Sizing a solar inverter - Oversizing?

Hi Amit, I’m thinking there might be an advantage to “oversizing” an inexpensive inverter that’s convection-cooled, rather than spending more on one which is fan-cooled (or has a better thermal design in some other way). I say this because my best-guess is that my five year old Goodwe NS-3000 will derate itself (perhaps by limiting its output current) when it overheats… and I think some modest level of overheating happens after a few hours above 40% or 50% of its maximum-rated power input.

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I believe it’s routine to derate power electronics when they get above 45 degrees C, to avoid premature failure.

The spec sheet on the Goodwe NS-3000 is pretty minimal with respect to its operating conditions, saying only “-25~60°C (>45°C derating)”.

This inverter is mounted indoor, pretty high up on a wall in a hallway that’s pretty well ventilated. It rarely gets above 30 degrees C at my location in Auckland NZ. The inverter runs pretty hot under even this modest loading, for example I’m looking at a day last week when its temperature crawled above 48 degrees C at 2pm – when the panels were producing about 1200W. Peak that day was 12.50pm – panels producing 1440W. My rooftop array is small: 6x Peimar 300/305WP Mono SG. The maximum they have ever produced is about 1900W, i.e. they wouldn’t overrun a Goodwe NS-2000 – unless it is derated for high-temperature operation. But I’m thinking a Goodwe NS-2000 would run even hotter when powered above 1200W than my Goodwe NS-3000 – which seems ok (albeit a bit marginal) in my installation.

All to say that I’m thinking that a convection-cooled inverter similar to the Goodwe NS line might appropriately be derated – perhaps by 30% or even 50% – even when it is run indoor in a mild climate near sea level (e.g. Auckland NZ at 300m). The idea is to avoid it ever running hot (i.e. degrading its life-expectancy by being under high load at a temperature much above 40 degrees C), and also to avoid it ever throttling itself (to avoid overheating) which will result in some of the available PV power “going to waste”.

I don’t yet know – but plan to do some analysis on 5 years of data from this installation – whether either of these “bad things” is occurring at all frequently on my Goodwe NS-3000 with an array on the roof that never produces more than 2kW.

I don’t expect to find any detailed specs on Goodwe NS-3000 thermal performance under load (as that’d depend on operating conditions e.g. ambient temperature and altitude)… but I have found a failure-rate plot for a power thyristor at https://www.darrahelectric.com/uploads/techLib/Dynex-AN4870-Effects-of-Temp-on-Thyristor-Performance__633821529348719168.pdf, which I’d guess would more-or-less applicable to the failure-prone power electronics inside the Goodwe NS-3000.

Amit, can you perchance point me at anyone who has analysed the operating performance of the Goodwe NS-3000 at all carefully, or point out some mistake or misunderstanding in what I wrote above?

As the world is following the process of sustainable development, the invention of Solar Panels is a revolutionary change. Bothering about solar energy is something that is a renewable, affordable, and inexhaustible source of energy. It is believed that – Solar energy is a cheaper source of energy that can be wasted, and we are doing the same thing. Therefore, it is analyzed that this is the high time to begin utilizing solar energy. Solar energy is available in abundance.

From the investment perspective, investing money in solar energy is a significant one-time investment. The continuous use of solar energy has resulted in the reduction of consumption of electricity, which directly affects the electricity bill. The availability of solar energy is in abundance, so it can be seized and used in several ways.

Have you ever heard about solar inverters? Let us know about the solar inverters.

This renewable resource requires convertible equipment to put this energy into proper use. Therefore, the need for an inverter gave birth to solar inverters. Solar inverters are the essential elements of a solar panel system.

The energy absorbed from the sun is stored in the batteries in the form of direct current (DC); later, this stored energy is further converted into electrical energy, which is named alternating current (AC) with the help of solar inverters. In simple words, solar inverters are used to convert the variable direct current and alternating current so that they can be utilized as a power supply. All electrical appliances run on ACs, and therefore these inverters play a very vital role in the utilization of solar energy.

If a person or community wants to use solar energy as their main source of energy, then solar panels need to be installed along with solar inverters. Prior to the installation of solar panels at your home, it is mandatory to choose a size for solar inverters. The size of the inverter is an important matter of consideration.

Why is the size of the solar inverters a matter of consideration?

The variability of the solar inverter is determined by its size. The size of the inverter plays a significant role in overall electricity production, and as a result, it affects the supply of the solar inverter.

The DC rating of the solar panel determines the size of the inverter. It is important because, in the solar panel converter, the capacity of the inverter should be capable of handling DC electricity.

The installation services come with guidelines, and it is the role of the vendor to train their clients about the dependability of electricity supply on solar inverters.

How do you determine the size of the inverter?

