Off Grid solar irrigation controller for community park

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
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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

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