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production of hydrogen which is stored and converted to electricity in hydrogen fuel cells.

The need for seasonal storage arises primarily with solar cells (also with hydropower where however large dams already exist). As discussed in section 2.4 a maximum of 35-40% of the electric energy from solar cells need be stored from sunny summer months to winter months. Storage of hydrogen over longer periods seems to be relatively expensive (62). Another alternative is to supply oxygen and hydrogen from electrolyzed water to methanol production. The solar electricity would thus be connected to the energy system in the form of methanol. We utilize 20 TWh of the production of solar cells in this way. Through the existence of hydrogen storage (and oxygen storage) it would seem possible to absorb a (smaller) part of the load variations.

By having a large proportion of electricity production occur near the user and some of the evening out of the load occur at the point of utilization, the demand for high capacity electricity grids can be limited (compared to if the load variations were to be absorbed only on the production side with large installations nydropower, pump storage etc.).

The losses in the electricity system have been estimated at approximately 21 TWn, of which distribution losses are 15 TWh and losses in short time storage approximately 6 TWh. Distribution losses in 2015 are assumed to be 8%. Today they are approximately 10%. The lower figure is justified by shorter transfer distances. Electricity for end use is thus 148 TWh. (20 TWh from solar cells used in methanol production is not included.)

Thus there does not seem to be a scarcity of electricity in Solar Sweden. This is not because the demand has been adjust towards a small proportion of electricity but because several of the renewable production methods give electricity (hydropower, windpower, photovoltaic cells). It is also because part of the heat need, primarily

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district heating in the larger cities and part of the need for process heat, cannot be supplied by direct solar heating for various reasons. This causes heat to be available for production of power from counter-pressure generation, which further increases the availability of electricity.

We have chosen to introduce only one new energy carrier in Solar Sweden. We have chosen methanol rather than the frequently discussed hydrogen. The reason is primarily a wish to avoid building a large scale network for distribution of gas in the country, since this is both expensive and strongly determines options for locating industries and other activities. Hydrogen can however be available locally in large quantities.

Methanol, CH3OH, is a liquid. One can consider it as two molecules of hydrogen with a molecule of carbon monoxide added to make it liquid. The energy density of methanol is approximately half that of petrol. Methanol is colourless, water soluble and odourless. It freezes at - 98°C and boils at 65°C and has a density of 0.8g/cm3. In the US approximately 4 million tons of methanol were produced in 1972. It was sold at a price of approximately 0.25 Sw. Crs per litre (74, 75, 76).

A new energy carrier must be introduced in Solar Sweden, primarily to replace petrol in the transport sector. Several factors point to methanol. It is possible to store, it is liquid and can be gradually introduced into the existing transport system. Hydrogen would demand an entirely new technology without the same possibilitiy for gradual change. Gas has the same limitations.

Methanol can be produced from biomass, peat, natural gas or coal.
It can also be imported e.g. through contracts with some country

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with large resources of natural gas, where gas is not today used but burnt at the well-head due to lack of alternatives.

Methanol can be used in many ways. It burns with a clean blue flame. It can be used in combustion engines of today's type. Utilization in fuel cells is also possibility, which we have

assumed in the future transport sector.

An important advantage is that methanol can be mixed with petrol.
The amount can be 15 20% and be used in present car engines
with very limited changes. In this way a production of methanol
can be built up. If the alternative of mixing petrol and methanol
in the pumps at petrol stations is chosen (in a similar manner to
mixing with oil for two-stroke engines) a distribution network
is also created. Use of methanol in petrol means that the lead
additive is not necessary and other emissions can be reduced.
This is of great importance and can be relatively quickly carried
out. With somewhat larger changes Ottocycle engines can be fueled
by pure methanol.

Methanol has been shown to be a useful fuel in fuel cells. A
fuel cell has been developed which has run continuously for more
than 30,000 hours on methanol and air (74). The fuel cell utilizes
tungsten carbide and coal as electrodes and sulphuric acid as
electrolyte.

Conversion of natural gas, coal or biomass to methanol entails loss of part of the energy content. So far methanol has been produced primarily from natural gas and coal. The energy conversion efficiency is today 55% at production from natural gas and 45% from coal. By more efficient reclamation of heat 75% can theoretically be reached. 65 - 68% is deemed a realistic level (76). Methanol has not previously been produced from wood or waste, but this ought not to be problematic

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since they can be gasified (77). The sulphur content in these fuels is lower than 0.1 %, whereas coal has 2 % or more. Since the catalysts used in methanol production are particularly sensitive to sulphur, the low sulphur content of wood and solid waste is an advantage. The conversion efficiency is 35% from wood and waste, but it can be considerably higher or lower depending on the size of the plant and the heat reclamation (77).

Surplus electricity from solar cells (during summer months) is assumed to be added to the methanol production in the form of nydrogen and oxygen (electrolysis of water)! Since hydrogen is a high quality fuel this gives a higher efficiency. We have in our calculations used an average efficiency of 55 %.2) Part of the

waste heat has also been utilized.

In fuel cells the chemical energy of the fuel (rich in hydrogen) is converted directly to electricity (direct current) without an intervening combustion or heat cycle. No cooling water is needed. A single cell produces a voltage of 0.5 1 V with a current pro

portional to the area of the cell. The cells are connected in series. In this way they are combined to modules.

1)

Electrolysis of water to hydrogen and oxygen has today in commercially available plants an efficiency of 60-70%. The interest in developing efficient methods of electrolysis has previously been weak since hydrogen for industrial use has been obtained cheaper and more simply from oils or methane (73). The theoretical efficiency is 120 % because the cells take heat from the surrounding environment (8). We assume here that it is possible to develop the processes and to use waste heat from methanol production to an efficiency of 100 % in converting electricity to hydrogen and oxygen.

2) In accordance with what is shown in EFA 2000 (11) page 97,for conversion of biomass to methanol at the level of technological development expected for 1990.

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The fuel cell was invented in 1842 and has been a technical innovation which has lacked applications. Not until the advent of the US Space Program could the fuel cell play a role (80). In recent years they have been of interest to the US power industry because of some interesting characteristics (81):

- modular construction

- good environmental characteristics

- high conversion efficiency even when only a fraction of the maximum power is used.

- immediately responsive to load changes

- moderate cost.

The modular construction allows capacity to be built up in accordance with demand and the relatively small units to be located near the user. Thereby a high degree of utilization of waste heat is made possible. Of the energy supplied the output is approximately 40% as electricity, 25% as heat (at approximately 165° C) suitable as process steam and 30% as low temperature heat (approximately 70°C) (78). This is true of fuel cells with an acid electrolyte (phosphoric acid) working at a temperature of 160 - 200°C. For these fuel cells to reach the set goals for development it is necessary that a break through concerning the functioning of the air catode occurs (82). Development is also taking place for cells using molten carbonate working at temperatures of 600 - 700°C and cells with an alcaline electrolyte (100 - 150°C). The latter has the problem that the electrolyte reacts with carbon dioxide making it necessary to eliminate this (82). Techniques to remove carbon dioxide are vital for this type of fuel cells.

Towards the turn of the century an efficiency of 55% in converting biomass to electricity may have been reached (83).