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How do I set up a solar photovoltaic panel to get the best energy output?


This is a question that I've been asked in the field so I wanted to share it with everyone on KnowledgePoint

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The simple, and obvious, answer is ‘by pointing it at the sun’! However, this can be more involved than it first appears. The sun tracks across the sky from East to West and at its zenith (highest point, around midday)) will generally be in the direction of the equator – South in the northern hemisphere, and North in the southern hemisphere. Near the equator at midsummer, it can overtop to the opposite pole. The vertical angle of the sun (azimuth) varies through the seasons, highest at midsummer and lowest at midwinter. The midday azimuth at the equinox (midpoint between midsummer and midwinter) is the same as the angle of latitude for the location.

A photovoltaic (PV) module (‘solar panel’) will receive the most energy when it is pointing directly at the sun. Ideally, the module would track the sun east to west during the day, and tilt higher or lower during the seasons. Many plants do this, sunflowers being a great example. Tracking systems are available but these are generally expensive and inherently less reliable than a fixed mounting. It is quite simple to arrange a frame that can be raised or lowered every few months to match the season, but this adds the potential for human failure (forgetting to change it from winter to summer angle) and reduces one of PV’s best points that it is virtually ‘fit and forget’. The cost of PV is now so low that it is usually most cost effective to fit a slightly larger panel and orientate it for the best average performance for the year. The simplest approach is to mount the panel pointing towards the equator tilted at an angle from the horizontal equal to the latitude of the site. So, in Zimbabwe, this would be facing North at an angle of about 20 degrees, and in Pakistan it would be South at about 30 degrees.

If you are mounting the module on an existing structure such as a roof, it may not be pointing the right way. It is possible to set up a frame to adjust for this, but this can be quite fiddly. In general, if the main direction is within 45 degrees of the equator direction the loss of output is only a few percent. There are a couple of other considerations for the tilt. Output from the module will reduce significantly if it gets dirty. Where rain is very seasonal, it is important to clean the panel during the dry season (when there is also typically more dust). However, it is best practice to use at least 10 degrees of tilt to help self-cleaning during rain, even at the equator (with latitude zero).

The second consideration for tilt angle is how the load varies with season. In high latitudes, there is a significantly shorter day length in the winter, when a system intended primarily for lighting will have a much higher load, whilst at the same time receive a lot less solar energy as the sun ... (more)

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