Allotment 12v solar/wind power set-up

topbobster · Post by **topbobster** » Sat Aug 14, 2021 1:47 pm

Hello Everyone,

In my allotment polytunnel I currently have an automatic watering system running from a 12v car battery with 20W solar panel - perfect little set up that has served well for years...Now is time for the upscale:

I have the opportunity of getting a cheap 235W solar panel (Max Volts 29.7V, Max Amps 7.94A, only a couple of years old - from a solar farm so will be good quality,) and one or two free wind turbine(s) (12v, up to 2.5A each in windy conditions - they are from the Antarctic so good quality but oldish,) along with a second 12v car battery (and third/fourth if necessary to build up the power bank,) and would like to set up a 12v system to run the following:

(References to summer are spring and summer, and references to winter are autumn and winter):
1, Summer and perhaps winter: Same small scale watering system (Solar panel should cover this in summer and a bit in winter due to much less watering.)
2, Summer only: 2 x 12 inch car radiator fans (6.5A max each) to help with cooling the polytunnel and airflow (solar panel should cover these as they will be run on a thermostat.)
3, Winter: Under soil heating cable (2-3m square - max 300W) to keep the over-wintering plants from freezing and in late winter/early spring to raise temp a little to help seedlings germinate earlier. This will need to be run off 12v to 220v ac inverter.

Assumptions are that solar will provide power in summer i.e. when it is most needed: more sun, more heat in polytunnel, more water needed, more solar power gained.) And in winter less solar power but hopefully more wind power from the turbine(s).

I have purchased a 100A cheap solar mttp charge controller.
I have purchased a cheap 500W inverter.

I'm ok with hooking up the solar side but it's the addition of the wind turbines that's throwing me, am I just being silly and hook them up into the charge controller with the solar panel or do I need to handle them differently?
Also, is there anything I'm missing?
Is there anything I should be careful/wary of?
Am I doing anything downright wrong/stupid?

Any help would be MUCH appreciated!

Regards, Rob

Someone-Else · Post by **Someone-Else** » Sat Aug 14, 2021 3:11 pm

Try a wind turbine on its own first.
The thing I found was that they* do need a lot of wind to actually work, hence try just one to see how it goes.

* Obviously it depends on make/model of wind turbine not to mention its location/height.

kellys_eye · Post by **kellys_eye** » Sat Aug 14, 2021 4:09 pm

Many MPPT devices have separate inputs for solar and wind and sort the power distribution themselves although (device dependent) you can program various options/parameters.

big-all · Post by **big-all** » Sat Aug 14, 2021 5:06 pm

general comments
forget any idea off other than lighting or the odd 20mins enough to watch a tv connect on the inernet or boi a single cup off water via a cup heater
even lighting will need frequent trips home to charge batteries on cloudy days

Someone-Else · Post by **Someone-Else** » Sat Aug 14, 2021 7:02 pm

Assuming you are good to go with both (Do take and post pictures) you are going to need a solar and wind charge controller to keep one from "cooking" the other.
Also before you spend anything, make sure they are the same voltage, no point in having a 12v solar panel if the turbine is 24v

I am also thinking would fans work as you expect? Since all a fan does is move air, it doesn't cool it, and if it is hot outside, a fan will not cool your poly tunnel, only move the air, to what avail?

I would also suggest you buy This Also ask for the wind turbine specs, and look for minimum wind speed, and compare. You could always try a cheaper method These

topbobster · Post by **topbobster** » Sun Aug 15, 2021 8:24 am

Someone-Else wrote: ↑Sat Aug 14, 2021 3:11 pm Try a wind turbine on its own first.
The thing I found was that they* do need a lot of wind to actually work, hence try just one to see how it goes.
I did see that the first one I got did need about 8mph to start (this was going to be the possible second one) I haven't seen the second one yet - I'm hoping it might have a slightly lower start speed. But yes, trying it is the only way really. Thanks.

