Saturday, December 9, 2017

Cogeneration & Decentralized energy

One thing Hurricane Maria has taught us is what a hollow shell PREPA is. The thousand plus megawatts of generation (Palo Seco plus San Juan plus various gas turbines) should supply the metro area. An almost criminal lack of maintenance makes those plants unavailable. A million people sit in the dark because of this neglect.

It is time to take some eggs out of the PREPA basket. We don’t need a few big plants located far from the point of use. We need hundreds or thousands of small plants generating electricity where it’s needed.

It’s time for massive cogeneration.

Any generator plant, whether a large plant like Aguirre or a 5 KW home plant, converts about 30-40% of the energy input to electricity out. The rest is wasted mainly in the exhaust and, in the case of a gasoline or diesel plant, the radiator.

A cogeneration plant generates electricity normally but captures the waste heat and puts it to use. It can make steam or hot water if needed. More usefully in Puerto Rico, the waste heat can power an absorption chiller (Wikipedia can explain) to make chilled water for air conditioning. Cogeneration plants operate at 60 to 70% efficiency or more. The high efficiency makes even small, 50KW+ cogeneration plants technically and economically feasible.

Cogeneration efficiency is also boosted by the lack of transformers. Transmission distances, and losses, are measured in feet rather than miles.

Even better, they help the environment. They do this by using a higher quality fuel, diesel instead of bunker C or coal. Higher efficiencies mean they use less of it. A double win.

In Puerto Rico we’ve rightly learned not to trust PREPA. That’s why so many businesses and restaurants have standby generators. Many could be converted to cogeneration turning the generator from a cost to a profit.

Cogenerators still need to be connected to PREPA for backup power when their plant is shut down for maintenance or fails. This works both ways and can benefit both cogenerator and PREPA.

My favorite restaurant, Lolita’s in Fajardo, has a 150KW standby generator to allow normal operation during power outages. If they used the waste heat for air conditioning, they may only need 100KW for the rest of the business.

That gives them 50KW they could sell back to PREPA. That adds 50KW of reliable power to PREPA’s capacity. Modern dispatching technology takes care of power flows in both directions depending on whether the restaurant or PREPA needs it at a given moment. 

Many small distributed plants will be more reliable in aggregate than a few massive central plants.

Cogeneration is a proven technology that has been in wide use for more than a century. 

PREPA has resisted it in the past. They need to be brought into the 21st century.

Maybe it’s time for President Bush’s “Thousand points of light” in Puerto Rico.

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