How to Check if Solar Panel is Charging Battery: 10 Essential Steps

By Pence July 25, 2023 Solar Panels 0 Comments

Solar energy is becoming increasingly popular as a renewable and sustainable energy source for homes and businesses. Solar panels convert sunlight into electricity that can be used to power devices or stored in batteries for later use.

However, it’s important to monitor your solar system to ensure the panels are functioning properly and charging the connected batteries as expected.

This article provides a comprehensive guide on how to check if your solar panel is effectively charging the battery.

Overview of Solar Panel and Battery System

A basic solar system consists of solar panels, charge controller, inverter, and batteries. Here is a brief overview of each component and how they work together:

Solar Panels – Made up of photovoltaic cells that convert sunlight into direct current (DC) electricity. Multiple panels are connected together to form an array that produces more power.
Charge Controller – Regulates the voltage and current from the solar panels going to battery to prevent overcharging. Some controllers also have MPPT (maximum power point tracking) to optimize energy harvest.
Inverter – Converts the DC output from solar panels and batteries into alternating current (AC) that can power home appliances.
Batteries – Stores the DC energy from solar panels for use when the sun is not shining. Common options are lead-acid, lithium-ion, and saltwater batteries.

The solar panels produce electricity whenever sunlight shines on them. This charges the batteries either directly or via a charge controller. The inverter then converts the DC from batteries into usable AC power. Any excess solar energy not used immediately is stored in the batteries.

10 Ways to Check if Solar Panel is Charging Battery

There are a few easy ways to monitor your solar system and confirm that the panels are in fact charging the connected batteries throughout the day.

1. Check Charge Controller Display and Indicator Lights

The charge controller is the central device that manages the power flow between the solar panels and battery bank. Most controllers have an informational display and LED indicator lights that provide charging status.

Battery Voltage – Display may show the live battery voltage, which should increase as the battery charges up.
Amperes – Shows current flow in amps from solar panels to battery. Higher values indicate active charging.
Charge State – LEDs indicate the battery charge level, like full, charging, floating, etc.
Errors – Error warning LEDs can indicate fault conditions inhibiting charging.

Observe these indicators periodically to confirm active charging when sunlight is present.

2. Monitor Battery Voltage

One of the best ways to directly check if batteries are charging is to monitor the battery bank voltage. Use a multimeter to measure the voltage periodically through the day.

Check Voltage in Morning – This will reflect battery state before solar panels start charging. Should be lowest voltage reading for the day if panels are charging as expected.
Check Voltage in Afternoon – As the solar panels charge up the batteries, voltage should increase significantly from the morning reading. For a 12V system, proper charging should boost voltage above 14V.
Check Voltage at Night – Voltage will taper back down when solar panels stop charging in evening. But should still be higher than morning voltage if batteries charged up during day.

Ideally create a log tracking battery voltage readings at set times throughout the day. The voltage curve should climb steadily as batteries charge then decrease overnight as batteries discharge to power loads.

3. Inspect Battery Electrolyte Level

For liquid lead-acid batteries, one sign of charging is electrolyte bubbling and rising in the cells. The battery electrolyte contains sulfuric acid and water. As charging current enters the battery, electrolysis occurs which produces hydrogen and oxygen bubbles.

Check early in the morning before any solar charging begins. Electrolyte level should be relatively low.
Once solar panels start charging, small bubbles will begin swirling in the electrolyte and the level will rise.
After charging current stops in the evening, the electrolyte level should fall again as the bubbles dissipate.

If the electrolyte level does not change much throughout the day, the solar panels may not be charging the battery bank as expected.

4. Measure Battery Terminal Voltage

Measuring directly across the battery terminals with a multimeter is another way to detect charging.

Check voltage across terminals in morning before charging starts.
Check again in afternoon when solar panels are producing maximum power. Voltage should be higher if battery is charging.
Repeat check in the evening after solar charging ends. Voltage will drop back down if charging was occurring as expected.

