Water rules for cleaning solar panels!

Water is nature's best cleaning agent.

Listed below are important factors to consider before setting out to clean your solar panels with water, even if you intend to outsource the cleaning to professionals.

If you want to know about the larger picture of solar panel handling & cleaning, sign up for our free webinar on Monday, Apr 27, 2020! Register now - https://www.renewsysworld.com/webinar

1. Type of water:

Reverse osmosis (RO) water is the ideal option.

If RO is not available, rainwater or tap water with low mineral content and a total hardness that is less than 75 mg/L may be used.

Water with a significant amount of dissolved minerals, often known as hard water, leaves behind a residue on the glass. This causes the formation of stains or scaling on the glass that damage the glass and reduce the amount of sunlight going through.

Hence before you clean your panels, you should consider water availability.

2. Pressure

Water pressure should not exceed 35 Bar at the nozzle.

The water pressure being referred to here, is the force with which the water will exit the pipe being used to clean the panels. It is also an indication of the force with which the water will hit your solar panels.

A nozzle is used at the end of the pipe to control the water's pressure. Nozzles come with a variety of added features like attachments for cleaning fluid and are capable of a wide range of pressure settings.

3. Temperature

The temperature of the water being used for cleaning should ideally be the same as the solar panel temperature at the time of cleaning.

A maximum difference of 20 degrees is acceptable. The grater the difference between the water and the solar panel the greater the chances of the glass cracking due to a sudden temperature change (thermal shock).

4. Time of the day

Solar panels should be cleaned only during low light conditions.

After sunset and before sunrise, when the production of solar power is at its lowest, is the ideal time to clean panels. This is because when the panels are not generating power the risk of an electrical shock hazard is minimum.

The panels will also be cooler at these times and thus closer to ambient temperature so they are less likely to be at a very different temperature from the water being used to clean it.

5. Stubborn Stains:

Soak the stain in a stream of water. Use a soft sponge or micro-fibre cloth or a very soft bristle, non-conductive, non-abrasive brush. Rinse the module subsequently with plenty of water.

Never, ever scratch/ scrub the surface of the solar panel to remove stains.

This irreversibly damages the ARC i.e. 'Anti- Reflective Coating' on the glass of the panel.

If the stains have been on the panels for a while, we recommend contacting your panel installer/manufacturer for options of approved cleaning agents.

6. Panel Back-side

The back surface of the solar panel doesn’t require routine cleaning like the front surface.

Specific cleaning of dirt or debris may be carried out if dirt is observed on the back sheet. Only a soft sponge or micro-fibre cloth may be used.

While cleaning the dirt on the backsheet it is important to avoid the use of any sharp object, which can damage the material cause a slit.

Register for our Webinar on solar panel handling and maintenance here.

PID - Potential Induced Degradation

Over the last two weeks, we have connected with nearly 2000 customers through our webinars, from across countries, who are curious and worried about the impact of Potential Induced Degradation (PID) in their solar systems.

This post is intended to be a simple go-to source, any time that you want to quickly recap everything you need to know about PID.

The links to the relevant webinars are also listed below.

What is PID?

PID is a phenomenon or situation that hampers solar panel performance. It causes a drop in output of a solar system that ranges anywhere between 5% to 30% or more!

How does PID occur? or What is the Mechanism of PID?

This graphic below details the mechanism of PID within a solar module or solar panel.

PID is caused by stray currents or leakage currents that occur when there is a potential difference between the solar PV cells in a solar panel and the ground.

This potential difference causes the flow of positive ions from the glass, frame and mounting structure towards the solar PV cell, and damages the cell's P-N junction.

Panels towards the negative end of a string are the ones that are directly affected as opposed to the panels at the positive end of the string.

And, the higher the number of panels connected in a string and the higher the system's voltage, the greater the possibility of a system being subject to PID. Thus the probability of PID increases from 1000 V to 1500 V.

Factors That cause PID

An interplay of several factors may cause PID. These include:

• Quality of the raw materials: used in manufacturing the components of the solar panels - i.e. Glass, Encapsulant. E.g. Presence of higher amounts of sodium in the manufacture of the glass could have detrimental effects.

• Quality of solar panel components: Like the Encapsulant and PV Cells used. Whether or not they have undergone extensive reliability testing and are certified as being PID resistant.

• Location: Where is the solar power project installed? Latitude, longitude, local climatic conditions, along with exposure to high heat and humidity may make the solar panels more susceptible to PID.

• Voltage and size of the system: The higher the system voltage the greater the probability of PID. Generally, 1500 V systems are at greater risk than 1000 V.

• PID mitigation measures: Negative grounding and the presence of PID prevention devices mitigate the risk of PID related power loss.

Preventing PID

There are several aspects to consider when ensuring a PID resistant system.

1. Solar Panel Components - Encapsulants - Solar panel manufacturers and installers alike should insist on the use of PID resistant Encapsulants. These PID resistant Encapsulants act as an additional layer of protection against PID and guarantee higher system output across seasons. Know more...

