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Wind powered electric heating
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adam2
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PostPosted: Fri Aug 08, 2008 1:55 pm    Post subject: Wind powered electric heating Reply with quote

Wind power is inherently variable, Therefore almost any off grid wind turbine will require battery storage for lighting and essiential loads.

When the battery is full, power must be diverted to a dump load or loads in order to avoid damage.

In the case of a small wind turbine the dump load is generally a resistance in a ventilated box mounted on or adjacent to the controller.
Since this equipment is often in a shed etc, any power diverted into the dump load is lost.

Except in very small installations it would be preferable to use this energy for heating, rather than waste it.
The simplest approach is simply to relocate the dump load to a living area, this means the heat is used rather than wasted.

If the dump load is only 1KW or less, thats not enough for much space heating, but could heat water in a storage cylinder. This is especially worth while if solar hot water is used in the summer.
Although 1KW may not sound much, it may heat the hot water for a family, if available for enough hours a day.
Remember that a typical 3KW immersion heater may only run for three or four hours a day, 1KW for nine or twelve hours would work just as well, presuming a large enough storage tank.
Ideally a hot water tank should have two elements, top and bottom. The surplus power is first used to heat the top part of the tank, when this reaches say 60 degrees, then the power is switched to the bottom element and the whole tank heated, possibly to near boiling point if the wind is sufficient. It is therefore advisable to fit a tempering valve to the outlet to avoid scalding in the bath etc.

If more than about 1KW is available then space heating becomes a possibility.
The simplest approach is simply to use one or more standard electric radiators as dump loads, this works quite well but is not ideal in changing wind conditions.
If the wind suddenly blows hard just after the stove has been lit, the room would be overheated and the coal or wood wasted. Likewise if the wind suddenly dropped on a cold night, the room would soon be chilly.
If the existing heating is oil or gas, and therefore readily turned on/off, then this system works quite well. Every hour of decent wind is an hour in which oil or gas has not been burnt.

A system with thermal storage is better, and is especially worthwhile if several KW is available.
Suitable storage provides a more stable space temperature despite very variable wind.
Numerous ways of storing heat are available, including
1) standard electric storage heaters, cheap and simple, although not inteneded for this sort of use they often work well.
2)a very large, very well insulated tank of water heated with surplus wind power, and pumped through conventional rads.
These radiators should be oversized to give sufficient heat at a relativly low temperature, and a mixing valve should be used to maintain a constant temperature, even when the store is near boiling.
3)Under floor electric heating, highly recomended but only viable if a new solid floor is being installed, the floor must have very substantial thermal mass. Either heating elements set into the floor can be used, ot hot water pipes and an electric boiler.
4) Probably the best is a home built thermal store/electric masonery stove (details to follow, I only know of one in the UK)

Finaly, remember that loss of the dump load to a wind turbine may destroy the battery or the turbine, therefore duplication is essiential in most cases.
What happens if an electric heater fails? or the water in a thermal store reaches the limit stat setting on the immersion heaters? or a storage heater becomes full and the thermostat turns off the elements?

Large wind turbines produce a lot of power, seek advice for all but the smallest and simplest.
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snow hope



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PostPosted: Fri Aug 08, 2008 2:20 pm    Post subject: Reply with quote

Great post - thanks Adam. Smile
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adam2
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PostPosted: Sat Aug 09, 2008 9:14 am    Post subject: Reply with quote

Home made thermal store, for wind/electric heating.

(these details are only provisional, relying on my imperfect memory)

Some years ago I assisted in building a home made thermal store, to make best use of surplus wind power for heating.

The wind turbine generated 3 phase current, at a voltage and frequency dependant on the wind speed. the maximum ouput was about 7KW at 120/208 volts, three phase AC.
The average in the winter months was about 2 to 3 KW

The control unit produced a regulated output of 27.5 volts for charging a nominal 24 volt battery.
After the battery charging load was satisfied, any surplus power was diverted to 4 dump loads, switched in sequence by the controller.
In addition, when the wind was sufficient, a large three phase motor could be used, directly from the turbine, this was used to drive a saw bench, or to grind flour or animal feed. The motor and the turbine would stall if the wind dropped, and was therefore not suitable for unattended operation.

