Solar PV layout and how it affects performance

In his latest article for Installer, Mark Allison discusses variations in solar system layout and the impact on performance.

March already! Writing these monthly articles is an even stronger reminder of the ever faster passing of time.

But it brings an exciting period for my solar PV friends, the sun is rising in the sky and systems start to deliver ever larger volumes of power from the sun. We now have a reasonable collection of completed systems and data pool to draw into. It’s interesting to see how orientation and pitch play such a vital role in system performance. Secondary only to the actual sunshine!

I wanted to run through some examples of the variations in system layout and how that can affect performance. It can sometimes also alter how we propose to install based on the occupier’s lifestyle and consumption.

The below examples show how things can move around even with very similar system components. To keep things understandable for any non electricians reading I will base it in units of electricity rather than power ratings. This is in essence what you can take away from grid consumption and as a rough guide most households use around 12-20 units per day. Unless things like EV charging and heat pumps are in use.

For example, we have 3 similar sized systems but with very different layouts. Firstly, we have 14 x 435W panels at a 35-degree pitch pointing perfectly south. This system is already pumping out 25 units plus of energy on sunny days. Even in late February/early March. Set on a cliff top in Scarborough with no shading it is about as perfect conditions as ever will be possible in the UK. However, the bulk of the generation occurs between 11:00-14:30 which makes the battery super useful in collecting this to use throughout the day.

The 2nd system is slightly smaller with just 12 panels but at a stronger pitch of 46 degrees, again south facing. It was a steep one! At the moment it is getting towards 18 units of energy but held a strong output through winter of a steady 5-10 units in bright conditions. Aided no doubt by its pitch, which won’t help it so much in the peak of summer. This one is in the Midlands and the occupier has a pretty high base load thanks to a hot tub. Much of the generation is self-consumed with the battery utilised for cheap over night charging. Again, the peak generation occurs through midday due to the south orientation.

The final example is a recent one with a flat roof mounted system of 12 x 435W panels split east to west at 10 degrees pitch. Data on this is less easy to analyse as it’s one week old. However, on the sunny day we had it produced 15 units which is to be expected due to the pitch and orientation of the system. Most interestingly is the longer window of generation due to the east/west split. This is particularly useful for early morning and late afternoon/evening production. Say when people return home from work and cook/wash etc. Rather than storing power in a battery or exporting large peaks of production you see a bell like curve of generation which can be really helpful. This system should do better and better as the days get longer through to summer. Rather than a tall peak through midday the generation is consistent and holds a steady peak from 10am to 4pm thanks to that east west split.

Winter generation

The main take away from all the data is that generation still plays a part even over winter. At my own home with a pretty shaded outlook thanks to the trees and sun staying low in the sky I still saw 2-5 units of generation per day over deepest darkest winter. Of course, far below the 40-unit peak of summer but still useful. It is a misconception solar systems shutdown for winter but it’s really important to keep system owners’ expectations in mind. We had a recent enquiry from a customer who believed the system would output to its max in the hours of daylight. Sadly, that isn’t how it works.

Something else that plays an important role is temperature. You would think the hot and sunny July/August days would provide the best potential for maximum generation. However, its often early May that comes out very strong. Because of those cooler temperatures. Solar panels perform better the cooler it is. So, a bright May day at, say, 12C could outperform an August day of 35C quite considerably in some cases.

For those entering the solar PV space it’s something else to learn and understand as system proposals are so important. Taking into account system owners’ lifestyles, expectations, roofs available and lots more we have to come up with the best fit which also works inside the client’s budget.

I often get asked about the proposal aspects and we use software from EasyPV and Open Solar to help. So many options in terms of equipment and layout are available it can become quite complex.

That’s before we even get into dealing with the DNO on G99 applications, hand over packs and the actual installation itself.

My take away comment would be don’t forget to measure roof pitch. It plays a vital part in the output predictions. A shallow pitch is great for summer while a strong pitch better for winter (south facing). Over the course of a year it can have a varied but impactful consequence to overall generation.

I will end this month’s article with a reminder about InstallerSHOW 2024! Details will be all over the website, but it would be great to meet as many as possible during the event on the 25 to 27 June at the NEC in Birmingham. Get yourself registered and come say hello. It is bigger than ever and well worth a visit in your 2024 calendar.

If anyone would like to suggest topics for future articles, please reach out on social media or via the apprentice 121 website.

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