Total n00b question about microinverters and water heating

So I'll be the first to admit that I don't know jack about microinverters other than they turn the panel's DC straight to AC like a normal inverter, they're just really small.

But I've read many posts about trying to get solar panels to run heating elements and having to match Ohms and panels to exact elements and sometimes it works and sometimes not and it seems to be a HUGE hassle to get everything just right.

Couldn't you throw a used microinverter onto a panel and feed the AC right to the heating element? That's what the elements were designed to take in the first place. Yes, watts would be low and such but wouldn't that eliminate the hassles of getting all the exact right panels to talk at the exact right resistances and such? Then you could just use a bog-standard off-the-shelf element and parallel up a couple panels and walk away for the day, right?

I assume I'm missing something here. Please be gentle. Microinverters are all grid-tie type meaning they do not produce output unless they are connected to a source of utility quality AC. One notable exception is the new Enphase IQ8, these are set up to be grid-tied do have an operating mode where they can form their own microgrid. According to the information I read, you will need a Smart Switch and most likely their Gateway. It could work but going to be expensive and inefficient. I agree with what time2roll said above, a heat pump water heater makes much more sense but would intolerant of voltage fluctuations so then at least a small amount of battery storage would be needed.
Probably better to just go with a direct solar water heater system. If you don't need super hot water maybe an inexpensive black rubberized pool heater is good enough. If hotter water is desired then a concentrator or enclosed tube type is best.

So could a small solar system with a 100w PSW inverter "convince" the microinverters to work by providing that "activation source"?

I just see microinverter units on the 2nd hand market for pretty cheap more often than I see solar panels themselves and was wondering...

Not asking whether it Should be done, only if it Could be done.

No, I have no idea what I'm talking about which is why I asked. :D

Theoretically, your proposed system will kind of work BUT it would be highly unstable and most likely be unsatisfactory so I'm going to agree with what svetz said. "Nope, Not directly anyway".
To clarify. A grid-tie inverter can be induced to turn on with a suitable source of clean AC power. However, grid-tie inverters have no internal means of output control. In other words, they always try and produce as much, or little, electricity as possible with whatever solar radiation is available at that instant.
If a fixed load is connected then the system will only work when the load demand is PERFECTLY balanced with the sun intensity, angle, temperature Etc. Under any other conditions the voltage, frequency or current will go out of range (see UL anti-islanding specs.) and the micro-inverters will just shut down if you are lucky. The other scenario is the 100W PSW has a bunch of extra current pushed back through it and gets smoked.
I would seriously caution you from pursuing this line of thought any further unless you are prepared to install a suitable UL hybrid inverter and set up the system properly for AC coupling with the microinverters.

Also need the available amps or the voltage from the panels will fold down into the power curve. Need close to 20 amps to fully drive that element at 200+ volts.

Of course. I'm thinking along the lines of typical old school SHW's which, give or take, need an entire day to fill up the 80G -120G water heater they are using for storage.

Using a 250w 60 cell module for easy math. Vmp of ~30v and 5 in series is ~150v. I theorize that the element would gobble up all watts for a few hours a day and you'd end up with a far simpler and less expensive solar water heater then the old standard SHW's with heat exchangers, antifreeze, piping to and from your roof and pump.

Ohm's law says that element will draw up to watts at that voltage. Seems like a nice match to me so I'm going to try it someday when it's not snowing and I'm not covered up with work. I've got a g atmospheric storage tank tied to my wood boiler and radiant in floor heating system. That tank would make a nice place to put that heat.

jetsam

Minister of Fire

Dec 12,

5,337

Long Island, NY

youtu.be

• Dec 29,

• #1

I just went solar, and I want to get rid of my oil-fired water heater (used every day) and my oil-fired boiler (connected to 3 zones of hydronic baseboards, not used unless we go on vacation).

My first thought was to swap the water heater for a heat pump water heater (like the popular Rheem hybrid), leave the oil boiler there for emergency/vacation use, and maybe get some heat pump minisplits in to help heat and cool the upstairs.

