1. EE535: Renewable Energy: Systems, Technology & Economics
Solar Plant Engineering

2. Solar Power Plants The output of a solar power plant (SPP) may be
Thermal Energy for direct use in heat processes
Electricity for use in an autonomous network or fed into a utility grid
Electricity may be generated :
Directly from solar radiation using photovoltaic modules in photovoltaic power plants
Via intermediate thermomechanical conversion in thermal solar power plants

3. SPP vs Conventional power plant
Input to conventional plants is combustible matter (coal, oil, gas, biomass) or nuclear
Needs to be extracted from geological deposits
Becomes an article of commerce
Needs to be transported to location of plant
Stock of primary raw material can be stored and utilized as required
Solar Power Plant
The primary energy input to the SPP (radiation) has no raw material form & is dilute
Terrestrially accessible only available during daylight hours
Availability depends on latitude, season, time, topography of location, meteorological conditions
Cannot be stored directly for later use
Not usually abundant in places where bulk energy is required
Free, indigenous, renewable
Free from toxins or radioactivity
Inherently very low risk
Nature, quality and availability of input energy to a SPP differs significantly from a conventional power plant

4. Site Requirements
Engineering (‘mining’) and supply functions must be carried out at the site of a SPP
Power rating of the plant is directly proportional to the effective collector surface area
Consequently SPP’s require more on-site land area than conventional power plants
No off-site land is needed for energy raw materials mining, processing, handling and transport, disposal of (sometimes hazardous) residues

5. State of the Art
Technology for producing electricity from solar energy is technically proven for PV and solar thermal
354 MW solar thermal plants using trough technology have been operational in the US since the 1980’s
Large PV plants (circa 50MW) are now in operation

6. Solar Plant Design Parameters
Design Point:
Provides basis for sizing of SPP, in combination with specification of output power capacity under rated conditions.
Conventional power plant facility usually sized based on nominal (nameplate) output conditions. Operation at these conditions may be maintained for extended time periods (base load supply)
Solar energy is fluctuating – need to specify conditions on a certain day, time, etc – design point
Rated power capacity of a SPP is usually stated in terms of Design Point.
Performance:
Actual performance will differ from design point and must be calculated be calculated temporally.
Key factors impacting performance include meteorological conditions (irradiation), plant parasitics and losses.
Performance can often be enhanced by use of an auxillary energy source.

7. Solar Plant Design Parameters
Solar Multiple:
ratio of collector subsystem output power at design point conditions to that needed by the Power Control Unit for generating nominal output.
Necessary to obtain better performance on ‘average irradiation days’
With SM > 1, excess energy can be stored (e.g. charge thermal storage)
Capacity Factor:
Plants never operate at rated capacity over a full year due to maintenance, service or costs, etc.
Main factors affecting CP are: location-specific irradiation conditions, the SPP type and configuration, operating reliability
Field-receiver ratio:
to increase number of hours at which receiver can operate at its design point rating, the converter may be oversized at the design point by 10 – 15%

8. Cell Design Criteria
Semiconductor materials need to be of high quality and consistent properties
Mass production with high levels of precision
Final product lifetime > 20years in hostile environment
-30C to + 200C
No contact corrosion
Redundancy included in design to mitigate against system failure A B
Solar modules are usually composed of several individual cells
Individual cells can be connected in series or parallel
Each cell generates its own emf and current density J
Arrangement A produces a higher output voltage – usually about 3V needed above battery voltage for charging
Arrangement B lower voltage but higher current

9. 3 Generations of Solar Cells
First generation solar cells are the larger, silicon-based, photovoltaic cells that have, and still do, dominate the solar panel market. These solar cells, using silicon wafers, account for 86% of the solar cell market. They are dominant due to their high efficiency. This despite their high manufacturing costs; a problem that second generation cells hope to remedy.
Second generation cells, also called thin-film solar cells, are significantly cheaper to produce than first generation cells but have lower efficiencies. The great advantage of second generation, thin-film solar cells, along with low cost, is their flexibility. Thin-film technology has spurred lightweight, aesthetically pleasing solar innovations such as solar shingles and solar panels that can be rolled out onto a roof or other surface. It has been predicted that second generation cells will dominate the residential solar market as new, higher-efficiency cells are researched and produced.
Third generation solar cells are the cutting edge of solar technology. Still in the research phase, third generation cells have moved well beyond silicon-based cells. Generally, third generation cells include solar cells that do not need the p-n junction necessary in traditional semiconductor, silicon-based cells. Third generation contains a wide range of potential solar innovations including polymer solar cells, nanocrystalline cells, and dye-sensitized solar cells. If and when these technologies are developed and produced, the third generation seems likely to be divided into separate categories.

