The potentials of wind power and solar electricity production from PV and concentrating solar power stations are discussed in the following. Except where otherwise indicated, the calculations are based on meteorological data of the European Centre for Medium-Range Weather Forecasts (ECMWF) and, in the case of solar energy, also on data of the National Center for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) [ERA-15] [NCEP 99].

• 3.1 Potentials of Wind Energy

The potentials of national wind energy are dependent not only on prevailing wind conditions but also on factors such as population density or nature preserves and other restrictions. According to [Qua 00], for instance, the realizable wind power capacity on land sites in Germany can correspondingly be estimated at 53.5 GW. A total annual wind power production of about 85 TWh is assumed to be achievable as a result. This figure represents about 17% of total consumption (approx. 490 TWh) and is equivalent to 1600 full-load hours (FLH) of wind power per year. The additional offshore wind potential is taken to be about 79 TWh at nearly 3400 FLH [Qua 00]. In another study, the German offshore wind potential is given as approx. 240 TWh [GMN 95], even though a maximum distance of 30 km has been assumed between the offshore wind turbines and the coastline. This limitation has been rendered superfluous by more recent planning (s. e. g. [BSH 04]), so that a far greater potential may be assumed. If only locations are considered where the water is not deeper than 40 meters, with offshore turbines erected entirely at locations not previously declared nature preserves, military zones, or otherwise unavailable, a "conflict-free” potential of about 67 TWh results according to [IGW 01]. These assumptions may be considered particularly conservative. Permit applications have already been made for water depths of 45 meters [BSH 04], opening the way to a high multiple of "conflict-free” sites compared with the above considerations. Nature preserves and areas used by the military have also come under consideration [BSH 04]. Consequently, the yearly production of several hundred TWh is easily imaginable. In addition, the German portion of potential wind power sites in the North Sea makes up only about one-eighth of the total area with a depth of less than 50 meters (s. also [Czi 00]). Considering the use of the southern North Sea with Denmark’s northern tip as the northernmost point, an area of roughly 200’000 square kilometers with sea floor depths less than 45 meters can be found [Czi 00]. Here theoretically, neglecting all restrictions, an area sufficient for 1600 GW of rated offshore wind power would be available for generating up to 6000 TWh of electricity. This is roughly three times EU consumption, thus demonstrating that even after taking major restrictions into account a huge North Sea potential might still be realisable. Furthermore, shallow areas in other European seas with abundant wind resources would cover more than two times the area of the southern North Sea [Czi 00]. Greenpeace has recently published a scenario in which a capacity of 237 GW offshore wind power would be installed in EU coastal regions by 2020 to produce more than 720 TWh, while covering only 3.4% of the area available after all constraints

had been have been taken into account [Gre 04]. Notwithstanding differing estimates of potential, a significant contribution to electricity production is harnessable. The full use of offshore wind energy necessitates a wide spectrum of cooperative measures among European countries for arriving at the most favourable scheme of implementation.

According to conservative estimates of the Danish company BTM Consult, the technical wind power potential of land sites within the EU and Norway is 630 TWh, corresponding to 315 GW of installable wind capacity [EWEA 99]. The very simplified assumption has been made in this case that all turbines would be delivering 2000 FLH a year, meaning they would operate at an effective average capacity of roughly 23% at each site. In relation to the total electricity consumption within the EU of about 2350 TWh (with Norway, 2450 TWh), this technical potential could thus be harnessed to fulfil about one-fourth of electrical energy demand [DOE 02]. Another particularly detailed analysis of the wind conditions at a relatively narrow strip of land along the Norwegian coastline determined a technical potential of 1165 TWh at an average turbine load of 2900 FLH, not considering any possible restrictions, with the most favourable sites producing 156 TWh from turbines delivering an average of 4100 FLH [Win 03]. According to our own conservative estimates based on meteorological data of the ECMWF [ERA-15], a selection of wind sites within the European Union could generate about 400 TWh of wind energy with an average turbine performance of 2670 FLH using about 150 GW of total installed capacity, taking into account restrictions due to densely populated areas. Under the particularly favourable meteorological conditions prevailing in Ireland and Great Britain, far more electricity from wind power could be produced than estimated here. Due to the conservative assumptions adopted, however, their contribution has been limited to 25% of the total capacity installed in the EU and Norway. The respective electricity generation under these conditions would equal 32% of the electricity consumed in Ireland and Great Britain. In other countries, by contrast, the corresponding figure lies below 10% of domestic consumption. As previously mentioned, an annual average turbine operation of roughly 2700 FLH can thereby be achieved, whereas an even distribution of wind generators within the EU would only allow approx. 2000 FLH to be realized [Gie 00]. If in fact the total achievable potential for Great Britain and Ireland could be exploited, the generated electricity would slightly exceed their current demand. To insure that these possibilities may be realized, the transmission grid to neighbouring countries should be expanded in response to the growing use of wind energy to anticipate and stimulate the multilateral integration of wind power capacities.

