Why You Should Oversize Your Solar Array

It may seem counterintuitive to buy more solar than you need; particularly when one of the main benefits of switching to solar energy is centered around saving money. But as odd as it sounds, oversizing your solar array is the best investment. An oversize array will deliver the maximum amount of energy at the lowest possible cost to you. Allow us to explain:

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The Role of a Solar Inverter

Let&#;s get back to basics: solar panels produce DC electricity, which passes through a solar inverter that inverts it to AC electricity. AC electricity is what powers your home or business.

All solar arrays need an inverter, and inverters each have their maximum capacity &#; that is, the maximum amount of DC electricity it can invert at one time. The &#;DC-AC ratio&#; refers to your solar array size (DC) relevant to your inverter capacity (AC). For maximum production, DC-AC ratio over 1 is preferred.

When you think about how the sun travels through the sky in a single day, it makes sense that your solar panels will capture less sunlight in the mornings and evenings when the sun is low in the sky, and more sunlight in the afternoon when it&#;s shining overhead. The afternoon hours are considered &#;peak&#; production times.

A larger array of solar panels captures more DC electricity and therefore generates more AC electricity during the mornings and evenings, or off-peak times. During peak sunlight hours, your array may produce more DC power than your inverter can convert to AC &#; so the extra DC power is lost, or &#;clipped.&#;

You would naturally think that if your array is capturing more electricity than it can invert to usable energy, this just means your solar array is too big for your needs, right? Wrong!

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What is Solar Inverter Clipping?

Clipping refers to moments when your array is collecting more DC energy than it can invert, and some energy is lost. It is healthy for an array to clip during peak hours, when the sun is strong and perfectly overhead. Prime conditions don&#;t often last long, so sizing your array to clip will enable it to perform better throughout the day and the various sun conditions throughout the year.

Scixxor said:

As for the amp limit that's where I'm not so sure, I've heard of people exceeding it just fine but I'm not certain. In a separate thread, @rmaddy said that exceeding the amp limit is just fine and any excess would just be ignored/unused.

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To be clear, there are two amp limits on a solar charge controller. If you look at the specs for the EG4 EHV-48 you will see a "Max Input Current Draw" of 18A and the "Max Charging Current (PV)" of 80A.

The first must not be exceeded. Since the OP is referring to panels with an Isc of 11.5A this means the panels can only be put in series. Putting panels in parallel will exceed the max input current draw.

The latter can technically be exceeded and is referred to as over paneling but the SCC will never provide more than the rated charge current. In this specific case the SCC will max out at a battery charge current of 80A. If the battery charge voltage is 56.8V then this means the SCC can make use of up to 80A x 56.8V = W. To reach the stated 5kW max the battery charge voltage would have to be 62.5V (5kW / 80A) which is certainly much too high for LiFePO&#; batteries. But remember that the W max is what the SCC can take advantage of. You can have more wattage connected to the controller. That over paneling allows you to get closer to the W even when there is less ideal solar conditions. In cases where the panels could produce more than W from the installed panels then no more than W will be used (assuming the 56.8V charge voltage).

Scixxor said:

Okay so with the voltage you have to stay under the max VOC, going over it is how you destroy it. For both of your examples, you would be flying too close to the sun with that VOC as the lower the temperature the higher your VOC goes. In your examples, if it ever got to 25 degrees it would exceed the 500 VOC limit.

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With a Voc of 50.8V and a temperature coefficient Voc of -0.26%/ºC, 9 of the panels will be 457.2V and will exceed 500V at a temperature of about 13ºF/-11ºC. So 9 panels will only be viable if there it never gets colder than that where the panels will be located. One record cold snap could fry the all-in-one if it gets too cold. 8 panels would be the limit if there's risk of temperatures that cold.

Burnrate said:

Example two I have two sets of 9 panels in series. The two sets are in parallel so there is 457.2 volts with watts and 18 amps.

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You can't since you'll have an Isc of 23.0A, not 18A. Though I would verify with Signature Solar. The stated "Max Input Current Draw" of 18A could mean one of two things. 1) Do not exceed at all or risk killing the all-in-one. or 2) You can go over this a bit but the input current will be clipped to 18A. If option 2 turns out to be the case then two strings in parallel will have an Isc of 23.0A but will be clipped to 18A.

To be clear, there are two amp limits on a solar charge controller. If you look at the specs for the EG4 EHV-48 you will see a "Max Input Current Draw" of 18A and the "Max Charging Current (PV)" of 80A.The first must not be exceeded. Since the OP is referring to panels with an Isc of 11.5A this means the panels can only be put in series. Putting panels in parallel will exceed the max input current draw.The latter can technically be exceeded and is referred to as over paneling but the SCC will never provide more than the rated charge current. In this specific case the SCC will max out at a battery charge current of 80A. If the battery charge voltage is 56.8V then this means the SCC can make use of up to 80A x 56.8V = W. To reach the stated 5kW max the battery charge voltage would have to be 62.5V (5kW / 80A) which is certainly much too high for LiFePO&#; batteries. But remember that the W max is what the SCC can take advantage of. You can have more wattage connected to the controller. That over paneling allows you to get closer to the W even when there is less ideal solar conditions. In cases where the panels could produce more than W from the installed panels then no more than W will be used (assuming the 56.8V charge voltage).With a Voc of 50.8V and a temperature coefficient Voc of -0.26%/ºC, 9 of the panels will be 457.2V and will exceed 500V at a temperature of about 13ºF/-11ºC. So 9 panels will only be viable if there it never gets colder than that where the panels will be located. One record cold snap could fry the all-in-one if it gets too cold. 8 panels would be the limit if there's risk of temperatures that cold.You can't since you'll have an Isc of 23.0A, not 18A. Though I would verify with Signature Solar. The stated "Max Input Current Draw" of 18A could mean one of two things. 1) Do not exceed at all or risk killing the all-in-one. or 2) You can go over this a bit but the input current will be clipped to 18A. If option 2 turns out to be the case then two strings in parallel will have an Isc of 23.0A but will be clipped to 18A.

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