Cogeneration in the US

by ‐ Tags: alternative energy, building science, green living

A few weeks ago, we had a guest post from Shiva Prakesh with New Ecology, discussing residential cogeneration. Micro-CHP (Combined Heat and Power) systems are a smaller-scale evolution of the more common CHP systems serving large sections of cities or industrial complexes. At WegoWise, we love cogeneration systems because they drastically improve energy efficiency of power production. Tom Casten (an expert in the co-gen field) predicted in 2008 that by using cogeneration systems, the US could provide about 20% of its energy needs from simply recycling industrial waste heat. 

We Can All Learn From Denmark...

In the US, cogeneration supplies about 8% of all energy.  It's much more common in other parts of the world, especially Europe.  Denmark, the most energy efficient country in the world, is also considered the leader in the co-gen sector, with about 55% of its total energy use coming from cogeneration. This means that by turning waste heat into useful heat, over half of their energy needs are accounted for.


Avedore CHP plant in Denmark

Before the energy crisis in 1973, Denmark used to be 90% reliant on imported oil for its energy, realized that this was not sustainable, and since 1975 has used cogeneration (and other forms of sustainable energy) to be able to produce domestically much more energy than it needs today. Just one of Denmark's CHP programs- CTR- is able to provide the 270,000 homes in the five municipalities which it services with 90% of their heating needs.

Since the early 1970s, Danish energy consumption per square meter has fallen 50%, and since 2004, Denmark has saved 8-11 million tons of CO2 per year. (Information taken from the Danish Energy Agency Energy Statistics 2010 Report).

District Cogeneration Systems in the US

District energy systems can cover everything from a residential development of many buildings to an entire city

ConEdison in Manhattan runs the largest steam-based district energy system in the country to provide heating and cooling to many commercial buildings in the city. More than 50% of the steam that serves this system is produced through cogeneration. In ConEdison’s large steam plants, both electricity and steam are produced in tandem through cogeneration. The steam is piped underground throughout the city. Large buildings that are served by this system do not have to have their own building-wide heating systems, such as a large boiler. The district steam system can provide power, heating and cooling. It is clear that a CHP approach is significantly more efficient when compared to the more common practice of just wasting thermal energy because it is essentially a recycling process. The extent of the increase in efficiency is made clear by the drastic reduction in carbon emissions seen in numbers: ConEdison’s report on their steam production estimates that using cogeneration saves 1.5 million tons of carbon dioxide per year when compared to individual electric and steam production methods.

Check out the map below to get an idea of how extensive the steam network in the city really is:

Con Edison steam map

(Read a report by Con Edison outlining their current steam business and plans for expansion)

The city of Boston has an old and intricate system of piping underground that allows for similar larger scale use of waste heat from electricity production (it is much smaller than the Manhattan Steam District). Evidence of this underground network can be seen on the streets in downtown Boston (where WegoWise’s office is located), where you will occasionally see steam coming out of the manholes. This occurs because water (from the street surface runoff and rain) will hit the hot steam piping underground and turn into steam vapor.

Benefits of Co-Gen Methods

Since cogeneration harvests the heat produced by generating electricity, it can raise the efficiency of an energy source to about 80% (from roughly 40% efficiency). The benefits greatly outweigh the costs of the technology, which will only go down as demand increases. 

Greenhouse gas emissions have the potential to be decreased significantly by implementing cogeneration processes in industry (See Denmark paragraph above). If the US raised the percentage of energy produced by cogeneration to 20% (from 8-9%) by 2030, the US could reduce its greenhouse gases by 600 million metric tons of CO2. That would essentially be the same thing as taking 109 million cars off the road

While co-gen is not exactly perfect, it is a well-tested and common sense way to help bring our world down to the classification of zero-net-energy use.