Solar off-grid products are now more powerful and feature rich, yet affordable

While impressive features and reliability are boosting demand for solar off-grid products, the real game changer is the dramatic decline in the cost of these products

By Richa Chakravarty

Monday, October 13, 2014:  Demand for off-grid solar PV products is increasing, particularly in small cities and in the rural areas that are power starved and currently depend on expensive solutions like diesel gensets, inverters, batteries, etc. Hence, products like solar home lighting systems, solar water pumps, solar chargers, etc, and components like solar charge controllers are rapidly evolving, offering new features even while becoming affordable.

Solar charge controllers

A solar charge controller is required in virtually all solar power systems that utilise batteries. It regulates the power going from the solar panels to the batteries, and saves the batteries from overcharging. So far, pulse width modulation (PMW) charge controllers were being used, but with more recent technological advances, maximum power point tracking (MPPT) regulators have become popular with solar solutions providers. MPPT-based solar charge controllers are almost 95-97 per cent efficient and provide better battery life.

The computer-driven circuitry in the MPPT controller scans the voltage of both the battery bank and PV array at regular intervals, and calculates the optimum match between the two. So, under different weather conditions such as when there is minimum sunlight, energy gains of up to 35 per cent are possible. MPPT controllers have another big advantage of allowing higher-voltage PV arrays, which operate more efficiently and require smaller wire sizes from the array to the controller. In some cases, especially when the PV array must be located at a long distance from the battery bank, the extra cost of the MPPT is offset by the savings from using wire that has a smaller gauge.

Su-Kam’s MPPT solar charge controller is equipped with microcontroller and digital signal processing (DSP) technology. It fully protects the solar power system against transient over voltage and reverses the current flow while charging the battery. This enables the solar charge controller to increase the energy transfer efficiency by up to 30 per cent compared to traditional charge controllers. Easy installation with parallel connection capability makes this MPPT solar charger controller the perfect solution for residential as well as any large solar system application, sources in the company claim.

Phocos’ CIS-MPPT charge controller is based on similar technology. This can be operated via a CIS-CU IR remote control unit and is compatible with 60-cell PV modules. This charge controller comes with an integrated data logger that provides an insight into the system’s operations, displaying important information such as system status, voltage, current, etc.

Gautam Solar offers solar charge controllers of 6, 10, 20 and 40 Amp. These controllers have been designed with the zero drop switching function. They come with reverse battery and reverse panel protection, ensuring no physical damage.

Protonics Systems’ PRO MPPT charger also employs DSP technology for accurate and definite tracking of the maximum power point, irrespective of environmental factors such as temperature and solar irradiation. A high speed modified algorithm has been implemented to optimally harvest and transfer maximum energy from the connected solar panel to the batteries.

Solar water pumps

Manufacturers are today focusing on developing much more affordable solar water pumps, which are generally of two types—submersible and surface pumps. The pump type depends on the water source. In the case of a well, the pump has to be placed underwater. Surface pumps, on the other hand, can be placed at the side of a lake or on top of the water. Surface pumps are less expensive than submersible pumps, but they are not well suited for suction and can only draw water from about 6.5 metres below the ground. Surface pumps are excellent for pushing water over long distances.

Depending on the user’s requirements, manufacturers offer solar water pumps that can operate from 30V DC for very shallow wells to over 200V DC if the water source is very deep. Most of the pumps work on DSP technology, and require a pump controller to match the solar array’s output to avoid premature motor failure.

Elcomponics offers solar water pumps that can lift water up to 304.8 m of vertical head and can run for much longer distances on horizontal head. Generally, if water pumps are not used for long periods, they break down due to non-friction. Elcomponics has taken care of this problem; so its pumps can run smoothly even if not used for months. They are designed so that no fatal current passes while they are being used (as the pumps run on low voltage), but yield a higher efficiency delivering maximum water.

USL solar water pumps function on MPPT technology that works according to the intensity of the sunlight. The solar water pump inverter adjusts the output frequency automatically to achieve maximum power point tracking. It comes with a solar pump inverter with an LED display that is easy to operate.

Solar home lights

Addressing the requirements of the rural populace, solar players offer reliable and cost-effective solar home lights. From solar LED home lighting systems to search lights, solar torches, etc, today, manufacturers offer a wide range of lighting options. Manufacturers like Selco Solar, GreenBrilliance, Moser Baer, Gautam Solar, etc, provide a complete range of indoor and outdoor lights and lighting solutions. With regard to lighting solutions, most of the players incorporate the panel, the battery and a light source to run for the required time period. Also, the number of light sources can be decided upon based on the voltage available.

Tata Power Solar’s Venus home lighting solution is tough, long lasting and cost-effective, company sources claim. Omega Solar, yet another solar solutions provider, offers home lighting systems with various qualitative features. These home lighting systems are available with battery chargers that maximise the output from the solar module 12 DC white main battery/solar module disconnects switch with safety fuses.

Solar chargers

Solar battery chargers can charge both lead acid and Ni-Cd batteries. Generally, manufacturers use microcontroller/DSP-based high efficiency (more then 90 per cent) based PWM-controlled three-stage dynamic chargers that rapidly charge the batteries with maximum efficiency and increase battery life to deliver the best power from panel to battery. KB Electronics offers a wide range of solar battery chargers ranging from 35 W to 1500 W standalone with overload and short circuit protection. These are robust and fully automatic float/boost chargers that are suitable for all battery types. The company uses state-of-the-art SMPS technology with a high power density to manufacture these solar battery chargers.

On the other hand, Waaree offers a solar mobile charger with in-built battery charging. It comes with a battery status indicator and an emergency flashlight. With its compact size, it is ideal for all kinds of mobile phones.

How to choose a solar PV product

When buying a solar charge controller, the user should look for a product that is of 12 V, 24 V or 48 V, and can work with a battery bank’s voltage. The user should calculate the maximum amperage of the controller before buying it.

Similarly, in case of solar water pumps, one needs to first check whether the requirement is for submersible or floating/surface water pumps.

It is recommended that users should carefully check the specifications for the maximum recommended array wattage for different battery bank voltages required for a solar charge controller, a water pump or a solar home lighting system, because off-grid solar products have different maximum amperage ratings at different system voltages.

Next, users should decide on a PV array voltage. If they prefer to go with a non-MPPT controller or solar water pump, the nominal array voltage must match their nominal battery voltage. If the user chooses an MPPT controller, many manufacturers have a spreadsheet or online calculator pre-loaded with the specifications for many popular PV modules. This helps users understand whether the product will meet their desired voltage and power requirements.

Another important factor is safety and the warranty of the product. It is advisable to check whether the product is MNRE-approved and if it comes with IP protection. MNRE approval is an assurance that the product has been tested on various quality and safety parameters and complies with industry standards. Hence, it is recommended that buyers procure their products from MNRE-approved vendors so as to avail the maximum benefit from the product.