3.8.4.3.4 Solar Energy
An estimation of solar energy potential based on available land in various
regions (Tables 3.33a and 3.33b)
gives 1,575 to 49,837 EJ/yr. Even the lowest estimate exceeds current global
energy use by a factor of four. The amount of solar radiation intercepted by
the earth may be high but the market potential for capture is low because of:
- the current relative high costs;
- time variation from daily and seasonal fluctuations, and hence the need
for energy storage, the maximum solar flux at the surface is about 1 kW/m2
whereas the annual average for a given point is only 0.2 kW/m2;
- geographical variation, i.e. areas near the equator receive approximately
twice the annual solar radiation than at 60° latitudes; and
- diffuse character with low power such that large-scale generation from
direct solar energy can require significant amounts of equipment and land
even with solar concentrating techniques.
| Table 3.33a: Key assumptions for the
assessment of the solar energy potential |
 |
| Region |
Assumed annual
clear sky irradiancea
kW/m2
|
Assumed annual
average sky
clearanceb, %
|
|
| |
Min
|
Max
|
Min
|
Max
|
| |
| NAM (North America) |
0.22
|
0.45
|
0.44
|
0.88
|
| LAM (Latin America and the Caribbean) |
0.29
|
0.46
|
0.48
|
0.91
|
| AFR (Sub-Saharan Africa) |
0.31
|
0.48
|
0.55
|
0.91
|
| MEA (Middle East and North Africa) |
0.29
|
0.47
|
0.55
|
0.91
|
| WEU (Western Europe) |
0.21
|
0.42
|
0.44
|
0.80
|
| EEU (Central and Eastern Europe) |
0.23
|
0.43
|
0.44
|
0.80
|
| FSU (Newly independent states of the former Soviet
Union) |
0.18
|
0.43
|
0.44
|
0.80
|
| PAO (Pacific OECD) |
0.28
|
0.46
|
0.48
|
0.91
|
| PAS (Other Pacific Asia) |
0.32
|
0.48
|
0.55
|
0.89
|
| CPA (Centrally planned Asia and China) |
0.26
|
0.45
|
0.44
|
0.91
|
| SAS (South Asia) |
0.27
|
0.45
|
0.44
|
0.91
|
| |
| |
| Table 3.33b: Assessment of the annual
solar energy potential |
| |
| Region |
Unused land
(Gha)
|
Assumed for
solar energyd
(Mha)
|
Solar energy
potentiale
(EJ/yr)
|
|
| |
Availablec
|
Min
|
Max
|
Min
|
Max
|
| |
| NAM (North America) |
0.5940
|
5.94
|
59.4
|
181.1
|
7,410
|
| LAM (Latin America and the Caribbean) |
0.2567
|
2.57
|
25.7
|
112.6
|
3,385
|
| AFR (Sub-Saharan Africa) |
0.6925
|
6.93
|
69.3
|
371.9
|
9,528
|
| MEA (Middle East and North Africa) |
0.8209
|
8.21
|
82.1
|
412.4
|
11,060
|
| WEU (Western Europe) |
0.0864
|
0.86
|
8.6
|
25.1
|
914
|
| EEU (Central and Eastern Europe) |
0.0142
|
0.14
|
1.4
|
4.5
|
154
|
| FSU (Newly independent states of the former Soviet
Union) |
0.7987
|
7.99
|
79.9
|
199.3
|
8,655
|
| PAO (Pacific OECD) |
0.1716
|
1.72
|
17.2
|
72.6
|
2,263
|
| PAS (Other Pacific Asia) |
0.0739
|
0.74
|
7.4
|
41.0
|
994
|
| CPA (Centrally planned Asia and China) |
0.3206
|
3.21
|
32.1
|
115.5
|
4,135
|
| SAS (South Asia) |
0.1038
|
1.04
|
10.4
|
38.8
|
1,339
|
| World total |
3.9331
|
39.33
|
39.33
|
1575.0
|
49,837
|
| Ratio to the current primary energy consumption
(425 EJ/yrf) |
-
|
-
|
-
|
3.7
|
117
|
| Ratio to the primary energy consumption projectedg
for 2050 (590-1,050 EJ/yr) |
-
|
-
|
-
|
2.7 - 1.5
|
84 - 47
|
| Ratio to the primary energy consumption projectedg
for 2100 (880-1,900 EJ/yr) |
-
|
-
|
-
|
1.8 - 0.8
|
57 - 26
|
| |
| |
Photovoltaics
The costs of photovoltaics are slowly falling from around US$5,000/kW installed
as more capacity is installed in line with the classical learning curve (Goldemberg,
2000). Present generating costs are relatively high (20 – 40c/kWh), but
solar power is proving competitive in niche markets, and has the potential to
make substantially higher contributions in the future as costs fall. Photovoltaics
can often be deployed at the point of electricity use, such as buildings, and
this can give a competitive advantage over power from central power stations
to offset higher costs.
Conversion technology continues to improve but efficiencies are still low.
Growing markets for PV power generation systems include grid connected urban
building integrated systems; off-grid applications for rural locations and developing
countries where 2 billion people still have no electricity; and for independent
and utility-owned grid-connected power stations. The size of the annual world
market has risen from 60MW in 1994 to 130MW in 1997 with anticipated growth
to over 1000MW by 2005 (Varadi, 1998). This remains small compared with hydro,
wind, and biomass markets. Industrial investment in PV has increased with Shell
and BP-Solarex establishing new PV manufacturing facilities with reductions
in the manufacturing costs anticipated (AGO, 1999).
