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Contract No. DE-AC36-08GO28308

Evaluation of Maxim ModuleIntegrated Electronics at the 

DOE Regional Test Centers

Preprint

Chris Deline and Bill Sekulic

National Renewable Energy Laboratory

Josh Stein

Sandia National Laboratories

Stephen Barkaszi

Florida Solar Energy Center

Jeff Yang and Seth Kahn

Maxim Integrated

Presented at the 40th IEEE Photovoltaic Specialists Conference

(PVSC-40)

Denver, Colorado

June 8-13, 2014

Conference Paper

NREL/CP-5J00-62024

July 2014
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Evaluation of Maxim Module-Integrated Electronics at the 

DOE Regional Test Centers

Chris Deline,

1 Bill Sekulic,1 Josh Stein,2 Stephen Barkaszi,3 Jeff Yang,4 Seth Kahn4

1

National Renewable Energy Laboratory, Golden, CO, 80401, USA

2 Sandia National Laboratories, Albuquerque, NM, 87123, USA

3

Florida Solar Energy Center, Cocoa, FL, 32922, USA

4

Maxim Integrated, San Jose, CA 95134, USA

Abstract — Module-embedded power electronics developed 

by Maxim Integrated are under evaluation through a partnership 

with the Department of Energy’s Regional Test Center (RTC)

program. Field deployments of both conventional modules and 

electronics-enhanced modules are designed to quantify the 

performance advantage of Maxim’s products under different 

amounts of interrow shading, and their ability to be deployed at a 

greater ground-coverage ratio than conventional modules. 

Simulations in PVSYST have quantified the predicted 

performance difference between conventional modules and 

Maxim’s modules from interrow shading. 

Initial performance results have identified diffuse irradiance 

losses at tighter row spacing for both the Maxim and 

conventional modules. Comparisons with published models show 

good agreement with models predicting the greatest diffuse 

irradiance losses. At tighter row spacing, all of the strings 

equipped with embedded power electronics outperformed their 

conventional peers. An even greater performance advantage is 

predicted to occur in the winter months when the amount of 

interrow shading mismatch is at a maximum.

Index Terms — partial shading, MLPE, embedded power 

electronics, PV system performance, diffuse view factor

I. INTRODUCTION

The U.S. Department of Energy (DOE) seeks opportunities 

to increase U.S. manufacturing and deployment of 

photovoltaics (PV). A key barrier to the success of new PV 

technologies is demonstrating the performance and reliability 

at a level that gives investors adequate confidence for largescale investments. The DOE created the Regional Test 

Centers (RTCs) to help companies bridge this “valley of 

death” by providing infrastructure to rapidly test new 

products. The RTCs include field installations and 

performance-monitoring infrastructure in five states (CO, NM, 

FL, VT, and NV), along with collaborations with multiple 

commercial partners.

Maxim is one such RTC partner, with evaluation systems 

currently installed in Colorado and under construction in New 

Mexico and Florida. Maxim Integrated is a manufacturer of 

power electronics chips and modules, including a line of PV 

module-embedded power electronics. The VT8012 and 

VT8020 printed-circuit assembly (PCA) is designed for direct 

integration within the PV laminate to improve energy delivery 

under mismatch conditions.

Maximum energy delivery for a traditional PV system 

suffers when there is any source of power mismatch between 

PV cells, such as: manufacturing tolerance mismatch, 

temperature gradients, nonuniform shadowing, soiling, and 

cell aging [1-4]. Using a high-efficiency DC-DC converter 

and fast MPPT algorithm, the VT8012 PCAs reduce energy 

losses resulting from mismatch within and between PV 

modules.

Interrow shading can be one source of mismatch in a PV 

system, and can occur particularly in PV installations with a 

high Ground-Cover Ratio (GCR). GCR is variously defined 

as the ratio of module area to total land area, or, neglecting the 

unshaded first-row: GCR = L/R, where L is the length along 

the array and R is the row-to-row pitch (Fig. 1). The tighter 

the row-to-row pitch, the larger the GCR.

R

30 ̊

Array Length = L

Row Pitch = R

GCR = (L / R)

Fig. 1: Interrow shading can be calculated as a function of the GCR, 

defined as the ratio of PV module area to land area, or simply as the 

ratio of the array length L to the row pitch R.

