Optimizing PV Systems July 2014.pdf

OPTIMIZING PV SYSTEMS 

PART 1 - INVERTERS 

JULY 2014 

SELECTED CONTENT 

THREE STAGES PAGE 3 

OF OPTIMIZATION 

ELECTING THE PAGE 5 

RIGHT INVERTER 

THE EFFECTS PAGE 7 

OF SHADING 

MYTHS AND PAGE 12 

MISCONCEPTIONS

OPTIMIZING PV SYSTEMS 

BY GREG SMITH, SENIOR TECHNICAL TRAINER, SMA AMERICA 

As a solar professional, it’s 

important to carefully 

consider the photovoltaic (PV) 

design that will generate the 

highest return on investment 

(ROI). While the specifics may 

differ between residential 

and commercial systems, the 

themes are almost always the 

same: fast install and fast 

payback. However, the really 

savvy PV companies are 

starting to consider more 

factors, such as PV system 

optimization, which will help 

keep them profitable for a 

long time. 

Optimized and properly 

maintained PV systems have a 

much higher rate of return and 

produce more energy over the 

lifetime of the plant. However, 

there is much more to 

optimizing a PV system than 

just simple string sizing. The 

1 Optimzing PV Systems eFeature | July 2014 

right inverter choice can make 

the difference between a 

worry-free install and an 

operations and maintenance 

(O&M) nightmare. The largest 

integrators in North America 

are realizing that there is no 

one-size-fits-all inverter 

solution and that they must 

expand their product 

portfolios if they are going to 

extract every last watt-perhour 

from their systems to 

gain better ROI. 

WHAT DOES PV 

OPTIMIZATION MEAN? 

PV plant optimization means 

different things to different 

people. To some, it is the 

number of modules they can 

fit on a string, or AC combiner 

bus bar calculations for large 

commercial rooftop projects. 

Others focus on the inverter 

choice: central or string 

inverter, string or micro 

inverter. Or, perhaps they are 

considering using DC 

optimizers. For many, “PV 

plant optimization” refers to 

the ROI of the installed 

system. 

According to Andy Black, solar 

financial analyst and CEO of 

California-based OnGrid 

Solar, PV system owners can 

now get a very close estimate 

when they want to know how 

long it will take to recoup their 

investment. Black said, “…the 

payback question can now be 

givenaseriousanswer,backed 

by solid math and 

accounting.”1 Basically, the 

math involves comparing the 

savings on an electric bill yearby-year 

to the amount of the 

loan taken out for the PV plant. 

Although it sounds easy 

enough, the system payback 

www.worldofphotovoltaics.com

OPTIMIZING PV SYSTEMS - PART 1: INVERTERS 

speed depends heavily on a few moving 

targets: local weather conditions, utility rates 

and solar rebates and incentives, just to name a 

few. 

THREE STAGES OF OPTIMIZATION 

There are basically three different stages of PV 

system optimization, beginning at system 

design, continuing through installation and 

ending with scheduled operation and 

maintenance for the life of the plant. 

1. DESIGN 

The design stage includes selecting the right 

inverter, designing the array, performing a site 

survey and talking to the customer. It is very 

important to understand the customer’s needs 

and consider what is optimal for them. Do they 

value the public image benefit of offsetting all 

of their power use? Or, perhaps your customer 

would like a high ROI, which may mean a 

smaller "peak $/kWh" shaving system. By 

identifying their key drivers and then 

considering site-specific limitations, an 

integrator can make an informed decision 

about technology choice. 

Careful consideration must also be given to 

array and inverter access for future servicing. 

Array layout is influenced by local jurisdiction 

requirements, building and electrical code 

standards and often old-fashioned tribal 

knowledge. Residential and commercial 

installations require preventative 

maintenance for worry-free operation, with 

vegetation management, rodent control and 

visual inspections just a few things to take into 

account. Inverter installation manuals usually 

include a preventative maintenance section 

that includes periodicity. 

String sizing is a necessary practice when 

designing arrays for string and central 

inverters. Properly designed systems will 

ensure the following thresholds are achieved: 

adequate PV start voltages, inverter operation 

within the maximum power point window and 

maximum system voltage below either 600 V 

3 Optimzing PV Systems eFeature | July 2014 www.worldofphotovoltaics.com

www.worldofphotovoltaics.com 

or 1,000 V DC. Designers use their string sizing 

tools to keep these voltage milestones in 

check; however, recent studies have shown 

that operating the inverter close to the 

maximum power point (MPP) voltage could 

actually be more efficient than operating at 

MPP voltage. 

