just a thought about a shower

right, here in the uk we run 240v, my electric shower has two heating elements, one is about 5.5kw (18.5A@240v)....
in reality, something like this would be run through an inverter, however, wouldnt it be more efficent to run it directly off the batteries if i could get them batteries at 240v etc there is no motor and a heating elementis just like you'd have in a e-vape coiljust running higher power...

dont quote my correctness it was a wee time ago but i think it measured 13ohms

as this is the only thing that uses high power i wouldnt like to buy a 6kva inverter just for that, id rather spend my money on batteries and a smaller inverter for everything elsehahaaha

Yes, you can run your AC powered water heater off of DC. However, you want to match the voltages. So you don't want to run 48VDC on a 240VAC element. The efficiency will drop drastically as well as the wattage.
You could either get a 48VDC element and install in your tank, or use a step up to make a 240VDC source, or build your battery banks to make 240VDC.

The 48VDC elements you could probably find in relation to RV parts. For simplicity, I would probably downgrade the element voltage to 120V as it is easier to achieve that voltage with the least inefficiency. Going from 48V to 240V is a huge leap.

http://forum.solar-electric.com/discussion/19785/120-ac-dc-water-heater-element

eBay: https://goo.gl/bhTHor $25USD

Instead of direct heating when showering you can also swap that out to indirect heating that keeps the water heated. Then you would go from 5-15kW elements to 500-1500W elements... Thats a bit easier to work with but yes there are a tiny bit more losses in the stored heat.

Then with above you can easily find elements that run on 48VDC systems. Like the one Korishan linked in. In my case its not doable since i got almost 100meter between batteries and the heater

daromer said:

Instead of direct heating when showering you can also swap that out to indirect heating that keeps the water heated. Then you would go from 5-15kW elements to 500-1500W elements... Thats a bit easier to work with but yes there are a tiny bit more losses in the stored heat.

Then with above you can easily find elements that run on 48VDC systems. Like the one Korishan linked in. In my case its not doable since i got almost 100meter between batteries and the heater

Click to expand...

sadly i dont have a hot water supply like that, its all mains heated as on demand hot water...

I have also been wondering about my shower, which in winter is set to use 7KW.
My system will be whole house AC coupled, and myfirst inverter will be 2KW and I may parallel another one to it later to get 4KW, once I have more cells.

My current thinking is thatit's not worth it for me to buy a huge inverter of ~10KW (even assuming I had enough cells to run it)just for a couple of minutes a day in the shower. Also, the showeruses more current in the winter when there is less sun to charge the powerwall anyway, and so I will probably be buying some grid power at that time of year.
So I will probably just allowmy powerwall to supply what it can and just pull the balance from the grid (obviously not an option for those who are off-grid though).

On demand hot water is difficult off grid, i agree with watts-on.
agrid tie or a hybrid inverter is the way to go if hot water is the only high power appliance you have.

Edit:
Just a thought, a (diy) step up converter from 48vdc to 200vdc ?? a water heater is a pure ohmse load, it do not care much about the kind of purity of the connected power...

I agree with wim. The only issue I see is with amperage draw. Boost converters tend to not have a lot of amp boosting as well. Altho, you could do a dirty (square wave) AC conversion from 48VDC to 48VAC, and then you could use a transformer to take it the rest of the way up. Then you'd carry along the needed amps.
I haven't done the math on this, but in theory I think it would work.
Now, if the 220VDC heating unit only needs like 5A, then the boost converter could work just fine. If it's needing 15A, then you might have an issue (unless you put several in parallel to add up the amps)

Consider the power requirement.
5.5kW is needed to heat the acceptable flow rate of water to the acceptable temperature.
To do it from batteries, we would still need 5.5kW... regardless of what voltage, dcor inverted ac, it might be.
Lets say we choose a 48v pack. 5.5kW means 115 amps.
Allow for some losses in cables and converting or inverting the electricity, and you are going to be drawing 125 amps from the pack.
Now with used salvage cells do you really want to run them at over 1 amp each?
No? So you are looking at a 13s125p pack of 18650s... 1625 cells dedicated to this task!
Run every cell at 10 amps, and you could divide the pack size by 10, but that is going to invite trouble from salvaged cells, probably sooner rather than later.

