Optimizer for solar panels
Do you have a solar project where the solar panels are partially in the shade? Or where the panels are not functioning optimally for some other reason? Then an optimiser helps you get the best out of each individual panel in a string. We offer optimisers from the likes of SolarEdge and Tigo Energy.
A solar optimiser is a device that can be integrated on one or all panels in a string. Its purpose is to optimise the yield of each panel in the string. The yield of all panels in a string is as high as the lowest-performing solar panel. When one or more solar panels are performing less due to shade, for example, an optimiser can bypass these module(s) so that the total string can work optimally.
Optimisation at the solar panel level allows the user to optimise the power output of each of the solar panels individually.
What is a ‘string’?
A string is a number of solar panels connected in series. Depending on the number of solar panels and the power of the inverter used, there are multiple strings.
In a string, current flows from panel 1 through to panel 2, to panel 3, etc. If one of those panels is in the shade, the current flowing through that panel is limited. In other words, any constraints experienced by one panel limit the flow of generated energy through all other panels. If one of the solar panels only operates at 60% capacity due to shade, the other solar panels in the string will also operate at only 60%. In these cases, a solar optimiser for solar panels can provide a solution.
How do power optimisers for solar panels work?
In order for end users to take full advantage of self-generated solar energy, ingenious technology is available. Most solar installations are equipped with solar panel power optimisers, which optimise the energy output of the solar panels. What exactly are power optimisers and how do they work?
Optimisers take DC power, regulate the output of the module and deliver energy to the central inverter for the final DC to AC conversion of usable energy. The optimisers increase the overall energy output of the string by consistently tracking the maximum power point (MPPT) of each individual solar module.
Who can install an optimiser?
Power optimisers are preferably installed by a professional. That way, as an end user, you are assured of a safe installation, you can claim warranty and there is also someone available to fix any malfunctions during use.
A specialised electrician installs the optimiser under the solar panels so that it is neatly concealed. There are a few different brands on the market, the best known being SolarEdge and Tigo Energy Optimisers. The method of installation varies by brand.
Maximum Power Point Tracking (MPPT)
Maximum power point tracking is a technique of tracking the operating point of PV system and extracting the maximum power output at any given working condition. MPP tracker is never an actual separate component itself but it always comes with a DC-DC converter in a PV inverter system. However, it is a very important integral part of the power optimization process.
The behaviour of PV cell can be illustrated by the characteristic curve of I-V relation. The module temperature and solar irradiance are the two most important factors on which the IV curve changes.
Now let’s FOCUS on the operating point, which can be termed as the voltage and current at which the PV module operates at any given point in time.
For a given irradiance and temperature, the output power at this operating point is given by:
When the operating point IV curve matches to the point on the maximum power-voltage (P-V) curve then it is called as the Maximum power point (MPP).
In case of electrical load, the operating point of PV array is directly proportional to the electrical load. Hence in this case to make the module to work at MPP is to force the voltage of the PV module to be at MPP point i.e. also known as otherwise the MPP is dependent upon the external factors such as temperature and irradiance i.e. if these factors change, the P-V and I-V curve also changes a bit. Therefore, these changes need to be continuously tracked so that the operating point can be moved to achieve the maximum power at any given external condition. Hence, this tracking process is called as Maximum Power Point Tracking (MPPT), with the help of MPP Trackers.
There are two types of MPP Trackers:
1] Indirect MPPT: Indirect MPPT is simple method consisting few measurement steps. There are mainly 2 methods namely Fixed voltage method and Fractional open circuit voltage method.
a) Fixed voltage method: In the fixed voltage method, the operating voltage of PV array is adjusted based on season change. In this method, MPP voltage are kept constant throughout the year. Also, this method works best where, there is a very low deviation in the irradiance throughout the different days of the year. Hence this method is not very accurate for every geographical site location.
b) Fractional open circuit voltage method: This is the most common indirect MPPT technique, used in practice. In this the value of
Where, k = constant (for crystalline silicon, the value comes between 0.70.8.
The open circuit voltage of any system can be easily carried out, therefore, changes in can be easily calculated by just multiplying with the constant k. Hence, this method is very easy to implement.