When choosing an array row pitch, a trade-off exists 

between increased energy production per land area (kWh/m2

),

and reduced production per rated kiloWatt (kWh/kW) owing 

to interrow shading losses. This trade-off has been 

investigated before in several instances of fixed-tilt [5,6] and 

tracking [6-8] PV systems. By including embedded power 

electronics, partial shading losses can be reduced, which in 

turn makes higher power-density installations more 
2

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economical. Detailed performance and economic models such 

as PVSYST [9] and SAM [10] can be employed to estimate 

the impacts of different row spacing, and the use of embedded 

electronics. It is the intent of this work to help experimentally

validate such models.

II. DESCRIPTION OF MAXIM EMBEDDED ELECTRONICS

Other commercial module-level power electronics (MLPE) 

provide power conversion at the module level, with products 

either mounted to the module frame or installed in the PV 

junction box [11]. By contrast, Maxim’s VT8012 and VT8020

chips are embedded directly into the PV laminate, and 

distributed every 12–24 cells, for a total of 3–6 per module in 

place of conventional bypass diodes (Fig. 2). Integration with 

the PV laminate is done directly on a conventional PV 

manufacturing line, greatly reducing the cost associated with 

MLPE by reducing packaging and cabling costs.

VT8012 chips employ a buck DC-DC converter to match the 

currents of lower-producing solar cells to the current of the remaining 

cells in the series string. The converter boasts a CEC efficiency of 

98.7% and small footprint (< 350 mm2

), as well as compatibility with 

standard flash IV curve measurement methods.

The performance benefits of these distributed electronics accrue by 

enabling different portions of the PV module to operate at different 

peak operating currents. Conventionally, partial shading on one 

portion of a module would result in one of two behaviors. The bypass 

diode can short out the shaded submodule, preventing that section 

from contributing any power to the series total. Alternatively, the 

entire module and series string might be operated at the reduced 

power level of the shaded submodule. When equipped with 

distributed electronics, subsections of the PV module are able to 

operate independently from each other, with each portion of the 

module peak power tracked individually, and contributing to the 

system total (Fig. 3).

Maxim Solar Cell Optimizers perform maximum power-point 

tracking (MPPT) on each cell string within the PV module. The 

Optimizer replaces the bypass diode, providing both protection and 

MPPT functions from one device.

Conventional VT8020

80W 80W -5W 80W 80W 40W

Fig. 3: Comparison of effect of partial module shading. In the 

conventional case, bypass diodes short out shaded submodules to 

match current in the rest of the string. With power electronics, 

shading loss is reduced.

All MLPE systems can offer the ability to mitigate the 

impact of module-to-module mismatch mechanisms, such as:

factory binning tolerances, field degradation, and mismatch 

from soiling, and near-object shading. However, the 

submodule optimization offered by Maxim significantly 

improves performance in cases where the loss mechanism is 

not spread uniformly across the panel itself. In these 

examples, not only does each panel perform to its maximum 

potential but each cell-string within the panel does, as well.

One common and powerful example is the ability to 

mitigate row-to-row shading losses in fixed-tilt arrays. Row 

spacing is typically chosen to limit losses from interrow

shading. Isolating and optimizing each cell string within the 

panel offers a significant opportunity to improve production 

by increasing array density; enabling a PV system to be 

designed with a more economical trade-off between seasonal 

shading exposures and higher installation densities.

Figure 4 shows a typical shade derating plot, illustrating 

how energy production decreases as ground coverage is 

increased. Panels enabled with Maxim’s VT8012 afford the 

ability to design the array at much higher ground-coverage 

ratio while producing the same kWh/kWp performance rating.

Fig.4: Modeled shade derating with conventional versus Maxim 

embedded PV modules conducted for the CO RTC site described 

below. Model results follow methodology of Section III.

1,200

1,250

1,300

1,350

1,400

1,450

1,500

1,550

1,600

1,650

0.00 0.20 0.40 0.60 0.80 1.00

PRODUCTION (KWH/KWP)

GROUND COVERAGE RATIO

ANNUAL ENERGY - COLORADO RTC SITE

Conventional

VT8012

Fig. 2: Maxim VT8012 chipset embedded in the PV laminate. This 

“smart module” includes submodule power conversion in place of 

backplane diodes. Six of these DC-DC converters are integrated into 

each VT8012 PV module.
3

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As indicated by the gray arrow, panels with embedded 

Maxim electronics can enable the same energy production per 

panel at higher ground-coverage ratios and tighter row pitches. 

An area-constrained roof or ground site can be packed at a 

higher density to provide more energy at an equivalent or 

lower levelized cost of electricity (LCOE).