Frankly, it'd be more sensible to run the whole house from such a powerwall, rather than only something to be run for minutes per day.


High voltage DC is dangerous, and I wouldn't fancy any possibility ofmeeting even 48v with a lot of amps behind it in the wet conditions of a shower room. So I'd forget about running 130 amp dccable somehow into the innards of your existing water heating unit.


Storing hot water in a very well-insulated tank might be terribly 20th century, but it does, as Daromer indicated, allow the accumulation of energy supplied at a slow rate (like solar pv excess) which can then be used at a higher rate (as when you take a hot shower).
There are diverter systems that will skim any unusedwattsfrom your pv, and send them to your tank's immersion heater element - rather than have those watts exported to the grid. In view of his post above, this approach might be of interest to watts-on.
One such product is called Solarimmersion, and it can be had in the UK for 200 or less.


Although the 'instant' hot water shower uses power at a rather high rate, because it isn't used for long, the smalltotal amount of energy used simply isn't worth a large investment in an alternative system for this single task.

5.5kW is needed to heat the acceptable flow rate of water to the acceptable temperature.
To do it from batteries, we would still need 5.5kW... regardless of what voltage, dc or inverted ac, it might be.
Lets say we choose a 48v pack. 5.5kW means 115 amps.
Allow for some losses in cables and converting or inverting the electricity, and you are going to be drawing 125 amps from the pack.

Click to expand...

Yep, totally agree. Watts is Watts is Watts. Doesn't matter whether it's DC or AC, it's still Watts.

I agree with daromer and dougal on the tank style and accumulate the heated water over time. You don't even need to use solar electric completely to heat the water. You can use a combination of solar radiant and wind electric to do the job (depending on where you are located at).
Solar Radiant uses a collector to concentrate solar heat (infra-red) into water and then transport the water to a reservoir. One such unit is a parabolic trough. This is the method I plan on using. I'm about to build the prototype in the next few days (I hope, if the weather will allow it). Basically you take a parabolic surface, coat it in highly reflective material (mylar, for example), and the light is reflected to a central spot above the trough onto a copper tube. This tube will get enormously hot, even enough to turn the water to steam, if set up correctly. You can then either use a DC pump to move the water thru the pipe to a tank, or set it up so that the tank is higher than the collector and let convection do the job. I'm going to try for convection first.
I'm not even going to take out my water heater tank. But I'm going to splice into the input/output of the tank so I can circulate water from the reservoir into the water heating tank in the house. As, the house is already plumbed for hot water from that central location.

hmmmm these replies are interesting reading...
so i got either high cost of an inverter or high cost of cells to run an on-demand electric shower or;
buy a hot water tank, have new plumbing and have a low voltage heater and pump and replace my shower....

some math i think is needed for myself here;
shower uses 5.5kw /60min then X by 5min gives allmost 460w for the 5min its been on...
on an inverter its going to be very effective but innefficent at the 48vdc to 240vac at that high current.

sigh... im now thinking a kettle of water in a bowl would have to suffice lol

You wouldn't need to replace your shower, or even the ondemand heating unit. You would just need to splice into it. Yes, you would need to run more plumbing as it's just a cold line up to the heating unit, then it T's off and you have 2 lines, hot and cold. I would leave the unit in place in case later on down the line you end up using it. Unless you wanna sell it to recoop some of your costs.
Water heater tank isn't all that expensive as you don't need to buy a "new" one. You could just get one off of Craigslist (or equivalent in your area), Recyclers Yard, Yard Sale, etc. and just replace the heating elements with new ones and the thermostats. Unless the unit leaks, you can reuse an old unit. Then, for added heat retention, wrap some thermal blankets around it (not the shiny ones in an emergency kit, they sell them at home building stores).

