In an off-grid solar system, it is advised to design it with some redundancy. Multiple inverters can be an ideal way to balance the solar power generated by separate solar arrays or optimize the AC-loads to the inverters optimally.
It is better to have two or more inverters linked and managed centrally than to have one large output inverter running below 50% power load. Solar inverters operate best when the AC-load draw on each inverter is between sixty to eighty percent of the maximum rated inverter power output.
Installing multiple inverters on your solar power system has numerous advantages:
- More cost-effective than one large inverter
- Provides redundancy in case of an inverter failure
- Allows the AC-load per inverter to be optimally managed
- Allows for split-phase connection to the load control panel
- Allows for modular expansion of the solar power system hardware
Let’s review how to plan your solar system for modular development and built-in redundancy.
Multiple Inverter Based Solar Power Generation Systems
Intuitively one would think that a single large inverter would serve you better than two or more inverters. One 10kW inverter should surely cost less than two 5kW inverters and take up less space to install. This is somewhat true, but there are significant drawbacks.
The cost of power inverters would only constitute about 9% of the price of a solar power system. Trying to save money by limiting the number of inverters to only one is not an intelligent decision. You should plan to grow your system in a modular manner if you cannot afford to do a total installation upfront.
Two 5kW Inverters
Inverters in the 5kW output range are the most prevalent in domestic installations and, therefore, the most cost-effective installation. Instead of installing one 10kW inverter, installing two 5kW inverters in your system would be more advantageous.
- The operational efficiency of an inverter is between 95% and 98%, depending on the state of charge of the battery bank and the AC-load draw on the inverter.
- When the inverter is loaded to between 20% to 80% of the maximum rated design output, it operates optimally.
The operational lifespan of the inverter is also optimal when it is run at 80% of the maximum rated design output. Running an inverter at peak output for extended periods will lead to overheating the components and the cooling fans running continuously, leading to premature failure.
Inverters have a much shorter lifespan than solar panels, charge controllers, or battery storage systems and will thus fail first during the system’s operational life. A single inverter in the system will result in the entire system going out of operation when the inverter fails.
Having two or more inverters in the system provides the redundancy required to allow one inverter to fail or be serviced with no adverse impact on the AC power supply to the loads. It is unlikely that two inverters will fail simultaneously, and it is a great way to ensure an uninterrupted power supply.
Inverters connected in parallel should ideally be the same make and specification and be designed to communicate with each other. Such an arrangement will allow you to program the inverters to operate efficiently.
The AC loads will be shared between the two inverters to allow each unit to perform at the best possible efficiency.
In the event of an inverter breaking down, the second inverter will be able to continue providing power to some critical appliances in the house.
Inverters can also be connected to the load control panel in parallel with each inverter supplying one phase of AC power, and when combined, the two phases can be synced to a 240V AC output.
Start Small and Expand Array and Inverters
Investing in a solar-powered future for your home does not have to be done in a big bang approach. You can start with a simple solar array and grid-tied inverter and start learning how much you can save without investing too much capital upfront.
As you become convinced of the reliability and cost-efficiency of solar, you can expand your system by investing in additional solar power generation capacity and a power storage capacity.
You can add solar panels, charge controllers, inverters, and batteries as you become better acquainted with solar power’s benefits and freedom.
If you have the conviction to invest in a complete solar system upfront, it will still be prudent to design a built-in backups (redundancy) system.
Separate Solar Inverters For Separate Solar Arrays
Individual solar panels in a solar array wired in series can limit the power generation performance when one or more panels are shaded.
To overcome this problem, solar panel arrays should be wired in a pattern where the entire array receives optimal exposure during the same time each day.
Suppose there are areas of the roof that will be partially shaded during some portion of the day while other areas enjoy total sun exposure. In that case, it will be wise to wire such solar arrays to dedicated charge controllers or inverters.
Separate solar arrays must be connected to a single inverter or charge controller to ensure that the maximum amount of incident solar energy is converted to output power.
Constant Strength – Amperage
Solar panels that are connected in series will generate the sum of the voltage potential of each solar panel at a constant current strength (Amperage). Solar panels connected in series will create the sum of the current strength of each solar panel at a constant voltage.
Similarly, inverters can be linked to the load control panel in parallel to provide the sum of the current output generated by each inverter. Some essential appliances can be wired to continue running at the load control panel while other loads are shut off if the power is insufficient to sustain all loads.
Designing redundancy into the solar power supply system will help you maintain power supply to critical loads if a component in the system breaks down or needs maintenance.