Fuel Cells Overview

Introduction

Fuel cells consume a fuel such as hydrogen or methane to produce electricity directly instead of via charging a battery through a generator. This may be worth checking out but it seems more likely that the biogas should be used directly as fuel for a genset. In that application it would simply be a local alternative to transporting other fuels such as diesel, LPG, petrol or kerosine. For moderate quantities of electricity and corresponding small quantities of fuel the benefits of using biogas as fuel may not be worth the complication. The available biogas is presumably more suitable for direct use in heating and lighting. But if it was possible to avoid the cost of a genset by using a cheaper fuel cell for tiny amounts of battery charging, that could be interesting.

Biogas

Biogas is a mixture of methane, carbon dioxide and other gases produced by a "digestor" mainly from cow dung and other excreta (eg pigs and humans). Used mainly for cooking, plus lighting.

There is an extensive Biogas Support Program

in Nepal which appears to have been quite successful and a model for other least developed countries. The technology and design summary at above link indicates output of 1,000 to 2,000 litre of biogas per day from 2-5 cows. Biogas stoves are described as consuming 400 litre per hour. There is a large collection of links to publications via above link, including a 2009 year book with extensive details.

The year book mentions average energy output of 7.6 kWh per day from each installation. It also provides useful background on the kind of organization involved to sustain a successful program that actually reaches remote areas.

A detailed report

to the main sponsor provides even more insight.

 

With the use of a compost heap covering the generator for heat, installations have been reported

as high as 3,850m.

 

Biogas is also generated in developed country dairy industry as described here

. Motivation is the emissions reduction rather than the fuel production.

 

Biogas from large sewage treatment plants has been used for electricity generation with large fuel cells. A check should be made on feasability of use with small fuel cells. Note that there is likely to have been little study of this possibility so far as it would not be relevant at all in developed countries and the benefits of biogas without electricity generation in least developed countries are sufficiently clear for any such additional benefits to be of only secondary interest. Also small fuel cells potentially cheap enough may be quite recent technology.

A major difficulty may be that gas quality is a critical issue for fuel cells.

This presentation confirms that using the biogas directly as fuel for a genset would be bettr than using a fuel cell. The remaining issue is whether there is a (low) threshold at which a fuel cell could be cheaper for tiny amounts of electricity without needing a genset at all.

Portability

At present there are no applications where fuel cells would be cheaper than charging or transporting batteries.

However in situations where charging stations are not available and transport is by porters in remote regions, carrying fuel cartridges could be more practical than carrying an equivalent amount of power stored in batteries.

Mobion

For example MTI Micro Fuell Cells has announced it will market a Mobion hand held portable charger for USB powered devices at the end of 2009. The 25 Wh methanol cartridges are smaller and lighter than battery packs with a specific energy of 1800 Wh/kg.

The intention is mass production for portable consumer electronics markets so eventually the pricing could become relevant, but initially it looks likely to be a premium on top of the costs of lithium batteries.

Nevertheless, in situations where total demand does not justify a scalable generator, a device like this could be easier to use reliably than portable solar blankets etc.

Mobion USB device charger with 25 Wh cartridge.

 

 Thanks to Tom Biegler for the link to Mobion.