6V Mini Solar Panel Library for Proteus V1.0 (Arduino, INA219)

Hello friends, I hope you all are doing great. Today, I am going to share the new 6V Mini Solar Panel Library for Proteus V1.0, the second part of our renewable energy series. If you have ever built a solar garden light, a solar phone charger, a solar-powered Arduino or ESP32 node or a school experiment with the sun, you have used this part: the small black 6 V mini solar panel of 1 to 3 W, with its dark-blue cell strips under clear epoxy and two thin wires on the back.

This library puts that panel into Proteus as a part of its own - with its real I-V curve. Its current follows the light, its voltage follows the load, and one point on its curve gives the most power: the maximum power point. It also shows the two things that surprise people with small panels. There is no bypass diode, so a single leaf on one cell takes about three quarters of the power and drives that cell into reverse - a hot spot. And indoors it still shows 5 V on a meter while it gives only milliwatts. The demo measures it with our INA219 current sensor from an Arduino UNO V4.0.

NOTICE: a mini solar panel looks like a little 6 V battery - but it behaves nothing like one. Our team put a lot of effort into building a panel that behaves like the real thing: 12 cells with their I-V curve, the heat, the light, the shade and the hot spot of a shaded cell. Your feedback is the fuel that keeps us going, so please tell us what you think in the comments below or in the Motor Driver board of our forum. And if our free libraries help you, you can buy us a coffee. So, let's get started with the 6V Mini Solar Panel Library for Proteus V1.0:

What is a 6V Mini Solar Panel?

A mini solar panel is a small string of photovoltaic cells, cut from full-size silicon cells and laminated under epoxy or PET on a thin board. Each cell gives about 0.6 V with no load, whatever its size; the cell's area sets the current. A "6 V" mini panel has 12 cells in series, which gives about 7.2 V open-circuit and about 6 V at its best point - just right to charge a single Li-ion cell through a small charger, or three or four NiMH cells.

The I-V Curve and the Maximum Power Point

A battery holds its voltage and gives whatever current the load wants. A solar panel does almost the opposite: the light decides its current, and the load decides where on its curve it sits. Ask for a little current and the voltage stays high, near Voc. Ask for more and the voltage drops slowly - until the current gets close to what the light makes, and then it falls off a cliff. Power is volts times amps, so it is small at both ends and peaks at the knee of the curve: the maximum power point (MPP). On a 2 W mini panel in full sun, that is about 5.8 V and 0.34 A.

Why a Mini Panel Has No Bypass Diode

Big panels, like the one in our 12V Solar Panel Library for Proteus, split their cells into strings and give each string a bypass diode, so a shaded string can be skipped. A mini panel has no junction box and no room for diodes: all 12 cells are one string. In a string, every cell carries the same current, so the weakest cell sets the current for all of them. A leaf on one cell starves the whole panel - and when the load pulls harder, the 11 lit cells push the shaded one into reverse, where it burns power instead of making it. This library shows exactly that.

5 V Is Not Power

The open-circuit voltage hardly changes with the light: a mini panel under a desk lamp or by a window still shows about 5 V on a meter. But its current follows the light, and indoor light is a hundred times weaker than the sun. So the panel that shows 5 V gives only a few milliamps - far too little for an Arduino. Many first solar projects fail right here, and the demo shows why.

What's New in 6V Mini Solar Panel Library for Proteus V1.0

• A part of its own - just the panel: the dark epoxy board with 12 dark-blue cell strips and their silver busbars, and the red and black wires.
• A real I-V curve in the circuit: the single-diode model for every cell, fitted so the panel gives exactly its rated watts at STC.
• Light, heat and shade: four light levels from night to full sun, the voltage falls 0.33 % a degree, and a leaf or a shadow over half the cells.
• The hot spot: with no bypass diode a shaded cell is driven into reverse by the others - the model gives its voltage and warns about it.
• A pop-up window with four pages - Panel, Graphs, Event log and Check - with the live I-V and P-V curves, the maximum power point and the sky, a room lamp or the night over the panel.
• An A3 demo on our Arduino UNO V4.0 with our INA219 and its DC load: the volts, the amps, the watts, the best point - and whether the panel could run an Arduino.

