Power Electronics Needs and
Performance Analysis for
Achieving Grid Parity Solar
Energy Costs
T. Esram, P. T. Krein, P. L. Chapman
B. T. Kuhn, R. S. Balog
Grainger Center for Electric Machinery and
Electromechanics
Dept. of Electrical & Computer Engineering
University of Illinois at Urbana-Champaign
SmartSpark Energy Systems
Outline
•
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•
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The nature of grid parity.
Solar production and value.
Performance analysis.
Power electronics requirements.
Parity expectations.
Timelines.
2
Potential
From Solar Energy Industries Association,
“U.S. Solar Industry – Year in Review, 2007”
3
Background
• The issue: small photovoltaic systems.
• For reference: 25 year operating life. www.midwestiso.org
• Energy performance
uses National
Renewable Energy
Lab (NREL) 30-year
solar database.
• Electricity “cost” based
on locational marginal
price (LMP), the standard utility tool for cost
tracking and bid evaluation.
4
Grid Parity
• Solar energy becomes economically
competitive. But what does this take?
• Solar energy is not base load.
Comparisons to
nuclear, coal, hydro,
or even wind power
have limited validity.
Navajo coal plant
techalive.mtu.edu
5
Possible Grid Parity Values
• Spot parity -- $1000/MW-h.
– Appears under extreme conditions
– Sometimes argued to justify fuel cells,
microturbines
www.microturbine.com
– But, integrated impact is a few percent at most
• Peak parity -- $200/MW-h
– Cost of diesel or natural gas peaking
– The basis for PV power tariffs in parts of Europe
– But, solar intensity peak is shifted from system peak
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Possible Grid Parity Values
• Retail parity -- $120/MW-h.
–
–
–
–
The usual measure
Ignores timing or potential premium
PV systems as “negative load”
But, main impact for residential
• Cost parity -- $50/MW-h
– Expands PV relevance to industrial
markets
– Can bid within the total resource mix
– But, extremely difficult to achieve
www.protesoft.com
7
Grid Parity Reference
• Average LMP, California ISO 2005: $55.90/MW-h.
• Average LMP, Ameren 2007: $44.28/MW-h.
• When actual solar incident radiation is integrated
over actual hourly LMPs, the integrated value is
about 25% higher. Price
200
180
160
140
120
100
Price
80
60
40
20
0
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
8
Solar Production
• Reference location: Bondville, IL 8/15/08
(approximately 89° west, 40° north)
• Notice peak shift,
about 3 hrs.
9
Solar Production
• NREL 30-year database:
– Actual measured incident solar energy is
4.8 kW-h/day/m² on average over 30 years.
– Taking the reference nominal power as
1 kW/m², a ratio of 4.8 is observed.
• Implication: for any PV technology, the
expected delivered energy is 4.8 W-h
per day for each of 1 W nominal power.
• Capacity factor is 20%.
10
Solar Production
• Ideal would be 24 W-h/day per nominal
watt.
• But, include de-rating
factor of 80% delivered
to the grid, expected in
small installations.
• Result: 16% solar
capacity factor to the grid..
11
Solar Production – Value
• 25 year production: 35.0 kW-h per nominal
watt.
• Energy value per nominal watt, 2008 dollars:
Parity type
Peak parity
0% real
increase
$7.00
2% annual real
increase
$8.97
Retail parity
$4.20
$5.38
Cost parity
$1.75
$2.24
12
Power Electronics Requirements
• A retail U.S. system today costs about $9
per peak watt before subsidies.
– Roughly 1/3 cells, 1/3 mounting, 1/3 inverters
and panel packaging.
13
Power Electronics Requirements
• If solar cells were free, cost parity and retail
parity could not be achieved. ($1/W??)
• Power electronics today: separate inverter.
• Costly dc connections.
• Inverter life issue.
• Inverter price today:
$0.722/W plus
installation.
14
Power Electronics Requirements
• Power electronics can be a major driver in
parity.
– Increase operating life  match panel life
– Facilitate installation
– Improve energy delivery
• Current price of $0.722 is
misleading: installation,
repair over limited life.
15
Parity Expectations
• Increase operating life
• Inverters today have mean time between
failure (MTBF) of less than 10 years
• Must match panel capability
– Eliminate electrolytic capacitors
– Avoid delicate power devices
• Computed MTBF above 100 years has
been achieved in recent modular solar
inverters.
16
Parity Expectations
• Installation flexibility.
• Conventional system requires precision
rail mounts for aiming and integrity.
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Parity Expectations
• Instead: modular inverter
for “plug and power” ™
installation.
• No dc protection or wires.
• Mount and connect.
• Each module delivers
maximum power, for high
total output.
Photovoltaic ac module
SmartSpark Energy Systems, Inc.
18
Parity Expectations
• There is at least as much system cost
improvement to be gained from power
electronics as from photovoltaic cells.
• Packaging, mounting, installation, …
• Are there synergies in working on
aggressive cost reduction in power
electronics and PV cells?
19
Adapted from Solar Energy Industries Association,
“Our Solar Energy Future,” 2004
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Timelines
21
Timelines
• Improvements in PV cells alone do not
lead to grid parity.
• Given present trends for PV cost
reduction, and assuming high investment
in power electronics cost reduction:
– Retail parity by 2015 seems to be attainable.
– Cost parity by 2030 is plausible.
22
Conclusion
• Highly reliable modular
solar inverters have the
potential to be an
explosive breakthrough.
• Cost parity is a target
that opens vast solar
markets.
• Cost parity may be
possible by 2030.
commons.wikimedia.org
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Solar Two thermal solar power plant
www.nrel.gov
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