III. PERFORMANCE MODELING METHODOLOGY

Performance modeling of cell-string level optimization is 

possible using the PVSYST performance modeling software. 

The software tool provides sufficient flexibility to model the 

ground coverage density benefits achieved with Maxim’s 

embedded power electronics. 

Considerations for modeling cell-string level optimization 

are similar to those made when modeling different solar panel 

racking and wiring configurations. For example, when 

conventional panels are mounted in a stacked-racking 

configuration, the DC wiring is typically strung horizontally 

across the racks so that the series of panels closest to the 

ground are not electrically in series with panels higher off the 

ground. With this configuration, shown in Fig. 5, an interrow

shadow impairs only the bottommost row of panels while the 

more elevated panels remain at full production.

1

2

3

3-Up Landscape Racking 

1

2

2-Up Portrait Racking

Fig. 5: Electrical regions and shadow susceptibility of conventional 

panels

PVSYST simulations account for these designs with 

appropriate selection of the “# of electrical regions” 

parameter: 3 for the landscape example, and 2 for the portrait 

example in Figure 5.

As shown in Fig. 6, the Maxim chips offer improved shade 

tolerance due to the granularity of electrical isolation and 

degree to which PV performance is maintained under partial 

shading conditions.

1

2

3

4

5

6

7

8

9

3-Up Landscape Racking with Maxim VT8020

1

2

3

4

5

2-Up Portrait Racking with Maxim VT8012

7

8

9

10

11

6

12

Fig. 6: Electrical regions and shadow susceptibility of VT80XX 

panels

PVSYST simulations can properly account for the cellstring level optimization, again with an appropriate selection 

of “# of electrical regions” parameter. This parameter should 

be set to 9 for the VT8020 landscape example and to 12 for 

the VT8012 portrait examples above.

IV. EVALUATION INSTALLATION

The 40-kW field evaluation described here is intended to 

investigate the energy produced under four different rowspacing conditions. With rows spaced closer together, losses 

from interrow shading and diffuse field-of-view blocking 

increase. The ability of VT8012 chips to recover lost 

performance at closer row spacing will be evaluated over a 

multiple-year performance assessment.

Evaluation installations are under construction at three of 

the RTC sites, in CO, NM, and FL. This initial publication is 

focused on the Colorado installation, completed in April 2014 

(Fig. 7). Valid side-by-side comparisons are enabled by 

including conventional PV modules in rows along with the 

Maxim product. To ensure a fair comparison, the 

conventional modules and Maxim modules are sourced from 

the same manufacturer, using a similar bill-of-materials.

Fig. 7: Maxim installation at the Colorado RTC site

The layout of the Maxim demonstration site is designed to 

enable two comparisons. The first is the performance of 

Maxim modules against conventional panels for the same 

interrow spacing; this is possible because several rows contain 

strings of Maxim panels and strings of conventional panels. 
4

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The second comparison is the performance of different row 

spacings against the unshaded first row. Because the first row 

contains both a conventional string and a Maxim string, 

subsequent close-packed rows can be compared with the 

performance of the associated first-row string. 

Figure 8 shows a layout of the different modules within the 

Maxim installation. The installation consists of five rows of 

72-cell panels in 1-up portrait configuration with a 30-degree 

tilt angle. Three separate GCR values are chosen to define the 

system interrow spacing.

Panels are deployed in strings of 10, with each string 

individually peak-power tracked. To limit “edge effects”

where early-morning shade can be cast at an angle to the rows, 

the outermost three modules in each row are included in 

separate strings. These “dummy” strings are not considered in 

this analysis.

Fig. 8: Layout of the Maxim installation at 3 RTC sites. Strings are 

indicated by the bold line boxes. Yellow R1 – R3 strings are 

conventional “reference” modules without power electronics. Blue 

V1 – V7 strings are Maxim VT8012 modules. Row spacing 

decreases toward the back of the installation to increase shading loss.

Unmarked panels at the edge are “dummy” shading panels.

Each string of 9–10 panels is indicated by R1–R3 for the 

conventional “reference” modules without electronics, and 

V1-V7 for the Maxim VT8012 modules. Rows 1–3 include 

both Maxim and reference modules for side-by-side 

comparison (V1 vs R1, V2 vs R2, etc.). Rows 4 and 5 were 

designed to only include Maxim modules. Successively 

smaller interrow spacing is used to increase the amount of 

interrow shading on each row. This will allow the 

performance of the VT8012 modules to be judged at different 

row spacing.

