This is one of our first solar rooftop home installations that was done in 2012 for one of our customers residing at Whitefield, Bangalore. As the policy on net metering hadn’t been drafted yet, our client decided to go for 3.15 off-grid solar system with 14 numbers of 250Wp solar modules, 60A/48V morning star charge controller, 2.2
kVA studer off-grid inverter and 510 Ah, 48V VRLA Battery bank from Amarraja
. This system was designed to power their entire home using solar with minimal power usage from GRID (BESCOM) in Bangalore. The entire system is designed to provide a power of 9-12 units from solar alone.
This system was designed such that there are no major outages of their critical loads at any time of a day even during harsh monsoons when the sunlight is scarce. As such we have customized the client’s system such that the batteries are charged with Solar as the primary source and the Utility grid, BESCOM, Bangalore as the secondary source. Utility grid will charge the batteries only in an extreme case when the battery voltage drops down to a certain preset value of 46.4V indicating that the battery capacity has depleted certain minimum threshold value and more than 12 units of energy as per the design has been used inside the building.
Designing the system:
The main goal of the project was to provide the customer with the seamless power supply to their house without much intervention and make the project near zero maintenance, except cleaning up the modules during dry seasons and checking up the condition of electrical components as explained at https://www.ecosoch.com/art-solar-power-plant-maintenance/.
Choice of Equipment in this project:
: we choose to go with 285W poly crystalline modules from Waaree, as that was the highest rated efficient module available at that time in 2012. In 2017, we have started using modules of size 330 W – 335 W. Going forward, there are high chances that we would be using 350W modules in near future. For more details on Waaree, please visit http://www.waaree.com/manufacturing-plant
The solar panels are connected in such a way that the output of the solar inverter is 48V so that the panels could be connected to a 48 V battery bank via a 48V charge controller. This is achieved by connecting two panels in series and by paralleling the 7 pairs of these panels connected in series.
We choose to go with 60 A 48V Morning Star Tristar TM
charge controller from Morning Star, USA
. There are fewer companies in India that make charge controllers. Most of them claim to be MPPT. However, in reality, we find these charge controllers to be inefficient and prone to failures. They result in either over charging or under charging the batteries. These charge controllers are also designed to work with higher voltages like 96V and 120V, because of which the batteries have to be designed to work at higher voltages. It’s not recommended to have a battery at such higher voltage as it could a safety hazard at home. Morning star’s TriStarTm is a three-function controller that provides reliable solar battery charging, load control or diversion regulation. It is rated at 45 or 60 amps, both at 12-48 volts. For more details check https://www.morningstarcorp.com/products/tristar
Normally, most system integrators only go for Lead Acid Tubular Batteries as they are cheaper and are easily available in the market. However, these batteries need maintenance and are be refilled with distilled water periodically. We chose to go for VRLA ( Valve Regulated Lead Acid Batteries) from Amarraja, the company with over 70% market share of VRLA batteries in India, as these batteries don’t need any maintenance and take less space as they are vertically stackable, and have minimum cabling requirement. For more details refer here. https://www.amararaja.co.in/pdf/Powerstack_(IP20).pdf
We choose to go with the 2.4
kVA 2400-XTM Studer/Stecca inverter. The advantages of Studer inverter over conventional inverters are many. You can find more about the Studer inverter here in this blog. The main reason is that a 2.4 kVA Studer inverter can take up surge power of 6 kVA up to 5 seconds, ~ three times the rated capacity. See below for its ratings.
Apart from that, most conventional Indian inverters are very inefficient and none of these inverter manufacturers have ever got their inverters tested for their efficiency. Efficiency test report of Studer can be found here. Importantly, at 50% load, Studer is 96.27% efficient.
Measuring the generation and grid usage:
Most system installations in India are done without any measuring meters.
