See: http://www.principalsolarinstitute.org/webinar/1119 Dan Lepinski, a forty year veteran of the solar industry will share his experience and insight on DC to AC power conversion. This webinar will cover an overview of the technology and hardware, as well as applications in residential, commercial and utility-scale solar power facilities. Cost, reliability and efficiency are all factors in selecting the best inverter technology in any application. We have seen tremendous cost reductions in the installation of solar power over the past several years. Most of this is attributable to the steeply declining price of PV modules. What will it take to see similar progress in other Balance of System costs, such as inverters? Please join us to share Dan’s vast expertise and experience, and gain valuable insight to the next frontier of solar power generation.

1. Principal Solar Institute
Dan Lepinski
North Texas Renewable Energy Engineering
Dan has been professionally involved in solar energy for more than 40 years. He founded and for
15 years ran a unique business involving several cutting-edge technologies: telecommunications,
computers, and solar energy. He also spent more than a decade as a Senior Engineer designing
inverters for off-grid and grid-tied solar applications.
Dan now consults in the solar energy and energy conservation industries.
Myths and Legends of Microinverters
&
Other DC Power Converters for Solar Energy

2. Questions and Discussion
Dan Lepinski
North Texas Renewable Energy
Engineering
Dan@ntree.org
Please enter your questions into the Chat window.

3. Questions and Discussion
Introduction:
 UL 1741 / IEEE 1547 Standards Technical Panel
 Solar America Board for Codes and Standards ("Solar ABCs")
 Electric Power Research Institute Smart-Grid Development Committee
 Solar Industry National Electric Code Work Group (NFPA-70)
(Sections 690 and 705)
 Honoree - Texas Solar Energy Industries Association
Special Achievement Award for Excellence and Accomplishments
in the field of Solar Energy.

4. Questions and Discussion
Topics Today:
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Microinverters
AC Modules
DC Optimizers
String Inverters
Central Inverters
We'll discuss a few ...
Facts. Myths. Legends.
Costs. Choices. Options.
… Present - and Future.

5. Questions and Discussion
1. Basics:
Microinverter: < 400W (typ). Stand-alone inverter, usually attached to the PV
frame or mounting rack. AC output.
AC Module: PV-embedded microinverter. Pre-attached to the PV by the
manufacturer. AC output.
Optimizer: Connects to PV, similar to a microinverter. Adjusts individual PV
output current to match the array. DC output.
String Inverter: 2 - 30 kW (typ). AC output.
Central Inverter: Large! "Utility-scale". 100kW - 1.5 MW+.
AC output (typically 3 phase).

6. Questions and Discussion
Microinverters AC Modules
General Product Applications
 Incrementally-sized systems.
 Area unsuitable for string system.
 Fill in empty space.
 Customer wants them.
 Same as micro-inverters .. but ..
 ... generally less labor involved.
 No concern for perfect PV match.

7. Questions and Discussion
Because ...
shade happens.
(See the birds?)
There are also other
causes…
Why Use Microinverters, AC Modules, and Optimizers?

8. Questions and Discussion
Multiple string inverters can connect to a circuit.
String Inverters .. One … or many:

9. Questions and Discussion
Large systems. Multiple PV arrays connected. Three-phase.
Central Inverters:

10. Questions and Discussion
Some what you hear about inverters, AC Modules, and optimizers is
marketing hype.
2. Myths .. Legends .. and Facts.
“Truth” or “Fiction” Also Depends on Whom You Ask.

11. Questions and Discussion
#1: Will electrolytic capacitors fail prematurely?
Other manufacturers say “yes”, and tell us “film”
capacitors are superior.
Some manufacturers say “no”.
First, what is meant by “failed”?
There’s a difference between “failed” and “worn out”.
Myths .. Legends .. and Facts.

