When using solar panels to generate your own electricity, the inverter has a very important function. Solar panels produce direct current (DC), just like a battery, but most of your home appliances need alternating current (AC) to operate. A solar inverter converts DC power into AC, so your electrical devices can use the kilowatt-hours produced by the solar panels.
However, solar inverters have another important function that is a bit less known – they synchronize with the voltage and frequency of the local power grid. This way, homes and buildings can switch between solar and grid power at any time, or they can also use both sources simultaneously — all without using a physical switch.
Traditional string inverters are designed to convert DC power from solar panels only, but many systems now include batteries. If you are planning to use an energy storage battery with your home solar system, you will need a hybrid inverter.
A hybrid inverter is designed to manage solar panels and batteries working together. Below we will discuss the main features you should look for in solar inverters, and we will also compare the main types available on the market today.
Choosing a High-Quality Solar Inverter
If you want to achieve the best possible results with solar power, the inverter quality is just as important as the solar panel quality. Keep in mind that all the electricity produced passes through the inverter before your home appliances can use it. You could be using the most efficient solar panels in the market, but the overall system performance will be poor if your inverter is of low quality.
When comparing different solar inverter models, you should look for the following specifications as a starting point:
- Conversion efficiency from DC to AC power
- Manufacturer warranty
Solar inverters from leading manufacturers have a typical conversion efficiency above 97%. In other words, they deliver more than 97 kWh of usable electricity (AC) for every 100-kWh produced by solar panels (DC). The following table compares several 5-kW inverters that are popular in-home solar systems:
|Solar Inverter Brand||Product||Conversion Efficiency|
|SolarEdge||HD-Wave (5 kW)||99.2%|
|Huawei||SUN2000 (5 kW)||98.4%|
|Sungrow||SG Series (5 kW)||98.4%|
|SMA||Sunny Boy (5 kW)||97.6%|
|Fronius||Primo GEN24 Plus (5 kW)||97.6%|
High-quality solar inverters have a typical service life, and they normally include a standard 5-year warranty. However, depending on the specific inverter you pick, manufacturers offer extended warranties that cover 10 years or more.
Pro Tip: Having a solid warranty is very important: if your inverter fails during the coverage period, you can get a new one for free. Make sure you contact a qualified solar installer, to ensure that solar panel and inverter warranties are not voided by an incorrect installation!
An efficient inverter with a long warranty ensures a stable power supply from your solar panels. However, there are other important features you must consider when comparing inverters.
What Solar Inverter Size Do I Need for My Home?
There is a common misconception that your solar inverter capacity should match the total wattage of your solar panels, but this is not the case. Inverters are sized with lower capacity than their corresponding solar arrays.
- You can only determine the optimal inverter capacity with a professional solar design. However, solar power systems typically have a DC-to-AC ratio of 1.25 or higher.
- For example, if a 6kW solar panel system (DC) is connected to a 5kW inverter (AC), the DC-to-AC ratio is 1.20.
- This value is also known as the inverter load ratio or ILR.
There is a technical reason to use an inverter capacity below the photovoltaic array wattage. Consider that solar panels are tested under ideal laboratory conditions, which don’t represent the actual conditions of a rooftop installation. As a result, solar panels only generate their nameplate watts during a small fraction of their operating hours.
If you install an inverter that matches the total wattage of your solar panels, it will operate below rated capacity most of the time. In other words, you’re paying for extra inverter capacity that is almost never used. You can achieve a better return on investment with a smaller and less expensive inverter, and “clipping” the occasional peaks of surplus solar power.
What Does MPPT Mean in Solar Inverter Specifications?
The best solar inverters have a feature called MPPT, which stands for Maximum Power Point Tracking. MPPT is a power optimization method that increases the electricity output of solar systems – when they are more productive, your power bill savings are also higher. MPPT technology is based on the following principle:
- Sunlight conditions are constantly changing, depending on the hour and season, and the ideal operating voltage and current of solar panels also change.
- An MPPT circuit is constantly adjusting the voltage and current of the photovoltaic array, and solar panels can deliver more electricity as a result.
Sunlight conditions also vary depending on the orientation of solar panels. For example, east-facing panels get more sunshine during the morning, and west-facing panels get more sunshine during the afternoon.