2. INSTALLATION 

The installation phase, which often has a 

checks and balances effect on the previous 

stage, includes wiring methods, installation 

best practices (proper torque, wiring 

selection, etc.), code adherence and baseline I- 

V traces (mostly for commercial applications). 

While these are all important facets of the 

process, proper system commissioning is 

critical. Commissioning a small residential 

system usually is no problem, even for the 

novice installer, but the thought of 

commissioning a 100 kW or multi-megawatt 

installation using hundreds of string inverters 

could intimidate even a seasoned installer. 

While there are a few inverter manufacturers 

who offer commissioning services for these 

larger systems, the underlying message is 

clear: slower is faster. Every inverter 

installation manual has a section on 

commissioning the unit. Also available is the 

North American Board of Certified Energy 

Practitioners (NABCEP) Photovoltaic Installer 

Resource Guide2, which helps PV industry 

professionalsthroughtheprocessofPVsystem 

design, installation and commissioning, for 

free download on the NABCEP website. 

Following a clear, repeatable, step-by-step 

process ensures a safe environment when the 

inverters are brought online. 

3. OPERATION AND MAINTAINANCE 

This final stage consists of a well thought-out 

and properly executed O&M plan that will 

ensure a worry-free and profitable PV system 

for decades to come. Larger arrays may require 

routine inspections using I-V curve and 

Optimzing PV Systems eFeature | July 2014 

4


thermal temperature tools. These periodic 

audits can provide useful trend analysis 

reports to identify and prevent future 

problems. Equipment servicing per 

manufacturer’s recommendations is a must 

and vegetation management for larger 

arrays could become part of a scheduled 

maintenance routine. 

NABCEP Certified PV Installer Brian Mehalic, 

project engineer for O2 Energies in North 

Carolina, has over a decade of PV experience 

and has commissioned hundreds of 

residential and large commercial plants. 

With more than 23 MW of PV qualityassurance 

inspections, Mehalic highly 

recommends a sensible O&M strategy for 

larger PV systems. When teaching the Solar 

Energy International (SEI) operations and 

maintenance course3, he emphasized the 

need to, “Schedule early follow up...one 

month, 90 days, whatever is necessary, and 

keep an eye on the production early on. 

Failures/issues tend to follow a bathtub 

curve.” 

All three stages are important for the longterm 

health of the PV system, but most 

questions arise during the design stage - and 

it is easy to understand why. It is the stage 

most rooted in tradition, tribal knowledge or 

perhaps even ignorance of alternatives. Most 

solar industry professionals do not want to 

debate the best inverter topology, but it is 

definitely worth spending some time 

discussing. 

INVERTER SELECTION 

When considering inverter selection, one 

must ask, “What problem am I trying to 

solve?” Generally speaking, for residential 

applications there are two main categories of 

inverters: string inverters and module-level 

power electronics (MLPE). Commercial 

applications favor string inverters and/or 

central inverters, with the latter typically 

chosen for large utility-scale applications. 

Each has its strengths and weaknesses and 

there is no one-size-fits-all approach if you 

value a positive ROI and consider the O&M 

involved with the system. 

While there are commercial installations 

using MLPE, typically they do not yield a 

reasonable ROI since the higher capital 

expenses are often not offset by the O&M 

system costs. In the end, more profit can be 

madeoverthelifetimeofthePVsystemusing 

a string inverter for large commercial 

applications rather than an MLPE. 

STRING INVERTERS 

String inverters are well known in the 

industry and have been the de facto standard 

for PV installations for decades. There are 

three topologies associated with string 

inverters: low frequency transformer, high 

frequency transformer and transformerless, 

with the latter being the lightest and most 

efficient of the three. Leading string 

inverters are easy to maintain, require little 

O&M and have become lighter, more reliable 

and more efficient as the years have passed. 

String inverters are named for the process of 

connecting a string of modules in a series to 

increase the system voltage. Depending on 

the size of the inverter, multiple strings are 

connected in parallel to increase the total 

currentofthePVarray,thusincreasingtheDC 

power of the array. 

MODULE-LEVEL-POWER ELECTRONICS 

This broad category includes devices that are 

mounted onto or behind the solar modules 

and consist of two different types of 

converters: micro inverters and DC 

optimizers. Both types of devices are 

connected to an individual module, but they 

differ in their conversion process. 

