Replies

1. 
   charlie_sullivan | May 04, 2021 12:01pm | #1

   It's an interesting concept. It wouldn't have made sense 20 years ago when PV was super expensive, but now it could make sense. From a quick look, considering just the solar thermal collectors vs. the PV modules, PV costs only about 1.5X as much as solar thermal. Then you have to ask about the balance of system costs in either case: pumps, heat exchangers, plumbing, etc. in one case, vs. this inverter and the wiring in the other case. It's hard to say without this having a cost listed for this product. But one good thing about the PV option is that it's probably lower maintenance--it's certainly never going to freeze.

   Here's a company that has a similar product and sells you the full PV water heating system--or a solar thermal system. They are about the same price. http://www.thermo-dynamics.com/products.html#PVsolarboiler

   You could also consider a system in which PV drives a heat pump water heater, and modulates the speed of the heat pump according to the PV power available. It's probably better, however, to connect both pieces of equipment to the grid, so you can sell your excess PV to the grid once that water is hot. You could have some smart controls to favor heating water hotter than needed before starting to export electricity to the grid. I expect that kind of thing, perhaps with even more utility interactive controls, will be the future of solar water heating.

2. 
   joshdurston | May 04, 2021 12:43pm | #2

   I think it makes more sense to have the inverter capacity generally usable rather than associated with a specific load. If you have DC, it probably makes sense to use DC elements as a diversion load for when the batteries are charged to avoid putting a lot of continuous load on AC inverters with a big resistive heating load.

   Solar direct (no grid/no batteries) is interesting, I just think it makes sense to install all your panels and inverters to be as flexible as possible and not just useful for DHW. This might be an old way of thinking though since panels are getting so cheap.

   That product looks a lot like this one (seems expensive for what it is though):
   https://practicalpreppers.com/product/acdcx-asymmetric-inverter/

1. 
   charlie_sullivan | May 04, 2021 11:04pm | #6

   Interesting link. It looks like hotspot energy, the parent company of Chiltrix, is rebranding a diffferent model CyboInverter for a slightly different use case. Their page:

   https://www.hotspotenergy.com/convert-air-conditioner-to-solar/

   CyboEnergy has range of different versions for different use cases:

   http://www.cyboenergy.com/products/productsoverview.html

   I was hoping it would be inexpensive, because you don't need a sine wave for a water heater element, but it looks like it's pretty expensive.

3. 
   rockies63 | May 04, 2021 09:34pm | #3

   Josh, I first found the Cyboinverter on the Practical Preppers {Engineer775} Youtube channel.

   https://www.youtube.com/watch?v=LmMsTN8b9Hg

   He found the Cybo after he couldn't find some other brand being sold anymore. It might have been the product you mention.

   Since heating water is such a heavy load for a PV system I think it makes sense to remove heating DHW from your battery backed PV system and have it run on its own, much like some people put a well pump on a separate PV system.

   I would still use a battery backed system for lights, appliances, etc but I'm betting that the battery bank would have to be a lot smaller without the DHW load on it.

   I wonder how their Cyboinverter would manage an induction stove?

1. Expert Member
   NICK KEENAN | May 04, 2021 10:47pm | #4

   It wouldn't work with induction stove and would be ill-suited if it did. The whole idea of this is that it's a way of storing energy that is intermittently available. A water heater is perfect for that because you have the tank and you only need to heat a day's worth of water over the whole day. With a stove, when you want to cook something you need heat now.

1. 
   charlie_sullivan | May 04, 2021 10:50pm | #5

   If your plan is to make dinner in the morning, put it in a pot, and put it on the stove it hopes that it will cook when the sun is out, you would probably be better off putting it in a solar vacuum cooker.