Performance and Cost Discussion

The AC, grid-connected systems characterized here range in size from 20 kW to 20 MW. All systems are fixed, flat -plate for simplicity of design and use. Actual systems will vary, without major impact on costs. The systems use th e best available thin film in any given year (unknown at this time). See References 17-19, 22-33 for details on projected efficienci es and costs. Since 'capacity factor' depends only on tracking and system loss assumptions, capacity facto r is assumed constant (21% for average sunlight, 26% for high sunlight) throughout the period. It may improve slightly during the period covered.

The expected economic life of the system is 30 years, although this is somewhat arbitrary. Solid-state devices suc h as PV modules may eventually last fifty years or more, although other mechanical and electrical aspects of systems may never be as robust. An ongoing outdoor thin film module test at NREL, and parallel accelerated tests [34], form the basis for reliabi lity projections for thin films (see Figure 2). The system construction period is assumed to be less than one year, based on the fact that many such systems are already being built in similar construction times .

Table 1. Performance and cost indicators.

Base Case

INDICATOR

1997

2000

2005

2010

2020

2030

NAME

UNITS

+/-%

f/-%

+/-%

+/-%

+/-%

+/-%

Plant Size (DC Rating)

MWp

0.02

3

10

20

20

20

Plant Size (AC Rating)

MW

0.016

2.4

8

16

16

16

Plant Size (module area)

m2

333

33,500

91,000

143,000

125,000

118,500

PV Module Performance Parameters

Efficiency

- Laboratory Cell (best)

%

18

19

5

20

5

21

6

22

7

23

8

- Submodule (best)

%

13

15

5

17

5

18

6

19

7

20

8

- Power Module (best)

%

10

12

6

15

10

17

10

18

10

19

10

- Commercial Module

%

6

9

10

11

15

14

25

16

25

17

25

- Commercial Module Output

Wp/m2

60

90

10

110

15

140

20

160

20

170

25

- System Efficiency

%

4.8

7.2

8.8

11.2

12.8

13.6

System Performance in Average-Insolation Location (global sunlight, in plane, 1800 kWh/m 2-yr)

AC Capacity Factor

%

20.7

20.7

5

20.7

5

20.7

5

20.7

5

20.7

5

Energy/Area

kWh/m2-yr

86

130

10

158

15

202

25

230

25

245

25

Energy Produced

GWh/yr

0.029

4.4

15

15

20

29

25

29

25

29

30

System Performance in High-Insolation Location (global sunlight, in plane, 2300 kWh/m

2-yr)

AC Capacity Factor

%

26.4

26.4

5

26.4

5

26.4

5

26.4

5

26.4

5

Energy/Area

kWh/m2-yr

110

166

10

202

15

258

20

294

20

313

25

Energy Produced

GWh/yr

0.037

5.6

15

18.6

20

37

25

37

25

37

1. For each of the six time frames, estimates of uncertainty (+/- %) are provided.

2. Output energy (kWh/m2-yr) is reduced by 20% to include operational losses as compared with module and system peak watt (W p) DC ratings. Output energy is used to calculate the busbar energy cost. The system's AC Rating already includes this 20% reduction. The 20% reduction from the peak power of the modules is as follows: 8 % for module performance at higher operating temperatures (about 50 °C instead of 25 °C); 2% for dust accumulation; 5% for wiring and matching modules in array; 5% fo r DC-to-AC conversion and power conditioning to utility needs. Note that the operating temperature loss is lower than today's array losses because high-band gap material s such as CdTe and amorphous silicon have inherently lower temperature dependencies than crystalline silicon and have half or less losses due to operating at hig h temperatures.

3. Substantial uncertainties exist in both the magnitude and timing of the projections, since progress in PV depends critically on continued research advances. Long-ter m projections (2030) are based on reaching cost and performance that look practical, based on today' s technologies and understanding. It is likely that actual 203 0 achievements will be better than those assumed here because of innovations that are beyond what we can envision today.

4. Energy delivery equals AC Capacity Factor, times plant size (AC Rating), times 8,760 h/yr; it also equals system efficiency, times system area, times available sunlight pe r unit area, because, for this kind of simple, nontracking system, downtime is negligible.

Table 1. Performance and cost indicators. (cont.)