The 6V Mini Solar Panel in Proteus

Search solar in Pick Devices; the device MINISOLARTEP is in TEPMINISOLAR.LIB (category Electromechanical, Renewable Energy) and its model is TEPMINISOLAR.DLL. The symbol is just the panel: the dark epoxy board, 12 dark-blue cell strips in two rows of six with their silver busbars, and the red and black wires from behind its left edge leading to the + and - pins.

At Run the cells come alive: their glare follows the light, they go dark at night, and a leaf or a shadow over half of them lies on them when you choose one. On the board's bottom margin the value line shows the watts, volts, amps and the state, the OUT LED lights green while the panel delivers power, and OPEN PANEL opens the pop-up. The value line, the LED, the button and the shade on the cells are TEP additions; a real panel has none of them. The sun, the clouds, the room lamp and the night are drawn in the pop-up.

The Pins and the Properties

Download 6V Mini Solar Panel Library for Proteus

Click the button below to download 6V-Mini-Solar-Panel-Library-for-Proteus-v1.0.zip (about 1.2 MB, without the source code of the models):

6V Mini Solar Panel Library for Proteus V1.0

• README.txt: installation, the demo, the wiring, the properties, real hardware, troubleshooting and the limits.
• Proteus Library Files: TEPMINISOLAR.LIB and ArduinoV4TEP.LIB from our Arduino Library for Proteus V4.0.
• Proteus Model Files: TEPMINISOLAR.DLL and TEPARDUINO.DLL.
• Proteus Simulation: 6V-Mini-Solar-Panel-INA219-ArduinoUnoV4.pdsprj, MiniSolar_Demo.hex and copies of the DLLs.
• Arduino Code: MiniSolar_Demo.ino (only the Wire library of the Arduino core).

Good to know: the demo's INA219 and its DC electronic load are our INA219 Current Sensor library, a separate download that is not in this zip. Get it from its own article, the INA219 Current Sensor Library for Proteus, and install TEPINA219.LIB and TEPINA219.DLL the same way.

No Proteus yet? Read How to Download and Install Proteus 7 and 8. New to libraries? Follow How to Install a New Library in Proteus.

How to Install 6V Mini Solar Panel Library for Proteus

1. Close Proteus and extract the whole zip file, for example to your Desktop.
2. Copy TEPMINISOLAR.LIB and ArduinoV4TEP.LIB from Proteus Library Files into the LIBRARY folder of Proteus (usually C:\Program Files (x86)\Labcenter Electronics\Proteus 8 Professional\LIBRARY).
3. Copy TEPMINISOLAR.DLL and TEPARDUINO.DLL from Proteus Model Files into the MODELS folder. The two Arduino files are the ones of our Arduino Library V4.0; if you have it, they are the same.
4. Install the INA219 Current Sensor library the same way if you do not have it yet.
5. Delete TEPMINISOLAR.IDX from the LIBRARY folder if it is there.
6. Start Proteus, press P and search for solar.

Tip: keep the Proteus Simulation folder together, because the project needs its .hex file and the DLLs beside it. The library is tested in Proteus 8.5; Proteus 7 is not supported.

The Demo Circuit

Open 6V-Mini-Solar-Panel-INA219-ArduinoUnoV4.pdsprj. ARD1 is an Arduino UNO V4.0 from our Arduino UNO Library for Proteus V4.0, running MiniSolar_Demo.hex with its serial monitor built in. PV1 is a 2 W mini panel in full sun. Its + goes through U1, our INA219 in its pop-up version, and on into LD1, the INA219 library's electronic load, set to 340 mA - the current of this panel's maximum power point.

Why an INA219 and a DC Load?

A panel is easy to measure badly. Its open-circuit voltage says nothing about its power, as the indoor test below shows, and a fixed resistor only shows one point on its curve. The INA219 measures the real current through its 0.1 ohm shunt and the voltage at the same time, and the DC electronic load draws exactly the current you set - so stepping the load walks the panel along its I-V curve, just like a solar test bench.