2. Solar Panel Components - PV Cells - Solar Cells are primarily both the cause and the component most affected by PID. Hence it is extremely important that the cells used in a solar panel are certified PID resistant cells. To ensure that each batch of cells is PID free, additional PID testing at the solar panel manufacturers' end is also highly recommended. The testing of PV cells for PID resistance is carried out both after incorporating it in a module at regular intervals and more frequently in a specialized compact laboratory device that does not require the cells to be laminated.

3. Solar System Design - PV offset box/ Anti - PID/ PID resistant devices- Just like components of a solar panel, the components of a solar system are equally important in mitigating PID. Devices like the PV offset box apply reverse voltage on the system during the downtime i.e. after the sun sets ensuring that the solar panels are able to deliver their 25+ years of performance.

4. Solar system design - Grounding - An additional measure that is advisable from the safety and Anti-PID perspective is the negative grounding of the panels in a system.

5. Certification IEC 62804 & in- house solar panel testing - Lastly, a culmination of all of the measures above is the 'Certification System' that tests modules for PID resistance - IEC 62804. We strongly recommend being aware of the certification status and Bill of Materials used in the modules that you are procuring. Established solar panel or solar module manufacturers in fact have extensive in-house testing systems to ensure that their production practices are continually delivering solar panels of the highest quality.

Additional Resources

To know more about the mechanism of

PID take a look at this webinar.

To know more about the role of Encapsulants view this webinar.

When Solar Panels are put on a (Hot) Spot!

The average annual temperature, for the vast majority of our country is above 30 degrees Celsius.

Solar panels, also commonly referred to as solar modules, are installed in the open and operate at 15-20 degrees Celsius higher than the ambient temperature.

This means that the solar panels are operating at temperatures above 45 degrees Celsius regardless of the season. Though this temperature varies throughout the day, they are fairly equal through out the panel.

However certain factors can cause small, specific parts of the solar panels, to heat up to

temperatures that are much higher than the rest of the panel!

These localized areas giving out intense heat are referred to as 'Hot Spots'. They cause irreversible damage, degradation, and loss in output.

Actual field image of a hot spot

Actual field image of a hot spot

Hot spots are caused either due to Internal Factors or External Factors

Internal Factors include: Poor quality of solder bonds, use of substandard components, defective diodes, micro-cracks in cells, etc.

External Factors include: Shadows, soiling, bird droppings, sitting/ standing on the panel during installation, damage during transportation, etc.

To know more about the damage that shading causes click here.

How to safeguard against Hot Spots:

• Choose the right solar panel manufacturer

• Choose the right solar panel/ system installer

• Be Vigilant

Choose the right solar panel manufacturer

Solar panel manufacturers have to account for several factors to ensure the prevention of the formation of hot spots.

Every component should be of the highest quality and every process strictly adhered to.

Here are some key steps that are necessary to avoid the formation of hot spots while manufacturing a panel.

1. Ensuring that the required 'creepage' and 'clearance' distances are maintained according to applicable standards while designing and manufacturing the panels.

2. Using high-quality Encapsulant material that creates a cushion and protective covering on both sides of the PV cell to prevent the formation of micro-cracks because of external/ internal stress on the module.

3. Quality, automated soldering to prevent breakage of solder bonds. When the power produced by the PV cell cannot be transported due to faulty or broken solder bonds the energy is released as heat into the environment.

4. A robust Backsheet, comprising of quality raw materials and a high melting point (≥ 250 deg C) can help temporarily moderate the effect of the hot spot and maintain the insulation requirements for safety.

5. Consistent lamination of the panel is crucial to protecting the delicate solar cells. It prevents the formation of air bubbles, cell breakage and de-lamination of the solar panel after installation.

6. 100% EL imaging (electro-luminescence) before and after lamination. EL imaging allows the panel manufacturer to quickly check for defects in the cells, stringing, and presence of micro-cracks if any. (See how modules are manufactured here.)

7. Ensuring that the module manufacturer is using Electrostatic Devices for the Junction Box assembly to prevent damage to the diodes. Bypass diodes help reduce the damage of hot spots caused due to shade. However, if the bypass diode is itself defective, the hot spot temperature could go beyond 200 degrees C, resulting in permanent damage to the panel.

Choose the right solar panel/ system install

Ask your prospective installation partner about how they choose solar panels for a project, both the type of panel and the manufacturer.

Visit/ review reference projects.

Make the time to understand how a solar installer will help address your specific requirements before making a choice.

For example: Standalone homes have ample rooftop space, but the roof itself may not be easily accessible. Hence you will need to discuss both installation and maintenance that includes frequent cleaning of the panels with your installer.

A panel subjected to shading due to the growth of plants

Be Vigilant

Solar panels are built to last 25 years.

Keeping track of your solar systems' output and performance is an effective way to ensure a quick response to any changes that may be detrimental to your investment!

It could be something simple like trimming a few branches or something that requires a little help like cleaning your panels.

The only corrective action if one or more solar panels have a hot spot is to replace them before further damage is caused, both to the panel and to the entire system.

Hot spots reduce output and may be a serious safety issue, but with the right panel and installation partner, they are avoidable...