diy solar

diy solar

Solar hot water system, help choosing right approach

Hedges said:
Because it is VFD, should ramp up slowly so inverter doesn't have to supply a starting surge.
If it can run off two phases of the grid, maybe it can run from the "6000W" inverter, given a transformer to make 170V (of opposite phase) from 230V so it sees 400V between phases. And 230V from one phase to neutral. Or isolation transformer to make 200/400V split-phase.
Click to expand...
My inverters are definitely not designed to be synchronised, so I won’t be trying to do so, but the two alternatives you mentioned there are interesting and new to me. How much risk is involved in trying this, as i really have no desire to blow up or otherwise damage my €15,000 heatpump. However… to test if it will run on two mains phases is simple enough and I would wager the answer will be yes.

What would I need to buy to test either of the two approaches you suggested there and is there risk involved or to the appliance would it be indistinguishable from 2 phases of a proper mains supply? Would there be any added strain on the inverter, save for the fact it’s now carrying the load the heatpump draws from both phase supplies?
 
Hedges said:
Evacuated tubes have thin film coatings, and vacuum of course. Not a DIY fabrication project (for most of us.)
Some have a heat pipe making contact with inner wall of the thermos tube. Or, a working fluid can be used (must avoid freezing)
The heat pipes have much less fluid volume than empty volume, so no harm from freezing. They stagnate around 240F (above 100C), so stop transferring heat. Of course, at that point water in manifold has either been driven out as steam or is around 20 psi like a car radiator.

They are cheap enough to buy. I see ads that include a manifold and a few more tubes than it needs as spares.
Some ads in my area. Used to see other models. Think many are made in China.

www.ebay.com

solar water evacuated tube heater system with 80 gallon Rheem solar and electric | eBay

Find many great new & used options and get the best deals for solar water evacuated tube heater system with 80 gallon Rheem solar and electric at the best online prices at eBay! Free shipping for many products!
www.ebay.com

www.ebay.com

10 Evacuated Solar Vacuum Tubes 1800mm 6 ft 72" DHW for Water Heater Collectors | eBay

And most importantly: Evacuated tubes don't FREEZE or need antifreeze. They're great quality with a heavy solid conductor inside. The efficiency is incredible, as compared to PV solar. This is the large 6 foot size, usually for the big 30 tube collectors.
www.ebay.com

www.ebay.com

Case Of 10 Evacuated Solar Vacuum Tube 1800mm 6 ft 72" DHW | eBay

Find many great new & used options and get the best deals for Case Of 10 Evacuated Solar Vacuum Tube 1800mm 6 ft 72" DHW at the best online prices at eBay! Free shipping for many products!
www.ebay.com
Click to expand...
Thanks - I agree they‘re not hugely expensive, but nevertheless would have an awfully long payback time given my relatively parsimonious hot water consumption needs and in any case, I have much cheaper alternatives to explore which have been suggested earlier in the thread, so I’ll keep the evacuated tubes on the back burner for now.
 
sparrowhawk said:
The way I see it is very simple. I know you say that you don't have any room to add anymore panels to generate enough power to heat water. So I have to ask. Do you use every watt of solar power you generate everyday?
If you have any excess solar why can't it be used to heat water? You want to add a solar water heater collector, so why can't that space be used for more photovoltaic panels? Does your existing water heater tank have an electric backup heating element in it?
There are things that can be done with any excess power not being used. Some people use some sort of system that diverts excess power into a heating element in the water heater tank. Myself I use a timer that turns the water heater on at around noon time when the sun is highest and let my inverter power the water heater. I'm able to use my inverter because I replaced the original heating elements with lower wattage ones that allow water heating along with battery charging and powering of other loads simultaneously. The system has worked great for over 2 years now.
Click to expand...
Thank you for your post, I do see your logic. I suppose you’re right, if I‘m willing to put a thermal collector on my garage roof I should be able to do the same with PV panels, and yes I guess I can. The cable route from there to where my charge controllers and batteries fed from my current PV panels live would be complicated and maybe not feasible, so I might have to reckon on making a second, separate PV system just to heat the water.

I have in fact, during the last summer, used very nearly all my PV generated electricity, with my batteries achieving top of charge fairly rarely and only very late in the day. That’s a change to the previous year and due to me finding ways to use more PV power in my home as I switch more appliances from mains.

I wouldn’t rule out PV excess being used to heat my water in future, if I can’t make anything else work, and I do know it’s a popular solution, but I need to solve some of my logistical challenges around space for mounting panels and availability of cable routes before expanding my system.
 
Last edited:
Hedges said:
"Auxiliary heater, 3 steps kW 0/3/6/9"

Using the backup heating elements of the HPWH as dump load would be a simple approach. Just need to have suitable thermostat connected (and a signal when battery is full.)

