Panel Level Optimisation (PLO) explained

Jun 17, 2019 | Getting started with solar

When talking about solar power, most of us think about the black panels you see on roofs. While an integral part of a solar power system, it’s only one of the many components that make up a solar power system.

In a series of articles we’re taking a detailed look at all the different parts of a solar power system, what their function is and what you should be looking for when purchasing. This article is about Panel Level Optimisation solutions. If you’re interested in other parts of a solar power system, scroll to the bottom of the page where we list the other articles in this series.

Solar panels are like Christmas lights

Solar panels are connected in series. That means the current of every cell is passed onto the next cell in the string. Solar panels are designed that way so that the inverter receives the highest and most steady voltage possible. Old Christmas string lights were also designed this way. Every lightbulb in the string takes a little bit of energy from the total available energy to light up, and passes the rest of the energy on to the next lightbulb in the string.

When everything is working perfectly, this is a great and efficient way to get things done. The downside however is when things aren’t working perfectly. Because in a setup like the chain is only as strong as its weakest link.

In a Christmas lights that means the whole string of lights stops working if just one lightbulb goes out. In a solar power system it means that if one cell is underperforming the whole string of solar panels is limited by that one cell.

 

Bypass diodes

As one underperforming cell limiting an entire series of panels is far from ideal, manufacturers build something called ‘bypass diodes’ into their panels. A bypass diode is able to help the current go around a “blockage” in the panel, instead of having it be the limiting factor in the entire string of panels.

One typical residential solar panel has 60 cells and three bypass diodes. That means that the panel is able to bypass 20 cells at a time when they are underperforming, so that the rest of the panels aren’t affected.

Despite a large portion of these panels being in the shade, it’s unlikely bypass diodes would trigger on these panels
While this solution does help a little bit, it’s far from perfect. That is due to the fact that the bypass diode needs a certain amount of the cells to be blocked before it triggers the bypass. Depending on where the shade is being cast onto the panels, the bypass diode might not be triggered at all despite a large portion of the panel being in the shade.

(RELATED: Want to know out if you’re eligible for $2,225 Victorian solar power rebate? Check out our solar power rebate article that contains all the information you need. From the eligibility criteria to a quick step-by-step on how to claim the rebate.)

 

Available Panel Level Optimisation solutions

  • There are several PLO solutions available that are designed to overcome this problem.
  • Stand-alone DC optimisers
  • Smart panels (these have integrated DC optimisers)
  • Micro-inverters
  • Maxim smart panel optimisation

 

Stand-alone DC optimisers

DC optimisers are little boxes that mount to the back of a solar panel where it actively monitors the panel’s performance and – as the name implies – optimises the panel’s output without impacting the rest of the panels.

The reason stand-alone DC optimisers are a popular PLO solution is because you don’t have to put them on every panel you have, only the ones that will receive shade. With your average residential solar power system having about 16 panels, that can help save a fair bit of money versus other some of the other solutions.

You will often find retailers recommending them when part of your panels will be in the shade for part of the day. For example early in the morning or late in the day because of the position or angle of your roof, but also because you might have things on your roof that cast shade throughout the day, like your tv aerial.

 

Smart panels with integrated DC optimiser

Instead of having a stand-alone DC optimiser, some manufacturers build a DC optimiser straight into their panels. This solution is often a little cheaper than buying a panel and a separate DC optimiser.

The same advantages the stand-alone DC optimiser has, apply here too. A small downside is is that when either the panel or the optimiser breaks, you will have to replace both. Also, not every manufacturer offers this solution, so depending on the brand or type of panel you want, this might not be an option.

 

Micro-inverters

Inverters take the high voltage DC current generated by your solar panels and convert that into the 230 volt AC current that comes out of our power outlets. If an inverter does that for multiple panels at the same time, it’s called a string inverter (as it converts the output of a “string” of panels)

But it’s possible to scale an inverter down and have it do the same job for just one panel, instead of a string of panels. Hence the name ‘micro-inverter’.

This is a great solution with several benefits, but it has one simple downside and that is cost. 16 miniaturised inverters cost a fair bit more than a single “big” string inverter for all 16 panels.

