Everything you need to know before buying a solar pump
If you are looking for a solution to pump water, there are a dizzying array of options that can confuse even the most technical of us. Should I use a regular pump and run it on diesel or the grid or should i convert to solar? What are the costs/benefits of converting to solar?
If you are looking to be less dependent on the grid or on diesel power, the best option is to look toward solar energy. If you are looking toward solar energy, should you use a DC pump or an AC pump? If its an AC pump, should you use a single phase pump or a 3 phase pump? And what if I already have a pump? what should i do with that? I get asked questions like this almost on a daily basis. I shall endeavour to put these questions to rest in this article.
Is Solar a viable option for pumping?
The short answer is YES.
Lets assume a scenario where the grid is unreliable and therefore you are forced to use diesel to pump water.
The total cost of installing a 1HP solar pump solution will come around Rs.1L which includes panels, pump controller and a brand new pump. This solution will last you 25 years and will generate 30000 units of power (4 units/kw/day X 300 sunny days per year X 25 years). In effect, the cost per unit of power will be around INR 3.33 over a period of 25 years. This is significantly lower than using diesel which costs almost INR 21 per unit today and will continue to increase over the next 25 years. In effect, you will recover your investment over using Diesel in just around 3 years.
The costs reduce even further if you go for higher HP solutions. For e.g. If you choose a 5HP solar pump solution, the total cost will work out close to INR 3,50,000. The cost per unit works out to just INR 2.33 per unit and payback is just 2.5 years. All this is without the benefit of subsidies offered by governments
The calculation above pretty much settles this argument in favour of solar. So now, should i use a DC pump or an AC pump?
DC pumps come with their advantages. They start with low voltages and this is especially beneficial for 1HP pumps. This is so as 1KW panels are often unable to generate sufficient voltage to start a 220V single phase pump or a 415V 3 phase pump. There are new 110 V AC pumps being provided by manufacturers but these too come with their disadvantages. A DC pump or a 110V AC pump while good for solar applications are not compatible with the grid. So if you want to run your pump at night or on cloudy days, you are out of luck. If you however have a 220V or a 415V pump you can run it using the grid. In addition 220V single phase and 415V 3 phase pumps are cheaper and well tested given that they have been in the market for decades.
Now given that we are now down to the single phase and 3 phase AC pumps, which is the better choice? Most solar pump controllers have a built in VFD which works only in 3 phase. These VFD devices work on the concept of varying frequency and voltage to ensure maximum water output and this works only if the motor is a 3 phase. This ensures maximum efficiency, almost 20% higher than single phase pumps and therefore ensures much better returns for your investment. All said and done, 3 phase AC pumps are the clear choice.
However, there is still one issue that needs to be handled. 3 phase pumps run at 415V while pumps running 1HP and 2HP require panels that generate less than 415 volts as input. So are these a good choice? Will I require excess panels just to meet this voltage? Not really, just choose a pump controller that can boost lower voltage to generate 415V as output. In fact, this feature is useful even for higher HP pumps. The ability to boost voltage will help pumps start much earlier in the morning and end much later in the evening.
Lastly, remember that the solar pump controller is the heart of the system even though it will probably only cost 10%-25% of the cost of the overall system. The higher the efficiency the greater the juice you can extract from the solar panels. Buying an inefficient controller is akin to buying a BMW car with a Maruti engine. Also ensure that the solar pump controller has all protections built in so your installation becomes easy. In many cases, installation is a complex exercise due to a lot of programming that needs to be handled and professionals to handle such work are few and far between.
I hope this article has been helpful to you. For any queries, feel free to write to me at firstname.lastname@example.org. I will try my best to respond as quickly as possible.