However, while researching heat pump water heaters, I tripped over the LG Multi V. This is a commercial product that does domestic hot water, baseboard hot water, it feeds split system heads, and even uses heat scavenged from air conditioning to heat the hot water. On the down side, the smallest unit is 14kw, so they're not exactly targeting the home market here.

This got me thinking: It would be really nice to have the hydronic baseboards running off of an electric heat pump.

So on to the question: Is anyone familiar with a residential-sized heat pump that can do DHW and hot water for hydronic heating? How about one that also does cooling via minisplit-style heads?

woodgeek

Minister of Fire

Jan 27,

5,690

SE PA

• Dec 29,

• #2

Conventional wisdom is that HPs lose efficiency (COP) when heating water hot enough for normal US hydronic radiators.

If you have a low-temp radiation system, then is could work. That is why its drawn with in-floor heating. Reactions: jetsam

SpaceBus

Minister of Fire

Nov 18,

7,493

Downeast Maine

• Dec 29,

• #3

American solar technic offers a water to air unit that can do what you ask.

After looking at the website to get you a link I can't find it...

@tom in maine knows more and can probably furnish a link.

jetsam

Minister of Fire

Dec 12,

5,337

Long Island, NY

youtu.be

• Dec 30,

• #4

I just tried to do some googling to see how old hydronic baseboard systems perform with ~120° input water, and the results tend to be (often angry) opinions rather than data.

BUT... I also found (broken link removed to https://www.nordicghp.com//02/air-to-water-heat-pump-hot-water-baseboards-radiators/). Wanna know if it'll work? Just run your old system at 120° and see if it can heat the house!

All of the 160°+ heat pump boilers I've seen so far require a geothermal loop. Last edited: Dec 30,

jetsam

Minister of Fire

Dec 12,

5,337

Long Island, NY

youtu.be

• Dec 30,

• #5

I found some great info on running old hydronic baseboards on 120° water here. (The bottom line is that you should add lots of radiator; trying to avoid that.)

So if a air-to-water heat pump that can put out 160° doesn't exist, I could still use the existing baseboards to do some amount of heating for the house with an air-to-water heat pump.

Brian26

Minister of Fire

Sep 20,

694

Branford, CT

lml999

Minister of Fire

Oct 25,

636

Cape Cod, Massachusetts

• Dec 30,

• #7

I just went solar, and I want to get rid of my oil-fired water heater (used every day) and my oil-fired boiler (connected to 3 zones of hydronic baseboards, not used unless we go on vacation).

If you're only running the oil-fired boiler a couple of weeks per year, you're better off (financially) by just continuing to use it. You're talking about $100 or so in oil per week, during the winter, more or less.

On the other hand, if you spend three months away in the winter, you will have a quicker payback...

Highbeam

Minister of Fire

Dec 28,

21,354

Mt. Rainier Foothills, WA

• Dec 30,

• #8

This got me thinking: It would be really nice to have the hydronic baseboards running off of an electric heat pump.

Well yeah, we've been waiting for this basic technology for many years. Other countries have it. It's usually an all in one heat pump (monobloc) that is connected to the home with water lines instead of a split system with refrigerant lines.

No mainstream manufacturer sells these in the US yet. Crossing my fingers that the technology arrives soon. Tom's unit has the right specs but is what I would call a "grey" market appliance with few to no reviews.

Your need for super hot supply water is probably the reason that we don't see these things all over yet. For those of us that just want to heat domestic water or low temperature hydronic systems like a radiant slab it would be perfect!

peakbagger

Minister of Fire

Jul 11,

8,978

Northern NH

• Dec 30,

• #9

Search around for John Siegenthalers articles in PME, he is a big advocate of air to water but he pushes you need to have low temperature radiant emitters. Most homes with fin tubed baseboard were sized for high temp supply water so there is not enough baseboard to heat the house at low temps. If you have the wall space you may be able to triple the length and get away with it. John is big advocate of low temp emitters. He actually prefers inwall radiant and ceiling over in floor.