10. Costs Scenario: Module Price = 3€/Wp Infrastructure Price = 2€/Wp
cent/kWh
Capital Cost €/kW
Coal
4 - 9
1200
Gas
3 - 5
550
Wind
3 - 10
Hydro
3 - 14
900
Biomass
7 - 20
1100
Solar PV
Wim C Turkenburg, Utrecht
Scenario:
Module Price = 3€/Wp
Infrastructure Price = 2€/Wp
System Price = 5€/Wp
UNEP Energy Technology Factsheet

11. Table showing average cost in cents/kWh over 20 years for solar power panels
Insolation
Cost
2400
2200
2000
1800
1600
1400
1200
1000
800
kWh/kWp•y
200 $/kWp
0.8
0.9 1
1.1
1.3
1.4
1.7 2
2.5
600 $/kWp
2.7 3
3.3
3.8
4.3 5 6
7.5
1000 $/kWp
4.2
4.5
5.6
6.3
7.1
8.3 10
12.5
1400 $/kWp
5.8
6.4 7
7.8
8.8
11.7 14
17.5
1800 $/kWp
8.2 9
11.3
12.9 15 18
22.5
2200 $/kWp
9.2 11
12.2
13.8
15.7
18.3 22
27.5
2600 $/kWp
10.8
11.8 13
14.4
16.3
18.6
21.7 26
32.5
3000 $/kWp
13.6
16.7
18.8
21.4 25 30
37.5
3400 $/kWp
14.2
15.5 17
18.9
21.3
24.3
28.3 34
42.5
3800 $/kWp
15.8
17.3 19
21.1
23.8
27.1
31.7 38
47.5
4200 $/kWp
19.1 21
23.3
26.3 35 42
52.5
4600 $/kWp
19.2
20.9 23
25.6
28.8
32.9
38.3 46
57.5
5000 $/kWp
20.8
22.7
27.8
31.3
35.7
41.7 50
62.5

12. Economics
Cost of solar PV has reduced dramatically over the past number of years – but is still relatively uncompetitive
Reduction in cost due to improvements in manufacturing technology and high volume manufacturing & better conversion efficiency
Insolation is a major variable determining the economic value of a solar project
For remote locations (far from the grid) the economics of solar can be much more attractive

13. Economics
In grid-connected systems, the excess energy generated during the day can be exported to the grid, or stored
Equally, in grid-connected systems, any shortfall can be imported from the grid or a storage device
Government subsidies an tariffs and have a major impact on solar PV economics (e.g. Germany)

14. Grid Connected vs Stand-Alone
PV Panels
DC/AC
Grid Connect PV System
user
Storage
PV Panels
Regulator
Stand-alone PV System
user

15. Options to Reduce PV Costs
Increase conversion efficiency
Reduce materials usage
Mass production of PV components
Reduction of balance of system costs (e.g. multifunctional use of PV functional area)
Long term Aims:
efficiency ~ 40%
system cost < 1€/Wp
No hazardous or scarce materials
Long term stability (>40years)

16. Question
The capital cost of installing an array of solar panels that will produce 1kWp is €8000.
The annual solar energy density in the location where the panels are to be installed is 2000 kWh/m2.
The lifetime of the solar panels is estimated to be 50 years.
Assuming a discount rate of 6%, calculate the cost of electricity per kWh.

17. Solution Loan repayment factor: A = (1 – 1/(1+r)n) / r
NPV = EAC x A = Capital Cost = €8000
A = (1 - 1/( )30) / 0.06 =
EAC = NPV/ A = 8000 / = €581
Cost of Electricity = Celec = Net Present Value of Costs (cent) / Net Present Value of Output (kWh)
Celec = 581 / 2000 = € 0.29 / kWh

18. Solar Conversion : Solar Stirling
An efficient solar conversion technique involves placing a Stirling Engine at the focal point of a solar concentrator / collecting dish
The dish focuses the light onto the hot side of the engine – resulting in up to 30% efficiency. Engine usually contains sealed hydrogen gas.
Stirling is very quiet, reliable, safe, has a high thermal efficiency, has a completely external heat supply, has no emissions
The gasses used inside a Stirling engine never leave the engine. There are no exhaust valves that vent high-pressure gasses, as in a gasoline or diesel engine, and there are no explosions taking place. Because of this, Stirling engines are very quiet.
The Stirling cycle uses an external heat source, which could be anything from gasoline to solar energy to the heat produced by decaying plants. No combustion takes place inside the cylinders of the engine.

19. Stirling Engine Cysle
(1) a→b process, working fluid absorbs heat and raise temperature with constant volume;
(2) b→c process, working fluid absorbs heat and expands at constant temperature;
(3) c→d process, working fluid cools and lower temperature with constant volume;
(4) d→a process, working fluid cools and contracts at constant temperature.