But on the other hand, there are few drawbacks. Firstly, as we are using constant factor k, it gives us a rough approximation of the MPP. So, its hard to get the MPP to the exact point as it will hover around its proximity. Secondly, each time when the system must respond according to the irradiance, for that must be measured and for this the PV modules needs to be disconnected from the load (for really short period of time). But this will ultimately result in the reduction of output power. Which also directly affects the overall efficiency of the system.
But the good news is that this drawback can be easily overcome by adding a pilot PV module to the existing system. This pilot PV will have the same specification and will get same irradiance as rest of the modules. So now, the of the system is measured on this pilot PV module and can get estimated. Therefore, without even disconnecting the whole system from the load, the operating point can get adjusted to the MPP.
2] Direct MPPT: Direct MPPT is more involved as compared to indirect MPPT as it requires measurements of current, voltage and power. Also, Direct MPPT is more accurate in terms of output, in comparison with Indirect MPPT. There are two major algorithms used for measurement, which are as follows:
a) Perturb and Observe (PO) algorithm: This method is also known as “The hill climbing algorithm”. In this method, a deviation is provided to the operating voltage of the system, it leads to change in output power. By this logic, if voltage increases, the output power also increases. But for the operating point to reach at MPP, further perturbation towards higher voltage is required. In contrast, if an increasing voltage leads to a decreasing output power, then in this case further perturbation towards lower voltage is required in order to reach the MPP. The summary of possible options of PO algorithm is given below.
Array power optimizers
In many industrial applications the DC-DC converters with high voltage ratio are required. Conventional boost converters, except for an intense duty cycle, can’t have such a high DC voltage gain. A traditional system for generating PV is either a single- or multi-string PV array connected to one or more central PV inverters. For individual PV panels the use of an AC module or micro inverter was proposed earlier. Although this discrete solution for generating PV power can partially eliminate the shadow problem, a micro inverter structure restricts the conversion efficiency of the device energy and induces high costs. A solar power optimizer is a DC-DC converter that is used to maximize the energy collected from photovoltaic solar systems. Solar modules are connected in an array in series; to generate optimum power when all modules are performing well. As temperature increases, or leaves, snow or shadow partially cover modules, the output decreases, modules heat up, and drag down the other modules’ efficiency. This causes power loss in the series. In raising the downside, power optimizers can be used. Power optimizers are DC-DC converters which are individually connected to the board. Maximum output is drawn from the modules, allowing each module to operate at its maximum point of power (MPP). It causes the whole array to generate more electricity. Power optimizers for solar applications may be similar to micro inverters, in the sense that both devices aim to isolate individual panels to boost overall efficiency of the system. A solar panel or solar cell incorporated power optimiser to shape a Smart package. In a single case, a micro inverter basically incorporates a power optimizer with a small inverter that is used on each row, whereas a centralized inverter is used for the power optimizer for the entire array. Using this hybrid approach has the advantage of lower overall system cost and reduced electronics.
Input voltage range
It is important to consider that providing many parameters for the Power Inverter is very difficult. As a matter of fact, knowing the “valued input voltage” parameter is once and for all in photovoltaic device design. It’s able to follow certain technological requirements automatically.
This figure has 3 lines, reflecting grid connection inverter efficiency when three forms of input voltages are present. It is clear that different voltages have different effectiveness. Between them, the blue line 360V has the highest performance, followed by red line 500V and the lowest performance is the purple line 250V. This conveys the message that if the string voltage is built around the rated voltage, the inverter ‘s efficiency will be very high, and the capacity to produce power will be high. The explanation for this begins with the Power Inverter principle. For the string inverter’s DC-DC-Boost circuit, the DC voltage must be boosted and balanced to some value (this is called the DC bus voltage) before it can be converted to AC power. As for the 230V production, it will have a DC bus voltage of about 360V. The DC bus voltage should be around 600V as for the 400V output. As for the 500V output, it should have a DC bus voltage of around 750V. As for the 540V production, it will have a DC bus voltage of about 800V. Nevertheless, the connected voltage of the part series is usually not that high, and the circuit must be modified. Generally, the grid tie inverter is balanced by PWM. There is a term called duty ratio, equal to the voltage / DC bus voltage component series. The duty ratio is closely linked to productivity. A higher duty ratio tends to produce smaller difference in voltage and greater efficiency. Complex equations need not be determined by the power inverter part. Simply try to adjust the string voltage to the inverter ‘s measured operating voltage, you’ll have the highest output even at the extreme low temperature, the maximum voltage will not be exceeded. Throughout operation, it will also be within the range of full load MPPT voltage which is completely easy and practical.