Also, we now know that the unit uses 5.5kWh. So, that comes to 5500W / 60Mins = 92Watts/Minute. 92W / 48V = ~2Amps

Wait, am I missing some kind of math here? Or did I just calculate that correctly? If that's right, then he'd only be drawing about 2Amps @ 48V That can't be right ?!?!?

m6yru: If you have a clamp ampmeter, I'd suggest putting it on your hot wire at the breaker box that goes to your ondemand heating unit and see how many amps it's pulling under full load. That will drastically help the calculations here. I would hate for you to go out and do all this hard work and spend a lot of money and find out in the end that you could of just done it the way you thought out to begin with.
Or, if you know the model number of the unit give us that and we can get the specs based off that.

Is this unit using 5.5kW in an hour, or does it run @ 5.5kW under full load? That makes a HUGE difference in calculations

Click to expand...

Scratch all that above

Addendum:
Ok, I think I got it. It's pulling 5.5kW under full load. I looked at an electric element for a water heater tank, and it was rated at 4.5kW. Soooo, it would need:
5.5kW @ 240V = ~23 Amps
5.5kW @ 48V = ~115 Amps

So dougal is correct. Phew, thought I was goin nuts there for a moment

Ok, I don't see the problem with running 240V DC to the ondemand heater (if it'd use it). However, a 240V inverter would also allow it to work. The unit would only be pulling about 30Amps (including the inverter) during the operation. If he just had an inverted dedicated to the water heater (or one that ran the water heater and one that ran the stove or clothes dryer), then he'd be set. Just don't use those devices at the same time.

Now, if you had 40kW of storage (similar to Daromer) or more, I think you'd be ok on a daily basis, as long as you had enough solar to recharge the batts.
You also have to remember that the ondemand heater only heats the water up to a set temp. So, if the incoming water was ~45C, then the unit would only heat a little further up to needed temps. Even at 35C, it wouldn't run full blast. The way you achieve the preheated water is to use the tank with the solar heated water. But, that would mean you still would need to run an independent line to the ondemand unit as it would need to be cut off of the cold only line.

actually, come to think of it.... are we not doing things ass backwards...
shouldnt we be working out the math using voltage by resistance of ohms???

as i know the unit is 13ohms, if it was fed using "48v" cough cough it would have a watts output of 177w
if 13ohm and 96v was used then thats almost 709w

the resistance dont change, but the watts vs applied voltage would

Yes you cant feed the existing element with lover woltage. That will just not give you any heated water

For doing 48v as such you need another element

First you have to think about lowering the power consumption and that is sometimes challenge
6kw inverter and everything goes with and to be sustainable.....
I have a question..?
How do you heat your apartment house where you live in......?




The lowest consumption have heat pumps is 4 to 1 conversion or even new models 5 to 1
that means 1kw of electricity and 4kw heat....samsung inverter heat pumps or Panasonic inverter heat pumps is excellent choice or smaller only DHWatter and 100-200liter water tank last is about 500-700w consumption....
Try to think in that direction...... instant water heater is problematic for house wires thick cables, big fuses...
Big conection power.... Ect..

Power company's like to have you instant heating element.so they can charge you more....
Also they say is efficient and so on bullshit... is efficient if you have electricity for free...otherwise you pay to much... [emoji106]

Just a small note on the heat pumps...
Conversion 1 to 4 (Cop 4) is common, this is usualy the overall Year long Cop, this means in winter the Cop is lower ( more like 2 ) while in spring or autumn it will be higer ( 4 or 5 ).
Sowhendesigning a off grid system with a heatpumpyou have totake thisintoaccount.

Instant hot.... Humpf -

I chose instant hot because of several reasons - It only uses energy as needed, no need for storage tank, etc.
However, it is my second largest single draw on my PV system next to my Air Conditioner (I am in South Florida, so it gets hot).

This is what I did in a nutshell.
We're all DIYers here, right?

As I am currently collecting rain water (I have 1250 gallon cistern setup), with some hefty filtering for homeuse.
I also now collect more water and with simple filtering, that is what used for showers (and washing machine, etc).
Even with only a 1 micron filter, it is potable, and DEFINITELY usable for showers, clothes washing, etc.

Basically, I set up another 150 gallon tank - this tank is insulated, but has no heating elements in it.
It stores warm/hot water when circulated through the collection pipes running under my panels on the roof.