On the plus side you don’t have a single point of failure in your system. With the other solutions, if your string inverter breaks, your solar power system stops generating any electricity. With a micro-inverter one broken panel or inverter has no effect on the other panels in your system. This can be especially important when your home isn’t connected to the grid as a back-up for example and you need the redundancy.

Another benefit for some is that you don’t have a high voltage DC current running across your roof. While modern solar power systems are very safe when installed correctly, some people prefer the added safety of having the lower current that comes from multiple micro-inverters. For example due to concerns about fire on a thatched roof.

 

Maxim smart panels

A Maxim smart panel is not the same as the smart panels mentioned before. They don’t have an inbuilt DC optimiser. Instead they do something even smarter. In a Maxim smart panel, all three of the “dumb” bypass diodes are replaced by microchips, and because these microchips are “smart” they continuously optimise one third of the panel each to get the best possible performance, regardless of conditions. It isn’t an on/off switch like the bypass diode.

Because of that, Maxim claims their smart panel is the most effective Panel Level Optimisation solution in many situations. The reason for that is that all the other three solutions still rely partially on the crude optimisation done by the bypass diode, whereas in a Maxim smart panel bypass diodes don’t exist.

Not only that, a Maxim smart panel is also one of the most affordable PLO solutions.

Maxim doesn’t make their own panels, but instead sell their chips to exisiting manufacturers to make their panels smarter. Despite there being so many advantages to these panels however, Maxim smart panels unfortunately are somewhat difficult find in Australia as some manufacturers stopped importing them after reports of interference with TV reception.

 

Do I need Panel Level Optimisation for my solar power system?

If your panels don’t get any shade and you’re not too concerned about getting every last bit of efficiency out of your panels, there is no need for optimisation.

If there’s small things like TV aerials or plumbing vents on your roof that are casting a little bit of shade on some of your panels, it’s recommended you get a DC optimiser on those panels to prevent them impacting the rest of the system.

It’s also recommended to get DC optimisers if you have panels that are in the shade when the sun is low on the horizon. Like early in the morning or late in the day. These panels might be in full sun during most of the day, but they might rob you of the energy the other panels might still be generating during the beginning or end of the day if you don’t have optimisers. Your solar power retailer will be able to map out if your panels will be in the shade at any point throughout the day.

If you have shade moving across your entire roof, for example because you have a tree or powerlines between your roof and the sun, it’s recommended to get a Panel Level Optimisation solution for all your panels. Either with a micro inverter or with a DC optimiser.

 

Panel Level Optimisation for maximum performance

You might still choose to have a PLO solution installed because you want to get the absolute best performance from your solar power system. Due to manufacturer margins between panels, panels becoming dirty and clouds, there will always be a little bit of difference in performance between each panel. By choosing to install a optimisation solution, you will be able to squeeze every last bit of performance out of your panels. Sometimes as much as 10% more.

10% better performance is not always worth the added cost of adding optimisers, so make sure to check this with your solar power retailer. If however you were already on the fence about adding micro-inverters for example, this might help you make a decision.

Another benefit of adding an optimising solution like DC optimisers or micro-inverters is that you’re able to monitor the performance of each panel individually. Most people just consider that a nice-to-have, but if this is specifically important to you, optimisers are the way to go.

The final benefit is that PLO solutions like micro-inverters of DC optimisers add another layer of safety. Modern solar power systems are already incredibly safe when installed correctly, but by design, a micro-inverter or DC optimiser will improve safety even further by automatically shutting down a solar panel completely in the case of a fault.

Out of all the solutions available, a micro-inverter is considered by most to be the best available PLO solution. Unfortunately the benefits provided by them comes at a cost. For an average system of about 6kW micro-inverters can be as much as 40% more expensive than a regular string inverter.

 

Other solar power components explained

Solar power battery storage

Battery ready solar power system

 

MySolarDirect aims to empower and educate consumers with the right knowledge about solar power and help them to find the best product to suit their individual needs. We assess and review all installers we recommend and only work with providers who meet high standards of experience, customer satisfaction and quality.

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