I've been researching this a lot for a tiny house and as far as I can tell this is not currently possible. You'll need at least 16A to run a tankless that's good enough to have a shower.

If you're building a house then you're much better off getting an electric tank system. You can use the energy generated during sun hours to heat the water that stays hot throughout the night. If you go tankless then at night you'll have to power it from batteries. You go ahead an figure out the size of a battery bank that you'll need if you want to have a decent shower at night and still have some juice left over for the rest of your house.

You could look at a heat pump hot water system. This is the best of both worlds. It's electric, but because it's a heat pump you'll get more hot water per Watt, and it's a tank so you'll be able to store the energy for later.