In fact, sometimes it is too hot, but with a hot/cold diverter valve in the shower, i don't worry about that.

To get it to my shower and washing machine, I simply ran new pipes from that tank through a low power, dc, high volume on demand pump (7gpm) to send water to my shower and other places as needed.

Obviously, where you can harvest rays for energy, you can also harvest "heat" as such.
The sun can work for you - it doesn't cost much to push water around (a 12 v pump for example). Plumbing, circulating water through pipes under the panels and back down into the tank is a really easy thing to do.

This setup for me uses MUCH less electricity then what is needed for the traditional instant hot water system.

A 10 minute shower will use approximately 60 gallons on average. (6gpm).
This would reduce your KW load overall and save money in the long run.

Just some thoughts.
Howie

wim said:

Just a small note on the heat pumps...
Conversion 1 to 4 (Cop 4) is common, this is usualy the overall Year long Cop, this means in winter the Cop is lower ( more like 2 ) while in spring or autumn it will be higer ( 4 or 5 ).
Sowhendesigning a off grid system with a heatpumpyou have totake thisintoaccount.

Click to expand...

Yes some parts of this is true but you have to consider all things that goes with it..... Is complete solution and ask your self how many times it goes outside temperature that low that is coefficient of performance lower than 2 shuld we say that should be outside temperature -20degC not many times and only for short time....
Panasonic give you best results with 'total capacity' to -15 H model even lower..... without e-heater....
Long story short I have one and is far cheaper than to buy wood that is second option that is in one year expensive for about 200-300 and that's is not in calculated maintenance and yearly inspection and so on in my case....
Confort is one thing with heat pumps that not many sistems can provide.... [emoji106]

---

howiegrapek said:

Instant hot.... Humpf -

I chose instant hot because of several reasons - It only uses energy as needed, no need for storage tank, etc.
However, it is my second largest single draw on my PV system next to my Air Conditioner (I am in South Florida, so it gets hot).

This is what I did in a nutshell.
We're all DIYers here, right?

As I am currently collecting rain water (I have 1250 gallon cistern setup), with some hefty filtering for homeuse.
I also now collect more water and with simple filtering, that is what used for showers (and washing machine, etc).
Even with only a 1 micron filter, it is potable, and DEFINITELY usable for showers, clothes washing, etc.

Basically, I set up another 150 gallon tank - this tank is insulated, but has no heating elements in it.
It stores warm/hot water when circulated through the collection pipes running under my panels on the roof.

In fact, sometimes it is too hot, but with a hot/cold diverter valve in the shower, i don't worry about that.

To get it to my shower and washing machine, I simply ran new pipes from that tank through a low power, dc, high volume on demand pump (7gpm) to send water to my shower and other places as needed.

Obviously, where you can harvest rays for energy, you can also harvest "heat" as such.
The sun can work for you - it doesn't cost much to push water around (a 12 v pump for example). Plumbing, circulating water through pipes under the panels and back down into the tank is a really easy thing to do.

This setup for me uses MUCH less electricity then what is needed for the traditional instant hot water system.

A 10 minute shower will use approximately 60 gallons on average. (6gpm).
This would reduce your KW load overall and save money in the long run.

Just some thoughts.
Howie

Click to expand...

Howie
That's works good for you in sunny Florida..... [emoji106]
I am not so lucky... Central Europe

---

tbostjan said:

wim said:

Just a small note on the heat pumps...
Conversion 1 to 4 (Cop 4) is common, this is usualy the overall Year long Cop, this means in winter the Cop is lower ( more like 2 ) while in spring or autumn it will be higer ( 4 or 5 ).
Sowhendesigning a off grid system with a heatpumpyou have totake thisintoaccount.

Click to expand...

