DP system size. PV has paved part of the way. Standards alone won’t assure adoption of DP. For example, net metering laws can limit utility’s ability to resist.

[DOE “State Energy Alternatives” — this website gives specific information on the potential of selected renewable energy resources in each state as well as background information on each state’s electricity sector ]

[The Regulatory Assistance Project (RAP) provides assistance to state regulators. ]

— Environmental and Economic Impact Assessment — Howard Gruenspecht, DOE Office of Policy

The administration’s restructuring proposal addresses DP issues.

A pdf document (the 3rd one listed on the webpage) is an explanatory memo for the proposed legislation, and discusses DP issues in several aspects:

from CECA Supporting Analysis, Chapter 3, page 34

Distributed Power

“The revised Administration proposal includes a package of provisions designed to promote the adoption of efficient combined heat and power and distributed generation technologies. It proposes the development of nationally applicable interconnection standards, clarification of depreciation treatment to assure that distributed generation installations are not subject to unfavorable schedules for the depreciation of structural components, and State-level consideration of stranded cost recovery mechanisms that do not impede cost-effective and energy-efficient combined heat and power projects. It also promises continued efforts by the EPA and the DOE to explore and implement regulatory approaches that recognize the environmental benefits of combined heat and power technologies.”

Secretary Richardson held a “Midwest Electricity Summit” in Chicago on October 8, with several dozen invited stakeholders (utilities, regulators, local government, etc.) to discuss industry issues. Anyone is welcome in the audience. His prepared remarks are posted at:

Another is to be held somewhere in the Northeast in a couple of weeks — details tbd.

— Where Are We Going? A framework for planning White Paper on Interconnection and Controls for Large-Scale Integration of Distributed Energy Resources — Phil Overholt, DOE Program Manager, Transmission Reliability; Joe Eto, LBNL

This was a presentation of the 2nd of the 6 draft white papers.

See: 20 Sep99 UFTO Note-CERTS Draft White Papers
01 Mar99 UFTO Note-CERTS-New DOE Prog in Elec. Reliability

(There’s still time to provide comments on any of the 6 papers.
See 20 Sept note for details.)

— How Do We Get There? — Five-Year Planning (Breakout Sessions)

– Interconnection Standards, Certification and Testing
– Interconnect Hardware and Software
– Addressing Regulatory and Institutional Barriers
– Planning Analysis and Tools

These were facilitated sessions to develop recommendations for near and longer term destinations, R&D requirements, recommended program activities and resources. A summary is being prepared by DOE and should be available in 6-8 weeks.

UPDATE: It looks DOE’s DP program will have a budget of about
$4 million in FY2000.


IEEE SCC21 P1547 Interconnection Working Group
Sept 28-30

Topical Presentations:

The first morning of the 3 day meeting was a series of presentations to further the mutual understanding of technical issues.

— VAR Control from a DR Perspective (T.-E. Moen, ABB)
A detailed technical discussion of voltage source inverters (VSI) and how they can be an economic option for supplying VAR’s into a network.

— Distributed Resources in Downtown Networks (N. Ioannou, BGE) Downtown grid networks, covering perhaps 5% of the total US system, are very different from standard radial networks. There are two types which are very different from each other: grid (or secondary) and spot (or isolated). DP can be connected to either, though it can’t push power into a spot network.

— EEI Interconnection Study Update (M. Davis)
Progress is continuin g. Outlined a 7 step process to determine interconnection requirements, beginning with identifying the type of generator, i.e., induction (externally or self-excited), synchronous (cylindrical or salient pole) or inverter (line or self commutated) and then on to defining characteristics of the distribution system, etc. A great deal of material has been added to the Working Group’s “Resource Document”, a 2 inch thick compendium of information that backs up the standards development.

— Shifting the Balance of Power: Grid Interconnection of Distributed
Generation (Brendan Kirby, ORNL and Nick Lenssen,E SOURCE)

Examines the various issues that hinder DP deployment, mostly coming down to utility resistance, lack of uniform requirements and processes (which are based on large units, and are too extensive for most DP). Points out that loads aren’t very different from DP–both can cause harmonics, ripple, DC, fault current, etc., yet they receive very different treatment. Main difference is intentional injection of power. Existing system built for one way power, but in future may be configured to take better advantage of DP. DP are ideal ancillary service providers, but usually excluded from markets. Need to deal with conflict that utilities are both guardians of the public good, and a competitor in the same system. (This will be published as an E-Source report, with a summary version more generally available. I have a copy of the vugraphs if anyone wants them.)

[Note: check out re the “guerilla solar” movement–people hooking up to the grid without permission.]

— Proposed Revisions toNEC by EEI Elec Light & Power Group (P. Amos, ConEd)

— Proposed New NEC Article on Fuel Cells (K. Krastins)
(See email forwarded to UFTO list on 31 August)


I have email and tel #’s for everyone mentioned above, and some additional hard copy information. Please let me know if you want more details on any o f the above.