When solar panels with different orientations and sunshine conditions are wired to the same circuit, there is a negative impact on their efficiency. However, some solar inverters have two or more MPPT circuits — solar panels can be grouped and wired together based on their orientation, and the entire system becomes more productive as a result.
Traditional Solar Inverters vs Hybrid Inverters – Which Do I Need?
As mentioned above, a traditional inverter is only designed for solar panels, while a hybrid inverter can also control a battery system. The ideal inverter choice for a home solar system will depend on your plans:
- A traditional string inverter is recommended if you only want to install solar panels, and you have no plans to add batteries in the future.
- A hybrid inverter is necessary if you want a home solar system with energy storage.
Solar batteries are still expensive, and their payback period can vary depending on local incentives and electricity tariffs. If your electricity provider offers net metering with favorable conditions, you can use the local grid as your “battery” — surplus electricity from solar panels is sent to the grid around noon and subtracted from your consumption after sunset.
However, not all electricity providers have favorable net metering conditions. Some of them only give you partial credit for surplus generation from solar panels – for example, you may be charged 16 cents/kWh, and only paid 8 cents/kWh when exporting solar power. There are also electricity providers that don’t offer net metering, and all kilowatt-hours sent to the grid are lost without getting any credit.
Combining solar panels with batteries makes sense when net metering is not available, or when the feed-in tariff is very low. In this case, you need a hybrid inverter to manage the energy flows of solar panels and batteries simultaneously. The following are some other scenarios where batteries can offer an attractive ROI:
- When your electricity provider charges time-of-use tariffs, which are typically higher in the evening. With a battery, you can store electricity from solar panels and use it during peak demand hours – removing the most expensive kilowatt-hours from your power bill.
- When your electricity provider has a demand response or virtual power plant program. In these cases, power companies will offer solar battery owners an incentive for joining their program. For example, you may be rewarded for supplying electricity to the grid during peak-demand hours.
If you only plan to install solar panels, but are considering energy storage in the future, a hybrid inverter is recommended. If you install a traditional inverter, you will be forced to replace it when you add energy storage. However, a hybrid inverter can operate normally with only solar panels, and batteries can be simply connected and configured in the future.
Power Optimizers & Micro-Inverters: When Do They Make Sense?
Maximum power point tracking (MPPT) technology is available with both traditional and hybrid inverters, increasing their electricity output. However, MPPT optimizes the power output of the entire solar array, and there may be cases where you need to optimize solar panels individually. The following are some examples:
- Some roofs may have complex designs with different elevations, orientations, and pitch angles. Grouping solar panels to have similar sunlight conditions may not be possible in these cases.
- Some roofs are suitable for solar panels, but they may have shading issues at some times of the day or year. In such cases, an optimal solar panel layout may not be possible due to shading. Solar panels are connected in string circuits, and a single shaded panel affects all others in the circuit.
Power optimizers and micro-inverters accomplish the same function — controlling each solar panel individually, to maximize the total electricity output. However, each device accomplishes this function in a very different way.
Power optimizers are comparable to MPPT circuits. They are small devices that connect to each solar panel, optimizing voltage and current according to sunlight conditions.
- Power optimizers increase the DC output of solar panels, but they don’t convert it into AC power – you will still need a solar inverter for this purpose.
- Huawei and SolarEdge are two leading inverters brands offering power optimizers that are compatible with their products.
There are hybrid inverters that are compatible with power optimizers. In this case, you increase the output of solar panels individually, while adding energy storage for the entire array.
Micro-inverters can also optimize the electricity output of solar panels, while converting it to AC power. Thanks to this feature, you will not need a separate solar inverter. However, micro-inverters are not directly compatible with battery systems, since electricity has already been converted to AC, and batteries are charged with DC voltage. You will need a separate inverter just for the battery system in this case, making the project more expensive.
As you might expect, power optimizers and micro-inverters both increase the cost of a solar power system, since each panel is equipped with a power conversion device. For example, an array with 30 solar panels will need 30 power optimizers or micro-inverters. These technologies are only recommended when solar panels cannot be grouped optimally, and when their extra cost can be compensated by the increased power generation.
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