Watch for at least a 0.2V (or greater) increase from morning to afternoon. You can log terminal voltages to further verify the batteries are accepting current from the solar panels when exposed to sunlight.

5. Monitor Battery Temperature

A battery’s temperature will rise as it accepts current and charges up. This occurs due to internal resistance and chemical reactions inside the battery.

Use an infrared thermometer to measure battery temperature at various times of day.
Expect a higher temperature reading in afternoon versus morning if solar charging is occurring as expected.
Temperature difference may only be a few degrees. But any measurable rise tends to indicate current flow into the battery.

A battery remaining stone cold implies the solar panels are not actively charging it.

6. Check Specific Gravity

For lead-acid batteries, checking the specific gravity of the electrolyte is a direct way to determine if charging is occurring.

Use a hydrometer to test the specific gravity in the morning before solar charging begins.
Once batteries start charging, take another reading in afternoon when solar production is high.
Specific gravity should be higher in afternoon measurement if battery is accepting current.

Specific gravity increases as a battery charges because the sulfuric acid concentration goes up during the chemical reaction. This confirms energy is being pumped into the battery bank when exposed to sunlight.

7. Touch Battery Terminals

WARNING: Touch battery terminals very briefly and lightly. Avoid shorting terminals together.

You can get a rough sense if charging is occurring by cautiously touching the battery terminals with dry bare hands.

Positive (+) terminal should feel slightly warm.
Negative (-) terminal should feel cool.

This temperature difference indicates current flow into the battery. If both terminals feel room temperature during hours of solar irradiance, the panels may not be charging battery.

8. Listen for Bubbling Sound

As mentioned earlier, charging bubbles the electrolyte in liquid lead-acid batteries.

If you listen closely near the battery vents, you should hear a faint fizzing or bubbling sound when the solar panels are actively charging the battery bank.

The absence of any noticeable sounds may imply charging is not taking place. Just be careful not to breathe in any battery gases when bent over the battery.

9. Monitor Battery Discharge Time

Keep track of your battery bank discharge time to estimate if solar charging is sufficiently replenishing capacity each day.

Time how long evening loads can run until battery reaches discharge cutoff voltage.
Compare this time to previous days/weeks when system was working normally.
If discharge time gradually decreases over days/weeks, battery is not getting fully recharged each day.

Reduced discharge time suggests solar panels are no longer adequately charging batteries during daylight hours.

10. Measure Solar Panel Voltage

Use a multimeter to check DC voltage directly at the solar panel terminals. Very little voltage indicates panel issues rather than battery charging problems.

Check voltage during daylight hours when sun is shining on panels.
Compare output to panel specifications. Significantly lower voltage could mean soiled panels, shading, wiring issues, etc.
Higher voltage closer to open-circuit value implies panel is functioning but battery is not charging properly.

Low solar panel output indicates the root cause lies with the panels rather than battery charging.

Top Causes Why Solar Panel May Not Charge Battery

If your checks reveal the solar panel is not sufficiently charging the battery as expected, here are some common troubleshooting issues to investigate further:

Accumulated Dirt and Dust on Panels

Dirt buildup on solar panels over time can significantly impede power output. Solar panels work by absorbing sunlight. But grime prevents light from reaching the solar cells, cutting production.

Carefully clean panels with water and mild detergent. A dirty panel may only generate about half its rated power. Avoid using abrasive brushes or cleaners that can scratch the glass.

Battery is Defective or Reached End of Life

If the solar panels are clean and producing expected power output, the issue may be with the battery bank. Individual defective batteries or a bank that has reached end of life will resist charging.

Check batteries for cracked cases, corroded terminals, bulging sides, etc. Test individual battery voltages if possible. Replace any faulty batteries that are dragging down the entire bank.

Battery is Disconnected

It may seem obvious, but check that the battery is still physically wired to the solar charge controller or panel output. Loose connections or corroded cables can interrupt charging current flow to the battery.

Inspect all wiring for damage. Use a multimeter to check for continuity through cables. Tighten any loose terminations. Replace damaged wires restoring full battery connection.