To make best use of surplus power, a giant dump load/home made storage heater was constructed, in the middle of the main open plan living area.
This was a solid brick/concrete block construction, about 1M high, 2M long, and 1M deep from front to back.
It was built on the existing solid floor, one course of concrete blocks being laid first, then the heating elements bedded in sand, then paving slabs over the sand, and the remainder of the structure being built up with bricks laid in a weak lime mortar.
The innner bricks, nearest the heating elements were special thermal storage bricks obtained from scrap storage heaters.
High temperature cables to the heating elements were joined in a nearby junction box to ordinary single core wires in large conduit, laid under the floor.
Two spare elements were installed, not connected, for future use in case of failures.
An internal temperature sensor was installed, and has reached 200 degrees, though a bit over 100 is typical.
The sides of the structure were faced with local stone to improve the apearence.
The top was covered with smooth stone slabs, again for appearence.
A weak lime mortar was used throughout, to ensure stability without excessive strength, in case dismantling is required in future.
Although a very bulky construction, the finished item looked quite attractive, and if not too hot, may be sat upon (if not covered in cats!)
The surface temperature varies from about 40 degrees to about 60, and laundry may be dried on or near it without risk of fire.

The alternative heating is a coal fire or portable gas heater, neither is very economical, but they are used so little that this is of little importance.
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hardworkinghippy



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PostPosted: Sat Aug 09, 2008 2:44 pm    Post subject: Reply with quote

Thanks so much for all this stuff Adam, this couldn't have come at a better time !





We still have a lot to do before the turbine will be generating electricity so we've got plenty of time to chew over your ideas - so keep them coming please. Cool
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Andy Hunt



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PostPosted: Mon Aug 11, 2008 10:49 am    Post subject: Reply with quote

Great photos as ever HWH . . . there were loads of those Rutland generators at the Northern Green Gathering I've just come back from on the weekend - they were working incredibly well. The whole festival was running on wind and solar alone - no generators allowed!!

Very impressive indeed . . .
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hardworkinghippy



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PostPosted: Mon Aug 11, 2008 4:11 pm    Post subject: Reply with quote

I hate noisy generators. We had a couple who stayed in our little wooden cabin once and they brought a generator and a satellite dish with them for the duration of their stay. Shocked

I wish Rutland would produce much bigger generators, I'd love to have bought one from a name I could trust and get spare parts from easily, all the cheaper low wind start ones seem to be Chinese.

Anyway, even the cost of this tower would have been nearly 600 in France and it was included in the price of the windgenerator - as was the controller and inverter. I'm keeping my fingers tightly crossed that it will all work OK.

We'll have to wait a few weeks for the cement to dry, and need to do a bit more building work on the extension and install the water system before we can get the mast up and connect the head.

Everything takes so long - still, one of my pals who paid over 12 grand for hers 18 months ago is still waiting for the installers to get the thing to work... Neutral
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adam2
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PostPosted: Thu Jan 08, 2009 12:14 pm    Post subject: USE OF "OFF THE SHELF" STOREAGE HEATERS WITH WIND Reply with quote

Standard night storage heaters are of course intended to use off peak grid power.
Although not ideal, such heaters are sometimes used for wind power as well.

Virtually all wind power installations use a battery for storage, and a dump load when the battery is full.

As noted above, water heating is more likely to be viable than space heating, if only about 1KW is available.

If however more than about 1KW is available, a NSH is sometimes used as the dump load.
The choice is whether to dump the surplus at battery voltage or at line voltage, or at the wind turbine output voltage which will be variable.
Most large invertors have the facility to energise one or more dump loads, and this could be used to supply a NSH.
Alternativly the dump load could be at battery voltage, this will probably require custom made elements due to the low voltage.
Use of the wind turbine output voltage, if high enough, may permit the use of standard elements.

The main drawback of useing a standard NSH with a wind turbine, is that all such heaters incorporate an electricly operated damper to control the release of hot air from the unit.
When the heater is energised from the off peak supply, this damper is closed, and the heat retained for later use.
If the NSH is energised for some hours at normal voltage, from a large inverter, then it will work as normal, the NSH does not "know" whether the power came from the grid, or from an inverter.

In most installations though, the NSH wont be energised continually for hours, but will be cycled on/off repeatedly as the wind speed or power used varies.
If the power is on for 10 minutes and then off for another 10, any heat stored in the first 10 minutes will be released a few minute later when the damper opens, and not stored as desired.
Also if the NSH is energised at a lower than intended voltage, this probably wont work the damper correctly.

Therefore the damper must be controlled in some other way for good results.
The damper is not normally directly electricly operated, but is thermostatic and partialy opens/closes in response to the room temperature, this being acheived by a sealed vial containing a volatile liquid, which moves the damper by means of an expanding bellows.
To ensure that the damper is fully shut when the NSH is being charged, a very small electric heating element is placed next to the thermostatic vial, which becomes heated thus and shuts the damper.

