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The difference between Livint's Firestar solar pump inverter and a VFD
September 19, 2016
Many farm owners are increasingly looking at solar as a viable option to run their pumps considering that they are currently faced with poor power supply. To cater to this increasing demand, many people now provide services to this effect. The standard solution is to go with the seemingly cheapest possible solutions i.e use the cheapest panels, the cheapest controller and the cheapest pump. More often than not, this turns out to be the most expensive option. Case in point, a customer has an existing 5HP pump which he wants to convert to solar. The standard formula applied today is for every 1HP for a pump you need 1KW of panels. Nothing really can be further from the truth. In reality, the panels required are a function of the kind of panel (polycrystalline, mono crystalline or thin film), panel wattage, voltage, efficiency, pump head, pump efficiency and type of irrigation (flood, drip or storage tank) and efficiency of the controller.
For now, I will focus on the last item, the efficiency of the controller. Prevailing thought is to put in the cheapest possible Variable Frequency drive (VFD) to run the pump. However, most VFDs often have an efficiency of just 80%-85% and don't contain a bonafide MPPT thereby producing less than optimal power.
Consider the cost of a 5HP pump to be converted to solar. The total cost per KW of panel installed at site is around INR 60,000 (USD 900) while the cost of a drive is INR 20000-25000 (USD 350-400). If the efficiency of the controller can be upped to 95%, panels can be reduced by around 10% which translates to a cost saving of INR 30000 (USD 450). LIVINT's Firestar pump controller has an efficiency of 96.63% which means you can easily save money by reducing the number of solar panels required by at least 10%.
What about the quality of panels? In many cases, VFDs have a narrow input voltage range which means that you are restricted by the kind of panels you can use to achieve the voltage range. An extreme case is for a 1HP pump where installers are using 12 100W panels to achieve the necessary voltage. Compare this with our Firestar solar pump controller where all you need is just 4 250W panels of 44 volts each. This itself translates to a saving of over 25% on panels alone. Similar cases also occur in 2HP and 3HP pumps where specific panel combinations are required to achieve optimal input voltage. Since the Firestar solar pump inverter has an input voltage range of 150V to 700V you are free to use any choice of panels that may suit you.
In addition VFDs were typically made for industrial automation but are now being used in agriculture. Industries are clean environments while agriculture is exactly the opposite. VFDs are not built to cater to the rough external environment which means one is forced to provide suitable enclosures to it. All this means additional cost and time for the installer. The Firestar solar pump inverter is IP65 certified as it is built only for running 3 phase AC pumps in rough environments
And whats more, most VFDs do not come with built in protections for dry run, lighting, short circuit etc. All these have to be added in at additional expense of time and money. And in many cases, due to the fragmented nature of the installer community, such skills are in short supply
In conclusion, we believe one should have different horses for different courses and therefore VFDs for agricultural applications are not necessarily the right choice in terms of reliability and cost. The most cost effective solution will more often than not be the solution with the highest efficiency. Given this, its better to use a solar pump controller with an integrated MPPT, inverter and VFD. The question for you is to the decide whether to use the Firestar pump controller or one from a competitor.
For more information, do feel free to write to me at firstname.lastname@example.org. I would be happy to be of assistance.