The Arduino Code

The sketch needs only the Wire library of the Arduino core. New to Arduino? Start with Arduino Tutorial for Beginners and Introduction to Arduino UNO. It talks to the INA219 at its default address, and it knows roughly what an Arduino UNO needs:

const byte INA = 0x40;
const float SHUNT_OHM = 0.1;
const float ARDUINO_W = 0.25;                 // an Arduino UNO: about 50 mA at 5 V

Every INA219 register is 16 bits, most significant byte first: write the register's number, then read two bytes:

int16_t readReg(byte reg) {                    // a 16-bit register, MSB first
  Wire.beginTransmission(INA);
  Wire.write(reg);
  Wire.endTransmission();
  Wire.requestFrom(INA, (byte)2);

Volts, Amps and Watts

The shunt register counts in 10 uV steps, so the current is the shunt volts over 0.1 ohm. The bus register counts in 4 mV steps in its top 13 bits and gives the load's volts; the panel's own volts are that plus the shunt's small drop. The sketch reads the bus before and after the shunt:

  const float bus1 = ((uint16_t)readReg(0x02) >> 3) * 0.004;    // 4 mV a step
  int16_t raw = readReg(0x01);
  if (raw >= -1 && raw <= 1) raw = 0;                            // +-10 uV is the INA219's offset, not a current
  const float shuntV = raw * 0.00001;                           // 10 uV a step
  const float bus2 = ((uint16_t)readReg(0x02) >> 3) * 0.004;
  const bool steady = fabs(bus2 - bus1) < 0.05 + 0.01 * bus1;    // the panel did not change during the reads

Two details matter at the small currents of a mini panel. A single step of the shunt register is only 0.1 mA, and with no load the INA219 can read one step either side of zero; our first test run printed a minus sign in front of zero amps with the load switched off. The sketch now treats one step either way as zero. And the bus is read twice: if the load changes between the reads, the volts come from before the change and the amps from after it, so a reading taken while the panel changes is marked and does not count:

  if (steady && watts > bestW) { bestW = watts; bestV = volts; bestA = amps; }

Enough for an Arduino?

Each report ends with a short note. The order matters: a reading that is changing comes first, then a collapse, then the question every mini-panel project asks - is this enough to run an Arduino?

  if (!steady) Serial.print(F("  - changing"));
  else if (amps > 0.001 && volts < 2.0) Serial.print(F("  - collapsed: the load wants more than the light makes"));
  else if (watts >= ARDUINO_W) Serial.print(F("  - enough for an Arduino"));

The collapse test starts at 1 mA, because a mini panel indoors collapses at only a few milliamps; our first run used 5 mA and missed exactly that case. The last two notes tell an open circuit from a dark panel:

  else if (amps < 0.002 && volts > 5.0) Serial.print(F("  - open circuit"));
  else if (amps < 0.002) Serial.print(F("  - no light"));

The Report Loop

The loop never waits: it reads the serial commands and reports when the next report is due, by default every second:

  if ((long)(millis() - nextAt) >= 0) { nextAt = millis() + rateMs; report(); }

rate 500 changes that interval (200 to 5000 ms), best prints the best point so far and reset forgets it. The sketch also writes the INA219's calibration register once, so the chip's own Current and Power registers work too - the INA219's pop-up then shows them:

  writeReg(0x05, 4096);                        // the calibration: 0.1 mA a step in the Current register

The HEX file is in the package. To change the sketch, open it in the Arduino IDE and export the compiled binary, as in How to get the HEX file from Arduino. It needs 9,060 bytes of flash (28 % of the UNO) and 496 bytes of RAM.

Running the Demo

Press Run. The UNO's serial monitor, the panel's pop-up and the INA219's pop-up open over the schematic; move them aside. The sketch introduces itself and starts reporting every second:

6V Mini Solar Panel demo - The Engineering Projects
The panel feeds the DC load through the INA219 (0x40 on A4 / A5, 0.1 ohm shunt). Set the load on its pop-up.
Commands: best | reset | rate 1000 | help

At the Maximum Power Point

In full sun with the load at 340 mA, the panel sits right at its best: "AT THE MPP - 5.87 V x 0.340 A = 1.997 W (1000 W/m2, cells 25 C): the most this light gives". That is the label's 2 W, because the cells are still at 25 C.