The land-based wind power potentials in the EU are limited to the estimated levels identified above, due less to technical and meteorological restrictions than to the population densities of particular regions. If it were possible to use land areas freely, electrical energy requirements could be fulfilled many times over with wind power alone (s. Fig. 1). Restrictions due to the high population density are of secondary importance in many distant windy regions surrounding Europe. The population densities of northern Russia and western Siberia, northwestern Africa, and Kazakhstan lie between 0 — 2 inhabitants/km2 and are thus at least two orders of magnitude below those of Germany with its 230 inhabitants/km2 (s. e. g. [Enc 97]). In addition, these areas are steppes, deserts, semi-arid regions, or tundra of practically no inherent economic value, so that wind electricity generation may be instituted as a beneficial means of "farming in the desert”. The potential electricity production from wind power is shown in Fig. 1. Even considering only land sites at which more than 1500 FLH can be achieved (within the rectangle roughly 40% of the land area), and without further restrictions, the area shown within the rectangle comprising Europe and its neighbours could deliver 120’000 — 240’000 TWh of electricity from wind power at a installation density of 4 — 8 MW/km2. This result constitutes a maximum of about one hundred times the current electricity demand of the

EU or fifty times the electricity consumption of all countries within the selected area. If only the best wind sites with the highest production at an installation density of 8 MW/km2 were employed, just 4.3%o of the land area would be required to provide the equivalent of the annual electricity consumption of the entire area within the rectangle shown on the map. About 2.5% of the area would be adequate for covering the equivalent of the electricity demands of the EU. Furthermore, the area covered by the turbines and accompanying infrastructure themselves is typically only about 2% of any land dedicated to wind farming. (The figure of 2% applies generally to wind farms consisting of individual turbines of 600 kw rated capacity. The area is reduced if larger single units are employed.) Therefore, the land space required for generating the equivalent of total EU electricity consumption is actually less than 0.05% of the entire marked geographical area. By comparison, the roughly 6% of total land area in Germany currently sealed by streets, buildings, and other infrastructure covers a thousand times bigger fraction of space.

The three regions previously mentioned — northern Russia with northwestern Siberia, northwestern Africa, and Kazakhstan — each offer a greater wind energy potential alone than required for meeting EU consumption requirements in their entirely. In the following treatment, therefore, only the areas within these regions with the highest yields have been considered. In Tab. 1, the size of the areas selected for the analysis, the installable turbine capacity for a conservative assumption at a moderate installation density of 2.4 MW/km2, the expectable average production of the turbines assuming wide-range turbine placement over the selected area, and the expectable yearly output are given. Because of the data used, the estimates tend to be conservative. In the case of southern Morocco, for instance, measurements have shown that load factors of far more than 4500 FLH may be assumed directly on the coast at favourable locations [ER 99]. In Kazakhstan, measurements and other investigations likewise indicate that yields significantly over 4000 FLH may be expected [BMW 87] [Nik 99]. The higher the topographical complexity of the terrain, the more significant the underestimation tends to be. Wind potentials in [CGM 03] calculated from Rise for the region at the Gulf of Suez in Egypt represent the most extreme underestimation of wind conditions in any complex terrain known thus far to the author. A comparison of this map and the date with the data depicted in Fig. 1 indicates a maximal average production of roughly 2200 FLH at low spatial resolution (like the data derived from ECMWF data, which build the basis of the scenarios), while the high-resolution Rise

data corresponds to 6000 FLH (for better comparison, see also [Czi 01]). Even if this example is particularly extreme, such underestimation is rather typical for complex terrains, making clear that the scenarios represent a very conservative approximation of actual possibilities and thus provide compelling reasons for further argumentation, since — as the example shows — there must be substantially better wind potentials worldwide at many places than can be inferred from the data bases used for the scenarios. It appears certain that high-yield locations would be exploited first if they were known, whereby high potentials could be expected at high quality sites. [31]

at about 190 GW (150 TWh), some 120 GW (95 TWh) of which would be on rooftops [Qua 00]. This figure corresponds to an average yearly full-load capacity of 770 FLH or 780 FLH on roofs. Our own calculations have shown that good modules employed on rooftops with optimum angular position and unaffected by shadows could produce about 950 FLH. The difference to the values given in [Qua 00] is due primarily to the inclusion of shadow and disorientation factors. Fig. 2 shows the potential yearly electricity production from PV.

Table 2 contains the potentials and FLH for a number of countries.

Tab. 2 Potential power (P) and electricity generation (EG) from PV (Module = 14%) on roofs as well as simplified assumptions on the expectable average equipment duty factor (L0) under consideration of the losses due to shadows and roof disorientation, or under optimum conditions (Lopt). It has been assumed that the same roof area per inhabitant is available in all countries as in Germany an that it is distributed in th countries according to the population. [32]

Africa could satisfy 500 times the electricity demand of all EU countries. Since domestic consumption is comparatively low, however, this high solar energy potential could only be realized to a significant extent if solar power were exported outside the northern African region. The output of this solar thermal power plants with parabolic arrays depends crucially on their design. Therefore, the performance characteristics can be stated only with reference to the design parameters. The use of thermal storage units is of major importance in this respect. The quality of the site can be determined by the heat production of the mirror array, independent of the specific parameters of the power plants, as shown in Fig. 3.

The heat may be employed in a conventional thermal power plant to generate electricity at an efficiency of about 35%. If heat storage is included in the overall design, a larger linear mirror array is employed to charge the storage medium during the day. In this way, electricity may be produced throughout the night while supplanting the fossil fuels otherwise necessary for continuous operation of the plant. The storage facility therefore provides greater flexibility and reduces the cost of the solar electricity produced, since the conventional part of the power plant utilizes more solar heat, which during the night is delivered from storage. Therefore, the specific costs of the conventional part are lower, while not entirely compensating for the investment in storage capacities. In order to estimate the achievable electricity generation at certain locations, it is assumed that the storage has been generously dimensioned for 14 FLH, so that the solar heat produced in the mirror field will never be partially wasted due to the limited influx capacity of the conventional section. Such a parabolic trough power plant could attain nearly 5600 FLH in southern Morocco (western Sahara). Farther south in Mauritania, more than 5800 FLH would be possible, while 3000 FLH could be expected at a good location on the Iberian Peninsula.