The Desertec plan

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An organization called DESERTEC [www.desertec.org] is promoting a plan to use concentrating solar power in sunny Mediterranean countries, and high-voltage direct-current (HVDC) transmission lines (figure 25.7) to deliver the power to cloudier northern parts. HVDC technology has been in use since 1954 to transmit power both through overhead lines and through

Figure 25.3. Stirling dish engine.

These beautiful concentrators deliver a power per unit land area of

14 W/ m2. Photo courtesy of Stirling

Energy Systems.

www.stirlingenergy.com

Figure 25.3. Stirling dish engine.

These beautiful concentrators deliver a power per unit land area of

14 W/ m2. Photo courtesy of Stirling

Energy Systems.

www.stirlingenergy.com

ifisM

Figure 25.4. Andasol - a "100 MW" solar power station under construction in Spain. Excess thermal energy produced during the day will be stored in liquid salt tanks for up to seven hours, allowing a continuous and stable supply of electric power to the grid. The power station is predicted to produce 350 GWh per year (40 MW). The parabolic troughs occupy 400 hectares, so the power per unit land area will be 10 W/ m2. Upper photo: ABB. Lower photo: IEA SolarPACES.

submarine cables (such as the interconnector between France and England). It is already used to transmit electricity over 1000-km distances in South Africa, China, America, Canada, Brazil, and Congo. A typical 500 kV line can transmit a power of 2 GW. A pair of HVDC lines in Brazil transmits 6.3 GW.

HVDC is preferred over traditional high-voltage AC lines because less physical hardware is needed, less land area is needed, and the power losses of HVDC are smaller. The power losses on a 3500 km-long HVDC line, including conversion from AC to DC and back, would be about 15%. A further advantage of HVDC systems is that they help stabilize the electricity networks to which they are connected.

In the DESERTEC plans, the prime areas to exploit are coastal areas, because concentrating solar power stations that are near to the sea can deliver desalinated water as a by-product - valuable for human use, and for agriculture.

Table 25.6 shows DESERTEC's estimates of the potential power that

Figure 25.5. The celebrated little square. This map shows a square of size 600 km by 600 km in Africa, and another in Saudi Arabia, Jordan, and Iraq. Concentrating solar power facilities completely filling one such square would provide enough power to give 1 billion people the average European's consumption of 125 kWh/d. The area of one square is the same as the area of Germany, and 16 times the area of Wales. Within each big square is a smaller 145 km by 145 km square showing the area required in the Sahara - one Wales -to supply all British power consumption.

Country

Economic potential

Coastal potential

(TWh/y)

(TWh/y)

Algeria

169000

60

Libya

140 000

500

Saudi Arabia

125000

2 000

Egypt

74 000

500

Iraq

29000

60

Morocco

20 000

300

Oman

19 000

500

Syria

10 000

0

Tunisia

9 200

350

Jordan

6400

0

Yemen

5100

390

Israel

3100

1

UAE

2000

540

Kuwait

1 500

130

Spain

1 300

70

Qatar

800

320

Portugal

140

7

Turkey

130

12

Total

620000

6 000

(70 000 GW)

(650 GW)

could be produced in countries in Europe and North Africa. The "economic potential" adds up to more than enough to supply 125 kWh per day to 1 billion people. The total "coastal potential" is enough to supply 16kWh per day per person to 1 billion people.

Let's try to convey on a map what a realistic plan could look like. Imagine making solar facilities each having an area of 1500 km2 - that's roughly the size of London. (Greater London has an area of 1580 km2; the M25 orbital motorway around London encloses an area of 2300 km2.) Let's call each facility a blob. Imagine that in each of these blobs, half the area is devoted to concentrating power stations with an average power density of 15W/m2, leaving space around for agriculture, buildings, railways, roads, pipelines, and cables. Allowing for 10% transmission loss between the blob and the consumer, each of these blobs generates an average power of 10 GW. Figure 25.8 shows some blobs to scale on a map. To give a sense of the scale of these blobs I've dropped a few in Britain too. Four of these blobs would have an output roughly equal to Britain's total electricity consumption (16 kWh/d per person for 60 million people). Sixty-five blobs would provide all one billion people in Europe and North Africa with 16kWh/d per person. Figure 25.8 shows 68 blobs in the desert.

Table 25.6. Solar power potential in countries around and near to Europe. The "economic potential" is the power that could be generated in suitable places where the direct normal irradiance is more than 2000 kWh/m2/y.

The "coastal potential" is the power that could be generated within 20 m (vertical) of sea level; such power is especially promising because of the potential combination with desalination.

For comparison, the total power required to give 125 kWh per day to 1 billion people is 46 000 TWh/y (5 200 GW). 6000 TWh/y (650 GW) is 16 kWh per day per person for 1 billion people.

Figure 25.7. Laying a high-voltage DC link between Finland and Estonia. A pair of these cables transmit a power of 350 MW. Photo: ABB.

Concentrating photovoltaics

An alternative to concentrating thermal solar power in deserts is large-scale concentrating photovoltaic systems. To make these, we plop a high-quality electricity-producing solar cell at the focus of cheap lenses or mirrors. Faiman et al. (2007) say that "solar, in its concentrator photovoltaics variety, can be completely cost-competitive with fossil fuel [in desert states such as California, Arizona, New Mexico, and Texas] without the need for any kind of subsidy."

According to manufacturers Amonix, this form of concentrating solar power would have an average power per unit land area of 18 W/m2.

Another way to get a feel for required hardware is to personalize. One of the "25 kW" (peak) collectors shown in figure 25.9 generates on average about 138 kWh per day; the American lifestyle currently uses 250 kWh per day per person. So to get the USA off fossil fuels using solar power, we need roughly two of these 15 m x 15 m collectors per person.

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Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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