Base Case

INDICATOR

1997

2000

2005

2010

2020

2030

NAME

UNITS

+/-%

+/-%

+/-%

+/-%

+/-%

Capital Cost (1997$)

Direct Module Production Cost

$/m2

150-200

25

135-185

30

85-105

30

50-80

30

48-62

30

40-50

30

Power-Related BOS (converted

$/m2

60

25

54

30

44

30

35

30

32

30

25

30

from $Wp to $/m2)

Area-Related BOS without Land

$/m2

109

25

100

30

78

30

48

30

42

30

39

30

Land Costs (total system area

$/m2

0.4

0.6

0.8

0.8

1.2

1.2

basis)

Indirect Cost Factor (on modules

multiple

1.3

50

1.21

50

1.16

50

1.1

50

1.1

50

1.11

50

and systems)

Indirect Costs (on modules and

$/m2

100

50

66

50

35

50

15

50

13

50

11

50

systems)

System Total

$/m2

445

30

380

35

252

35

163

35

142

35

120

35

DC Unit Costs

Module Cost (w/overhead)

$/Wp

3.8

30

2.2

35

1.0

35

0.5

35

0.38

35

0.29

35

BOS Cost

$/Wp

3.7

30

2.1

35

1.3

35

0.7

35

0.53

35

0.43

35

(w/overhead & land at $0.02/Wp)

System Total

$/Wp

7.5

30

4.3

35

2.3

35

1.2

35

0.91

35

0.72

35

System Total

$M

0.148

30

12.7

35

23

35

23

35

18

35

14

35

AC Unit Costs

System Total Capital Cost

$/Wp

9.3

30

5.3

35

2.9

35

1.5

35

1.11

35

0.88

35

Operations and Maintenance Cost

Maintenance (annual)

$/m2-yr

2

30

1

30

0.5

50

0.4

50

0.3

50

0.3

50

O&M (AC unit costs)

^/kWh

2.30

30

0.77

30

0.31

50

0.20

50

0.13

50

0.12

50

Total Annual Costs

$/yr

666

30

33,000

30

46,000

50

57,000

50

38,000

50

36,000

50

Total Operating Costs

$/yr

666

30

33,000

30

46,000

50

57,000

50

38,000

50

36,000

1. For each of the six time frames, estimates of uncertainty (+/- %) are provided.

2. Plant construction is assumed to require less than 1 year.

3. Module manufacturing and BOS costs, when given in units of $/m 2, do not include overhead. However, final costs are fully loaded when given in $/W p units. The difference is the 'indirect costs' given as a separate line. This overhead is used to indicate the fully loaded BOS, module, and installed system costs.

4. Most direct costs are given as $/m2 because most costs are area-related (e.g., module manufacturing costs). Giving costs in terms of areas is a strong indicator of technica l issues and evolutions. For example, critical parameters such as yield, materials use, and process rate are all proportional to module area produced.

5. Substantial uncertainties exist in both the magnitude and timing of the projections, since progress in PV depends critically on continued research advances. Long-ter m projections (2030) are based on reaching cost and performance that look practical, based on today's technologies and understanding. It is likely that actual 203 0 achievements will be better than those assumed here because of innovations that are beyond what we can envision today.

A key indicator is the projected efficiency of commercial modules. The output of a PV system is nearly proportiona l to the incident sunlight, and that proportionality is called the 'efficiency' of the system. Efficiency is defined for bot h energy and power. Power can be used as a measure of the instantaneous amount of sunlight on an array, or the amount of electric power the array produces (units of watts); energy is the power over a period of time (units of kWh). For example, if a PV system produces 180 kWh/m2-yr in an average U.S. location (with 1,800 kWh/m2-yr of sunlight), it is said to have an efficiency of 10% (since 180/1,800 is 10%). Similarly, if the instantaneous amount of sunlight i s 1,000 W/m2 (about the solar power at noon on a clear day; part of the definition of standard peak power conditions' ) and the PV system produces 100 W/m2 of power, its efficiency is also 10%. Efficiency is the most critical figure o f merit for PV, since both output and cost are strongly coupled to efficiency. Cost is inversely proportional to efficiency. A system installed for $1,000 that produces 100 watts has a price of $10/W ($1,000/100 W). One that is twice as efficient in converting sunlight to electricity produces double the power (200 W) for the same $1,000, and thus ha s half the price (per unit of power), or $5/W.

11/88 11/89 11/90 11/91 10/92 10/93 10/94 10/95 10/96

Figure 2. Results from eight years of outdoor thin film module tests.

More than a decade of technology development focused on thin films is beginning to pay off in the form of excellen t performance. Table 2 shows the best 'one-of-a-kind', pre-commercial, thin film prototype modules [35,36]. Thes e modules are the basis for our confidence in our cost and performance projections.

The base year (1997) status [18-20, 35-36] of thin films supports these projected levels. For example, cell-leve l efficiencies have reached 16-18% in two different polycrystalline thin films (copper indium diselenide and cadmiu m telluride; see Figure 3). Submodule and module efficiencies are closely related to cell efficiencies, with minor losse s (about 10%) due to some loss of active area and some electrical resistance losses. Today's best laboratory-leve l modules are about 8-10% efficient (see Table 2). When the product-level technology (which includes all the proces s development needed for manufacture) has adopted all the technical capabilities now observed in laborator y experiments, the best lab modules will be about 90% of the efficiency of the best cells. Off-the-shelf commercia l modules will be about 90% as efficient as the best prototype modules. The timing of how these R&D advances actually o it 5.0

Figure 2. Results from eight years of outdoor thin film module tests.

