Power Electronics Needs and Performance Analysis for Achieving Grid Parity Solar Energy Costs T. Esram, P. T. Krein, P. L. Chapman Grainger Center for Electric Machinery and Electromechanics Dept. of Electrical & Computer Engineering University of Illinois at Urbana-Champaign B. T. Kuhn, R. S. Balog SmartSpark Energy Systems

2 Outline The nature of grid parity. Solar production and value. Performance analysis. Power electronics requirements. Parity expectations. Timelines.

3 Potential From Solar Energy Industries Association, “U.S. Solar Industry – Year in Review, 2007”

4 Background The issue: small photovoltaic systems. For reference: 25 year operating life. 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.

5 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

6 Possible Grid Parity Values Spot parity -- $1000/MW-h. –Appears under extreme conditions –Sometimes argued to justify fuel cells, microturbines –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

7 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

8 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.

9 Solar Production Reference location: Bondville, IL 8/15/08 (approximately 89° west, 40° north) Notice peak shift, about 3 hrs.

10 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%.

11 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..

12 Solar Production – Value 25 year production: 35.0 kW-h per nominal watt. Energy value per nominal watt, 2008 dollars: Parity type0% real increase 2% annual real increase Peak parity$7.00$8.97 Retail parity$4.20$5.38 Cost parity$1.75$2.24

13 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.

14 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.

15 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.

16 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.

17 Parity Expectations Installation flexibility. Conventional system requires precision rail mounts for aiming and integrity.

18 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.

19 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?

20 Adapted from Solar Energy Industries Association, “Our Solar Energy Future,” 2004

21 Timelines

22 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.

23 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 commons.wikimedia.org

24 Solar Two thermal solar power plant