The pop-up has the look of our TEP Serial Monitor Advance for Proteus and four tabs: Panel, Graphs, Event log and Check. The Panel page draws the I-V curve (blue) and the P-V curve (green) for the light of the moment, with the maximum power point in green and the panel's real operating point in orange - here right on the peak. Beside them are eight live values, and below them the sky and the panel: the sun, its beams and the shade, if any. The trace shows the power against the most the light can give over the last 10 seconds.

The INA219's pop-up sees the same from the measuring side: "MEASURING - BUS 5.840 V, SHUNT 34.02 mV, CURRENT 340.2 mA, POWER 1.986 W". Its bus voltage is taken after the shunt, so it is about 34 mV lower than the panel's own voltage. Its toolbar holds the DC load's presets and the switch that turns the load off, which is how we change the load in the next steps.

Enough for an Arduino

Click the UNO 50 mA preset - about what an Arduino UNO draws. The panel answers with a higher voltage and far less power: "OUTPUT 7.08 V x 0.050 A = 0.354 W - 18 % of the 1.995 W it could give at 5.80 V".

On the curves the orange point has slid far to the right, close to Voc. The panel could give more than five times as much, but the load does not ask for it. For a project that is fine: the monitor says "enough for an Arduino", since 0.35 W is more than the quarter of a watt an UNO needs. The spare power is what a battery charger would take on a sunny day.

Asking for Too Much

Now click MOTOR 800 mA - more than twice the 0.37 A the light makes:

The voltage falls off the cliff: "COLLAPSED - the load wants more than the 0.370 A this light makes: 0.27 V x 0.370 A = 0.099 W". The panel gives all the current it has, but at almost no voltage, so the power is close to nothing. A small motor or a pump wired straight to a mini panel does exactly this: it stalls, and the panel sits at a fraction of a volt.

A Leaf on One Cell

Click SERVO 250 mA on the INA219 and Leaf on the panel's pop-up. A leaf now covers one cell of the top row:

With no bypass diode, all 12 cells share the shaded cell's current: "A LEAF on one cell (set on the panel), no bypass diode: all 12 cells starve - the best now 0.488 W at 6.77 V". One cell in twelve is covered, and the best the panel can now give has dropped from 2 W to under half a watt. The 250 mA load wants more than that, so the panel collapses - and the shaded cell does something worse than starve:

"SHADED CELL IN REVERSE - driven to -6.1 V by the others (a hot spot): 0.22 V x 0.105 A = 0.023 W". The 11 lit cells push their current through the shaded one, and it can only pass it in reverse, through its leakage, with several volts across it. The panel delivers almost nothing, and the power the lit cells make is turned into heat in that one cell. On a real panel that is a hot spot: left for hours it browns the epoxy and can crack the cell.

The Check page goes through the light, the operating point, the load, the shade, the hot spot, the cells, the polarity and the energy, each with a coloured dot. With the leaf the shade row says "a leaf on one cell: with no bypass diode all 12 cells carry its current", and the hot spot row remembers the reverse voltage. Its tips at the bottom explain what happened.

Back to UNO 50 mA with the leaf still on: "OUTPUT 6.96 V x 0.050 A = 0.348 W - 71 % of the 0.487 W it could give at 6.76 V". A small load fits under the starved current, so the shaded cell stays out of reverse - the panel works, inside the quarter of its full-sun power that the leaf allows.

A Shadow Over Half the Cells

Click Half shade: a shadow now covers the right half of the panel, six cells at 30 % of the light:

"A SHADOW over 6 of the 12 cells (set on the panel), each at 30 % - the best now 0.642 W at 6.08 V". With the 50 mA load: "OUTPUT 6.72 V x 0.050 A = 0.336 W - 52 % of the 0.642 W it could give at 6.08 V". Half the panel in shade costs two thirds of its power, because the shaded half sets the current for the whole string. Notice that the leaf did more damage than this big shadow: a dark spot on one cell is worse than light shade over many.