We want our clients to be able to measure their generations and consumptions as it was originally promised and to ensure that the system is working fine. We noticed that this is an aspect that most system integrators don’t want to do as it means more service calls. This is an aspect that we think is very important. For any service issues in the future, it’s important to know whether any solar generation has happened or how much of grid power has been used to charge the batteries.
Normally we could put an expensive DC meter to measure the solar generation. Considering that this is a small off-grid system, we installed two static energy AC meters that could give us the solar generation indirectly. Meter 1 measures the total consumption (house loads) of power from the battery. Meter 2 measures the amount of utility (BESCOM) used to charge the battery. The grid will charge the batteries, only if the solar charging is very less or the battery is drained fully.
In order to get the total generation from solar. The customer has to just subtract the Total output from Grid input (Meter 1) – Grid charging ( Meter 2). This simple set up was used so that our off-grid customers are aware of how solar on their roof is performing. A typical solar generation under off-grid system generates 3 units/ kWp of the solar rooftop system.
Remember that this was in 2012. Since then we have got better digital online monitoring systems that not only could measure the solar generation and grid charging, but also can measure the total consumption of the loads from the batteries along with the battery state of charge and discharge. Here is the image of the new monitoring system for an off-grid system
- DC Side components: We had connected a DC switch along with the Surge protection device(SPD). An SPD is used to protect the voltage spikes that could happen because of any lightning strikes. A DC switch is used between PV modules and the charge controller in order to manually disconnect the solar from rest of the system during installation and maintenance. We have connected the Fuses between the batteries and the inverter. Same fuses are connected between the batteries and the charge controller as well. These fuses are used to protect from Surges in the current. They are provided as an additional safety mechanism in order protect the equipment and batteries from any short circuit currents.
- AC Side components: On the AC side, we had provided the MCB’s (Miniature circuit breakers) on both the input side of the cable connected to the Studer inverter used for charging the batteries from the grid and the output side of the cable connected to the Studer inverter for supplying the power to the loads in the house. An MCB is similar to the fuse, except that it automatically switches off if there is a faulty short circuit or overload conditions. It can be turned back on once the faulty condition is rectified. It’s also used during maintenance.
- Change Over Switch: Although we have taken care of all of the conditions in order to ensure that the system can work seamlessly without much disruption, there are still chances that the components could still break out our client could go without power during the night. During faulty condition, in order to completely bypass the entire solar power that’s supplied from the inverter and use the power directly supplied from the grid, we have provided a change-over switch. This is to be used as a last resort only if there are some faults in the system and the customer could continue using the power as if the solar system is switched off.
A typical solar rooftop system is designed such that it lasts for the life of the solar panels at least, which is 25 years. In order to ensure that the life of the solar mounting structure lasts as long, we at Ecosoch Solar use Aluminium Structure and SS Fasteners. For more on the Fasteners and Aluminium mounting structure please read here. https://www.ecosoch.com/art-solar-power-plant-maintenance/
Apart from that, we use the prefab ballasts made out of concrete. These ballasts are made at our premises and are just taken to the client site to fix them on the roof. These ballasts are movable and are not routed on the roof. This is useful because we don’t grout the rooftop, which might cause any water leakage because of poor water proofing. Apart from that if the client decides to move the solar system to another roof, it’s very easy to dismantle the full structure along with the panels and to move them to a different roof. It’s with this intention that we choose to go for Aluminium structure with the prefab ballasts.
Aesthetics of the installation: One of the requirements for us from our client was to ensure that the height of solar panels structure can’t be shown from the road and spoil the elevation. Our system was designed such it interferes the least with the front elevation. Apart from the entire wiring of the system was taken through conduits such that no cable is exposed out and requires the least maintenance. For more information on the maintenance, please read it here. https://www.ecosoch.com/art-solar-power-plant-maintenance/
We want our customers to demand the best and we would go all out to cater to their needs and customize the system as much as it is technically feasible and is within their budget. You deserve the best and we at Ecosoch Solar strive to please beyond the best.
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