Help power 220v motor with solar panels and battery

fcgadelha

Hi guys,
I'm new to the solar power world. I have 5 aerators in a shrimp farming powered by my regular house supply 220v AC but I want to go green and make them solar powered. The motors in the aerators are all 220v motors. What kind of batteries and solar power panels would you recommend? These aerators are on only at night for 12 hours straight. Thanks guys 

mike95490

The simple way is Grid InterTie connection, where your panels feed a special inverter that backfeeds the grid and unwinds your electric bill.    Simple, Cheap, and payback in 5-10 years, depending on the cost of electricity,
 Batteries are the most complicated way, expensive and you will never save money, you will spend 5-10x as much as grid power would cost you.
  But batteries give you a backup if the grid fails and the air stops.   Can you buy shrimp insurance for death from lack of air ? Is insurance against "crop failure" cheaper than batteries & solar ?

BB.

I agree with Mike that, if you can (local laws/regulations), grid tied solar (solar panels -> GT inverter -> utility mains) is the best solution. In general, GT solar will be about 1/4 the price of a full off grid battery system to install and operate over time (new batteries every 5-10 years, new electronics every ~10+ years, new panels every ~20 years).

However, if you are really interested in running the pumps at night, first you need to find the most energy efficient pumps and motors you can, and the minimum amount of run time needed, conservation is almost always cheaper than building out a larger solar power system--Here is the basic math:

Assume that you have 1 HP motors that run 12 hours a night at ~1,400 Watts and you have during 9 months of the year around 4 hours of sun minimum per day (need your approximate location). The solar array will be fixed and tilted to your ~latitude, and you will use utility power/genset for bad weather/backup power.

• 4 pumps * 1,400 Watts * 12 hours per day = 71,800 WH per day = ~71 kWH per day

That, by the way, is a huge amount of electricity for an off grid solar power system, especially if running the loads at night. A "medium size" solar power system for an energy efficient home is probably around ~3.3 kWH per day

Battery bank sizing--2 days of storage, 50% maximum discharge, 48 volt battery bank:

• 71,000 WH per day * 1/0.85 inverter eff * 2 days of storage * 1/0.50 maximum discharge * 1/48 volt battery bank = 69,961 AH @ 48 volt battery bank

Next, I would suggest around 10% to 13% rate of charge (from solar) for a full time off grid system battery bank (to keep the batteries happy):

• 69,691 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 53,338 Watt array nominal
  
• 69,691 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge =69,339 Watt array "cost effective" maximum

And then there is array sizing based on hours of sun per day (summer lots of sun, winter usually not so much). 4 hours is a fair amount of sun for USA in many areas (9 month minimum of the year). Other places, in winter, you can get down to 2 hours or less hours of sun (or if you are in an area with a marine layer, etc.).

• 71,000 WH per day * 1/0.52 off grid system efficiency * 1/4.0 hours of sun per day "break even" = 34,135 Watt array array minimum
  

The above is based on a full off grid set of rules of sun... If you can use utility power during bad weather, perhaps you only want 1/2 battery capacity (enough for 1 night of power and 50% maximum discharge). That would save you some money (bit smaller recommended array, less out of pocket for initial install). But, battery cycled 2x deeper (50% per night vs 25% per night) will last about 1/2 as long--So there is no long term savings in battery costs.

Also, I guessed on your pump size and hours per night--You can certainly change my assumptions. My numbers are "conservative" -- Which may make a larger system than you really need.

And the similar math for a GT based system (solar panels+GT inverters are relatively "cheap" and maintenance free for 10+ years):

• 71,000 WH per day * 1/0.77 GT system efficiency * 1/4 hours per day nominal = 23,052 Watt array "break even" on power

You need to check with your utility. In some areas, you may by utility power at $0.10 per kWH at night, and feed back ~$0.20 per kWH back in to the utility during the day (technically, you need 1/2 the size of array, at least during summer time for "time of use" power). You may also get farming/utility rate breaks by buying "lots of power" at night, and using little power during the day (utilities typically have lots of "excess capacity" after 9pm until 8am the next morning.

Anyway--that is the basics for the math/solar power options. There are a lots of details to work out--So take this as a starting point, not the final quote/end point.

-Bill

fcgadelha

Guys thank you so much for your help. This farm is located in South America in a town right underneath the Equator so there's lots of sun light all year long from 5 am to 5 pm. I will try now to understand your comments. Lots of things to work on now. Thank you so much for your time. 

BB.

Use one of these links (or others) to figure out "hours of sun" for your location:

http://solarelectricityhandbook.com/solar-irradiance.html
http://pvwatts.nrel.gov/pvwatts.php

Both of the above take weather into account (morning fog, afternoon thunder storms, etc.).

-Bill