Solar charge controller for rooftop systems with storage – first look at the Bluetti SolarX 4K

For anyone looking to store power from a larger (roof-mounted) solar array, the SolarX 4K could be a key component. It converts high voltages into levels that battery systems can “digest” more efficiently. It pairs perfectly with Bluetti’s own Apex 300 storage unit, and in theory, it can also work with third-party systems — assuming you’ve got the right cables on hand.

That’s also where one of our small complaints comes in: Bluetti doesn’t include the pricey DC output cables or the fuse box mentioned in the manual. Depending on your setup, that adds both cost and effort that users should factor in ahead of time. To make matters a bit more confusing, Bluetti’s own battery lines use different connectors (P090D vs P150D), which doesn’t exactly make things easier for customers. When it comes to accessories, there’s definitely room for improvement.

Bluetti told us that the necessary cables are sold separately, though the SolarX 4K is also available in various kits that each include one essential cable. For example, the SolarX 4K with a P090D cable is priced at $699.

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Most battery storage systems can only handle solar input voltages between 12 and 60 volts. The SolarX 4K, however, can take up to 500 volts, making it compatible with larger rooftop systems. It steps down those high voltages and passes the converted energy directly to a battery storage system.

That means even energy from a big rooftop array can be stored for household use — off-grid, since the SolarX 4K doesn’t connect to the power grid.

In our setup, it charged Bluetti’s Apex 300 units (or multiple in parallel) with up to 4,000 W of solar power. Without the SolarX 4K, the Apex 300 tops out at 2,400 W, so the boost is substantial.

The 7.6 kg SolarX 4K is housed in a metal enclosure with air cooling (≤ 50 dB). The bright metallic front panel is held by four hex screws with a rubber gasket underneath. While sturdy, it’s not weatherproof — it should always be installed under cover.

The SolarX 4K must be mounted vertically on a dry wall — not laid flat or at an angle. No wall plugs are included, and the supplied screws are rather short.

For testing, we connected several solar panels rated at 37.5 V open-circuit voltage each in series, giving us around 150 V input, the minimum required for the SolarX 4K. Of course, the device is really designed for much larger installations.

Only after connecting the battery can the solar panels be hooked up. The PV switch goes in between — with its positive and negative poles connected to the SolarX on one side, and the panels on the other. The panels themselves should have an open-circuit voltage between 150 and 500 V and deliver no more than 20 A.

Once everything’s wired up, close the front panel and flip the switch — the SolarX 4K powers up and starts feeding energy into the Apex 300.

The Bluetti SolarX 4K efficiently converts high voltages from rooftop solar systems into lower voltages suitable for battery storage — letting homeowners store their solar energy for personal use. However, both voltage and current limits still apply, and depending on your solar array’s size, you may need multiple SolarX 4K units to handle the load.