Note:1988 modules are 1ft2 (0.093m: 1990, 92, 94, are 4ft2 (0.37m2)

Note:1988 modules are 1ft2 (0.093m: 1990, 92, 94, are 4ft2 (0.37m2)

become available in the marketplace is far less certain; projected ranges are used to capture this uncertainty withou t completely begging the question.

Table 2. The best thin

film modules (1997).

Thin Film Material

Size (cm2)

Efficiency (%)

Power (Watts)

Company & Comments

CdTe

6,728

9.1

61.3

Solar Cells Inc.

a-Si

7,417

7.6

56.0

Solarex (Amoco Enron Solar)

CIS

3,859

10.2

39.3

Siemens Solar Industries

CdTe

3,366

9.2

31.0

Golden Photon Inc.

a-Si

3,906

7.8

30.6

Energy Conversion Devices

a-Si

3,432

7.8

26.9

United Solar Systems (USSC)

a-Si

1,200

8.9

10.7

Fuji (Japan)

CIS

938

11.1

10.4

ARCO Solar (now Siemens Solar)

CdTe

1,200

8.7

10.0

Matsushita (Japan)

a-Si

902

10.2

9.2

USSC

Note: Efficiencies verified independently at NREL.

Note: Efficiencies verified independently at NREL.

Submodules not shown in Table 2 have reached 13-14% at about 100 cm2 in area [36]. Efficiencies are 10% to 11 % on square-foot (0.093 m2) sizes, and 7% to 10% on larger power modules ranging in size from 4 to 8 square feet (0.370.74 m2) in area. A few years ago (1990), no thin film modules larger than four square feet (0.37 m 2) were being made. The transition from laboratory-level cell prototypes to pre-commercial modules is underway. These same modules now form the basis for design and construction of larger-capacity manufacturing facilities, which are in-progress at man y U.S. thin film companies. Meanwhile, additional technical progress is in the pipeline [36]. Figure 3 shows the recent progress in polycrystalline thin film laboratory cells. The changes implicit in the best 16-18% efficient cells have not yet been incorporated in the modules of Table 2. When they are, efficiencies will rise commensurately. The progres s in thin film cel ls provides a strong basis for our belief that the ambitious performance goal of 15% for commercia l modules will be met, since a reasonable translation of existing cell efficiencies to future module efficiencies would b e nearly sufficient to meet the goal. Figure 2 shows outdoor tests of six CIS-based thin film modules at NREL. Thes e modules have been outside for almost eight (8) years. They show no apparent change in performance. Two-yea r stability data is available for CdTe modules.

Module and system costs are frequently given in $/m2 as an indication that most PV costs are proportional to module area. (Some costs, such as those for inverters, are proportional to power, but can be converted to $/nf using area and a known output per unit area). A module might have a fully loaded cost of $400/m2 to manufacture. If it produces 100 W/m2 under 'standard conditions', it is said to have a cost of $4/Wp (Wp stands for the watts produced under peak sunlight). Today's PV modules sell at about $3.5 to $5/Wp; and PV systems sell at about $7 to $15/Wp. Peak power for a system is found by adding up the power of the individual modules, rated at their peak power. System economics are then calculated based on kWh output during real or average conditions at a specific solar location.

The base year (1997) system is modeled after two recent thin film systems: an APS a-Si 400 kW system at PVUS A ($5/Wp) and a Solar Cells Inc./ 25 kW CdTe system at Edwards Air Force Base ($6.3/Wp, [37]). Although both of these systems are below the indicated $7.4/Wp that we assumed (see Table 1), it is probably proper to estimate that the companies installed them for somewhat below true cost.

Today, PV module costs are about half the total system costs for most PV systems and are the primary opportunity for cost reductions. The technology option considered here (thin films) was originally investigated because its potentia l cost per unit area is significantly lower than existing PV based on wafer silicon [16-20]. In addition to module cost , the module performance defines system output. This combined influence on capital cost and system unit output cos t is why modules are the critical cost driver in PV. Structural costs are highly dependent on economies of volum e production. They are expected to fall as production increases. But they, too, require some focused developmental work to reach optimal levels. However, module efficiencies and module manufacturing costs are the key areas of focu s determining PV system costs. Work on improving PV modules (both in terms of efficiency and cost optimization) i s most likely to pay off in reductions in PV prices.

Boeing

Boeing

EuroCIS

Boeing

Univ. of So. Florida Photon Energy AMETEK

> Boeing kUnlv. of Maine

Living Off The Grid

Living Off The Grid

Get All The Support And Guidance You Need To Be A Success At Living Off The Grid. This Book Is One Of The Most Valuable Resources In The World When It Comes To When Living Within The Grid Is Not Making Sense Anymore.

Get My Free Ebook


Post a comment