Off Grid solar irrigation controller for community park

Jose263

Hi - I joined last night - I volunteer at a community park doing gardening education. We have city water but no power available. Need to install an irrigation controller- prefer.using solar power.- looking for advice/guidance. HELP
We are non profit so least expensive is the plan. We want to install an 8-10 station controller (is there such an animal compatible with solar panels. we hope use Rainbird/orbit items from HD or Lowes - the valves require 24vac.
I am a newb and don't know what to ask. We want to establish solar power (plenty of sun available - need to power a small irrigation controller probably 120vac -.we do not need to run a water pump- It would also be nice to have a 120vac outlet available on site. .
Looking for advice.
TJ

solarix

You need a small off-grid AC solar system. Xantrex makes one called "PowerHub" that is probably bigger than needed, but is a nice package. Could also just go with simple PWM charge controller feeding a single battery driving a small 200 - 400W inverter like you can get from any truckstop. You will need AC for sure because of the 24Vac irrigation valves. Irrigation Timers are also all AC.

BB.

TJ, welcome to the forum.

Yes, there are a fair number of solutions for off grid irrigation controllers... They range from something like this that run son 1x 9 volt radio battery:

http://www.rainbird.com/landscape/products/controllers/TBOScontroller.htm

To native solar powered models like these:

http://www.dripirrigation.com/drip_irrigation_categories/59
http://www.hunterindustries.com/irrigation-product/controllers/xc-hybrid

You could go with standard AC controllers--But then the cost for the solar power system would be pretty expensive... Just to make some guesses at what such a system would look like:

Say each valve uses 6 watts (around 1/4 amp @ 24 VAC). And the electronics use near nothing, but need to be ran 24 hour per day (keep timer running).

8 valves * 1 hour per day * 6 watts = 48 WH per day
1x 300 Watt TSW AC inverter * 6 Watts * 24 hours per day "tare losses" = 144 WH per day
===========================================================================
196 Watt * Hours per day of 120 VAC power

• 196 WH per day * 1/0.52 system eff * 1/4 hours of sun per day (9 months a year growing season) = 94 Watt solar panel minimum

Battery bank:

196 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 maximum discharge * 1/12 volt battery bank = 77 Amp*Hour @ 12 volt battery bank

The rate of charge to keep the battery bank "happy" runs around 5-13% rate of charge:

• 77 AH * 14.5 volts charging * 1/0.77 solar panel+charge controller eff * 0.05 rate of charge = 73 Watt minimum solar array
• 77 AH * 14.5 volts charging * 1/0.77 solar panel+charge controller eff * 0.10 rate of charge = 145 Watt array nominal
• 77 AH * 14.5 volts charging * 1/0.77 solar panel+charge controller eff * 0.13 rate of charge = 189 Watt array cost effective maximum

For a full time off grid power system, to allow for aging, bad weather (you don't want to haul out a genset to recharge the battery bank), and just to keep the system maintenance to a minimum, I would suggest approximately a 189+ Watt array. It would also give you a little bit of extra 120 VAC power (run a radio, charge cell phone, etc.).

If you want significant amounts of extra AC power, you need to measure/calculate those loads (using a Kill-a-Watt type meter can be very educational), and size the battery bank+solar array+AC inverter to power the total loads.

All in all, I would go with the battery powered, or irrigation system designed for off grid/solar use. The first think is they use special valves that "latch" on or off... They only use power to change states (they typically have a small motor that opens or closes the valve). They use a whole lot less power and a system can run from a hand-full of AA cells or even a 9 volt transistor radio battery.

Off grid solar power is expensive and over kill in this case. And somebody would have to monitor the system (especially during cloudy weather) to make sure that the system is running correctly and the battery is not being over discharged.

-Bill

Jose263

solarix wrote: »

You need a small off-grid AC solar system. Xantrex makes one called "PowerHub" that is probably bigger than needed, but is a nice package. Could also just go with simple PWM charge controller feeding a single battery driving a small 200 - 400W inverter like you can get from any truckstop. You will need AC for sure because of the 24Vac irrigation valves. Irrigation Timers are also all AC.

solarix and BB -Thanks for these links and discussion- seeing pictures of the wiring setup and components involved is very helpful. I asked my initial question about irrigation controllers - but looking at the equipment involved - I think we need to address all our electric needs with a single solution - and have a safe place to install this equipment - this is a public park and some visitor have sticky fingers - so now I am thinking that the system should be installed in the locked 40 ft container van we use for storage on site. The solar panels could be placed on the roof of the van and the equipment inside. we can run 24vac wire to the water valves. The Xantrex Powerhub is pretty fancy for our needs. We need AC power for a small 120vac irrigation controller, .inside lights in the van and a couple of 120v AC outlets. We might want to run an electric mover - currently use a portable generator when we want to use the mower - I believe the mower is 12 amps. Harbor Freight has cheap inverters and frequent sales.
I think I have a basic concept now- what size system would you recommend if we wanted to power the electric mower or power tools. That may be overkill but if not a lot more $ initially it is probably better to go bigger.
What brand/size solar panels and controller would you recommend?
Thanks,
TJ

BB.

Jose,

It all depends on your loads you want to supply (and where it will be installed--Hours of Sun per day for your locations/seasons), and such.

A good place to start would be to get a Kill-a-Watt type meter to measure your loads (Watts) and energy usage (Watts*Hours per day).

Until you know your loads, I really do not know how to help you design your system. Solar power is expensive--Too small of system is useless and too large of system is costly.

By the way, how much money are you budgeting for your system?

And even if you do go with solar power--I would still highly suggest the battery powered irrigation controller system. With solar power, conservation is usually the best bang for your buck. It is almost always cheaper to conserve than to generate energy with solar.

-Bill