To give suitable control over the damper, the small heater located next to the thermostat vial should be dissconnected from the main circuit, and energised from an independant 230 volt supply by a manuall switch, a timeswitch, or other suitable means.
If a reliable "allways on" 230 volt supply is not available, then the heater may be replaced by one of the same wattage, but suitable for the battery voltage.

The modification is not complex, but does require a certain amount of electrical knowledge, and will certainly invalidate any warenty.
Great care should be taken not to bypass the thermostat that controls the charging of the heater, it could otherwise become dangerously hot.

Remember also that when the NSH is full, the charge thermostat will open, therefore some other dump load must alsp be available.
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Last edited by adam2 on Thu Jan 08, 2009 5:34 pm; edited 1 time in total
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stumuz



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PostPosted: Thu Jan 08, 2009 12:37 pm    Post subject: Reply with quote

Fantastic Adam.

Many,many thanks for this, I have been searching for a while and it was on the forum I visit most!

Again, thank you for taking the time to post .
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adam2
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PostPosted: Thu Jan 08, 2009 1:18 pm    Post subject: Reply with quote

Another way of storing heat from surplus windpower, is to use water.
A small instalation is very simple.

Obtain a standard direct type hot water cylinder, and fit to this an immersion heater of a suitable voltage for your installation.

Mount a standard central heating radiator on the wall next to the water tank, with short lengths of 22mm pipe conecting the top and bottom of the radiator to the top and bottom side connections of the cylinder.
Ensure that the pipes slope slightly to avoid any air being trapped.
Fit a stop valve in one pipe.
Fit a drain vlave at the bottom of the cylinder.
Fit an open vent to the top of the cylinder, preferably to the outside.

Fill with water ( perhaps useing a hose, no permanent water supply is required)

Connect the immersion heater as a dump load to the wind turbine.

When surplus power is available the water will become heated, and may be used to heat the room by opening the stop valve on the pipe to the radiator. A thermoststic radiator valve may used if desired.
A circulating pump wont be needed if the tank and radiator are adjacent, but may be needed for long pipe runs.

An open vent is very important as water will certainly expand as it gets hot, and may even boil.
The tank should of course be well insulated to ensure that heated is only emitted when required by the radiator, and not all the time by the tank.
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PostPosted: Thu Jan 08, 2009 5:11 pm    Post subject: Reply with quote

Something to bear in mind with this is that when it's windy, the heating requirement of a building is likely to be higher due to leakage.
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PostPosted: Thu Jan 08, 2009 6:18 pm    Post subject: Reply with quote

I'm back on line after a long break and I'd like to say thanks again Adam for taking the time to share your knowledge.

Irene Smile
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Francis



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PostPosted: Mon Feb 23, 2009 2:36 pm    Post subject: Reply with quote

Hmm this is interesting. I haven't tried using wind power for electric heating yet. So far, the only renewable energy I have tried is solar energy. But thank you, Adam! I am intrigued to try wind power, too!
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adam2
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PostPosted: Tue Feb 24, 2009 5:07 pm    Post subject: Reply with quote

Francis wrote:
Hmm this is interesting. I haven't tried using wind power for electric heating yet. So far, the only renewable energy I have tried is solar energy. But thank you, Adam! I am intrigued to try wind power, too!


Wind powered electric heating has much to commend it in Europe, since the windy weather tends also to be cold, not sure if this is the case in Asia though.

Batteries are the weak point of any off grid system, and perhaps suprisingly, a larger wind turbine may need a smaller battery.
Supose that lighting and small apliances require on average 250 watts, a battery sufficient to supply this for perhaps 6 calm days will be needed.

If the size of turbine is doubled, from perhaps 4KW to 8KW then it is more likely to charge the battery in low wind conditions. Therefore the battery can be reduced in size (or kept the same size, with a greater reserve)
The extra power from the larger turbine being used for heavy duty use, only when the wind blows.
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PostPosted: Tue Feb 24, 2009 5:10 pm    Post subject: Reply with quote

An interesting use of a wind turbine would be under-floor heating polytunnel or greenhouse for the growing of food in winter.
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Francis



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PostPosted: Mon Mar 02, 2009 2:47 am    Post subject: Reply with quote

adam2, in some parts of Asia, the windy weather tends to be cold, too. But right now, I'm here in the Philippines...so, the weather here is warm. I haven't seen wind power here yet...but I've seen a few houses who have solar panels and solar lights in their homes.
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