There are many causes of shading
According to Aurora Solar, a leading solar design software provider, “Whenever a cell or panel does not receive sunlight due to a shaded obstruction, it lowers the amount of electricity generated by that solar section. Such obstructions can come from a variety of sources:
- Nearby objects, such as trees, antennas, or poles
- “Self-shading” from other PV panel rows
- Horizon shading from the terrain surrounding the installation site
- Other factors such as panel orientation, soiling or differential aging”
Most residential rooftops and many commercial buildings have some sort of shade present. And even without any shade, mismatch can occur from soiling and varied degradation rates of solar modules. To learn more about the other causes of mismatch and how it happens, we put together this whitepaper.
How do optimizers reduce the impact of shading?
According to Aurora, “when a solar cell is shaded, the current through the entire string is reduced. This is significant because every cell in the cell string has to operate at the current set by the shaded cell. This prevents the unshaded cells from operating at maximum power. So yes, only a small amount of shading can have a dramatic effect on the power output of a solar panel.”
Solar panels are typically installed in series (connected directly with one another in a chain) and the entire string operates with the same electrical current. When one panel has shade or mismatch, it can bring down the current – and therefore the electrical output – of the entire string of panels.
Optimizers mitigate mismatch by monitoring and adjusting currents and voltage when needed. By constantly monitoring the voltage and current that are passed between each panel, optimizers can learn the average rate and quantity at which the solar panel produces energy. If it senses a change in voltage or current that is caused by mismatch, it automatically adjusts to make sure each panel operates at the string’s maximum power potential.
Optimizers in action
Let’s take a look at a case study to see optimizers working in action. Here at Tigo, we offer optimizers that also have module-level monitoring and Rapid shutdown capabilities as a packaged deal. Therefore, system owners can get a glance of their system performance to ensure everything is working properly and have peace of mind with built-in safety features.
A homeowner in San Jose, California had a PV system without any module-level monitoring, Rapid shutdown compliance, or optimization and wanted to get an upgrade to increase power output from shading on the system from nearby trees (see Figure 2). After adding Tigo optimizers, specifically the TS4-A-O, onto each of the solar panels the homeowner was able to generate more electricity than they did previously and have more visibility into their system. To quote the homeowner,
“My PV system was originally installed in 2009 and adding Tigo optimizers to my system in 2017 was a big improvement. I’m getting more than 5% more output on average per year. I am also able to see when the solar modules need cleaning, and immediately see the results of each cleaning. I get interesting monthly reports showing which solar modules are producing the most and the least energy.”
Check out the full case study here. To see the live system performance of this homeowner’s house, check out the Energy Intelligence demo.
How Tigo optimizers work
If you look at the bar chart in the demo or in Figure 3, the green tips are Reclaimed Energy that is enabled by Tigo optimizers. Tigo is the only major MLPE provider that shows customers the additional electricity that is enabled by its optimization technology.
Tigo analyzed tens of thousands of sites with optimizers installed and the optimizers improved solar production by an average of 6.6%. If you have a 10-kilowatt (kW) system, this would produce 1,156 kWh more electricity and save you more than 6,000 over the 25-year life of the project (assuming electricity rates are
Summary
Optimizers are a very popular component of rooftop solar systems to help increase your energy production and help reduce the cost of your electricity bill. For any home, investing in optimizers is an easy way to meet safety codes, enable module-level monitoring, and maximize system energy production.
To join in on discussions about solar or ask questions on solar, visit our Tigo Community page. To leave a comment on this blog, click here.
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.18/kWh and growing at 3% per year). For more information on Reclaimed Energy, check out this case study.
