Calendar year

Figure 3. Recent progress in polycrystalline thin film laboratory cell efficiencies.

In terms of module production costs, various studies [22-32, 33] of materials costs, combined with energy inputs, labor, and capital costs, support the cost projections. Data on specific amorphous silicon and polycrystalline thin fil m technologies were provided by U.S. manufacturers to the DOE/NREL PV Manufacturing Initiative as part of their final reports [27-32]. These provide the most up-to-date information on module cost projections. General analysis of P V system costs can be found in References 38-40. Nearly all of these cost studies agree that ultimate thin-film modul e manufacturing costs for a future, optimized manufacturing scenario can be as low as $40-$50/m2. Since the issue of achieving very low module manufacturing costs, $50/m2 or less, is perhaps the most important of any aspect of these projections, it deserves some special focus. In-depth review of References 22-32 supports this assertion and reveal s a few important aspects of cost that are summarized in Table 3.

Table 3. Summary of thin film direct manufacturing costs: projections for practical long-term reductions._

Summary of Thin Film Direct Manufacturing Costs

Cost ($/m2)

Materials

Glass (2 sheets @ $5/m2)

10

Binder (between glass and module)

5

Active Materials (for PV thin film)

5

Subtotal: Materials

20

Capital equipment (manufacturing plant)

10

Energy used in manufacturing

2

Facilities

1

Labor

10

TOTAL

43

Materials: Most thin films use one or two pieces of inexpensive soda lime glass, which is sold in quantity at abou t $5/m2. A sheet of binder (between the glass and the module) is about another $5/m2. The amount of material in a micron thickness across a square meter of area is 1 cm3. There are about 3-10 g/cm3 of material in the various films . Film thickness is about 1-10 ^m, depending on the design, so a typical amount of material would be about 25 g/m2. Considering feedstock losses, if only 50% of the feedstock material actually ends up on the module, then 50 g/m 2 of feedstock are needed. Typical materials costs for the various materials used in thin films (at high purity) can vary from $20 to $200/kg, or $0.02-$0.20/g. Fifty grams would cost about $5/m2. This is the total cost of the active materials in a thin-film module and is a fairly typical number from References 22-32 for all the materials costs outside the glass and encapsulants. The total materials costs are about $20/m2 (adding the active materials, binder, and two pieces o f glass).

Manufacturing Plant: Thin film manufacturing plants are now being built or being planned. Their capital costs tend to fall into the range of $10M to $30M for 10 MW of annual production capacity (about 150,000 m2 of modules at 6.5% efficiency). That is $1-$3/Wp for first-year module production. If this cost is amortized over 5 years, this becomes $0.3-0.8/Wp for production costs (assuming a discount rate to take into account the time value of money). These costs must be translated into $/m2 to provide an insight into trends. Since today's module efficiencies are onl y 5%-8%, these plant costs are about $18 to $52/m2 (assuming 65 W/m2 multiplied by $0.3/W or $0.8/W). Today's first-ever manufacturing plants are quite rudimentary, from a technical standpoint. Capital costs can only get lower a s processes are optimized for faster throughput and other economies of scale. A 'best' future capital cost of about haf of today's lower costs, $10/m2, seems quite conservative. (For example, tripling the throughput rate would cut the module unit cost attributable to plant capital ($10/m2) by a factor of three. This kind of improvement is already being investigated at the lab level.)

Energy, Labor and Facilities: The remaining direct manufacturing cost components are energy, labor, and facilities. Various analyses of module energy input costs suggest that modules will pay back their energy output within one year of outdoor operation [41-42]. References 41 and 42 quantify the electrical energy in a thin film module as abou t 20 kWh/m2. At a price of $0.1/kWh, this is another $2/m2.

Adding all of the costs so far, yields $32/m2. Facilities costs are about $200,000/year for a 10 MW plant, or $0.02/Wp, which is $1.3/m2 (nearly negligible). Labor costs are the last item of significance. We estimate that an operationa l plant with reasonable automation would require about 10 operators/shift; 30 full time staff. These are technician an d operations-level positions. (Management and marketing, as well as other indirect costs, are included in overhead costs.) At direct costs of $50,000/yr, they would cost about $1,500,000/yr, or $0.15/Wp, or $10/m2. Adding together these estimates yields ($20/m2 for materials; $10/m2 for capital equipment; $2/m2 for energy; $1/m2 for facilities; and $10/m2 for labor) $43/m2. This number is both close to estimates of 'best future' manufacturing costs (about $40/m2) and also without the full value of the following optimizations: thinner semiconductors, improved materials use durin g deposition, higher-rate deposition processes, better yields, larger-sized or continuous substrates, reduced input energ y and substrate costs by either eliminating one sheet of glass or attaching PV production on the end of a glass line, an d complete automation of these rather straightforward in-line processing steps. All of these steps are obviou s technological improvements that are already underway in various forms, but their potential for improvement is far from being exhausted.

The $/Wp costs in Table 2 are simple restatements of these costs from a $/m2 basis ($/m2 divided by Wp/m2 yields $/Wp). Total system output is about 20% less than peak power rating due to operational de-rating (operating temperature, resistance and power-conditioning losses) [39,43]. Installed system costs are assumed to be about twice as high as module costs (assuming that increased volume production of systems will result in balance-of-system (BOS) cost reductions that parallel module cost reductions). BOS, or balance of system, costs are the costs associated with everything but the modules and overhead; i.e., land, support structures, module wiring, power conditioning and DC-to-AC inverter, installation, and transportation. Total system cost is the module cost, the BOS cost, plus overheads. Overheads occur at all levels, from overheads on manufacturing the modules and BOS components, to system desig n and installation overheads.

The overhead and BOS costs are expected to decline because the cost of today's systems is the sum of rather lo w material costs, fairly high DC-AC inverter costs, and very substantial design, engineering, and installation costs fo r doing different, small sy stems one at a time. Improvements in inverters have already been observed in other renewables (e.g., wind) when inverter sizes are large. Inverter costs in-line with those needed for low-cost PV have been achieved in these cases. Similarly, the other aspects of systems costs (design, engineering, installation, overhead) are all likel y to fall substantially as volumes and repetition increase. Many PV industry representatives believe that the material s costs in real PV BOS will be compatible with very low ultimate costs like those quoted here.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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