Per string peak-power tracking is accomplished by seven 

Power-One PVI-6000 dual-channel inverters. 1-minute 

sample DC string measurements are provided by the inverter,

as well. Comparison with isolated voltage transducers on four 

of the strings found the integrated inverter DC power 

measurements to be within 1% under steady-state irradiance 

conditions (< 10 W/m2 change in 1 minute) and for irradiance 

> 200 W/m2

. Plane-of-array irradiance is monitored with a 

thermopile pyranometer as well as with calibrated reference 

modules.

To account for any initial offset in performance due to

variations in module power ratings, outdoor performance data 

are adjusted by factory flash-simulator data collected at 

standard test conditions.

V. INITIAL PERFORMANCE RESULTS

A. Modeled Results

The simulations of partial shading response provide the 

estimates of annual performance losses shown in Table 1. The 

GCR value provided here is specific for the Colorado 

installation. 

TABLE 1: ESTIMATED SHADING LOSSES FOR DIFFERENT ROW SPACING

GCR ‘A’ GCR ‘B’ GCR ‘C’

Ground Coverage Ratio 0.45 0.53 0.63

Row Pitch 4.4m 3.7m 3.1m

Conventional Loss 2.9% 6.5% 17%

VT8012 Loss 1.8% 2.9% 5.9%

VT8012 Improvement 1.2% 3.8% 13%

As can be seen in the monthly production chart of Fig. 9, 

most gains from row-to-row shading are realized in the winter 

months. The case with ground-coverage ratio 0.53 is simulated

to have gains as high as 38% in the month of December.

Fig. 9: PVYST simulation results indicating expected monthly 

performance gains of Maxim versus conventional panels in the 

Colorado RTC site at the fixed ground-coverage ratio of 0.53.

B. Experimental Results

From simulations above (Fig 9), we can see that the 

majority of the predicted shading loss in the system occurs in 

the winter months from October–March. However, this 

evaluation installation was not completed until April 2014, 

which means that the performance data collected so far does 

not account for the most extensive shading conditions that this 

system will encounter. One type of partial shade mismatch 

that can be evaluated now is how diffuse irradiance is reduced 

at different row spacing.

0%

10%

20%

30%

40%

0

20

40

60

80

100

120

140

160

MONTHLY GAIN

MONTHLY PRODUCTION (KWH/KWP)

MODELED ENERGY PRODUCTION

COLORADO RTC SITE WITH GCR = 0.53

VT8012

Conventional

Gain
5

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Models for the effect of different row spacing on diffuse 

and reflected components of irradiance can be found in 

[12,13]. The reduction in diffuse irradiance is calculated 

through a “screening angle” ψ(z), which indicates the angle at 

which the view of the sky is reduced from a given point on the 

array. Geometry suggests that reduced row spacing increases 

the screening angle, and decreases the amount of diffuse and 

reflected irradiance available to the solar module. 

Interestingly, the same equations can provide different shadeloss predictions, depending on the height z along the PV 

module that is taken to calculate ψ. For instance, the bottom 

of the module z = 0 receives less diffuse irradiance than the 

very top. This is illustrated in Fig. 10 for a module at 30o tilt 

at three different row pitches. It is clear that the bottom half 

of the module receives considerably less diffuse irradiance 

than the top half. It is therefore also clear that the calculated 

performance loss for the system depends on what point along 

the module is chosen to calculate the shading loss for the 

system.

Fig. 10: Diffuse irradiance loss along a PV module (tilt = 30o) at 

three different ground-coverage ratios [12].

The authors in [14] suggest that PV performance is best 

modeled by assuming that module current is limited by the 

lowest irradiance; therefore z = 0 should be used to calculate 

reduced diffuse irradiance. The authors in [12] suggest that 

averaging ψ(z) over all z is the most appropriate, resulting in 

a less strict diffuse loss term. This ambiguity can be resolved 

by comparing different model assumptions with the 

experimental results. 

Figure 11 shows diffuse irradiance loss, predicted by the 

diffuse screening angle of [12] and the reduced groundreflected model of [13] at different ground-coverage ratios. 

Three different ψ(z) values are assumed, one by averaging 

over all z, one assuming a worst-case screening angle at z = 0,

and an in-between case taken 10% up the module (z = L/10). 

Ground albedo is assumed to be ρ = 0.2 for all cases.