Charge Controller Failure

The charge controller manages delivery of current from solar panels to battery bank. Failure of this device can prevent battery charging.

Charge controller issues include:

Input power side failure – Prevents current flow from solar panels to battery.
Output charge side failure – Stops current flow to battery for charging.
Logic/control circuitry failure – Unable to regulate charging properly.
Loose wiring connections – Interrupts current flow paths.
Short circuit or overvoltage – Damage from unregulated battery voltage spikes.

Carefully inspect the charge controller for damage. Check all connections. Review error codes if present. Replace or repair controller as needed to restore normal operation.

Battery Full and Charged

If the solar panels are producing power but the battery bank is already fully charged, the charge controller will stop current flow into the batteries to prevent overcharging.

Check the charge controller indicators for “high voltage” or “battery full” status. This is normal if the battery bank recharged faster than the power draw that day.

Excessive Battery Discharging

Drawing too much power from the batteries overnight will deeply drain the bank beyond the charging capabilities of the solar panels.

Load analysis is required to right-size the system battery capacity and panels for the intended loads. Adding more panels and/or batteries may be required to support excessive power demands.

Panels Shaded or Obstructed

For solar panels to charge properly, they need full sun exposure throughout the day. Shade from structures, vegetation growth, dirt buildup etc. can all reduce power output.

Inspect panels for any signs of shading during parts of the day. Tree growth is a common issue over time. Prune back obstructing branches to restore max sunlight access.

Battery Isolator Off Position

A battery isolator allows disconnecting the battery bank from the solar panels and loads when required. Check if isolator was inadvertently switched to the disconnected/off position.

Charge Controller Settings Incorrect

Check charge controller settings if equipped. Incorrect settings such as battery type, voltage, amperage etc. may prevent proper battery charging.

Reset the settings referring to battery manufacturer recommendations and panel specs to restore normal operation.

Faulty Wiring Connection

Inspect all wiring for signs of loose, corroded, or damaged connections. Any interference in the wiring can prevent charging current from reaching the battery.

Clean and tighten wiring terminals. Repair or replace any faulty cables or connections.

Blown Fuse or Tripped Breaker

Fuses and circuit breakers protect the solar charging system from current spikes and shorts. But these can also inadvertently trip and disrupt charging.

Check all fuses and circuit breakers along the charging system path. Replace blown fuses and reset tripped breakers.

Battery Fault from Sulfation

As lead-acid batteries discharge, sulfation can occur which crystals on the battery plates. This inhibits the chemical reactions needed for proper charging. Progressive sulfation causes permanent battery faults.

Severe sulfation may require battery replacement. Some sulfation can be reversed with an equalization charge if permitted by manufacturer.

Insufficient Solar Panel Output

Weak solar panel output can be caused by several factors:

Soiling – Clean panels to maximize light absorption.
Damage – Inspect panels for broken glass, split cells, etc.
Age – Output degrades slightly over time. Replace old panels.
Shading – Remove any obstructions blocking sunlight.
Incorrect Orientation – Track seasonal sun path changes.
Low-Quality Panels – Choose reputable solar brands for efficiency and longevity.
Sizing – Add more panels to increase power production.
Wire Gauge Too Small – Increase wire size to reduce voltage drop losses.
Wrong Temperature – Extreme cold can lower output.

Analyze your specific site and panels to determine what factors might limit production and battery charging capability.

Battery Charging Setpoint Too High

The charging setpoint is the minimum battery voltage that triggers solar charging to resume. This is adjusted on the charge controller or inverter charger if present.

If the setpoint is configured too high, the battery voltage may never drop enough to restart charging each day.

Lower the charging setpoint based on the battery manufacturer recommended charging voltage.

Testing Solar Panel Output

If battery charging issues persist after checking the above troubleshooting tips, the next step is to test the solar panel power output.

Here is how to check solar panel production with a basic multimeter.

