Solar Power to drive 2KW Motor

Ciaran Registered Users Posts: 3
Hi Guys,
I have a farm leased with no power on it and I was hoping to install a horse walker this Spring/Summer. The horse walker has a 2KW motor which will be running for about an hour or so every day(1-2hrs). Does this mean I need a 2KW system, will that work? 
I am new to solars and would really appreciate some help. I don't need all the calculations just yet but would like some assurance that this motor can run off solar panels. 

Thank you, Ciarán


  • BB.
    BB. Super Moderators, Administrators Posts: 33,404 admin
    edited March 2021 #2
    Welcome to the forum Ciarán.

    I will go through a very quick set of steps and calculations... Nothing is written in stone--Just points for starting the discussion.

    First, you need to measure the actual energy usage of the motor. It is doubtful that the motor will be taking 2,000 Watts during that entire time--Perhaps 1/2 that. But, for the sake of argument, I will assume that. Using a genset and a power meter (or measuring at a friend's place):

    One question (among many)--Do you need 230 VAC power elsewhere on the farm? Lights, laptop computer, cell phone charging, etc... Solar Power is not cheap--And building a system that will support other loads from one central system is generally less expensive.

    While it is possible to make a system that runs directly from solar panels--The drawback is that the system only works when the sun is up and shining.. A battery system will let you use day/night/cloudy weather--But it is more expensive, and batteries typically last 3-5 years (for simple deep cycle golf cart batteries).

    Battery sizing--2 days of operation (no sun), and 50% maximum planned discharge for longer battery life). Battery bank voltage typically 12/24/48 volts. For this system, 48 volt probably better:
    • 2,000 Watts * 2 hours = 4,000 Watt*Hours per day
    • 4,000 WH per day * 1/0.85 AC inverter efficiency * 2 days * 1/0.50 max discharge * 1/48 volt battery bank = 392 AH @ 48 volt battery bank (flooded cell lead acid deep cycle batteries)
    Next, charging the batteries.... 10% to 13% rate of charge is typical for full time off grid system:
    • 392 AH * 59.0 volts charging * 1/0.77 solar panel+controller losses * 0.10 rate of charge = 3,004 Watt array nominal
    • 392 AH * 59.0 volts charging * 1/0.77 solar panel+controller losses * 0.10 rate of charge = 3,904 Watt array "typical" cost effective maximum
    And we have to size the array for your loads and amount of sun per day you have. Assuming fixed array facing south:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 37° angle:
    (For best year-round performance)


    There is just not a lot of sun (if I have your approximate location correct in Ireland)--Take December:
    • 4,000 WH per day * 1/0.52 end to end off grid AC solar system eff * 1/0.94 hours average sun = 8,183 Watt array December break even.
    • 4,000 WH per day * 1/0.52 end to end off grid AC solar system eff * 1/3.0 hours average sun = 3,564 Watt array April-September
    Looking at a 3,004 to 8,183 Watt array (using the full numbers so you can see where they come from... For solar, +/- 10% is about the same... I.e., 3,000 Watt array +/- 10% or +/- 300 Watts). And a 2,000 Watt electric load may be much higher than the average loading...

    You could use less energy in winter/during bad weather... Your motor probably does not take 2 kWatts under normal operation, etc.. So you might get away with 1/2 sizes battery bank and 1/2 size array.

    My guess--This is a pretty large system and not much sun (unless you only need in April through September). An off grid solar+battery+inverter system may be too expensive for your needs... (that is a good size solar power system--Enough to run an energy efficient home).

    Other options... Petrol or Diesel powered (direct motor drive, or a genset+electric motor). There is another technology which takes power from the solar array and passes through a VFD (Variable Frequency Drive), and on to a 3 phase induction motor. These units are becoming quite common for water pumping--May work for your needs. The Solar Input VFD may take some shopping around to find one that meets your needs. VFDs can be programmed for variable motor speeds, and drop back in RPM in cloudy weather.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Ciaran
    Ciaran Registered Users Posts: 3
    Wow, Bill, 
    Thank you so much for your response. The motor would predominantly be for the summer months so it could possibly work. Would you have any idea what the cost of a battery solar system like what you described up there might cost as I'm not sure if I mentioned in original post it is circa €3-4,000 to connect to electricity and it is a leased farm so it would be nice if I could bring my system with me at the end of the lease rather than just dumping 3-4k. Also, there's always the adventure of can it work!? 

    Thanks again,

  • Ciaran
    Ciaran Registered Users Posts: 3
    Elsewhere it is suggested that a 2KW motor horse walker consumes .4KW/H but I haven't had that confirmed from any suppliers - just what the internet has told me. And yes, lights could be handy and a power socket or two. Thanks for your help, I'm just north of Dublin so those figures are very relevant :)

  • BB.
    BB. Super Moderators, Administrators Posts: 33,404 admin
    I am not in the "solar business", and I am in the USA--So our pricing, and sources (from our host NAWS, to Amazon/Ebay/etc.), new/used... Much of these just depends on how good at shopping you are, and if you are looking for new or used (solar panels last for 20+ years, AC inverters 5-10+ years, etc.). Batteries can be bought used (reconditioned forklift batteries, etc.)--But they are a bit of a gamble.

    "Cheap"/small solar power systems are 500-1,000 Watts. Mid priced solar power systems are 1,200-1,800 Watts... If you really need 4kWatts (to get the motor and horses moving, etc.)--That is not going to be "cheap". And there is always the question is this going to be a self install, vs paid installer.

    €3-4,000 is (in the USA) not that expensive to bring power to a piece of property (it depends--Edge of city, vs miles in the middle of nowhere)...

    I would be guessing that you are looking at $10,000-$20,000 minimum for such a large system (at least in the US from new parts).

    I understand the desire for building and moving your solar power system--But even that can be an issue. Solar panels need to be racked such that a wind store will not blow them over, grazing animals and horses do not rub up against or chew the wiring, etc.. And you need to pull down the racking (usually set in concrete pier footings), pull wiring, and safely pack those thing glass panels for transport elsewhere.

    Solar power system does not charge you x€/kWH (in the US around $0.10 to $0.40 per kWH).

    I would suggest not falling in love with solar... Build a system on paper that will meet your needs, and price it out.

    Compare that to €3,500 to bring power to the farm, and €1,000 per year for a reasonable amount of power (don't know in Ireland, but in the USA that would be ~300 kWH/month (small/efficient home) or 3,600 kWH per year....

    And after you lay out the bringing power to farm (one time charge)--That leaves you with your monthly/annual power bill (which solar solar does not have--But you have maintenance/new battery bank every X years, etc.).

    I would check with the owner of the land... Perhaps you work out a deal to share the costs, or arrange for longer term reduction in rent over a few years to leave the power installation for the next tenant (I would expect the electric utility connection would increase the value of the property--And increased rent).


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset