Is it good to oversize a solar PV Array?

What is Oversizing PV Array?

Oversizing PV arrays involve installing a rated DC power that is larger than an inverter's AC output.

Oversizing can be valuable for system designers seeking to deliver maximum energy at the lowest possible specific cost, but there are important factors worth considering before deciding whether or not it will work best in your particular situation.

Oversizing a PV array can be an excellent option, but remember that the system is only as good as its weakest link.

Inverters and controllers need to be sized according to what they will deliver at their best efficiency levels or else you could end up with major power losses on your hands.

Why Oversize your PV Array?

Use the inverter's AC output to its full potential.

PV modules are designed to operate efficiently under specific conditions. PV module ratings include power, current, and voltage at Standard Test Conditions (STC), which is defined as 25° Celsius with an air mass of 1.5 and 1000W/m2 insolation levels.

A PV module will rarely be subjected to these conditions under real-world operating scenarios.

Operating conditions can vary throughout the day and temperature greatly impacts a module's output power, as with higher temperatures come lower voltage and decreased wattage.

Solar panels produce less power when it is too hot out. In fact, at solar noon on a sunny day the average panel would only be outputting 77 of its rated 100kWp because they are operating above 25C.

If you buy a PV array that will never produce the rated amount of power, sizing an inverter to match its typical peak output can help you make better use of your AC capacity.

Reduce the specific cost of delivered energy

Oversizing a PV array can decrease the cost of delivered energy (lower $ or €/kWh) but may increase the upfront investment spent on PV modules and array racking for a system.

However, because this can be accomplished without necessarily increasing the quantity or rating of other balance of system components, the increased energy production can be accomplished at a lower $ or €/kW installed cost.

As a result, the specific cost of energy delivered by the system is reduced.

As a result, the specific cost of energy delivered by the system is reduced. For instance, by oversizing a PV array with a 5kW inverter, the annual energy yield of a system can be increased by more than 28% for only a 10% increase in total installation cost.

It is important that your calculations are done accurately in order for you to stay within budget while maximizing energy production.

Reduce inverter costs

Oversizing a PV array allows its DC energy output to better match the rated AC power of an inverter.

This means that a lower AC rating (and thus a lower cost) inverter can be used. As a result, the relative cost of inverters relative to the total system cost can be reduced.

Minimize space requirements for inverter installation

Inverters need to be installed in a location that is not always ideal for the user. In this case, regulations and the owner's preference may make it difficult or impossible to install as many inverters at one site as would otherwise be desired.

A solar inverter needs to be installed on an exterior wall where it will not receive direct sunlight. It is best if the area only receives indirect light or partial shade.

A solar inverter should not be installed inside any living spaces, such as closets, garages, attics, or basements.

Maximize the daytime energy potential

The value of daytime energy from a PV system for a business with normal working hours may differ depending on individual circumstances.

The solar output may be used to offset peak-capacity grid charges or simply to avoid constant loads at your site during this time.

Oversizing a PV array in such cases may provide a business with greater energy cost certainty, particularly given the low price of PV modules on the market today.

By oversizing a PV array, the inverter will hit its rated AC capacity earlier in the day and operate at that capacity until late in the afternoon.

Better match the PV array with the inverter in case you want to replace inverter.

It is not always possible to replace an inverter that is no longer under warranty with the same model inverter.

It may be necessary to purchase and install an inverter with a different AC output power in such cases.

The existing PV array could be better matched to the inverter's capacity by installing an inverter with a lower AC output power, and the system owner's replacement cost could be reduced.

Better utilize East-West PV arrays

PV arrays are often angled towards the equator to optimize energy production (north-facing in the southern hemisphere and south-facing in the northern hemisphere).

However, the array plane available for installing PV modules under these ideal orientation conditions may not always be as large as other less ideal array planes.

In circumstances where the area usable for east and west-facing orientations is larger, a PV array can be divided into east and west-facing strings.

Since the output power of an east and west PV array peaks at various times of the day, it is possible to significantly oversize a PV array (e.g. install a DC input power equal to the inverter AC output power for EACH of the east and west PV arrays).

Using the sizing capacity of an inverter in this way will result in higher overall energy production and more consistent AC output during the day.

How to Oversize your PV Array?

A lot of people wonder the answer to this question: Is it fine to install more solar panels than your inverter is rated to handle?

It is totally alright to install more panels on your roof than your inverter can handle. Assume you have a 3-kilowatt inverter. It made sense to install solar panels capable of producing 3 kilowatts of energy.

In fact, it is encouraged to install more solar panels on your roof than the capacity of your inverter.

In Australia, for example, you can add up to one-third more solar panels to your roof. So, if you have a three-kilowatt inverter, you can install panels that produce up to four kilowatts of power.

Inverters operate by drawing power from solar panels. The solar panels do not supply electricity to the inverter.

As a result, the inverter will never draw more power from the panels than it is capable of handling. So it's completely safe; in fact, you could theoretically put 20 kilowatts of panels into a 3-kilowatt inverter and be fine.

Let's face it, the Sun isn't always shining. In winter when you're dealing with overcast days and early mornings or evenings, your solar panels may not be able to produce as much energy because they don't have enough sunlight to work with.

If you've got 4 kilowatts of panels on your roof, for example, you'll be pumping out 1/3 more power than a 3-kilowatt system but you'll still be well below 3 kilowatts because the Sun isn't at its peak strength.

Also, the maximum output from your panels is obtained when it is really sunny but really cold because temperature degrades the efficiency of solar panels. As a result, your solar panels almost never operate at full capacity.

So having more solar panels on your roof allows you to generate a lot more power throughout the day.

In addition, the solar rebates are calculated based on the number of panels you have, not the size of your inverter.

You'd basically be paid per panel, so adding panels is actually very cost-effective.

Oversizing a PV array in relation to the inverter is an easy and cost-effective way to optimize solar power.

Simply put, it entails connecting panels with higher wattage ratings than your inverters rated output capacity which allows the unit to run at its full potential for longer periods of time during daylight hours.

It is important to understand the basics when it comes to over-sizing your PV arrays. This can be done by multiplying solar panel Wattage with the total number of panels in an array, for example, 16 x 250W produces a 4000 W (4kW) rated system.

To find out the size of an inverter, just look at its product label or check online. The answer is either labeled as “Rated Power” and/or P AC on the unit's own package and website respectively.

A typical 4kW solar panel produces a maximum of 4000 watts, but this doesn't mean you should get an inverter that matches the output. There are actually several reasons why it's not recommended to do so.

Consider a 250W rated panel; this panel is only rated 250W based on STC (Standard Testing Conditions), which are rarely met in real-world environments.

Temperature, weather, module defects, shading, and even local wildlife can all have an impact on panel performance.

Your solar panels may not be producing as much energy due to a variety of factors. Oversizing your system can help reduce the impacts that these factors have on production, ensuring you get more power from each panel.