One of the outcomes of 2015's COP21 summit was the push for a unified uptake of renewable energy to ensure a sustainable future for the planet. Solar power is one of the most reliable renewable sources, with a number of government schemes and initiatives in place across Europe to encourage more businesses to install panels. However, in order to ensure longevity of the panels themselves they must be kept clean and functional. Mark Burnett, VP of the Lubricants and Fuel Additives Innovation Platform at global water, energy and maintenance solutions provider NCH Europe, explains how effective solar panel cleaning is key to truly sustainable power.

As with all on-site power generation equipment, solar panels need careful maintenance in order to operate efficiently. However, most traditional sources of electricity have, for the most part, been very straightforward. Beyond installation, they havent required much attention unless something has gone technically wrong.

Solar panels are an entirely different beast. Photovoltaic (PV) panels, the type most commonly installed by businesses, work on a very simple concept — the more sunlight they can absorb, the more energy it can generate.

Using solar panels has a number of benefits for businesses. Many countries in Europe — notably the UK, Germany and Spain — offer feed-in tariffs that reward companies for using solar power by paying them to feed excess energy back into the national electricity grid. The more power generated by efficient solar panels, the more businesses will be able to return to the grid.

Sources of contamination
Unfortunately, standing between businesses and solar-related profit is panel contamination. PV panels might be a magnet to sunlight, but they also attract a large number of contaminants such as dirt, pollution and bird faeces. As solar panels must be outdoors, this is unavoidable.

While these may not immediately appear to be anything other than surface blemishes that only impact aesthetic of the panels, contamination effects the overall electrical output. As they operate by conducting sunlight, marks on the panels mean small surface areas are unable to properly detect light. Over time, this greatly reduces overall panel efficiency and capacity. Some solar panels even switch off completely if too much of the surface is obstructed with grime.

This decrease in efficiency makes for a lot of lost power. In 2009, Google found that cleaning solar panels can double energy output almost immediately. This may sound unlikely, but the company had installed its PV panels in 2007 and only cleaned them 15 months later, so the panels were underperforming prior to cleaning. When cleaned eight months later, the increase was 36 percent - still notable, but not as high because the panels were relatively well maintained. The more regular the clean, the higher the overall output.

There is little that can be done to prevent contaminants from accumulating in the first instance. Dirt and dust is transferred via gusts of wind, while general air pollution gathers on the panels as a by-product of nearby industrial activity or traffic. This typically makes for a moderate amount of panel contamination, but factories and automotive manufacturers will find this accounts for significantly more.

For example, businesses that have PV panels installed on a site that also has a cooling tower will find that panels attract a high volume of pollution. These plants also present a separate challenge in that droplets of water from cooling tower steam may come into contact with the panels, leaving smears and streaks of mineral contamination. Likewise, it is not uncommon for automotive manufacturers to find oily stains gradually appearing on their solar panels.

It is for the same reason that rainwater also poses a problem to solar panels. Other than by typically signalling a lack of sunlight to absorb, rain is bad news for PV panels as it leaves marks on the panel itself. Contrary to what many businesses may initially believe, rainwater will in fact make panels dirtier not cleaner. This is a result of the salt and mineral composition of rain drops as well as airborne particles that get captured during rainfall and settle on surfaces when the rain evaporates. This is why car windscreens gather grime where the wipers cannot reach, so panels will lose effectiveness if left to mother nature.

Cleaning your panels
The process of cleaning solar panels is much more intricate than just leaving it to mother nature. A number of factors should be taken into consideration, from timing to cleaning product, in order to properly remove grime from panels and ensure optimum performance.

One of the golden rules for cleaning solar panels is to pick the right time to approach the task. Given the heat of sunlight itself, it would certainly not be advisable to attempt to clean something that is currently the focal point for that light. It is therefore best to clean panels either early in the morning or late at night, when sunlight is at a minimum and the installations are cooler. Early morning offers the advantage of dew, which can help to loosen surface grime so less product is required to remove it.

The most important step in cleaning and maintaining solar panels is ensuring that you use the best cleaning product. Many standard panel cleaners are alcohol-based, which tend to leave behind sun-blocking smears during wipe down as the alcohol is insoluble. In effect, the cleaning product itself contributes to the obstruction of the panel.

There is reasoning behind the popularity of alcohol-based cleaners. The alcohol content helps to reduce the freezing temperature of the overall product, which make it suited for winter months and colder climates. However, this characteristic is unnecessary for the remainder of the year.

In order to achieve an effective clean that does not leave behind residue, maintenance engineers should use an alcohol-free alternative that provides the same cleaning ability regardless of season. As water-based products are subject to freezing, the best choice is an additive-based product.

Additive cleaning solutions are able to deliver the same quality of clean each time, regardless of conditions and without leaving residual blemishes. Beyond the cleaning itself, these products can also yield environmental benefits in their own right.

For example, NCH Europe has developed two versions of its additive cleaning product Screen Clean - one in tablet form, the other in powder form. This means that there is less environmental impact in the first instance as they do not require large shipments of water or the use of plastic bottles. This makes Screen Clean a greener alternative to most solar panel cleaners that are distributed in liquid formats.

When considering the environmental impact of a cleaning solution, it is also important to pay attention to the formulation of the product itself. While some additives have a PH-neutral solution that is safe for both the environment and people, some may use Volatile Organic Compounds (VOCs). These carbon-based solutions dry quickly at room temperature, but they are harmful to the environment due to their toxic composition.

However, when using additive solutions, it is important to choose a product compatible with the water type that will be used to dilute it. Screen Clean was designed to offer optimum results regardless of whether it is topped up with hard or soft water, but not all solutions offer this level of flexibility.

Maintaining cleanliness
Once cleaned with an additive-based product, a panel will be spotless and it can be months before another clean is required. While it makes logical sense to wash panels on a regular basis to ensure maximum conductivity, this can quickly become an expensive practice. It also increases the likelihood of scratches to the panel surface which may occur from abrasive scrubbing.

Cleaning solar panels once every four to six months enables businesses to make the most of the sun without a dip in efficiency or spending too much on cleaning solutions. In order for Europe to reach the renewable energy goals outlined in COP21, it is important that the installations are properly maintained so that the environments and businesses can truly see the benefits of solar power.