In the market, solar inverters are available in differentiated sizes. The ratings of the solar panels are made in Watts. In the same way, a solar inverter is also rated in Watts and symbolically represented as (W). The solar energy system will be producing and transmitting DC electricity to your inverter, so there is always a requirement for an inverter that can handle the load and convert it to AC power. This tells the appropriate necessity of the solar inverter.

Given below are the factors that determine the size of the inverter.

Geographical Factors

Geographical Factors play a vital role in sizing your solar inverter due to their impact on the production of solar energy. The locations that have high temperatures are expected to have a large amount of solar radiation. Thus such a type of area generates more electricity as compared to an area with low temperature.

These areas vary in temperature and solar radiation; they will produce different amounts of DC at a particular time.

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Under typical weather conditions, the solar inverter is likely to produce maximum output with its listed DC ratings.

Site Conditions

Another major factor to consider is the location. Solar PV inverter sizing is influenced by the solar array’s design and area of installation. The tilt of solar panels directly impacts the amount of electricity produced.

Other weather conditions like dust or moisture are also liable to affect the electricity production in solar panels. These are the major factors that act as a problem in the pathway of the sunlight that reaches the array.

The installation of solar panels comes up with equipment efficiency to overcome these hindrances. But these factors affect the production of electricity.

Size of Solar array

The size of the solar inverter is a major consideration. The inverter is liable to handle the electricity generated by the DCs by the solar array.

The inverter must have a similar size as the DC rating specified on the solar panels. For instance, when installing a 6-kilowatt solar energy system, the inverter must be 6,000W, give or take a few watts.

The size requirements for inverters are listed on the product sheet of the solar panel. The capacity that can be handled by the inverter is also listed there. Always keep in mind that using the incorrect size will diminish the warranty scheme.

Solar inverter sizing guide

The efficiency of the inverter drives the efficiency of a solar panel system as the role of the inverters is to convert Direct Current (DC) into Alternating Current (AC). These are utilized by the electric grid. This leads many to wonder what effect over-sizing or under-sizing an inverter can have. This type of entry helps the users to make better decisions with regard to their current or future solar photovoltaic installation.

The inverter used in the solar systems is optimally functioning within a predetermined operational ‘window’ (usually laid out in the inverter’s specifications) as the power generated by the system’s solar panels keeps on fluctuating. The ability of the inverter to convert its energy from DC electricity to AC electricity differs with factors. The inverter will operate optimally as long as the input from the panels falls under the range of the window.

Here we have mentioned a graph to clarify the concept. The graph depicts the red line representing average inverter efficiency, and the green arrow highlights the power output from your solar panels. The gray box shows the operational window of the inverter based on the input from the solar panels and the predetermined efficiency of the inverter. In such a scenario, efficiency is less than 83%, which would be considered ‘suboptimal’. Here the system must be sized to minimize the amount of time during the day that the inverter operates within this range.

Undersizing solar inverter

In order to understand the concept of Under-sizing your inverter, let us consider the above-mentioned graph. Under-sizing your inverter states that the maximum power output of your system (in kilowatts – kW) will be determined by the size of your inverter. Regardless of the output of the solar panels, the power output will be clipped by the inverter so that it does not exceed the inverter’s rated capacity like 3kW, 5kW etc.

The installer suggests an undersized inverter if they determine that the amount of incident solar irradiation (sunlight) on your panels will be lower than expected. This is all because of your area of location & climate, the orientation of your panels, and other factors.

Inverter under-sizing is understood as ‘overclocking’. The concept has actually become a common and widely accepted practice in countries like Australia. One of the largest inverter manufacturing companies is SMA which is a respected name in the industry.

Under perfect conditions, the maximum power output of a solar system will be clipped back to the inverter’s output through overclocking through the middle of the day. They can also be profitable in the overall amount of energy (kilowatt-hours – kWh) generated. The production gain is aroused from additional energy being produced in the early morning and late afternoon as a smaller inverter will turn on sooner and off later and operate more efficiently with lower DC inputs.

As per the Clean Energy Council rules for accredited installers, the solar panel capacity can only exceed the inverter capacity by 33%.

Oversizing solar inverter

Installing an inverter whose maximum capacity is greater than the nominal capacity of your solar panel array might be the correct option to go with if you are planning to expand your solar panel array in the future. The situation is not recommended over the globe. The overall energy yields from your solar system may be less than a perfectly-sized or under-sized inverter when they are oversized.

The inverters are designed to handle lower power inputs than their nominal capacity. One must raise a query to the installer about how your system will perform with an oversized inverter. The query may include- how would your overall energy yield be differentiated from the next 5-10 years with an oversized inverter v/s a ‘right-sized’ or under-sized inverter? Balance this against the cost of the various system configurations before making your final decision.

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