Report 5 (of 5): Fuel Cells/Solar Winter?

Introduction

Solar power is generated when energy from the sun is converted into electricity via solar cells. It is an excellent source of renewable energy for people who do not have access to power from a grid system. It is most appropriate for countries located in the "Sunbelt", that is, countries that are within thirty degrees north or south of the equator, where there is high direct solar radiation all year round. In Northern latitudes, there is little solar radiation in winter time.

In places requiring an electricity supply all year round, with a very small, if any, output of the photovoltaic array during the winter months, the use of seasonal photovoltaic energy storage or a hybrid photovoltaic-diesel system is needed. Although photovoltaic systems with lead acid batteries are widely used in remote areas for telecommunications and other stand alone applications, they are not practical for seasonal energy storage because the batteries are too expensive. Diesel generator back up for remote photovoltaic-battery systems has the disadvantages of requiring refuelling and maintenance.

Neste Advanced Power Systems

Since 1990, Neste Advanced Power Systems, a company based in Finland, has been developing innovative solutions to overcome these problems. If there is no solar radiation for several months of the year, it is possible to store the energy, from the summer sun for use in winter, as hydrogen gas. When solar cells produce electricity, the power they produce can split water into hydrogen and oxygen. The hydrogen is then stored in a closed loop autonomous energy storage system (figure 1) and used to make electricity in the middle of winter.

Photovoltaic Hydrogen Systems

In the closed loop hydrogen system, surplus photovoltaic electricity is used during summer time to produce hydrogen gas from water in a pressurised electrolyser. The hydrogen is stored in a pressure vessel and oxygen is vented to the atmosphere. During the winter, hydrogen can be used to produce electricity in a fuel cell with the oxygen taken from the air. The water produced by the fuel cell is recirculated back to the electrolyser which closes the loop. Not all the water from the fuel cell can be recirculated and the remaining water ("fuel") will be collected and purified automatically from rain water (figure 2).

The seasonal storage type of photovoltaic-hydrogen system is most applicable to systems in high latitudes with continuous loads of 50 Watt to 300 Watt. Although the fuel cell and the electrolyser are modular, the gas and water handling system needed for the pressurised electrolyser is not scaleable to very small systems.

The Fuel Cell

The most critical component is the fuel cell which must be able to operate even in severely cold climates. In the fuel cell, there is a series of metal plates and plastic membranes bolted together. These layers are porous and they let gases pass through. Hydrogen gas is fed through the perforated grey metal plates and passes through the other side. The gases react because of catalysts on the membrane. The reaction causes the protons of the gases to combine to form pure water and the electrons that are left behind are conducted in the metal plates as electricity.

Fuel Cell Back Up System

The principle of the system can be simplified from an autonomous Seasonal Energy Storage system by removing the hydrogen production (electrolyser) and water handling system and retaining the hydrogen-consuming fuel cell.

The gas supply is from one or two commercial gas bottles.

This fuel cell back up system is most suitable for systems with continuous local demand of between 10 and 50 Watts.

The hydrogen gas is supplied directly to the fuel cell without any humidification or recirculation except for some periodic flushing.

The main technical difficulty in this kind of system is the housing of the fuel cell for operation in cold and windy climates and for this purpose an insulated enclosure for the fuel cell has been designed.
 

For further information about the development of photovoltaic hydrogen systems, please contact:
 

Intermediate Technology would like to thank Neste Advanced Power Systems - in particular, Jyrki Leppanen and David Spiers - for providing the original notes and pictures on photovoltaic hydrogen systems for northern countries.
 

Further reading available from ITDG Development Bookshop

Solar Electric Systems for Africa
Mark Hankins
Describes how anyone, with help from an electrician, can adapt a small solar electric system to their own needs. Includes details on estimating local resources, choosing appliances and technology, wiring principles, and planning and maintenance.
£14.00, (Commonwealth Secretariat), 1992, ISBN 0 85092 453 7

Solar Electricity
Simon Roberts
A practical guide to designing and installing small photovoltaic systems.
£25.95, (Prentice Hall), 1991, ISBN 0 13825 068 5

Solar Heating in Cold Regions: A technical guide to developing country applications
Alain Guinebault and Jean-Francois Rozis
This book is primarily a technical guide to the design and production of solar installations in regions where heating is an issue of utmost importance. This book is written mainly for technicians, architects and designers who are interested in solar heating systems in cold regions of developing countries.
£9.95, (ITP), 1996, ISBN 1 85339 329 0
 

TVE/ Practical Action gratefully acknowledge support for the HANDS ON programmes from the UK's Department for International Development (DFID), the European Commission (EC), the UN Foundation and UNDP/The Equator Initiative in collaboration with the Government of Canada, IDRC, IUCN, BrasilConnects and the Nature Conservancy.