Tools and Supplies Needed

Digital multimeter
Wire with alligator clips
Solar irradiance meter (optional)

Testing Procedure

Disconnect the solar panel positive and negative wires from the charge controller or battery.
Attach the red (positive) multimeter probe to the panel positive terminal or wire.
Attach the black (negative) multimeter probe to the panel negative terminal or wire.
Set the multimeter to Volts DC mode. This may be labeled DCV or V with a dashed line.
Ensure panel has full sunlight access. Optional: Measure irradiance with a solar meter if available.
Read and record the open-circuit voltage from the multimeter. Open-circuit means the panel operating with no connected load while exposed to sunlight.
Compare voltage reading to panel specifications. It should be around 75%-95% of rated open-circuit voltage if functioning properly.
If low, test panel output at intervals throughout day. Dirt can lower morning output until sun is high. If output remains low, thoroughly clean panels.
Repeat test over following days. Consistently low voltage indicates panel issues preventing proper battery charging.

This voltage test reveals if solar panel is producing power normally before further investigating why battery is not charging properly. Keep safety in mind when testing electrical circuits.

Testing Current Draw with Solar Panel

Optionally, you can also attach a load like a small motor or light bulb to measure panel output current. This tests power production under a real load, but risks damage if overloaded.

Connect panel wiring to multimeter as before.
Connect test load positive to solar panel positive.
Connect test load negative to multimeter negative probe.
Power on load. Monitor current draw on the multimeter.
Compare to panel short-circuit current specification. Output should be around 75%-95% or higher of rated current.
Gradually increase load to test max current. Stop quickly if overheating or voltage dips too low.

Repeat testing on different days at different times to check consistency of panel performance before further troubleshooting why battery is not charging correctly.

Solar Panel Voltage and Current Curve

The graph below represents the typical voltage and current relationship of a solar panel during operation:

Key points on solar panel output:

Open-circuit voltage (Voc) – Maximum voltage when panel has no load applied. Around 75% of this value indicates proper performance.
Short-circuit current (Isc) – Maximum current when panel positive and negative terminals are directly connected. 75%-95%+ of rating is expected in full sun.
Maximum power point (MPP) – Point of peak power production, multiplied by voltage and current. Keep panel operating near this point.
Increasing current causes decreasing voltage – As more load is applied, output current increases but operating voltage drops due to internal resistance.

Understanding this performance curve helps when testing panel output and determining if production is within expected parameters. Consult the panel specifications for the rated open-circuit voltage, short-circuit current, voltage at maximum power, and other values.

Steps for Further System Diagnosis

If the solar panel testing indicates it is producing power normally, continue investigating why the battery is not charging properly:

Thoroughly inspect charge controller, fuses, breakers, isolator switch, and all wiring. Look for any damage or faults disrupting charging current flow.
Disconnect charge controller and connect panel directly to battery. If battery charges, controller issue is likely.
Load test battery bank. Faulty batteries can prevent accepting charge current even if panels are working.
Consult charge controller manual and verify all settings are correct for connected panels and batteries.
Contact solar equipment manufacturer with testing results for additional troubleshooting advice.
Consider hiring a solar specialist to inspect overall system health, performance, and installation.

Careful system diagnosis and process of elimination determines if its an issue of low solar panel power output or component failure preventing battery charging downstream in the system.

Key Specifications When Selecting Solar Panels and Batteries

When installing or expanding a solar system, keep these specifications in mind for solar panels and batteries:

Solar Panels

Output power rating – Measured in Watts. More power yields faster battery charging.
Open-circuit voltage (Voc) – Optimal operation 75%-95% of this value.
Short-circuit current (Isc) – Optimal output around this value in full sun.
Cell technology – Monocrystalline most efficient, polycrystalline less costly, thin film lower output.
Temperature coefficient – Panel output decreases as temperature rises. Check coeficient.
NOCT – Normal Operating Cell Temperature. Lower NOCT is better.
Durability – Important for roof mounting and longevity.
Warranty – At least 20-25 year power output warranty.
UL listed – Verifies quality, safety and reliability.
Peak sun hours – Critical factor with your location’s sun exposure.

