How a Solar Kit Connects: with a Hybrid Inverter or a Pure Sine Inverter and Separate Controller

What each part does

The U.S. Department of Energy sums it up like this:

• The charge controller regulates the energy flowing from the panels to the battery and to whatever is running, charges it without overcharging, and many cut off the loads when the battery has been drained too far.
• The batteries store energy for when there’s no sun.
• The inverter turns the batteries’ direct current into the alternating current of your outlets.

Note that the inverter only converts: it doesn’t charge the batteries. That’s why, with separate parts, an ordinary pure sine wave inverter works perfectly well; the controller does the charging from the sun.

With separate parts: the order of connection

1. Panels → charge controller. The panels connect to the controller’s input. An MPPT is better: it harvests more energy from the panels and can step their voltage down to the battery’s (we explain this in what’s in a solar kit). In between, a disconnect so the panels can be switched off.
2. Controller → batteries. The controller’s charge output goes to the batteries, with its fuse or breaker.
3. Batteries → inverter. The inverter connects to the batteries, with a fuse or breaker and thick cables, because a lot of current flows there (we work it out in what limits each part). Many controllers also have a load output, like the one in the photo, meant for small DC devices; given how much the inverter draws, it usually goes to the battery. Check the controller’s manual.
4. Inverter → appliances. You can plug appliances into the inverter’s own outlets. If you want it to power your home’s circuits, you need a transfer switch installed by an electrician, so the house takes power from the grid or the inverter, never both at once.

Also, according to the Department of Energy, all the equipment and metal parts are connected to a ground, and a surge protector against lightning is advisable (see how to protect your appliances).

What to check before buying

• The same voltage throughout: the controller, the batteries and the inverter’s input, at 12, 24 or 48 V.
• The controller’s amps: at least the panels’ watts ÷ the battery voltage. With 2,250 W of panels at 24 V, about 94 A.
• The controller’s maximum input voltage: the panels connected together mustn’t exceed it. It’s on the spec sheet.
• The inverter: pure sine wave, with continuous power above what you run at once and a surge rating that handles the largest motor starting. See the inverter article.
• The batteries: deep-cycle or lithium, with the capacity the solar panel calculator gives you.

What if I also want to charge the batteries from the grid?

With separate parts, the controller only charges from the panels, and the inverter doesn’t charge. If you also want to charge from the grid, for example to have the battery full before a scheduled outage, you need a device that does it: a separate battery charger or an inverter with a built-in charger (spec sheets usually call it an “inverter/charger” or “AC charger”). Ask the installer which suits you.

With a hybrid inverter

The U.S. Department of Energy distinguishes inverters for grid connection, for off-grid systems or for both. Those sold as “hybrid” are usually the last kind and combine several of the parts above in one unit. But they don’t all include the same things, so check the spec sheet for:

• A built-in MPPT controller: then the panels go straight to the hybrid.
• A charger from the grid.
• Automatic switching between grid and battery.

Pros and cons, plainly: a hybrid means fewer devices and fewer cables. Separate parts let you use an inverter you already have and replace each part on its own if it fails. Both approaches work; what matters is that everything matches and a professional installs it.

Always with a professional

This article is meant to help you understand how a kit fits together and know what to buy and what to ask. The connections, fuses and breakers, grounding and, above all, any connection to your home’s wiring are work for a qualified electrician or installer. The cables between battery and inverter carry so much current that a mistake can start a fire.