Micro inverters convert the DC directly into 

ACatthemodulelevel,usuallyeither240Vor 

208 VAC. This power is then sent to the main 

breaker in the installation via each 


neighboring micro inverter. The inverters are connected together either by using a 

trunkcabling system or by daisy chain. 

Optimizers do not convert the PV energy directly into AC, but rather perform a DC-to-DC 

optimization so that the attached string inverter has a constant voltage to work with for the 

DC-to-AC conversion. 

AC modules are a type of micro inverter that is directly connected to the module junction box 

and eliminates exposed DC conductors, but theydo not have the market penetration of the 

micro inverters or optimizers. 

Each type of MLPE provides a more granular level of PV system output than a string inverter 

since it is able to capture module-level data and present it to the end user. Some 

manufacturers offer this module-level monitoring for a nominal charge while others offer it 

for free. 

With so many inverter options available, it can be daunting to sift through the 

technicalspecifications of each topology to determine which one is best for a particular 

application. There are only a handful of inverter manufacturers that sell string, central and 

microinvertersandthereforeareintheuniquepositiontoactasasolarconsultantbyguiding 

the discussion to which inverter is best for the given application. 

Generallyspeaking,thethreetypesofinverterseachhavetheirownbenefitsandfitverywell 

into their respective applications when considering the following factors: 

As the table indicates, there are a few string inverters on the market that can actually handle 

these complex installation factors. Let’s take a look at some advances in string inverter 

technology that mitigate some of the concerns installers have about using them in 

www.worldofphotovoltaics.com Optimzing PV Systems eFeature | July 2014 6


challenging PV installations. 

THE EFFECTS OF SHADE 

Historically, there were a few challenges with 

string inverters, most notably the issue of 

shade. Partial shade affects PV array output 

and can be caused by an existing dormer, 

chimney or other roof protrusion. It also can go 

unnoticed on commissioning day and show up 

years later as a nearby sapling matures into a 

mighty oak. 

The market has demanded tools to help deal 

with the issue of shade and several 

manufacturers—such as Solmetric, Suneye 

and Solar Pathfinder, just to name a few - have 

responded. These companies make analysis 

tools called I-V curve tracers that are quickly 

becoming a valuable tool for installers. 

I-V curve tracers are able to graphically show 

the effects of shade on a PV array by plotting 

the corresponding current versus voltage (I-V) 

values onto a chart, or curve. These useful 

devices are more affordable than they once 

were and are in the toolbox of every serious PV 

installer. The curves can be saved 

electronically or even printed out. Regardless 

ofwheretheshadeisonanarray,theeffectsare 

always seen on the upper end of the I-V curve, 

as seen in this diagram from a Solmetric 

IV-600A: 

produced. 

MPP TRACKERS FOR 

ISSU 

The issue of static partial shading can be inescapable 

without restricting the size of the array. The challenge of 

shading presents itself particularly on commercial 

buildings with obstructions such as air conditioning units 

and irregularly shaped roofs, causing output losses of 

up to as much as 25%. Output is reduced if shading 

occurs on any part of an array, even if all other modules 

remain in direct sunlight. How much the output is 

reduced depends on how the array is configured. This 

is because modules are connected in series and 

shading on one or more of them will cause variances in 

the MPP voltage from the modules. Normally the 

inverter cannot find the optimal MPP point as it is stuck 

on the global MPP, but instead the new local MPP 

would generate more power. 

When one of Germany’s leading manufacturers of 

natural medicines, SALUS GmbH, took the decision in 

May to add a further 300kW to their existing system, 

installers at Elektrotechnik Pichler were presented with 

the challenge of shading. The 96m 2 east/west roofmounted 

system, which is located on the hydroelectric 

plant, has a large number of chimneys on the roof, so 

multistring inverters were required. 

