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What are MPPT controllers Steca Solarix MPPT

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MPPT controllers

Maximum power point tracking (MPPT) for PV arrays is the newest feature being integrated into many wholehousecharge controllers. PV modules’ voltage and current vary throughout the day depending primarily on temperature. MPPT uses a mathematical algorithm to “track” the optimal point of production of a PV array to maximize annual energy generation.

In most locations and applications, an MPPT controller will increase the annual output of your PV array by about 15 percent. Hot climates (like Palm Springs, California) will see a smaller increase in energy gain compared to colder places (like Denver, Colorado) because PV voltage decreases as the module temperature increases.

Here’s an example of why MPPT controllers are beneficial. It’s a cold winter day and your batteriesare at a relatively low state of charge and voltage (12.3 VDC). Let’s assume that the array is rated for 34 amps at 17.5 volts. Because it’s cold, the array’s maximum power point is actually 19.5 volts. A non-MPPT controller will operate the array at the batteryvoltage, in this case about 12.3 VDC. The array amperage may be a little higher at the lower voltage, say 36 amps. So in this example, the total wattage charging the batteries is 443 watts (36 A x 12.3 V).

If you use an MPPT controller, the array will operate at its maximum power point, producing 663 W (34 A x 19.5 V). Even if the charge controller is only 95 percent efficient, it will still deliver 630 watts to the batteries, an increase of 187 W compared to a non-MPPT controller.

As the array heats up, and the battery voltage rises during the daily charging cycle, the additional energy harvested by the MPPT controller will decrease. In the summertime, the array will be operating at a high temperature and its voltage will be relatively low.In addition, the batteries will typically be at a higher state of charge due to long sunny days. Under these conditions, the performance of an MPPT controller and non-MPPT controller may be about the same. But the bottom line is that an MPPT controller will increaseyour PV array’s annual production, especially during the short sun days of winter. The MPPT controller may cost $600 instead of $200, but that additional $400 gets you increased energy harvest when you need it most, year after year, and can often be offset right outof the gate by decreased wire and installation costs.

Another reason to use an MPPT controller is that nonstandard PV modules are becoming more common.Many modules designed for grid-tied PV systems are no longer being made with the industry standard of 36 or 72 cells. Panels with 40, 42, 60, or other numbers of cells are becoming more common, and some new technologies produce higher voltage per cell. An MPPT charge controller can easily convert an odd voltage array into a usable array for battery charging.

Matching PVs for MPPT

I would like to add to my solar-electric array and get a larger battery bank. My charge controller is a dutiful Heliotrope CC60, but since it is older and may fail, I am looking at the newer MPPT charge controllers. What are the panel specifications that need to be closest to allow a MPPT to function best? I cannot add more of the same panels to my old rack. Of course I am looking at brand name and cost per watt. Do I choose based on amps, voltage, or the shape of the power curve? What about the same panel-mixing situation while using the old controller? Thanks as always.

Adding an MPPT controller to an existing system is a very popular upgrade these days as people improve and expand their systems. MPPT controllers will get the most out of your PV array, and actually are more beneficial in off-grid applications because they produce the most benefit in the cold winter months when the batteries tend to be at a lower state-of-charge—right when you need the energy the most!

Using an MPPT controller with old and new panels can be done, but there are some limitations. The basic idea is to match the new panels as much as possible with the old ones to ensure that you get the maximum power from both sets. Using an MPPT controller that does a “true” MPPT routine, where it varies the operating voltage to find the maximum power point, is recommended. Some MPPT controllers just operate at a fixed ratio from the open circuit voltage, which is not ideal when the PV array is made up of different panel brands or ages.

The basic idea is to make sure the different PV modules have the same number of cells in series and are the same type—single crystal or polycrystalline. Do not mix brands of PV modules in series. Only connect series strings of the same PV modules in parallel with series strings of different PV modules.

You should also consider increasing the voltage of the PV array when doing the upgrade, to reduce the losses in the wiring between the PV array and the step-down-type MPPT controller. Some brands allow the array to be wired as high as 72 VDC nominal (six, 12 VDC PV panels or three, 24 VDC PV panels in series) and still have a 12 VDC or 24 VDC battery system. This can save you a lot of time and money because you may then be able to use the existing wire. With the voltage doubled, tripled, or more, the losses can actually be reduced while the wire is carrying higher power. Sometimes the savings in replacing the wiring can be more than the cost of the new MPPT controller, so the upgrade is “free” and you still get the MPPT benefits.

Mixing brands of PV panels with a non-MPPT controller can be done as well. In some ways, these controllers are more tolerant of performance differences in mixed arrays. But using a non-MPPT controller results in reducing the overall performance of the panels, which means less energy produced.

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