When selecting panels, choose a reputable brand and balance panel rated power, voltage, current and key specifications with your home power consumption.

Batteries

Capacity – Measured in amp-hours. Choose enough to meet nightly load needs.
Chemistry – Lead-acid, lithium-ion, saltwater each have pros and cons.
Voltage – Match to solar panel and inverter voltage.
Maximum charge/discharge rates – Impacts battery lifetime.
Cycles – Choose deep cycle batteries designed for solar apps.
Operating temperature – Important for battery life and performance.
Certifications – Look for UL listing and other quality certifications.
Warranty – At least 10 years, longer is better.

Properly sizing the battery bank capacity and state of charge window optimizes the system.

Carefully selecting high quality solar components that are compatible and sized appropriately ensures a robust and efficient renewable solar system. Consider consulting a solar specialist for recommendations and system design.

Summary

Maintaining solar production and battery charging is essential for an effective off-grid or grid-tied solar system. If batteries are not charging properly or as expected, use the troubleshooting tips provided in this article to diagnose the issue:

Monitor charge controller indicators and battery voltage/temperature/electrolyte level for signs of active charging.
Thoroughly inspect all system components and wiring connections for faults.
Test solar panel output with a multimeter to determine if production is within specification.
Compare battery discharge times to baseline norms to identify reduced capacity.
Consider shading, dirty panels, charge settings, load demands and other charging problems.
If panels are producing adequately, focus downstream for battery bank, controller or wiring issues.
Understand key specifications when selecting compatible solar panels and batteries.

Awareness of the full system performance day-by-day allows catching and resolving any charging problems early. Addressing battery charging issues promptly preserves the system reliability and return on investment that makes solar energy a wise choice for your home or business.

Frequently Asked Questions

How do I know if my solar panel is working?

Check the charge controller indicators, monitor battery voltage changes through the day, and test panel open-circuit voltage. Charging sign and typical voltage along with battery level rising indicates panels working.

How do I know if my solar charger is fully charged?

A fully charged solar battery will show a high steady voltage (14V for 12V system) and the charge controller will switch to a floating or standby charging mode.

Why are my solar panels not charging my batteries?

Common reasons include shading/dirty panels, charge controller failure, battery defects, reverse polarity, blown fuses, loose wiring, and insufficient sun.

How do I know if my solar battery is weak?

Signs of a weak solar battery include short discharge times, inability to hold a charge, low voltages, specific gravity readings and electrolyte bubbling. Testing load capacity can confirm poor battery health.

What does a red light on a solar panel mean?

A blinking or solid red light on a solar charge controller typically indicates a fault condition like reverse polarity, overvoltage, overheating or another error preventing charging.

How do you test a solar panel without sun?

Artificial light shining on a panel can generate a small voltage to confirm operation. However, full sun is best for proper solar panel testing and diagnostics.

Do solar panels stop charging when battery is full?

Yes, once the battery bank reaches full charge the charge controller will stop the charging current flow from the solar panels to prevent overcharging the batteries.

How long does a solar panel take to charge a battery?

Charging time depends on many factors like panel wattage, hours of sun, battery capacity, controller settings, wiring, etc. But generally solar panels take 5-8 hours in good sun to fully charge batteries.

Can solar batteries charge without direct sunlight?

Solar panels need direct exposure to sunlight to generate electricity and charge batteries. Artificial light and scattered daylight is not sufficient for substantial battery charging.

Can solar panels work at night?

No, solar panels require sunlight to produce electricity. They do not work at night without sunlight to power the photovoltaic conversion process. Batteries store daytime solar energy for night usage.

Can I use solar at night without battery?

A solar system without batteries can power devices directly from the panel output during daytime. But batteries are required to store and use solar energy at night when the panels are inactive without sunlight.

Do solar batteries charge at night?

No, solar batteries rely on solar panels converting sunlight during the day in order to recharge. At night, no charging takes place but batteries can discharge to power loads until dawn.