Backyard Aquaponics
A place to discuss aquaponics

I am planning to set up an aquaponic greenhouse that I hope to be able to still grow both plants and tilapia in the winter (I live in the UK so winter can get below freezing).

As such I definitely need something to keep the greenhouse warm, i am already planning to use bubble wrap and black water barrels to keep as much heat in as possible, and the fish tank will be embedded into the ground to help retain heat that way.

The greenhouse itself will probably be around 8x6 or slightly larger and the panes will be made of 4mm twin-wall polycarbonate to help there.

I've also run some basic calculations and have found that the average wind speed for where I am is about 18mph with the lowest be 10.7mph, using that and a Rotor swept area of 2.5m I came to the conclusion that I would make about 800w minimum, which will then run to a leisure battery.

This will definietly run my water pump, but with 1 or even 2 of these could I also run an electric heater to keep everything at growing temperature? What heaters would be available to me as this is obviously a 12v system and all the ones i find are 120v to 240v?

Also i was planning to use a car actuator to make the wind turbines myself on the cheap, is that a viable plan and could i expect to still get this kind of power even with gears to increase its turn speed?

Well...

Yes, you can heat water with wind generated electricity.

BUT

To make a meaningful difference you will need, many many hundreds of watts, possibly well over 1000 watts.

To get that much power you're on the right track, you will need a pretty big wind generator. Your neighbours might have something to say about it.

The thing is that for a wind generator to work well, it needs smoothe consistant air over it. Trees, buildings, things like that break the wind up so you'll need to whack it up on a pole or tower of some sort

When the wind isn't blowing you'll probably still want some heat, otherwise you risk your water temperatures going up and down a bit like a yoyo

To run 120VAC or 240VAC items off of a 12VDC you'll need to run an inverter.

Another option instead of an alternator from a car is the electric motor from some washing machines.

After extensive and confusing electronics research i need to confirm something, if hyperfetically i have 1000w going into a battery via an energy source its going in at 84 amps? Then if i connect it up to a 240v converter into a 1000w heater although the heater is only drawing 4 amps the inverter is still drawing 84 amps and because of this (ignoring the power drained for the inverter itself) my battery stay at the same level. Is that all correct?

It depends on the voltage that your wind generator is running at.

Most car alternators output somewhere between 13.5 and 14.5VDC

If you have 1000W@14.5VDC it is about 69Amps feeding into your batteries (you'll need more than one)

If you have a 1000W load at 240VAC it will be around 4.2A however some inverters run at more like 220-230VAC meaning the Amps will be higher.

Don't ignore the wastage from the inverter, on a big load that smallish percentage can add up to a fair bit.

Not allowing for the inverters wastage, the amps load on the DC side will be more like 69A whilst the wind is blowing and 84A when it's just running from the batteries.

It wont take long to drain your batteries with a load like that...

I assume you mean car alternator? ... and it is unlikely to work, as they require much higher rotation speeds than you will be able to produce with a small turbine. Gearing them up means frictional losses, so your output might only be 25% of the theoretical power obtainable with any given wind speed and turbine diameter. A 3.6m diamter WTG I built with a 24V truck alternator went through chains and sprockets within a few months, and belts never lasted long either, but I did get over 1kW out of it in strong winds.

You can buy 200-500W 12 and 24V Chinese wind turbine generators reasonably inexpensively, and they work well, although the regulator/dump load that comes with them is junk, but isn't really needed anyway. I've had over 750W out of a 24V 200W unit in strong winds by running it at higher voltage through an MPPT controller.

As noted above, you will need a significant capacity battery, and you will probably need a 20m or taller tower for the turbine, to get above turbulence, which is fine in rural areas, but you wouldn't get permission for one in an urban area.

BTW, if I was going to use a WTG to heat water, I would not waste energy by using batteries or inverters, I'd use a resistive element to heat a mass of phase change material and use that to moderate the water temperature. Gain extra heat when it is windy, and release it when it is calm.
I'd probably put up a suitable array of solar panels up too, for those calm clear winter days, running a separate resistive element directly into the PCM.

