Common (and costly) sources of PV yield loss – and how to avoid the

Bjarne Sønderskov, O&M manager, Obton

The pride associated with launching a new PV plant can quickly fade when the first data on the facility’s performance start to arrive. All PV projects are based on an estimated production that is the park’s theoretical annual energy production. And when the PV facility becomes operational, both operators and investors anxiously look to the actual power generated.

The facility’s first year of operation allows for calculation of the performance ratio – the difference between the estimated yield and the actual final yield. The performance ratio typically drops over time due to ageing of the PV facility, but all drops in performance should typically warrant further investigation, as an unattended inefficiency means lost yield. As an example, a 10 MW PV facility might lose as much as much as 1 percent of its output due to soil on the panels resulting in a lost production of 99.000 kWh. 

Three stages of potential yield loss 

There can be numerous reasons for a photovoltaic plant to be performing below expectations. The energy loss can typically happen at three different stages:

  • Pre-photovoltaic losses are losses of energy caused by dust, shade, snow or reflection preventing the solar energy from hitting the PV panels.
  • Panel losses are losses caused by inefficiencies or errors in the photovoltaic panels themselves
  • System losses are caused by wiring, transformers, inverters and so on.

Don’t throw shade at my PV plant

Unsurprisingly, photovoltaic plants don’t perform well in the shade, but few consider just how sensitive PV panels are to shade. Research from Kipp & Zonen (producer of solar irradiation measurement instruments) estimates that hills or far shade in the horizon may result in a 4 percent loss in solar irradiance. And while hills may be hard to move there are also benefits from getting rid of shadows closer to the plant. Near shading (for example trees) may result in a 1.1 percent irradiance loss.

Much research has been done regarding production losses due to dust or dirty PV panels. Dirt especially accumulates in arid regions but even in temperate regions with regular precipitation, dirt may result in losses up to 4 percent. Therefore, cleaning of panels can be necessary. Be sure to choose your O&M partner carefully. More on this subject in this article.

White is not good

PV plants inevitably age with time resulting in dropping power output and efficiency. One very visible sign of ageing photovoltaic panels is so-called delamination. Delamination is clearly visible as milky white decolorization of the panels and results in considerable performance loss. Especially if the panels are connected in sequence with no bypass diodes, in which case even a single delaminated panel can drag an entire row of panels down.

The inverters are another critical component of PV plants where they perform the crucial task of converting the direct current (DC) to alternating current (AC) for the electricity grid. Inverters however like the plants themselves are worn with time and may result in yield losses of up to 3 percent. 

Find the right local experts to avoid yield loss 

Your best insurance against costly yield loss from your solar photovoltaic plant is your O&M partner. Their team of local solar PV experts will help you monitor output continually looking for anomalies that might indicate an issue that needs urgent attention.

Related articles

Obton lands Canadian contract of record proportions: Signs Canada's largest PPA ever

The Danish solar developer Obton has just entered into the largest Power Purchase Agreement (PPA) to date on the sale of electricity from a 170-megawatt solar park in Alberta

5 things to do to become a green company

Climate changes challenge us and are much in focus in the public debate. So how can companies make the most sustainable choices? Obton talked to Christian Ibsen, director of the green think tank CONCITO.

The green finish line is a long way off

EU member countries will have to raise the bar to achieve the common 2020 goals for sustainable energy. As things stand now, we are headed in the wrong direction. Solar PV systems could be a future solution if the EU is to reach the next climate goals.

A revolution in sustainable investments? Meet the EU’s new list

The days of making wild and undocumented claims about sustainable investments may soon be over. With its new detailed list, the EU aims to provide investors with a clear framework for assessing whether an investment is sustainable or not.