Solution #3: Maxim Smart panels
Maxim is a microchip company that in 2016 invented a little chip that can optimise the power in an individual solar panel. In fact, they claim that replacing the three bypass diodes in a typical module with three of their chips will optimise the power at the solar-cell-string level.
In a Maxim panel these 3 microchips replace the bypass diodes.
As you’ve already seen, a cell-string is typically a third of the solar panel. If the current is reduced though a cell due to shading, a Maxim panel will get as much power as it can from the shaded cell-string while still allowing the other two cell-strings to perform at full power.
So a Maxim Smart panel, as well as ensuring that one shaded panel will not bring down the others in a string, will under many circumstances get more power from the partially shaded module too because it won’t simply bypass a third of it, but get as much power as it can from the shaded cell-string.
The extra cost for Maxim Smart panel optimisation is about 70 per kW. Maxim don’t manufacture the panels; they sell their chips to module manufacturers – at the time of writing, Jinko Solar, Trina Solar, Suntech and ET Solar. This is the cheapest way to get panel level optimisation. The downside is that we are seeing major TV reception issues with Maxim solar panels, to the extent that Jinko have decided not to sell them in Australia anymore and Trina, Suntech and ET have gone very quiet on their Maxim panels in Australia.
So if you really want Maxim modules, you will struggle to find any in Australia at time of writing. Which is a shame because they are a great value and effective solar panel optimisation solution (for people who don’t watch broadcast TV!).
Solution #4: Micro-inverters
A microinverter on the back of a solar panel.
Micro-inverters are a totally different approach to PLO. They take all the functions of a string inverter and miniaturise it to the solar panel level. Consequently, each solar panel has its own integrated optimiser and inverter attached either on or under each individual module on the roof:
Microinverters keep everything at 230V AC. No string inverter required.
The power generated is transmitted at 230V AC (not 200-600V DC) from each micro-inverter and connected in parallel, then connected directly to your switchboard.
They are the most expensive way to get PLO but they do have these features that the other 3 options don’t:
- No high voltage DC on your roof. The whole system is 230V AC
- No central point of failure. If one micro fails you only lose that solar panel. If a string inverter fails you lose the whole system.
Do you need Panel Level Optimisation At All?
- If you have a simple roof facing 1 or 2 (or possibly 3) directions with no shade, then there is no pressing need to spend more on PLO.
- If you have a simple roof with no shade, and want to squeeze 8-12% more energy from your solar panels, then PLO can do that by simply optimising everything better (by better coping with panel manufacturing mismatch, Cloud cover, dirt etc.).
- If you have a complicated roof, with lots of roof faces and/or lots of shade objects (flues, aerials, ventilation etc.) then PLO is a good idea.
- If you only have one or two small shading objects that will only shade a handful of panels, then retrofitting Tigo DC optimisers to the affected solar panels is the most cost effective solution.
- Microinverters and DC optimisers offer panel level monitoring, so you can see the power of each module on your monitoring. If that is important to you, then get it. But in my experience it soon gets boring!
- All well-installed solar systems are relatively safe. But microniverter systems are even safer by design (no high DC voltage), and DC optimisers and microinverters both shut down the solar panels fully in fault conditions – increasing their safety. So if that is important to you, consider PLO.
What have I got? On the house I live in I chose to install microinverters. The main reason being that the house is made of straw, and I didn’t like the thought of 600V DC going through the bales. But normal people without weird homes shouldn’t be too concerned – as already mentioned, a well installed DC system is perfectly safe.
So now you know everything you need to know about solar panel optimisation, or PLO, you can decide for yourself if you need or want it and if so which flavour to get. What have you chosen and why? Let rip in the Комментарии и мнения владельцев.
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I’m a Chartered Electrical Engineer, Solar and Energy Efficiency nut, dad, and founder of SolarQuotes.com.au. My last real job was working for the CSIRO in their renewable energy division.