The measured performance of 10 different strings (V1–V7 

and R1–R3) is then compared under overcast conditions. The 

first row of each module type (V1 or R1) is used as the 

reference against which each other row is compared. Data are

collected for three weeks, and selected for high diffuse 

irradiance conditions (EDiff/EPOA > 0.8) and EPOA > 200 W/m2

. 

Beam irradiance is further factored out of results by 

subtracting the estimated contribution of beam irradiance from 

each string’s power:

Pbeam ≈ PV1 �

Ebeam cos(αAOI)

EPOA �

where PV1 is the power of string V1, Ebeam and EPOA are the 

direct-normal and total plane-of-array components of 

irradiance, respectively, and αAOI is the solar incidence angle 

to the tilted module plane. The diffuse loss of strings V2–V7

are then calculated relative to the first row:

Diffuse Loss = 

PVX−Pbeam

PV1−Pbeam

− 1

where PVX is the power of string V2–V7. A similar method is 

used to determine the diffuse loss of strings R2 and R3, 

relative to the front-row R1. Figure 11 shows these values, 

averaged over the three-week period of performance. 

Fig. 11: Diffuse irradiance loss at three different ground-coverage 

ratios. Modeled results from [12,13] with three diffuse screening 

angles ψ(z) assumed—averaged across the entire module (average 

z), at the bottom of the module (z = 0), and 10% up the module’s 

length (z = L/10). Experimental VT8012 (triangle) and conventional

(circle) results displayed similar behavior, with VT8012 strings 

outperforming the conventional string at larger GCR. Measurement 

error bars are representative for all experimental data.

The experimental results suggest that the modeled case of 

z = 0 and particularly z = L/10 fit the experimental results

much more closely than the optimistic average z model. This 

can be explained from an electrical standpoint by noting that 

for conventional series-strung PV cells, the module current is 

limited mainly by the lowest-producing cell within that 

module. This is less strictly the case for modules with 

embedded electronics in them.

Comparing conventional with VT8012 results is difficult 

because no conventional strings were deployed at the tightest 

row pitch. Although all VT8012 strings slightly outperformed the conventional string at the middle GCR value, 

the performance of the conventional and VT8012 strings were 

more equivalent (within measurement uncertainty) at the 

0

0.25

0.5

0.75

1

-10% -8% -6% -4% -2% 0%

HEIGHT ALONG MODULE Z/L

DIFFUSE IRRADIANCE LOSS

GCR 0.54

GCR 0.65 GCR 0.45

-10%

-8%

-6%

-4%

-2%

0%

0.35 0.45 0.55 0.65

DIFFUSE LOSS RELATIVE TO ROW 1

GROUND COVERAGE RATIO

Model - z = 0

Model - Average z

Model - z = L/10
6

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broadest row spacing. Although additional comparisons at 

GCR = 0.65 would confirm this trend, it is possible that the 

VT8012 strings are outperforming conventional strings at the 

middle GCR value because the irradiance mismatch is greater. 

With a 6% diffuse loss at GCR = 0.54 and only 3% loss at 

GCR = 0.45, there is more opportunity for the losses to be 

recovered by VT8012 modules at the tighter row pitch. At 

GCR = 0.45, the relatively low mismatch may be too small for 

the Maxim DC-DC converter to provide much benefit.

It should be noted that the diffuse irradiance losses 

investigated here are only a portion of the expected losses 

from interrow shading in this system. The energy lost from 

beam shading is expected to be a larger contributor to annual 

system performance, but this shading occurs only in the winter 

months. A full year of performance monitoring is required to 

get a complete picture of the partial shading benefits of 

Maxim’s VT8012 modules.

CONCLUSION

Theoretical and experimental results are presented for a 

system employing module-embedded power electronics. 

PVSYST modeling of the system suggests that partial-shading 

losses are concentrated in the winter months, and that tighter 

row spacing can be used with Maxim VT8012 modules to 

achieve the same annual performance. 

A comparison of performance at different row spacing 

suggests that diffuse-irradiance losses are greater than some 

models predict. At tighter row spacing, the VT8012 strings all 

outperformed the conventional string, indicating that a 

performance advantage is conferred even under diffuseirradiance mismatch gradients as low as 6%. Performance 

data during the most-shaded times of the year have not yet 

been collected, which would enable a full evaluation of these 

modules’ partial-shading benefits.

ACKNOWLEDGEMENT

This work was supported by the U.S. Department of Energy 

under Contract No. DE-AC36-08-GO28308 with the National 

Renewable Energy Laboratory. 

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