Clouds, Indoors and Night

Click No shade and then Cloudy. The light drops to 200 W/m2, and so does the panel: "LIGHT 200 W/m2 - cloudy (set on the panel): the most it can give now is 0.364 W at 5.41 V". The 50 mA load still fits: "OUTPUT 6.01 V x 0.050 A = 0.301 W - 83 % of the 0.364 W it could give at 5.41 V".

Notice that the voltage on the curve hardly changed, but the current is a fifth of what it was. The 50 mA load now takes most of what the clouds allow - an Arduino on a cloudy day is right at the edge of what a 2 W panel can give.

Indoors: 5 V and Almost Nothing

Now click Indoors: about 10 W/m2, a bright room or a desk by a window. "LIGHT 10 W/m2 - indoors (set on the panel): the most it can give now is 0.008 W at 3.78 V". The 50 mA load is far too much: "COLLAPSED - the load wants more than the 0.004 A this light makes: 0.04 V x 0.004 A = 0.000 W".

Switch the load off with Switch the load off on the INA219's pop-up, and the voltage comes straight back: "OPEN CIRCUIT - 5.08 V and no current: nothing takes the power (the most it could give: 0.008 W)". This is the trap of testing a panel with a multimeter at your desk. The meter draws almost nothing and shows 5 V, which looks like a healthy panel - but the same panel cannot even light an LED properly in that light.

Finally, switch the load back on and click Night: "NIGHT - no light: 0.00 V, the panel makes nothing". The pop-up's sky turns to the moon and the stars, and on the sheet the cells go dark.

Back in full sun with the 250 mA load: "OUTPUT 6.43 V x 0.250 A = 1.609 W - 81 % of the 1.975 W it could give at 5.74 V". The monitor shows the whole story - and the best point it saw:

PV 6.01 V  0.050 A  0.30 W  - enough for an Arduino
PV 0.04 V  0.004 A  0.00 W  - collapsed: the load wants more than the light makes
PV 5.08 V  0.000 A  0.00 W  - open circuit
PV 0.00 V  0.000 A  0.00 W  - no light
PV 7.02 V  0.050 A  0.35 W  - enough for an Arduino
PV 6.43 V  0.250 A  1.61 W  - enough for an Arduino
best
Best so far: 2.00 W at 5.87 V, 0.340 A

Graphs and the Log

Graphs draws the power against the most the light can give, the volts and the current over the last 10, 30 or 60 seconds. The gap between the green power and the amber best is the energy left on the table; each drop of the volts to nearly zero is a collapse.

The Event log keeps every operating point with its share of the best, every change of the light and the shade with the new best point, and the warnings. Filter it to Output or Warnings, pause it, or clear it. More warnings you may meet: REVERSE CURRENT when something pushes current into the panel, such as a battery at night, REVERSED when a source is connected the wrong way, and HOT when the cells pass 75 C.

At the end of the run the Check page sums it up: "6.42 V x 0.250 A = 1.606 W: 81 % of the best", the Load row remembers that it collapsed the panel earlier, the Hot spot row remembers "a shaded cell was driven to -6.1 V in reverse by the others", the cells have warmed ("29 C (25 C air): Voc 7.1 V now - every degree takes 0.33 %"), and the energy row: "0.00503 Wh so far - 52 % of what the light offered". A fixed load and a leaf let almost half of the available energy go.

How the Model Works

Each of the 12 cells follows the standard single-diode model: a current source for the light, a diode, a series and a shunt resistance. Its numbers are fitted so the panel gives exactly its rated watts at 1000 W/m2 and 25 C, with 7.2 V open-circuit and about 5.8 V at the maximum power point. Shaded cells form their own group with less light; the groups are in series, so the panel's voltage at any current is the sum of the groups' voltages - and when the current is more than the shaded group makes, its voltage goes negative: the cell in reverse.