The installations use in total 24 string inverters including 

22 Fronius IG Plus inverters plus 2 new Fronius Symos 

to tackle the shading issues. The Fronius Symo 

inverters total 14.8 kW of the installation and were 

selected for their flexibility due to the high system 

voltage (1,000 V), wide input voltage range (150 V to 

800 V) and twin MPP trackers. 

Shading causes peaks on the I-V curve (shown 

in the diagram below) and each one is a 

potential maximum power point that the 

string inverter could track off on. The local 

peaks represent lower power output while the 

global peak represents the point on the I-V 

curve where maximum available power is 

Separating an array into two segments, each on their 

own MPPT, as has been done at SALUS GmbH, 

increases system harvesting. This is because shaded 

modules no longer have to be connected in the same 

string as those that are fully exposed - which keeps 

MPP performance in the non-shaded array high - 

Fronius UK Ltd | Maidstone Road | Kingston, 

Tel: +44 (0) 1908 512 300 | Fax: +44 (0) 1 


PARTIAL SHADING 

ES 

therefore maximising output. This eliminates the need 

for an additional inverter (with associated labour time 

and costs) to do effectively the same job. What further 

enhances the benefits of the two MPP trackers in the 

Fronius Symo is the very broad voltage range of their 

input, allowing connection of highly asymmetric 

configurations. This enables the system designer to 

solve most shading issues. In some cases even a 1:9 

ratio between MPPT1 and MPPT2 is possible. 

To generate maximum yield, MPPT performance is of 

critical importance. The Fronius Symo offers a new 

MPP tracking algorithm which dynamically adapts its 

behaviour when searching for the optimal operating 

point. This Dynamic Peak Manager allows the inverter 

to deliver the maximum output in all circumstances. 

What’s particularly impressive about this is that it 

automatically checks the entire characteristic at regular 

intervals to ensure it can always find the maximum 

operating point, even when partially shaded therefore 

no longer are there hidden Local MPP points. The two 

MPP trackers in the Fronius Symo work completely 

independently of each other, which guarantees 

maximum power and yields, even under difficult 

conditions such as (partial) shade, foggy weather, 

module failure and so on. 

The east/west system at SALUS that took just 2 days to 

install is set to produce 12,070kWh per year, of which 

800 – 900kW will be used for manufacturing natural 

medicines. Bernard Pichler, installer of the 100% selfconsumption 

system, found a solution for the shaded 

areas of the roof that would not only maximize yield, but 

save time and money and therefore increase 

profitability of the installation. 

Milton Keynes | MK10 0BD, United Kingdom 

908 512 329 | http://www.fronius.co.uk 


Shading analysis performed during the initial 

site survey can help predict the impact of 

shade on annual inverter yield and help 

identify any future surprises that could affect 

PV plant production. Partial shading has a 

direct impact on plant optimization, and, in the 

end, it costs the homeowner some ROI, but not 

as much as was once believed. 

While the best way to deal with partial shade is 

to avoid it altogether, partial shading can now 

be a non-issue for the industry, thanks to 

advancements in inverter technology. 

Multiple maximum power point trackers 

(MPPT) and shade-accommodating MPPT 

algorithms all but eliminate the effects of 

partial shade and multiple roof orientation 

concerns. 

MAXIMUM POWER POINT TRACKING 

CHANNELS 

Traditionally, string inverters had a single 

MPPT input, or channel, with which the 

inverter microprocessor would vary the 

inverter’s internal resistance to act as a load on 

the array. As the voltage went down, the 

current went up, and vice versa, all while the 

inverter was ensuring it was tracking the 

maximum voltageversa, all while the inverter 

was ensuring it was tracking the maximum 

voltage and maximum current on the I-V curve, 

which would produce the maximum available 

power from the PV array. 

Several sting inverter manufacturers have now 

designed products that have dual MPPT 

channels for residential and some commercial 

applications. The big advantage of this feature 

is that individual strings at different 

orientations can now be connected to its own 

Optimzing PV Systems eFeature | July 2014 

8


varying voltages and currents. Additionally, a partially shaded string will have no effect on 

the unshaded string since they are electrically isolated and tracked by their own MPPT. 

SHADE-ACCOMMODATING MPPT 

One of the biggest leaps in inverter technology is shade-accommodating MPPT algorithms. 

These algorithms perform an I-V sweep of the PV array, much like an I-V curve tracer, and then 

shift the MPP from a lower array power local peak up to the maximum power global peak. 

For those who prefer MLPE, module-level strategies can also be deployed to address partial 

shading, but they come at a higher cost. 

MODULE-LEVEL POWER ELECTRONICS IN RESIDENTIAL AND COMMERCIAL APPLICATIONS 

There are compelling reasons to use MLPE, even in applications where other topologies 

would make better sense with respect to ROI. Micro inverters and optimizers share these 

favorable attributes for some business models: 

For installers in states that do not offer attractive rebate structures, micro inverters allow 

them to add on to a residential PV system every year or so, as the homeowner is able to afford 

the expansion. 

