Direct water heating, 48v or 220v

[Windless]

Direct water heating, 48v or 220v
I’m a newbe(ish) investing in a 4,200mm turbine,
I will not be able to grid connect but maybe I could in the future.
I intend direct heating my immersion tank.
Should I be so lucky and have too much heat I’ll have a thermostatically controlled circulation pump which will draw the heat into my under floor heating.

My turbine will be at least 150m from my immersion
I want to avoid any unnecessary expense.

If my turbine is 48v
•   I will lose 13.29% of the power in a2.5mm2 wire
•   Possible to build direct heating system to feed a 48c immersion element (www.elemex.ie) No batteries needed (http://www.navitron.org.uk/forum/index.php/topic,131.0.html
•   This gives option to install 48 to 220 inverter for garage lighting & general use or future expansion to bigger battery pack and washing machine operation through one dedicated power socket.

However if the turbine is 220v
•   These losses are eliminated or I can save a few pounds on lighter wire, but I would have to lay some of it as armoured cable; cost saving lost.
•   I don’t know if it would be possible to build a controller for 220v.  Windy Boy inverter cost £1,200 plus safety switches.
•   I could use my existing immersion element.
•   Possible more efficient if in the future I can get a grid tie-in.
•   Is it difficult to get a good quality inverter for this high voltage? Suggested on http://www.navitron.org.uk/forum/index.php/topic,895.0.html

Would you advise 48v or 220v? I’m drawn to 220v

[biff]

hi windless,
          you might be a little confused  between ac and dc, your turbine and bank can be 48vdc and then converted to 220vac, i am no expert but the highest voltage inverter off grid that i can access is 120vdc,i know there are higher voltage controllers but i find them impossible to source unless one is prepared to buy a whole system,,,turbine,controller and inverter.
     ac travells better than dc,however higher voltage dc seems to lose less in transit, also there are turbines on the market which are used to heat water in 3 phase,i recall 3 stages in their system or 3 seperate imersion heaters which control the speed of the turbine and prevent it from overspeed.i thought it a simple but clever system.however it cannot for obvious reasons be used for single phase use. good luck,
                     biff

[billi]

Perhaps  off topic , but i still wonder why  not go for a heatpump ,battery , off grid inverter idea

Billi

[dhaslam]

It is probably best to use  dc  at the heating end.  This would mean rectifying the three phase  output  to  the maximum  DC voltage it is going to be.    If the resistance is correct the  immersion will  produce heat at varying speeds  but will  produce far more heat at higher wind speeds.     Not sure if it needs to be more complicated than this.   

There is also the problem of overheating to consider.  There may be times when the  cylinder is hot and the underfloor heating is not calling for any heat.     Wind is a lot less predictable than  sun  and you could get  a few kilowatts output fairly  continuously for a few days. 

[Windless]

Dhaslam, I’m inclined to agree with your keep it simple mythology.  What about start up impedance I assume I’d need some electronics to open the circuit once a specified voltage is reached.  Maybe this would not be an issue?

Billi, I love the idea of the turbine powering the heatpump but cost is always big on my mind.  Would you be suggesting; buying the heat pump (inc controls and piping), bury the outside pipe in the ground, tie it in instead of my oil heating and let it work away?  One would then have to consider a thermal store tank and changing radiators to low temperature rads.  The scale of the project would scare me.  If it was worth doing I’d imagine one should do this work first powered from the grid and then consider the turbine. 

Biff, I have no doubt but I get confused when it comes to certain aspects of electronics.  I had assumed if I went the 220v route I would have be receiving 3-phase power from the turbine, then use rectifier to convert it to DC (somewhere around 220v depending on wind).  I had assumed I would then need an inverter to convert to ac, regulate the voltage and control the power draw (example  http://www.sma.de/en/products/wind-energy-inverters/windy-boy-1200-1700.html) However after dhaslam post and talking to some immersion people I now understand I can run the rectified DC straight to the immersion element. 

Are there increased safety concerns in 220v dc vs. 220v ac?

Am I still confused? My brain hurts from thinking more than my recommend daily allowance.

