I live off grid with a 3.5 KW SMA sunnyboy system which is fine for us. However, in thinking about buying an ev, our system is not big enough to charge a car so am wondering if there is any system which I can take dc power from a new set of panels and directly charge the ev without having to put in an inverter to change to ac power and then a smart charger to reconvert it to dc for the ev battery?
I have never heard of a direct DC charger. This doesn’t exist, you would need a second system with battery storage to act a buffer during cloudy weather. All regular home EV chargers are AC chargers and need a minimum of 1400W to operate.
Your 3.5kW Sunnyboy inverter is AC-coupled with your Sunny Island inverter. (This converts DC to AC to directly charge your car during the day). You can just add more solar capacity using a second Sunny Boy inverter, depending on what size Sunny Island inverter you have. This is the most efficient way to charge an EV directly from solar.
It’s definitely within the realm of possibility to build a mode-4 (DC) EVSE that’d max out at 5kW but work reasonably efficiently down to 500W, and to build a controller that’d limit its power consumption to what your PV array is currently producing. DC-coupling such an EVSE to a PV array (as you would like to do) adds another layer of difficulty to the design. (As you may know, the DC output of a PV array has a wildly-variable voltage, and it’s the job of the MPPT on your existing Sunnyboy inverter to find the voltage that maximises the power output. If you don’t have an MPPT to mediate between your new PV panels and your (desired! not-yet-available!) DC-powered mode-3 low-power EVSE, you’d have a very inefficient system – you’d be better off to pay the overhead of the DC-AC conversion on a bog-standard solar inverter with an MPPT.
But, sad to say, it’s all still a pipedream… nobody is as yet selling such a system. Building it full-custom would be possible but very expensive – it’d probably be cheaper to put up 30kW of PV array and 30kWh of battery! See e.g. Innovative 30kw DC-DC EV Charger - DC Input - Ampernext
I think your best bet – especially if you live in a country such as the USA with a low-voltage (120VAC) supply – would be to purchase a mass-produced wallbox (mode 3) AC-powered EVSE that is “solar smart”. The AC charging standard for EVs allows them to go as low as 6A, which is only 600W (nominal) at Japan’s 100VAC supply, and only 720W at USA’s 120VAC. Even if you’re in a high-voltage country (at 230VAC), a solar-smart charger will run “happily” down to 1.5kW. But… you’ll need a battery backup in that system to keep the charge session running through cloudy periods. You’re offgrid already so must have some battery… but if you want to avoid draining your household battery “by mistake” when charging your EV on a partly-cloudy day, then maybe you’d want to build a separate wee offgrid EV charging system around a solar-inverter + battery that’s mass-produced for camping and caravanning. Bluetti comes mind, and indeed my websearch just now reveals that this is a selling point for them. See Can You Charge an Electric Car with a Portable Solar Panel?
You can use a solar-powered EV charger that directly converts DC power from solar panels to charge your electric vehicle without the need for an additional inverter. This type of system, often called a solar EV charger or solar carport, allows you to harness DC power generated by the solar panels and feed it directly to the electric vehicle’s battery system, eliminating the need for an AC inverter and smart charger. It’s an efficient and direct way to charge your EV using the energy generated by your solar power system.
That is exactly what I was looking for! Any suggestion as to where I might get such a device - I am in NZ.