[What have I got? On the house I live in I chose to install microinverters. The main reason being that the house is made of straw, and I didn’t like the thought of 600V DC going through the bales.] Yep, and since 2013, I have a microinverter-based system, too. The system has never been down 100%. Plus, I built it in subsets, and now am happy with 6 strings, 20,000-Watts of AC power. In 2019, I plan on retrofitting my system to give me a 10kW microgrid, that is, when the utility grid goes down, my solar will continue to operate — powerful. From recent blurbs at the Enphase shareholder meeting, it looks like all you will need is a single IQ8 battery or IQ8 microinverter plus the addition of an IQ Envoy, and it will be able to put all of the microinverters into the microgrid. I am hopeful. I always look at microinverters 100% decentralized power topology as a Cadillac solution, plus all the devices in my home were AC, so it made sense to have AC coming off of the roof. DC arc faults are real safety hazards, and, of course, a newly installed solar PV system is perfect and powerful, but put 10 years on it in Florida tropics, and the idea of a DC arc fault is very real. AC is the way to go. Great article Finn from the Land Down Under! Cheers from the States!
The Tigo product works well, but the company is let down by an awefull warranty claim process. The amount of ‘testing’ a installer needs to do (uncompensated) to prove a fault makes it a product that is essentially a liability to an installer who offers an extended workmanship warranty. It is a shame as the product is good and the software consumer friendly.
I think Tigo is the best company I have ever dealt with in my 40 years of contracting. If there is a problem they can log onto system, troubleshoot and see if they need to do something with the software or if there is a bad optimizer. I have never had the level of support I get with them with any company selling anything. I can’t say enough good things about them.
I have a solaredge system with DC optimisers and very happy with it. One thing that seems to occur and is rarely mentioned is the effect of the house next door, shading solar panels. Logic would suggest that solar panels should be fitted high up on the roof, but all installations seem to place them at the bottom of the roof, ie close to the storm water guttering. Why is this? In my case i get shading from the roofline of the home next door in the afternoon. (I have 5 panels on west roof and 7 on the Nth in a 4kW system)
Any solar installer worth their salt should take shading into account when siting panels. So it sounds like your installer got a little salt they weren’t entitled to if they had the option of placing the panels higher. That said, all else equal, it is best to avoid placing panels close to the roof crest as wind loading can be high there. This is especially important in cyclone areas.
Most if not all solar installs i see around here do the same thing. Panels low on the roof line. We are not in a high wind area either.
If it’s a tile roof they probably wanted to steer clear of the ridge capping. You pretty much have to fix your first rail at the bottom of your third tile down if you want to avoid disturbing an old/crumbling ridge line. Customers rarely consider blokes traversing their double storey roof carrying panels, yet they will 100% notice water dripping down a light fitting on a rainy day. I’d say this is likely reasoning for a lower install scenario as most guys would prefer to panel with tiles under their feet as opposed to the single tile above a gutter line.
hi I have a solar edge system but the led screen on the inverter. Is saying there are three pins failing which I believe are the optimisers on individual panels.one had not been working for a while but was still producing sufficient kw now two more have failed and it is producing next to nothing. should this happen Regards Christopher ……uk
I get awesome efficency from my Enphase Micro system even on the crappy winter day it will register a resonable amount of Solar, looking forward to seeing how the new I.Q range Enphase Micros go ! for me the nephase may be a bit more to spend but the simplicity of the application is a winner!
I have a enphase 5.5kw system it works awesome I had one panel go faulty after 3 years and you could see the problem, as that panel had a different color on the enphase app. This panel was replaced and system is working well. We get a lot of shade from the forest close by in winter as the sun drops behind the trees so it was a no brainer to get an Enphase.
Great article, thanks Ronald. Just a couple of points to add. One advantage of micro inverters that you didn’t mention is that you can add more panels to your system very easily without having to upgrade your inverter. And an advantage of any type of PLO (I was told this by a Tigo rep so I’ll be interested in your opinion) is that, as the panels degrade over time, they tend to degrade at different rates which leads to ‘voltage mismatches’ between the panels. Apparently this is bad but PLO is good because it fixes it. Also you dismissed panel-level monitoring as something that only geeks and nerds like you an me would be interested in but I think everyone would want to know if one of their panels was underperforming and with PLO it’s easy to find out which one is causing the problem. One question, with the Maxim chips, do you get the same sort of panel-level monitoring and fault detection as with optimisers or micro’s? Cheer, Andy