Report 3 of 5: Freiburg Solar Energy - Germany

Introduction

The sun is the source of the vast majority of the energy we use on earth. Most of the energy we use has undergone various transformations before it is finally utilised, but it is also possible to tap this source of solar energy as it arrives on the earth’s surface.

Solar energy offers a large number of advantages and it is set to become the energy of the future because it is available in unlimited quantities; it can be used without the emission of pollutants; and it can be deployed flexibly in a whole variety of ways.

The City of Freiburg’s energy policy

Freiburg is located at the heart of the warmest and sunniest region of Germany, yet it takes more than just this to make it into a solar city. The Freiburg energy supply concept focuses on:

• energy saving projects

• use of renewable energy sources

• application of innovative energy technologies

• extension of on-site and remote district-heating systems

Water heating technologies are usually referred to as active solar technologies, whereas other technologies, such as space heating or cooling, which passively absorb the energy of the sun and have no moving components, are referred to as passive solar technologies. Solar passive houses built to the very latest standards require only one fifth as much thermal energy as conventional buildings.

The whole city is involved in Freiburg’s solar policy. Many private companies and public facilities make their roofs available for solar modules. The people of Freiburg buy shares in the panels and are reimbursed when the power is sold to the city electricity scheme.

Passive thermal use of solar energy

There are many applications for the direct use of solar thermal energy, for example, space heating and cooling, water heating, crop drying and solar cooking. It is a technology which is well understood and widely used in many countries throughout the world. Most solar thermal technologies have been in existence in one form or another for centuries and have a well established manufacturing base in most sun-rich developed countries.

The most common use for solar thermal technology is for domestic water heating. Hundreds of thousands of domestic hot water systems are in use throughout the world, especially in areas such as the Mediterranean and Australia where there is high solar insolation (the total energy per unit area received from the sun). As world oil prices vary, it is a technology which is rapidly gaining acceptance as an energy saving measure in both domestic and commercial water heating applications. Presently, domestic water heaters are usually only found amongst wealthier sections of the community in developing countries.

Passive use can be made of solar energy through structural measures, such as windows and conservatories. It is possible for a building to be partially heated in this way. The solar energy is stored in solid parts of the building, such as walls, ceilings and floors.

Windows can make use of solar energy effectively and inexpensively. The solar energy penetrates the building virtually unimpeded via the window. Solar energy gained in this way is retained inside and stored in solid parts of the building. Windows thus act as a solar collector. To ensure that the heat is not lost via the windows again, however, these require high quality glazing offering good thermal protection, such as double or triple glazing with heat absorbing glass. Wood is the best frame material. A good solar house has a small number of big windows rather than a large number of small ones. Walls pointing northwards (north, north-west, north-east) should display relatively small window surfaces (less than 15%). South facing walls should incorporate a large number of windows – a window area of 25% to 50% has proved successful here.

Conservatories on the south facing side of a building also permit passive use to be made of solar energy. The glass annex is heated up by the sun and thus forms an intermediate thermal "buffer". This reduces the heat loss via the adjacent house wall, and the heated air in the conservatory can additionally be used to heat and air the main building. Conservatories should be fully thermally insulated from the main building and equipped with high quality glazing (using at least insulating glass and preferably heat absorbing glass).

Low energy dwellings incorporate highly effective heat insulation for all exterior components (including efficient windows) which reduces the heat loss considerably.

Photovoltaic use of solar energy

Solar photovoltaics (PV) is a technology that converts sunlight directly into electricity. PV systems have an important use in areas remote from an electricity grid where they provide power for water pumping, lighting, vaccine refrigeration, electrified livestock fencing, telecommunications and many other applications. With the global demand to reduce carbon dioxide emissions, PV technology is also gaining popularity as a mainstream form of electricity generation. Some tens of thousands of systems are currently in use yet this number is insignificant compared to the vast potential that exists for PV as an energy source.

Photovoltaic modules provide an independent, reliable electrical power source at the point of use, making it particularly suited to remote locations. PV systems are technically viable and, with the recent reduction in production costs and increase in conversion efficiencies, can be economically feasible for many applications. The solar cells on the market today can convert up to 17% of the solar energy that shines on them into electricity.

Applications remote from the grid

Consumers located a long way from the grid can be supplied with electricity by a photovoltaic system. Lead acid batteries are used to store the electricity. The solar installation should always be combined with energy-saving appliances, for example, energy saving light bulbs. In stand alone operations, PV systems are already able to compete with other electricity sources (mains connection, diesel generators) in economic terms.

Grid connected PV systems

PV systems can also be connected to the public electricity grid via an appropriate inverter. No means of storing the electricity is then required. On sunny days, the solar generator will supply the electric appliances in the house, and surplus energy will be fed into the grid. During the night and on days with unfavourable weather conditions, electricity will be taken from the grid. When planning a PV system, it is important to avoid having modules that are partially in the shade. Where possible, the solar modules should be positioned so that any shade occurs only during periods of weak sunshine (mornings, evenings and winter).

Active thermal use of solar energy

Solar collectors are used to convert solar radiation into heat. The black solar absorber inside the collector absorbs the solar radiation and converts it into heat. A heat transfer medium (generally water although air is used as well), is conducted through the absorber, heating up in the process, and transports the energy to the point of consumption or storage.

A good solar installation can provide about two thirds of the annual energy required to supply a household with hot water.

Collector installations

Roof mounted – the collector is installed above the tiles and the roof remains intact.

Roof integrated – the collector replaces the tiles, permitting savings on tiles, and is incorporated and sealed in the roof skin (with the aid of prefabricated installation systems).

Free standing – the collector is installed on a rack on the ground or on a flat roof at a specific angle of inclination.

Solar-Fabrik

Solar-Fabrik's photovoltaic modules are highly efficient, and easy and quick to mount. The high product quality of Solar-Fabrik modules has the following features:

• 6-inch single-crystal silicon cells with anti-reflection coating which gives top conversion efficiencies.

• The modules are reliably protected against thermal expansion damage and moisture penetration.

• The highly transparent and specially tempered glass front ensures excellent light transmitting capacity and robustness.

• The modules connect readily with all inverters commonly found on the market.

• 10-year output warranty.

• Mounting hardware and all other system components are available.

For further information, please contact:
 

The International Solar Energy Society (ISES) International Headquarters Villa Tannheim Wiesentalstr. 50 79115 Freiburg Germany Tel: +49 761 45906 0 Fax: +49 761 45906 99 E-mail: hq@ises.org Website: http://www.ises.org/

Solar-Fabrik GmbH Munzinger Str. 10 D-79111 Freiburg Germany Tel: +49 (0)761 4000 0 Fax: +49 (0)761 4000 199 E-mail: info@solar-fabrik.de Website: http://www.solar-fabrik.de/

Freiburg Municipal Utilities (FEW) –  Energy advisory service Leopoldring 7 D-79098 Freiburg Germany Tel: +49 761 279 2409

ITDG would like to thank the Environment Protection Department in the City of Freiburg and Solar-Fabrik for providing the original material on solar energy.

This document is an output from a project funded by the UK Department for International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of the DFID.

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.