This question shows foresight because many people end up expanding their solar power systems. There are many good reasons to expand your solar power system, and each reason will dictate which components are critical. You can make your solar power system expandable by choosing components that give flexibility, and by over-sizing them. In this article, I will explain in more detail how to apply this to your solar power system.
Use a hybrid inverter.
There are 3 main types of inverters:
Grid-tie inverters
Off-grid inverters
Hybrid Inverters (also called multi-mode inverters)
Grid-tie inverters interface with the grid, which allows them to take power from and sell power back to the grid. Their downside is that they will only produce power if they sense power from the grid. So with grid-tie inverters, loss of grid power will cause a power loss in your home.
Off-grid inverters cannot interact with the grid, so they work best in off-grid solar power systems. With these systems, you need multiple days’ worth of battery power to deal with cloudy days and other contingencies. The enormous investment in batteries makes off-grid systems the most expensive systems for their size.
Hybrid inverters can use power from the grid to charge batteries or power your home. They can also sell excess power from the solar panels or the battery back to the grid. Also, if the grid goes down, they can isolate from the grid and power the house’s critical loads in an off-grid mode. This flexibility allows you to expand your system’s grid independence and energy security. You can start with a smaller battery bank than with an off-grid system. You can then expand the battery bank as your budget will allow. It also allows you to increase the number of items on your critical loads, so you will have more things powered during a blackout.
Use a powerful inverter.
High-demand AC loads need a lot of power, and the inverter has to deal with them. An oversized inverter lets you expand the loads without a problem. The inverter’s continuous and peak power should be greater than the continuous and peak loads, respectively. If you plan on getting more electrical appliances in the future, then account for those when sizing your inverter. An oversized inverter also allows for more solar panels. This allows things like quicker battery charging and better solar collection on cloudy days.
To size the inverter, combine the wattage of all the appliances and lights you plan to own. When you do, account for:
The continuous and peak wattage of appliances with motors
Any appliance with a heating element
Make sure the inverter wattage exceeds the load wattage by a wide margin.
Use stackable inverters.
A stackable inverter lets you add other inverters of the same type to multiply the power output. It helps if the new loads exceed the inverter’s power output. This can happen if you switch to an electric water heater or if you get an electric vehicle charger. It is cheaper to add an identical inverter than to discard the inverter for a more powerful and expensive one.
Use an oversized MPPT charge controller.
Unlike a Pulse Width Modulated (PWM) charge controller, a Maximum Power Point Tracking (MPPT) charge controller does not need the solar panel array to match the voltage of the battery bank. The MPPT charge controller can use a wide range of solar panel voltages for each battery bank voltage. This will give you more flexibility in your solar array configuration.
You should also use an oversized controller because it lets you add a few more solar panels in the future without getting another charge controller. When choosing your charge controller, remember to multiply the solar array voltage by a 1.25 factor for cold temperature over-voltage, and another 1.25 factor for cloud edge effect. This will prevent damaging the charge controller.
Use larger conductors than you need for the batteries.
The conductors that connect to the battery bank need to be the biggest (and often most expensive) in your solar power system because they carry the greatest amperage. Regardless, 2 sets of these conductors are more expensive than one. So, size your battery cables for future loads so you don’t need to upgrade them. This might also save money if you get a second inverter.
After you determine the total wattage of the inverters, divide that number by the battery bank voltage. This will show the number of amps the battery cable will need to carry. You can then adjust for the ambient temperature using the tables in the NEC codes. This will let you know the size of the conductor that you need.
Use a large critical loads panel.
Many people who have a critical loads panel will want to expand it. So you should get one big enough to house many circuit breakers. It should also have a high amperage capacity to handle the loads that you add later.
Choose a critical loads panel that is at least the size of the main circuit panel and has at least the same amperage capacity. Also, make it big enough to handle future additions to the load.
Use Lithium-ion batteries instead of lead-acid batteries.
It is a bad idea to add new lead-acid batteries to an old lead-acid battery bank. The new batteries will quickly deteriorate to match the old batteries. This makes it hard to expand a lead-acid battery bank. Lithium-ion batteries have internal protections that stop this from happening. So, you can add to a lithium-ion battery bank without degrading the new batteries. Lithium-ion batteries last longer too, which makes them better as a long-term investment.
In summary, here is how you can make your solar power system expandable:
Use a hybrid inverter.
Use a powerful inverter.
Use stackable inverters.
Use an oversized MPPT charge controller.
Use larger conductors than you need for the batteries.
Use a large critical loads panel.
Use lithium-ion batteries instead of lead-acid batteries.
If you do these things, you can expand your solar power system to meet future needs.