Other installers, such as Nathan Charles of Pennsylvania-based Paradise Energy Solutions, 

cite high employee turnover rates and costly labor training for string inverters as reasons 

why they choose micro inverters. According to Charles, he can have a fully trained crew ready 

to deploy and install micro inverter systems within a matter of weeks. “As a whole, micro 

inverters require less training and personal protection equipment,” he said. 

For Charles, “The failure rate of micro inverters is an acceptable risk.” He informs his 

customers, who might be monitoring their module-level data on a daily basis, that failed 

units will be replaced annually and not when each one fails. “A failed inverter costs the 

homeowner about $30 per year,” he added, “which isn’t enough to justify rolling a truck.” 

Module-level monitoring does come in handy for quickly finding defective inverters and for 

locating ground faults caused by rodents. Ground fault localization is a time-consuming 

practice that is virtually eliminated when using MLPE. Knowing how many inverters will be 

replaced and which tools will be required for servicing are advantages of using MLPE. 


This strategy mitigates the installer’s O&M 

costs but it might not be the best solution for 

the customer, who paid for the modules and 

inverters to work consistently. Those failures 

could elevate their monthly utility bills into a 

higher tier. 

While the argument for MLPE sounds 

reasonable on the surface, with benefits 

ranging from reducing the effects of partial 

shading and soiling to the cost-cutting, preemptive 

strikes achieved by using modulelevel 

monitoring for O&M and servicing, 

MLPE are not the best choice for all systems 

and applications and should be applied when 

conditions favor their usage. 

MYTHS AND MISCONCEPTIONS 

There are scientific, peer-reviewed 

resources that partly support the claims of 

MLPE companies, but when those claims are 

given proper scrutiny, many questions and 

concerns arise. Here are the top three myths 

concerning MLPE: 

1. String inverters operate at the lowest 

performing module. 

A common driver of this myth is the notion 

that if a module is shaded by 50 percent, then 

the rest of the string output power is reduced 

by 50 percent. Here is a common image used 

to illustrate this “Christmas tree effect”: 



In reality, shading 50 percent of one module will 

reduce the output of that string by about 13 

percent. This loss will usually occur early in the 

morning or late in the afternoon when partial 

shade is most prevalent. Shading at solar noon 

will result in a negative ROI even when MLPE are 

used. 

Many whitepapers regarding this topic in the 

European Photovoltaic Solar Energy Conference 

(EU PVSEC) library have been reviewed by 

industry experts and none support the 

Christmastreeeffectwhenmoduleswithbypass 

diodes are tested. In fact, shading studies fall 

short of discussing and testing different shading 

effects on different module technologies. A 

particular paper in this library entitled 

“Performance Measurement and Monitoring of 

Shadow Effects on PV Systems4” concluded that 

shading had less of an effect on thin film than 

crystalline solar modules. 

2. MLPE have lower O&M and installation costs 

than string inverters. 

Since every installation is different, this is a 

highly subjective claim and one that requires the 

installer to perform a cost comparison. Some 

manufacturers suggest that the estimated 

20-year maintenance and replacement cost for a 

7 kW string inverter system is $5,1925 while the 

same size micro inverter system, using 30 

inverters, only costs $739. However, this 

informationdoesnotindicateifthe$739wasfor 

oneinverterreplacementorforall30,orhowthe 

$5,192 string inverter replacement cost was 

derived (that figure is highly dependent upon 

inverter manufacturer). 


Whileitmayonlycost$739toreplaceonemicro 

inverter, there are still 29 more that will 

eventually fail. This inevitability brings the 

replacement costs to a much more realistic 

number of 30 x $739 = $22,170, assuming the 

installerperformedaservicecalltoreplaceeach 

failed inverter. 

Lower installation costs are another dubious 

claim that requires examination for each 

installation. Balance-of-system (BOS) costs and 

installation times might favor either topology 

since there are AC conductors that must be run 

down off the roof, there must still be an AC 

service disconnect (AHJ dependent) and 

optimizer DC home runs must be connected to 

an inverter, therefore doubling the amount of 

work required for the same size install as a string 

inverter. 

3. Micro inverters and optimizers generate 

significantly more power in shaded areas than a 

string inverter. 

This claim requires no further research than a PV 

Evolution Labs (PVEL) study published in 2012. 

Using the NREL test protocol for conducting 

experiments on shaded arrays6, the PVEL 

concludedthatmicroinvertersdoproducemore 

energy than string inverters in light, moderate 

and heavy shaded conditions by 3.7 percent, 7.8 

percent and 12.3 percent, respectively. Since 

the overwhelming majority of partially shaded 

arrays in residential installations fall into the 

light and moderate categories, the heavy 

shaded array value can be discarded. Most 

respectable designers would not consider 

installing a heavy shaded array anyway and it 

would be very difficult to secure financing for 

this type of system. 