Yes some parts of this is true but you have to consider all things that goes with it..... Is complete solution and ask your self how many times it goes outside temperature that low that is coefficient of performance lower than 2 shuld we say that should be outside temperature -20degC not many times and only for short time....
Panasonic give you best results with 'total capacity' to -15 H model even lower..... without e-heater....
Long story short I have one and is far cheaper than to buy wood that is second option that is in one year expensive for about 200-300 and that's is not in calculated maintenance and yearly inspection and so on in my case....
Confort is one thing with heat pumps that not many sistems can provide.... [emoji106]

---

howiegrapek said:

Instant hot.... Humpf -

I chose instant hot because of several reasons - It only uses energy as needed, no need for storage tank, etc.
However, it is my second largest single draw on my PV system next to my Air Conditioner (I am in South Florida, so it gets hot).

This is what I did in a nutshell.
We're all DIYers here, right?

As I am currently collecting rain water (I have 1250 gallon cistern setup), with some hefty filtering for homeuse.
I also now collect more water and with simple filtering, that is what used for showers (and washing machine, etc).
Even with only a 1 micron filter, it is potable, and DEFINITELY usable for showers, clothes washing, etc.

Basically, I set up another 150 gallon tank - this tank is insulated, but has no heating elements in it.
It stores warm/hot water when circulated through the collection pipes running under my panels on the roof.

In fact, sometimes it is too hot, but with a hot/cold diverter valve in the shower, i don't worry about that.

To get it to my shower and washing machine, I simply ran new pipes from that tank through a low power, dc, high volume on demand pump (7gpm) to send water to my shower and other places as needed.

Obviously, where you can harvest rays for energy, you can also harvest "heat" as such.
The sun can work for you - it doesn't cost much to push water around (a 12 v pump for example). Plumbing, circulating water through pipes under the panels and back down into the tank is a really easy thing to do.

This setup for me uses MUCH less electricity then what is needed for the traditional instant hot water system.

A 10 minute shower will use approximately 60 gallons on average. (6gpm).
This would reduce your KW load overall and save money in the long run.

Just some thoughts.
Howie

Click to expand...

Howie
That's works good for you in sunny Florida..... [emoji106]
I am not so lucky... Central Europe

Click to expand...

---

Because of inverter it can adjust the power output and with that consumption...... max load is only needed in extreme cases most of the time runs with half power or lower depends on demand and capacity of heat pump.

@ Tbostjan
I am not against heat pumps, i use one myself for heating and hot water - even off grid... it is a water/water system, so the Cop stays the same the whole year...great technology, loving it for many years already.

Most of the heat pumps are air/air or air/water systems, theygo from 5 down to 2, even 1 on 1 if e-heating by -15 or so.... sooooo, and thats what i want to say in my post, you have to design your system (if off-grid) to the full 100 % of the power needed by the heat pump, worst case, not best case.

If you have a secondary way to heat your house andhot water (gas, wood) or living in Florida... well..., other story.

wim said:

@ Tbostjan
I am not against heat pumps, i use one myself for heating and hot water - even off grid... it is a water/water system, so the Cop stays the same the whole year...great technology, loving it for many years already.

Most of the heat pumps are air/air or air/water systems, theygo from 5 down to 2, even 1 on 1 if e-heating by -15 or so.... sooooo, and thats what i want to say in my post, you have to design your system (if off-grid) to the full 100 % of the power needed by the heat pump, worst case, not best case.

If you have a secondary way to heat your house andhot water (gas, wood) or living in Florida... well..., other story.

Click to expand...

Not in the moment secondary will come small wood fireplace that's conected to central heating...
Heat pump that I use is inverter air/water split sistem

tbostjan said:

wim said:

@ Tbostjan
I am not against heat pumps, i use one myself for heating and hot water - even off grid... it is a water/water system, so the Cop stays the same the whole year...great technology, loving it for many years already.

Most of the heat pumps are air/air or air/water systems, theygo from 5 down to 2, even 1 on 1 if e-heating by -15 or so.... sooooo, and thats what i want to say in my post, you have to design your system (if off-grid) to the full 100 % of the power needed by the heat pump, worst case, not best case.

If you have a secondary way to heat your house andhot water (gas, wood) or living in Florida... well..., other story.

Click to expand...

Not in the moment secondary will come small wood fireplace that's conected to central heating...
Heat pump that I use is inverter air/water split sistem

Click to expand...

That is the smart way....