If 3kW is too big a dump load, step-down transformer from 230V to 115V would make it
Click to expand...
The aux heater isn’t directly available for external connection in that way, it only comes on under the control of the heat pump software in circumstances where the heatpump cannot meet the needs of the house by pumping heat from the brine. Eg. Super low outdoor temps in winter or brine temp has dropped too low.

For reference, the last few winters we’ve had the system has coped with -28C outdoor temps and brine temps dropping below zero all without resorting to aux heater use.

The long and the short of it is, that heater element wouldn’t be available to me for a dump load unless i‘m willing to pull apart and require my heatpump internals ?
 
Sverige said:
Thank you for your post, I do see your logic. I suppose you’re right, if I‘m willing to put a thermal collector on my garage roof I should be able to do the same with PV panels, and yes I guess I can. The cable route from there to where my charge controllers and batteries fed from my current PV panels live would be complicated and maybe not feasible, so I might have to reckon on making a second, separate PV system just to heat the water.

I have in fact, during the last summer, used very nearly all my PV generated electricity, with my batteries achieving top of charge fairly rarely and only very late in the day. That’s a change to the previous year and due to me finding ways to use more PV power in my home as I switch more appliances from mains.

I wouldn’t rule out PV excess being used to heat my water in future, if I can’t make anything else work, and I do know it’s a popular solution, but I need to solve some of my logistical challenges around space for mounting panels and availability of cable routes before expanding my system.
Click to expand...

Another method would be adding another water heater and putting up more panels and feeding the water heater directly from the panels. You would need to come up with a way to disconnect the solar when the water is hot enough as the a/c thermostat will eventually fail when fed dc current and would turn your water heater into a ticking time bomb.
There are other problems with that method, one of which is the need to match the panels with the resistance of the heating element. I think it helps to add some sort of mppt controller to get the most out of the power available at any given time.
I considered doing that when planning my system but didn't want to add additional complexity to my set up and since I was already going to be running an inverter I just increased the size of my system and downsized the elements to come up with a happy medium.
 
Sverige said:
How much risk is involved in trying this, as i really have no desire to blow up or otherwise damage my €15,000 heatpump. However… to test if it will run on two mains phases is simple enough and I would wager the answer will be yes.
Click to expand...

I provide no warranty with my free advice (and hopefully you can't track me down.)

Feeding two lines not three is going to mean more ripple voltage on the capacitors, more heating, would shorten their life. You could ask the vendor if it is acceptable to run off single phase, split phase, two legs of 3-phase.

Sverige said:
What would I need to buy to test either of the two approaches you suggested there and is there risk involved or to the appliance would it be indistinguishable from 2 phases of a proper mains supply? Would there be any added strain on the inverter, save for the fact it’s now carrying the load the heatpump draws from both phase supplies?
Click to expand...

Current from AC course is carried through 4 diodes instead of 6, so those four have higher average current and heating (assuming diode front end; PFC with FETs would be a different circuit.)

If it runs off two legs of AC, I think transformer is what's needed. I'm not sure if 170/230 would work exactly the same, has a common mode voltage but so does 3-phase. Split phase (e.g. 200 + 200 = 400) has no common mode.

Main thing I would try to do is not exceed line/neutral or line/line voltage it was designed for.
 
Hi there. Why not use a combination of methods. Maybe not to heat the entire supply but to boost heat/preheat the water going to your heat pump thus making it more effective. I dont know your budget. But some solar, plus something like that 48v dc 1000w heating element coupled with the small charge controller and thermostat should do it. there are smaller elements available and in lower dc voltages. People always throw away electric water tanks away that can be repurposed for that particular need. Just an idea. (Nevermind sparrowhawk already mentioned something like that) still though.
 
Acuario said:
What make/model/power inverter do you have?
Click to expand...
I have two of these. One is 3000W, the other 6000W. Both good for about half the label rating, so 1500W and 3000W in reality:

www.banggood.com

Mensela IT-PS2 Pro 220V 60HZ Intelligent Screen Solar Pure Sine Wave Power Inverter 2200W/3000W/4000W/5000W/6000W/7000W DC 60HZ 12V/24V To AC 220V Converter

Only US$97.30, buy best Mensela IT-PS2 Pro 220V 60HZ Intelligent Screen Solar Pure Sine Wave Power Inverter 2200W/3000W/4000W/5000W/6000W/7000W DC 60HZ 12V/24V To AC 220V Converter sale online store at wholesale price.
www.banggood.com www.banggood.com

They are cheap, but have been working reliably for 2 years, so my confidence level has grown after initially thinking they might be too cheap to be relied upon. With these inverters I can run everything I have here, even 2kW appliances such as dishwasher and washing machine from my 4S LFP battery bank, with the exception of my heatpump which needs 3 phase. I run the 3000W inverter continuously to power stuff like lighting, fridge, freezer and TV then switch on the bigger inverter as needed for cooking, kettle, washing machine, etc..
 