Vermont is giving incentives for air to water equipment. The downside is there are very few companies you have heard of selling this equipment in the US so the volume is low.

Seasoned Oak

Minister of Fire

Oct 17,

7,215

Eastern Central PA

• Dec 30,

• #10

Leave your oil is place as a backup. Thats what i did. I also switched to a HPWH. Mini splits sound like a good option for your location. You could always use the oil for those short spurts of very cold weather with overcast skies when your solar would suffer.

Brian26

Minister of Fire

Sep 20,

694

Branford, CT

• Dec 30,

• #11

Chiltrix makes a unit that is in widespread use in the US. A google search wilk bring up tons of more information.

Chiltrix heat pump chiller. This is the AHRI-Certified small heat pump unit of the future that is very easy to install and eliminates all lineset length issues. Cooling or heating is transported via simple water/glycol lines. The outdoor unit is completely self-contained. Just add power and connect the water lines. The indoor units are also very simple to install, just add power, connect the water lines, and connect a condensation drain line. The CXI series DC-Inverter fan coil units are the quietest fan coil units on the market. Shown to the right are various indoor unit options, available in various sizes from ~1/4 ton (3,400 BTU) up to 1 ton (12,000 BTU). Larger indoor units can be special ordered. More indoor fan coil unit details are here. Up to 8 indoor units can connect to a single CX34. It also has options to easily connect to ducted/central systems, boilers, and hydronic / radiant heating systems.

jetsam

Minister of Fire

Dec 12,

5,337

Long Island, NY

youtu.be

• Dec 30,

• #12

Chiltrix has a unit. Lot of info out there on them if you google it.

Their CX34 (which appears to be their only heat pump) has a max operating temp of 122. The DHW anti-Legionnare's disease mode, which briefly pushes the DHW higher, requires a special resistive heater to be installed on the DHW tank.

Unless I am looking at the wrong unit?

We're looking for something that puts out (ideally) 180° water on a baseboard loop, and maybe 130°for the DHW output.

jetsam

Minister of Fire

Dec 12,

5,337

Long Island, NY

youtu.be

• Dec 30,

• #13

Leave your oil is place as a backup. Thats what i did. I also switched to a HPWH. Mini splits sound like a good option for your location. You could always use the oil for those short spurts of very cold weather with overcast skies when your solar would suffer.

This was the original plan, but I was eager to scrap it when I reasoned that I could use a heat pump to run the baseboards.

Now it seems that this is not practical without at least doubling the surface area of radiator in the house, which I do not think we're going to want to do.

It would actually be perfect for MY needs to hook up 120 degree water to the existing baseboard as backup heat, but since that system would no longer be able to carry the whole house in the winter, it would be pretty rough on resale value. ("This is the wood stove. If you don't like splitting wood, go look at a different house.")

jetsam

Minister of Fire

Dec 12,

5,337

Long Island, NY

youtu.be

• Dec 30,

• #14

Search around for John Siegenthalers articles in PME, he is a big advocate of air to water but he pushes you need to have low temperature radiant emitters. Most homes with fin tubed baseboard were sized for high temp supply water so there is not enough baseboard to heat the house at low temps. If you have the wall space you may be able to triple the length and get away with it. John is big advocate of low temp emitters. He actually prefers inwall radiant and ceiling over in floor.

Vermont is giving incentives for air to water equipment. The downside is there are very few companies you have heard of selling this equipment in the US so the volume is low.

Yeah, I see that greatly increasing radiator surface area is an option. If this was new construction or a renovation I'd consider that, but as is, I don't think I will be able to sell it to the wife Reactions: SpaceBus

Brian26

Minister of Fire

Sep 20,

694

Branford, CT

• Dec 30,

• #15

Did they size your panels to cover your last year average electrical consumption? Almost all utilities will only let you install like up to 110% of your last years average use. If you start adding a huge electric heating load you are most likely going to be paying for the electricity at cost.

What size is your system and did they not size it based on your past year usage?