[timbo]

Hi Windless,

I had a good direct heating system running a few months back using a 1kW Navitron turbine.

The output is 3ph. First I simply rectified it with 6 diodes, and connected directly to the 2 x 3kW 240V immersion heaters (which are just high power 19ohm resistors) in my 320l tank.

Worked OK but didn't start up until a good breeze was blowing. Never overheated the tank and worked beautifully alongside the wet panel (when the sun wasn't shining, it was windy!).

To solve the start up problem I built a switched load controller which just connected the second immersion load in parallel after a certain DC was reached across the first. This used one op-amp, a few resistors and a big (900V 10A) switching FET from a CRT TV. I set the thresholds to add the second load when the voltage exceeded 120V then switch it out again if the voltage dropped below 40V)

After a few months it turned out that the big FET, wasn't quite big enough and both loads were connected all the time again :-(

Just rebuilding now with a (380V/45A) solid state relay (£4 on ebay from china) I will switch the AC before the rectifiers.

Even with the switched load, it is a very simple setup.

No problems with DC on the elements instead of AC (it doesn't get wet ever) and the immersions are fine with many 100's V DC.
Losses in the cable (mine is 70m) are much less with higher voltage as higher voltage means lower current (at same power) and losses are I x I x R.
240V 3kW immersion elements are cheap as chips

Timbo.

[stephendv]

Hi Windless, 

Could you provide some more background information about your situation?  Are you currently off-grid or running on grid?  What do you currently use for heating?  Why will you not be able to grid connect the turbine?

[RobNute]

Hi Windless, we are mucking around atm with a direct heating set up running off a waterwheel, we have a 2.2kw permanant magnet generator from a wind turbine being driven by a 16 foot waterwheel, this produces 3 phase ac from 0 - around 230 volts on each phase. This then goes through a 3ph RCD and MCB before either going to a 2kw 3ph immersion or switched via a relay by the thermostat to a dump load. Here is a 3ph immersion,

http://www.cicn.co.uk/Merchant2/merchant.mvc?Screen=PROD&Product_Code=IIH3000-275&Category_Code=003

We have not had it all running for long as we are still finishing off various bits and pieces but as a simple way of heating water it seems to work fine, I understand you will have far less starting torque than us so some automatic disconect is required but it seems that these are not too hard to cobble together. I did not like the idea of high voltage dc and our genny seemed to prefer not having the rectifier anyway so that is why we have taken this route, time will tell if it was the right one! Like you we had a fair distance to put wire in and we used 5 core 2.5 armoured, not cheap but cheaper than batteries.  Where your system is simpler than ours is that you dont have to control the wind but we do have to control the water!! The good thing about connecting directly from the generator regardless of whether you go for low/high volts or ac/dc is that the load increases as the volts increase so you are always only using what you are able to produce at the time and the turbine will balance itself against the load if you match it right. From what I have found out immersion heaters dont really care what they get given, they are just rated at a certain wattage at a certain voltage and can be safely used below those figures with no problem. Another idea that I had was to have 2 immersions in the same tank giving you 3 power levels, both in series for half power, one on, one off for mid power, both in parralel for full power, cheap enough with single phase anyway. Hope this is of some use to you, we are new to the whole thing too and a few weeks ago I though my brain would burst, never been so tired just from thinking!! Best wishes.

[Philip R]

If using DC, then switching is more of a problem than with AC, due to the lack of zero crossing current on the waveform. Therefore any element with integral thermostat will show that it has a much lower DC rating than for AC.

As an aside, should you be unfortunate enough to get a belt, DC is much harder to let go of, than with with AC. Hence the term Dodgy Current.

[timbo]

I bypassed the immersion thermostats to avoid the possibility of the load being removed from the turbine.

Theoretically the tank can overheat.

In reality, a 1kW turbine a 320l tank, 3 teenagers in the house....the tank never gets above 55degrees.

Timbo.

[RobNute]

Have a look at this post from me, these products may be of some use to you if you go for high voltage ac.

http://www.navitron.org.uk/forum/index.php/topic,12380.0.html