12. Questions and Discussion
Fact: A quality electrolytic capacitor utilized within its ratings and
specifications will work in rooftop inverter and converter
applications up to 70 years in Phoenix, Arizona heat. (A
“worst-case” environment!)
Electrolytic capacitors are also much smaller and MUCH lower
cost than “film” capacitors.
Myths .. Legends .. and Facts.

13. Questions and Discussion
Electrolytic
22 uF, 400V
Height 22 mm
Diameter 16 mm
Volume 4,423 cu mm
Cost* $0.36 ea (5K)
Film
20 uF, 400V
Height 37 mm
Width 22 mm
Length 32 mm
Volume 26,048 cu mm
Cost* $10.69 ea (5K)
* Source: Digi-Key, Apr 02, 2014. www.digikey.com
Myths .. Legends .. and Facts.

14. Questions and Discussion
Fact: In systems without shade, and all PV facing the same direction and
angle, the performance difference among products is limited to the worst-
case tolerance in the photovoltaic modules.
#2: Microinverters and AC Modules Are More Efficient Than String
Inverters.
Myths .. Legends .. and Facts.

15. Questions and Discussion
#2: Microinverters and AC Modules Are More Efficient Than
String Inverters.
Systems that experience unavoidable shade may see up to 30% increased
output, depending on the severity of the shade. (Try to avoid shade in the
first place!)
Myths .. Legends .. and Facts.

16. Questions and Discussion
#4: Microinverter systems are more efficient than string systems.
#3: Optimizers with string inverters are more efficient than
microinverters.
#5: Microinverters have a 25 year warranty. This means they are
more reliable than string inverters.
Myths .. Legends .. and Facts.
#6: Microinverters and/or AC Modules can completely replace string
inverters and central inverters.

17. Questions and Discussion
Problem is, we have a paradox:
Downward price pressure
on inverters and other BOS
products, with simultaneous
upward pressure on life expectancy,
product performance, and warranty.
2014 National Electric Code changes will also add cost.
3. Decreasing the Cost…

18. Questions and Discussion
In the average residential system,
inverters represent only 5.7% of the
total cost.
Still .. any cost reduction helps.
So what can be done?
Decreasing the Cost…
Graphics copyright by and reprinted here by
permission of Rocky Mountain Institute,
www.rmi.org Data from 2012.

19. Questions and Discussion
#1: Manufacture high-voltage (250V+) PV for microinverters and
AC Modules. Very do-able in film PV. (Difficult to achieve in
a cost-effective manner in crystalline PV.)
This would eliminate the DC -> HV circuit, which represents 50% of the total
parts, and includes some of the more expensive components in
microinverter / AC Module products.
Net benefit: more than 50% decrease in cost, with increased efficiencies up
to 98.5% or better. This may also make possible use of plastics for
enclosures, such as are used by optimizers.
Decreasing the Cost…

20. Questions and Discussion
#2: Make the BOS hardware as “NEC Code-friendly” and
“installer-friendly” as possible.
#3: Consider designs that eliminate the PV junction box, bypass
diodes, and cables, and use the inverter in its place. At least
one optimizer company is already doing this.
Inverter manufacturers can do likewise.
These components represent approximately 7% of PV cost
today. In the world of manufacturing, this is significant!
Decreasing the Cost…

21. Questions and Discussion
What can we expect from future inverter and optimizer products? My
“crystal ball” shows…
 Neighborhood “Solar Gardens”.
 Active power-factor correction.
 Energy storage for surge peak abatement and more.
 Intelligent load control by energy-producing devices.
5. Looking Ahead…

22. Questions and Discussion
 “Smarter” use of the power we generate and use.
 Improved energy storage efficiencies.
 Hybrid on-grid / off-grid systems.
 Intelligent load control by energy-producing devices.
 Feed-in tariff rates matching value to time-of-day energy
production by PV systems.
Looking Ahead…

23. Questions and Discussion
Questions?
Dan Lepinski
North Texas Renewable Energy Engineering
Dan@ntree.org
Thank You.