ghostimage said:
Hi there. Why not use a combination of methods. Maybe not to heat the entire supply but to boost heat/preheat the water going to your heat pump thus making it more effective. I dont know your budget. But some solar, plus something like that 48v dc 1000w heating element coupled with the small charge controller and thermostat should do it. there are smaller elements available and in lower dc voltages. People always throw away electric water tanks away that can be repurposed for that particular need. Just an idea. (Nevermind sparrowhawk already mentioned something like that) still though.
Click to expand...
Thank you (y) It’s an option
 
Sverige said:
The aux heater isn’t directly available for external connection in that way, it only comes on under the control of the heat pump software in circumstances where the heatpump cannot meet the needs of the house by pumping heat from the brine. Eg. Super low outdoor temps in winter or brine temp has dropped too low.

For reference, the last few winters we’ve had the system has coped with -28C outdoor temps and brine temps dropping below zero all without resorting to aux heater use.

The long and the short of it is, that heater element wouldn’t be available to me for a dump load unless i‘m willing to pull apart and require my heatpump internals ?
Click to expand...

Do heating elements heat your water directly, or heat the brine that is source for heat pump?
Typical HPWH here are air to water plus have electric elements in the water.

Rewiring internals should be trivial. If there are 3, 3kW elements, likely they are enabled in a fixed order. The 3rd maybe you never use anyway. Assuming it does just heat your water, pulling a wire off it (including overtemperature thermal fuse in series), you should be able to power it. Need a thermostat as well, and only power as a load dump.

Here, our water heaters usually have 240V elements, and larger units have upper and lower element. I power off 120V for 1/4 the power, just takes longer. Upper vs. lower could support alternate sources. Time of use electric rates, so goal is to heat during off-peak. Will eventually automate use of PV during power failures when batteries full.

To not mess with the internals, some sort of additional heater on the brine tank could be a place to dump excess power, but still requires compressor operation to transfer to water.

Do you have a tempering valve so extra power can be stored in hot water? Maybe not, making tank hotter would be less efficient. But if able to run compressor while grid down, could be useful.
 
Hedges said:
Do heating elements heat your water directly, or heat the brine that is source for heat pump?
Typical HPWH here are air to water plus have electric elements in the water.

Rewiring internals should be trivial. If there are 3, 3kW elements, likely they are enabled in a fixed order. The 3rd maybe you never use anyway. Assuming it does just heat your water, pulling a wire off it (including overtemperature thermal fuse in series), you should be able to power it. Need a thermostat as well, and only power as a load dump.

Here, our water heaters usually have 240V elements, and larger units have upper and lower element. I power off 120V for 1/4 the power, just takes longer. Upper vs. lower could support alternate sources. Time of use electric rates, so goal is to heat during off-peak. Will eventually automate use of PV during power failures when batteries full.

To not mess with the internals, some sort of additional heater on the brine tank could be a place to dump excess power, but still requires compressor operation to transfer to water.

Do you have a tempering valve so extra power can be stored in hot water? Maybe not, making tank hotter would be less efficient. But if able to run compressor while grid down, could be useful.
Click to expand...
There is no brine tank, the brine pipes are plumbed directly into the heat pump cabinet and within there (hidden from my view) is a variable speed (geared) scroll compressor, heat exchanger, pump etc which extracts a few degrees C from the brine then sends it back down the borehole. Although we as engineering nerdy types understand it as a system, it’s a one box solution, a big tall slab sided cabinet with plumbed in connections for brine in/ out, hot water in/out, cold water supply and heating inputs and outputs. Quite honestly it’s nothing I’m going to open up and mess with! I need it to stay working to heat my house, it’s damn cold here in winter. ?

There will be tank within it somewhere with an immersion element or two for boosting the hot water temp, but I’ll never get to it so it’s moot. Apart from anything else the whole lot is encased in walls of 200mm thick expanded polystyrene insulation which took me weeks to put in, so really my opportunity for raising the water temp is to rig a heat exchanger of sorts to transfer heat into the pipework which is exposed within the garage between the heat pump and the house.
 
You must log in or register to reply here.

Similar threads

J
GTC Solar Water Heater - Evacuated Tubes - 14 years later
Replies
1
Views
267
kommando
K
Philip53
For Sale - Price Reduced: 80 Gallon Stainless Steel Solar Hot Water Tank - North Louisiana
Replies
1
Views
419
45North
4
H
No hot water problem solved
Replies
0
Views
384
Honolulu
H
onokai
Heat Pump water Heaters
3 4 5
Replies
83
Views
3K
hogback
H
J
Temperature in indirect hot water heater
Replies
1
Views
385
KITROBASKIN
KITROBASKIN
Back
Top