Solar Power to drive 2KW Motor

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):

https://www.amazon.co.uk/s?k=kill+a+watt+meter&ref=nb_sb_noss

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:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Dublin
Average Solar Insolation figures

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

Jan	Feb	Mar	Apr	May	Jun
1.08	1.79	2.48	3.42	3.91	3.76
Jul	Aug	Sep	Oct	Nov	Dec
3.70	3.42	2.93	2.06	1.42	0.94

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.

-Bill