PPOT Brain Trust: I have new gas tankless water heater - can I add an electric?
 

I live in Southern California and just about a year ago I installed a gas tankless water heater along with the a purpose-built battery backup. And we love it.
But since that time our. gas bills have tripled, NOT due to increased gas consumption, but due to a massive increase in what our utility calls a “commodity fee“.
Additionally, I own a 30 panel solar system which produces more electricity than we use. Historically the electric bill was always the challenge; natural gas was so cheap we rarely even thought much about it.
Here’s the question: considering our excess electrical capacity, can anyone shed some light on the pros and cons of adding a 220 V electric tankless water heater? I suppose in line somewhere with the gas unit? My house is on a raised-foundation and has a large crawlspace, so access/installation/plumbing/maintenance don’t pose many problems. We would most likely use the electric unit when it’s only my wife and I at home, but then boot up the gas unit when our children and grandchildren visit. And the gas unit would also be available if we should experience an electrical outage.
Anyways, go easy on me lol as this could be a really dumb idea, have pitfalls I haven’t even considered, etc. But who knows, maybe it’ll work. Your input appreciated.

I see no reason to not have both. Yes, it's redundant, but you make sense. Unless you install a simple switch to cut power to the gas unit and bring the electric one online, I see an auto switch as your only hurdle.

Sure. Just plumb it in to pre heat the water to the tankless unit.

Best
Les

Switch to propane?

Sound logic. Small challenge to automate it.
I'm sure you can daisy chain an eletric unit next to the gas unit....

Natural gas commodity prices are dropping. You may want to hold to see where things end up.

My dad has an electric tankless in-line with his hot water tank… surprisingly, it is unplugged and he runs off the tank.

Anywho… my only concern with an in-line system like this is if the inlet side of the downstream heater is designed to work with already hot water. You may want to consider this before you just hook stuff up at will. Maybe you go parallel with them so you can switch one side off and drain it when you aren’t using it?

The biggest gain you can get is to increase the inlet temperature of the water to the tankless, but how you do that... Using PV solar to an electric resistance heater is inefficient. But if you build/install a solar water preheating system (a mini greenhouse box of serpentine water copper tube) you will direct more of the solar spectrum energy to the water.

Otherwise, being in So Cal, perhaps look at a heat-pump style water heater. Those output cold air, as they pull heat out of the surroundings and push it into the tank. Although, keep in mind that those "hybrid" water heaters also have resistive elements that can kick in. ...perhaps that part can be easily deprioritized.

Anything that can increase the water inlet temperature will decrease the gas needed to bring it up to temp.

As others have said I would think that adding inline in front of the gas unit would work, do you have enough available current to run a decent size electric on demand?