* Obviously it depends on make/model of wind turbine not to mention its location/height.

topbobster · Post by **topbobster** » Sun Aug 15, 2021 8:26 am

kellys_eye wrote: ↑Sat Aug 14, 2021 4:09 pm Many MPPT devices have separate inputs for solar and wind and sort the power distribution themselves although (device dependent) you can program various options/parameters.

I'm trying to go as cheap as possible and something like those are probably out of my price range but thanks for the suggestion.

topbobster · Post by **topbobster** » Sun Aug 15, 2021 8:29 am

big-all wrote: ↑Sat Aug 14, 2021 5:06 pm general comments
forget any idea off other than lighting or the odd 20mins enough to watch a tv connect on the inernet or boi a single cup off water via a cup heater
even lighting will need frequent trips home to charge batteries on cloudy days

To be honest I didn't hold out too much hope for the winter set-up - the wind solution perhaps won't be up to task. But, the turbines were free so I may well give it a go and see what happens. Will try to post some results if I go ahead with it.

topbobster · Post by **topbobster** » Sun Aug 15, 2021 8:44 am

Someone-Else wrote: ↑Sat Aug 14, 2021 7:02 pm Assuming you are good to go with both (Do take and post pictures) you are going to need a solar and wind charge controller to keep one from "cooking" the other.
Also before you spend anything, make sure they are the same voltage, no point in having a 12v solar panel if the turbine is 24v

I am also thinking would fans work as you expect? Since all a fan does is move air, it doesn't cool it, and if it is hot outside, a fan will not cool your poly tunnel, only move the air, to what avail?

I would also suggest you buy This Also ask for the wind turbine specs, and look for minimum wind speed, and compare. You could always try a cheaper method These

Separate solar and wind controllers was one I thought might be the case - thanks for confirming.
The turbines are both 12v.
Moving air around in the polytunnel is as important as the fresh air being introduced. I know I wasn't clear, sorry; the two fans will be on each door (thankfully we have a door at both ends of 7m tunnel). One fan high at one end drawing warmer air out, and one at the other end drawing cooler air in - between the two I think it should introduce the airflow around the tunnel I need. The air temp within the tunnel gets to well over 50c at height of summer (our thermometer is only marked to 50 and the indicator is well above that.) so swapping this for outdoor air will work well I think.
Many thanks for your thoughts.

kellys_eye · Post by **kellys_eye** » Sun Aug 15, 2021 8:54 am

Using the cheapest of MPPT devices all you need do is apply all the various source supplies (solar PV, wind, generator, batteries etc) via their own blocking diodes and they will do the job of 'steering' the most prominent supply source into the MPPT.

Your biggest issue is going to be the batteries as the system will be reliant on them for most of the time unless you make arrangements to cut off the loads when voltages drop below acceptable levels. Otherwise you will put unnecessary strain on the batteries and damage them. If they aren't 'new' to begin with then don't expect any better than 60% (a good average - most are worse) capacity from the labelled value and damage can occur even quicker.

Automatic roof vents would be a better option than fans to move air - let the ability of warm air rising do the job without the need for fans! Such vents only consume power momentarily (to open or close). Another vent lower down would create the draft needed to move all the air necessary using thermals only.

Underground heating shouldn't be necessary (unless you have excess power load to 'dump') if you insulate under - a polystyrene floor with grow bags on top will stop ground frost.

How about a gravity-fed water distribution system - mount a tank above the level you need for distribution and fit solenoid valves (on a timer - maybe with a soil moisture sensor too?).

The lowest power consumption devices are those that don't use them in the first place - no point in MAKING a power consumption when alternative methods exist that don't require them and/or might mitigate them to much lower levels.

The suggestions made above would be powered entirely by a single battery with trickle charging from a single solar panel.

aeromech3 · Post by **aeromech3** » Sun Aug 15, 2021 9:43 am

My experience with a solar panel to keep my car battery topped up was: on a very bright day it made its rating, connected to a battery already at 12.5v it provided 0.2A but on a dull day it hardly made a fraction of volts such that it could not provide amps to the battery and not forgetting nil after dusk. Your 235W might drop to 25W at for 12v which will not maintain one working battery feeding 2x 6.4A fans!
Hope I am wrong!