Have you actually calculated the heat loss of your proposed greenhouse? http://www.littlegreenhouse.com/heat-calc.shtml

I couldn't add anything more to what you've been advised already. These replies are right on the money. I have a home-built Other Power http://www.fieldlines.com/index.php 800W 24V axial flux wind turbine a buddy and I built from scratch after attending a workshop in Colorado with Dan Bartman and Dan Fink. It uses permanent magnets because there is no exciter power needed to start the alternator. (Car alternators have hundreds of horse power to work from and are not at all efficient.) Permanent magnets are a must when trying to get energy from low speed winds. My 8 foot blade span turbine cuts in (starts creating power) at 8mph and ramps up the current according to winds speed. We need a dump load controller on this style of turbine as the 12 batteries which I have are 118AH gel cells will saturate after a sustained wind. As the batteries become fully charged the load on the turbine goes down and it can run away (over spin) so we dump the excess power into an electric element which can be a water heater. Being an alternator the output is alternating current which is converted to DC though a full wave bridge rectifier before being tied directly into the battery bank. I know this sounds complicated which it is a little, however it is quite simple compared to the charge controller in a photo voltaic system. Other Power has books for sale on how to do everything from carve your own wooden blades, to how to build the alternator yourself right down to winding your own coils for whichever voltage you prefer, the higher the voltage the better for efficiency. They have a good website with books and videos available http://www.otherpower.com/turbineplans.html Also not far from where you are is Hugh Piggott the man who started this home made power revolution http://scoraigwind.co.uk/windpower-workshop/ Also it is important to do yearly maintenance on these turbines and of course things go very wrong from time to time; We had several 85 mph wind gusts a few years ago and mine for some reason failed to furl and it toasted its second alternator. It currently in my workshop awaiting the time needed to build a new set of coils . Nevertheless home built turbine building is tons of fun. It can be a cheap way to create 800 plus watts of power as long as you pick a place to install a turbine where there is unimpeded wind available. I'll see if I can find pictures of my turbine if you like. Smiles,
Brian

Thanks David for the handy calculator i've worked it out as the radiator needs a BTU out of 1603 during the coldest parts of winter, i don't know much so please correct me if i'm wrong but from a quick search i can calulate the BTU of an electric heater as 1w * 3.41, so a 500w heater gives a BTU of 1705? which should be plenty right?


I am still trying to get my head around how the voltages and power draining works so Sean even with the alternator running at maybe 14.5VDC, doesn't the battery convert it to 12v anyway still making it 84A?

If this is true i'm not too worried about the battery draining as i calculated the turbine to make about 800w at 10mph speeds which about as low as it gets here, with the average speed being more like 18mph so i would hope to get probably a 500w heater.
i am also planning on adding a solar panel just to top it off on the very rare no wind days.

One word answer to all your problems....

Trout....

Except im completly new to aquaponics and from what i understand trout are much harder to keep than tilapia, also if i just do trout and dont worry about heating in winter i then still cant grow anything.

I started with 80 trout with no AP experience and it wasn't that hard to do. Plenty of plants will grow in winter in frosty areas, a greenhouse makes it relatively easy to do.

How cold does it get- what are your average winter min and max temps?

Maybe a species of carp then? I heard that people in the UK like carp (they're an evil pest here)

A better option could be to have heaters in black plastic drums of water that are in the greenhouse rather than in the AP water.

That should moderate the heat out a bit and keep the fish tank water temperature a bit more even.

I'll leave it up to the gurus on here to figure out if you could just use a resistive heat element straight off the wind generators then rather than using controllers batteries and inverters. Heat input to the barrels would be directly related to wind, but moderated out slowly over time from the barrels.

Just a thought, cold temperatures aren't too big of an issue here - it's winter and I still have tomoatos growing.

It looks like (from your calculation) that 800w would be about right to heat your greenhouse; considering the loss going into and out of the batteries; and enough extra power to recharge the batteries as needed.