Optimizers make the same kind of claim but use 

a different number before getting to the core of 

their extra yield. For example, a leading 

optimizer company, citing a similar NREL 

study7, claims “up to 25 percent more energy 

and 99.5 percent (max) efficiency” for their DC 

optimizer system. The 25 percent figure is, of 

course, the heavy shaded result, but they do 

www.worldofphotovoltaics.com Optimzing PV Systems eFeature | July 2014 

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claim “1.9 percent more energy than the 

string inverter” in the more likely scenario 

of light partial shade. 

Let’s put this 1.9 percent recovery value into 

perspective, starting with this PV industry 

universal truth: All inverters fail - eventually. 

Installers have to weigh whether the 

benefits of MLPE make up for the fact that 

they will have to go up on the roof at some 

point to replace all those devices. Optimizer 

systems are more involved because the 

installer will also have to replace the 

inverter. 

Taking the optimizer study at face value and 

assuming the average utility cost of $.12 per 

kWh, these variables can be used to estimate 

howmuchmoneytheoptimizersystemsaves 

on an annual basis for a 6,000 W system. The 

sobering conclusion illustrated below was 

derived from just a quick look at the 

production claims. 

In 2010, the Fraunhofer-Institute for Solar 

Energy Systems ISE submitted a whitepaper 

to the 25th annual EU PVSEC entitled, “Light 

and Shadow – When is Tracking MPP at the 

Module Level Worthwhile?”8 Gains in 

energy production due to soiling, shading, 

module mismatch and other factors were 

tested and the results are summed up in the 

following graph. The influencing factors are 

labeled on the outside of the wheel. The red 

hashed area represents the return for string 

MPPT, while the blue hashed areas are for 

module-level MPPT. 


The conclusion had this to say: 

“Generally, the use of MPP tracking at the 

modulelevel,inordertorecoverlossesdueto 

partial shading, is only profitable in very few 

cases for a medium level of partial shading.” 

The values for yield recovery in partially 

shaded conditions were almost identical to 

the NREL study. There are sections on the 

wheel where the blue shaded areas are 

outside the red areas and these influencing 

factorsareinfavorofMLPE,astheyshouldbe. 

The authors are revealing this truth but are 

also pointing out that those factors may not 

be worth while for MLPE with respect to the 

modest gains. This is not to say MLPE do not 

have their place since the authors (indirectly) 

validated my initial premise: there is no onesize-fits-all 

in this industry; every situation 

is different. 


FINAL THOUGHTS 

Optimizing PV systems has changed over the 

years and, as the technology evolves, perhaps 

the industry will adopt other ways of enhancing 

these systems. Whether it is string, micro, 

optimizer or central inverter, people will use 

what makes sense to their business models 

and/or what they feel comfortable with. 

Technology has changed this industry 

tremendously in the last 10 years and the good 

news is that the best has yet to come. The better 

news is that there is plenty of room in this 

industry for everyone. 

Optimzing PV Systems eFeature | July 2014 16


REFERENCE LIST 

1. Black, Andy, “What’s the Payback? How to calculate the 

return on your solar electric system investment before you 

buy,” OnGrid Solar.net, 2006. 

2. Brooks, Bill, and Dunlop, James, “NABCEP Photovoltaic 

Resource Guide,” August 2012. 

3. Tools and Techniques for Operations and Maintenance, 

Solar Energy International. 

4. Del Buono, Armani, Potz, Cattani, and Sparber, “Perfor 

mance Measurements and Monitoring of Shadow Effects 

on PV Systems,” EU PVSEC Proceedings, September 2008. 

5. Mohd, A, “The Evolution of PV Solar Power 

Architectures: A Quantitative Analysis of Micro Inverters’ 

Performance vs. Conventional Inverters,” EU PVSEC 

Proceedings, September 2011. 

6. National Renewable Energy Laboratory, “Photovoltaic 

Shading Testbed for Module-Level Power Electronics.” 

7. SolarEdge, “Performance of PV Topologies under 

Shaded Conditions.” 

8. Rogalla, Burger, Goeldi, and Schmidt, “Light and 

Shadow – When is MPP-Tracking at the Module Level 

Worthwhile?” EU PVSEC Proceedings, September 2010.


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