Conversion efficiencies of silicon cells continue to improve with 24.4% efficiency
obtained in the laboratory for monocrystalline cells and 19.8% for multicrystalline
(Green, 1998; Zhao et al., 1998), though commercial monocrystalline-based
modules are obtaining only 13%-17% efficiency and multicrystalline 12%-14%.
Modules currently retail for around US$4,000 – 5,000/kW peak with costs
reducing as predicted by the Worldwatch Institute (1998) as a result of manufacturing
scale-up and mass production techniques. Recent studies showed a US$660M investment
in a single factory producing 400MW (5 million panels) a year would reduce manufacturing
costs by 75%. KPMG (1999) and Neij (1997) calculated a US$100 billion investment
would be needed to reach an acceptable generating level of US$0.05/kWh.
Thin film technologies are less efficient (6%-8%) but cheaper to produce, and
can be incorporated into a range of applications including roof tile structures.
Further efficiency improvements are proving difficult, whereas both cadmium
telluride and copper indium gallium selenide cells have given 16%-18% efficiencies
in the laboratory (Green et al., 1999) and are close to commercial production.
New silicon thin film technology using multilayer cells, which combine buried
contact technology with new silicon deposition and recrystallization techniques,
enables manufacture to be automated. A commercially viable product now appears
to be feasible with an efficiency of around 15% and cost of around US$1500/kW
(Green, 1998). Recycling of PV modules is being developed at the pilot scale
for both thin film and crystalline silicon modules (Fthenakis et al.,
1999).
Advances in inverters (including incorporation into the modules to give AC
output) and net metering systems have encouraged marketing of PV panels for
grid-connected building integration projects either in government sponsored
large scale installations (up to 1MW) or on residential buildings (up to 5kW)
(IEA, 1998c; Moomaw et al., 1999b; IEA, 1999b; Schoen et al.,
1997). Japan aims to install 400 MW on 70,000 houses by 2000 (Flavin and Dunn,
1997) and 5000MW by 2010. Simple solar home systems with battery storage and
designed for use in developing countries are being installed and evaluated in
South Africa and elsewhere by Shell International Renewables with funding from
the World Bank. Integrated building systems and passive solar design is covered
in Section 3.3.4.
A promising low-cost photovoltaic technology is the photo-sensitization of
wide-band-gap semiconductors (Burnside et al., 1998). New photosensitizing
molecules have been developed in the laboratory, which exhibit an increased
spectral response, though at low efficiencies of <1%. Arrays of large synthetic
porphyrin molecules, with similar properties to chlorophyll, are being developed
for this application (Burrell et al., 1999).
Solar Thermal
In Europe 1 million m2 of flat plate solar collectors were installed
in 1997, anticipated to rise to 5 million m2 by 2005 (ESD, 1996).
Combined PV/solar thermal collectors are under development with an anticipated
saving in system costs, though these remain high at US$0.18-0.20/kWh at 8% discount
rate and 10 year life (Elazari, 1998). High temperature solar thermal power
generation systems are being developed to further evaluate technological improvements
(Jesch, 1998). The Californian “power tower” pilot project has been
successful at the 10 MW scale and is now due to be tested at 30MW with 100MW
the ultimate goal (EPRI/DOE, 1997). Dish systems giving concentration ratios
up to 2000 and therefore performing at temperatures up to 1,500oC
can supply steam directly to a standard turbo-generator (AGO, 1998). Capital
costs are projected to fall from US$4,000/kW to US$2,500 by 2030 (Moomaw et
al., 1999b) with other estimates much lower (AGO, 1998).
3.8.4.3.5 Geothermal
Geothermal energy is a heat resource used for electricity generation, district
heating schemes, processing plants, domestic heat pumps, and greenhouse space
heating, but is only “renewable” where the rate of depletion does
not exceed the heat replenishment.
The geothermal capacity installed in 20 countries was 7,873 MWe
in 1998: this provided 0.3% (40TWh/yr) of the total world power generation (Barbier,
1999). Geothermal direct heat use was an additional 8,700 MWth. This
energy resource could be increased by a factor of 10 in the near term with much
of the resource being in developing countries such as Indonesia (Nakicenovic
et al., 1998).
3.8.4.3.6 Marine Energy
The potential for wave, ocean currents, ocean thermal conversion, and tidal
is difficult to quantify but a significant resource exists. For example, resources
of ocean currents greater than 2 m/s have been identified, and in Europe alone
the best sites could supply 48TWh/yr (JOULE, 1993). Technical developments continue
but several proposed schemes have met with economic and environmental barriers.
Many prototype systems have been evaluated (Duckers, 1998) but none have yet
proved to be commercially viable (Thorpe, 1998).
Several ocean current prototypes of 5 to 50kW capacity have been evaluated
with estimated generating costs of around US$0.06-0.11/kWh (5% discount rate)
depending on current speed, though these costs are difficult to predict accurately
(EECA, 1996). The economics of tidal power schemes remain non-viable, and there
have been environmental concerns raised over protecting wetlands and wading
birds on tidal mudflats.