At every Newton step of the simulation the model works out the panel's current at that step's voltage and puts the tangent of its I-V curve into the circuit, so the panel and the load are solved together, wherever the load takes it. In transient the cells' capacitance (about 0.9 uF on a 2 W panel) is in the circuit too, which lets a too-heavy load collapse the voltage smoothly. The cells warm towards the air plus 31 C in full sun over about three minutes, and their voltage falls 0.33 % a degree.

We checked the model on a PC with 12 automatic tests: the 1, 2 and 3 W panels give 7.20 V open-circuit, 185 mA per watt short-circuit and exactly their rated watts at 5.81 V; 200 W/m2 gives 0.369 W; a room's 10 W/m2 gives 5.17 V open-circuit but only 3.70 mA and 7.8 mW; cells at 56 C give 13.0 % less; a full Li-ion cell pushes 1.88 mA into the dark panel; a leaf leaves 0.490 W and drives the shaded cell to -4.40 V at 2 V; half shade leaves 0.649 W; and the panel solves with the DC load at 0.05, 0.33 and 0.8 A. The pop-up has 4 more checks, and the demo project is read back from disk with 69 checks.

Troubleshooting

• COLLAPSED: the load wants more current than the light makes - a smaller load, more light or a bigger panel.
• OPEN CIRCUIT: nothing takes the power - check the load's wiring.
• SHADED CELL IN REVERSE: a shaded cell is driven into reverse by the others - remove the shade.
• REVERSE CURRENT: something pushes current into the panel, such as a battery at night - fit a blocking diode or use a solar charger.
• REVERSED: a source is connected the wrong way round - check + and -.
• The panel is not simulated: TEPMINISOLAR.DLL is missing from MODELS and from the project folder.
• No INA219 or no load: install our INA219 library (TEPINA219.LIB and TEPINA219.DLL).
• No UNO or no monitor: TEPARDUINO.DLL is missing; a closed monitor opens again with a click on the UNO's USB port.
• No pop-up: click OPEN PANEL on the panel's board, or turn "Open the panel at Run" on in its Settings.

Things to Know Before Wiring a Real Mini Solar Panel

• Expect less than the label: the watts are for 1000 W/m2 and cells at 25 C; on a sunny day expect 70 to 85 % (warm cells, the angle, dust) - and almost nothing behind a window or indoors.
• Keep it out of shade: with no bypass diode a leaf on one cell costs about three quarters of the power and heats that cell.
• Use a solar charger: a TP4056-type Li-ion charger, a CN3065 or CN3791 solar charger, or a small PWM controller for lead-acid. A battery straight on a panel runs back into it at night, and 7.2 V overcharges a Li-ion cell in the sun.
• Fit a blocking diode (a Schottky such as the 1N5817) if the charger has none.
• Measure the current, not the volts: a panel that shows 5 V on a meter can give almost nothing. For an Arduino, use a current sensor such as the INA219, and a 1:2 divider if you read the volts on an analog pin.

Limitations of the Simulation

• Not modelled: the angle of the sun (set the light instead), spectral effects, the shaded cell's temperature (the hot spot is reported, not heated), the breakdown of a cell far in reverse, cell cracks, the slow loss of power over the years, and a cell only partly shaded (a shaded cell is a whole cell at a share of the light).
• The value line, the OUT LED, the OPEN PANEL button and the shade on the cells are TEP additions.
• The model is our own implementation of the standard single-diode model, fitted to the typical data of 6 V mini panels; this library is not made or endorsed by any panel maker, Arduino or Labcenter.
• Licences: the demo HEX contains the Arduino AVR core 1.8.6 (LGPL) with its Wire library; the sketch is included and the README gives the source link. The INA219 and the DC load of the demo are our separate library.
• Tested in Proteus 8.5 in October 2026 with the demo as shipped: the maximum power point, 50 mA, 0.8 A, a leaf at 250 and 50 mA, half shade, cloudy, indoors with and without the load, night, and all four pages of the pop-up. Proteus 7 is not supported.

So, that was all about the 6V Mini Solar Panel Library for Proteus V1.0. I hope it helps you size the panel for your next solar project and see why the shade and the indoor light matter so much. If you have any questions, ask in the comments and I will help you out. Till the next tutorial, take care and have fun!