Solar talk by VINOD TIWARI on "Optimizing PV, Inverter and Storage Capacity to Create a Compelling Value Proposition" during November 2018

1. Optimizing PV, Inverter and Storage Capacity
to Create a Compelling Value Proposition
Vinod Tiwari
Director (Renewable Power Solutions) – TELECTRON

2. Optimizing PV, Inverter and Storage Capacity to
Create a Compelling Value Proposition
Photo Courtesy: iSELECT

3. Optimizing PV, Inverter and Storage Capacity to
Create a Compelling Value Proposition
Optimizing of Solar Power System is VERY important to create VALUE proposition
It can be achieved by following 3 BEST practices:-
1. Choosing BEST Technology and Specification
2. Designing and Sizing the BEST solution
3. Making the BEST Installation and Maintenance
The presentation is made to optimize major components used for Off-Grid type Solution
Storage device – Battery,
Inverter/Charge Controller,
Photovoltaic Solar

4. BEST -Technology and Specification: BATTERY
Majorly available Battery Technologies are based on electrolyte involved:-
• Lead Acid : Good, Less Cost, Reliable & proven technology
• Nickel cadmium : Good, Moderate Cost, less foot print, proven technology
• Lithium Ion : Good , High cost, very less foot print, new technology
Lead acid battery can be classified into two types based on technology construction-wise:-
• Flooded type (Top up required)
• VRLA type (Maintenance free)
VRLA Maintenance free batteries further can be classified into two types based on separators:-
• AGM type (Absorbed Glass Mat) and GEL type (Gelified Electrolyte)
Photo Courtesy: GNB Exide

5. For Solar Application - AGM/ GEL type - Deep cycle batteries are preferred :-
• Excellent Cycling performance – 1200 - 3000+ cycles at 60% Depth of Discharge
• Strong tubular plate technology – for longer life in the toughest conditions
• Proof against deep discharge – Greater long term energy delivery
• Robust design – resilient in harsh conditions
• Maintenance free - No electrolyte topping up required
• Horizontal/Vertical Mounting possible – Easy installation and less footprint
• Globally recyclable design – Low CO2 footprint
• Lowest Energy Consumption – Saving Costs
BEST -Technology and Specification: BATTERY
Photo Courtesy: GNB Exide

6. BEST – Designing and Sizing: BATTERY
IEEE 485 provides general guidelines for sizing battery for Stationary Applications:-
• DOD (Depth of discharge) - The measure of how deep a battery has been discharged.
Maximum DOD for a typical lead acid cell is 80% and maximum SOC is assumed to be 20%
• Temperature Correction - As temperature decreases the capacity of a cell decreases (and vice
versa). Manufacturers quote cell capacity at a given temperature and appropriate correction
factors. Temperature correction factor is required to ensure capacity match the load.
• Aging Factor - Battery performance is relatively stable through out its life, dropping of rapidly
towards the end. To ensure the battery can meet design load requirements, initial capacity
must be used as 125% of the design capacity.
• Autonomy - The term autonomy means the number of days a battery bank can provide the
load/appliances connected to the system without recharged by the solar panels. The general
rule for days of autonomy is 2 to 3 days for non-critical loads and 5 to 7 days for critical loads.
Photo Courtesy: GNB Exide

7. BEST – Installation and Maintenance: BATTERY
• Proper housing - Make sure your batteries are housed in a safe, easily accessible place.
Most batteries require an enclosure that is lockable, sealed, insulated and vented.
• Interconnections - Solar batteries do come with bus bars for inter-cell connections, but
most battery banks need cables for series and parallel connections. Cables should be large
enough to handle maximum continuous Amps.
• Temperature - Battery voltage is temp-sensitive, and you’ll need to ensure that batteries
are not overcharged when they are hot and not undercharged when they are cold. Most
chargers have remote temperature sensor.
• Charging Specs – Under/ Overcharging is one of the common factor to shorten the
battery life. Undercharging can cause sulfate crystals to build up on the plates, reducing
the battery’s capacity and shorten life. Overcharging leads to excessive gassing, lowered
electrolyte level (cannot be replaced in VRLA ), wear/tear of internal plates.
Photo Courtesy: GNB Exide

8. BEST – Installation and Maintenance: BATTERY
• Regular Maintenance - Even if a battery bank is working well performing, routine
maintenance can prevent future problems. All batteries should be thoroughly inspected
at least once or twice annually. The cases and terminals should be kept clean and
corrosion-free. Also check the terminal connections and inspect the battery cables for any
loose crimps. Recoat terminals with thin layer of anticorrosion.
• Recording - One of the best ways to track your batteries health is to keep regular, precise
records. During your maintenance checks, measure individual battery or cell voltages.
Ideally, readings should be taken after the batteries have been at rest for 12 to 24 hours
and are fully charged. These checks can alert you to bad cells or let you know, if the entire
bank may be on its way out.
• State of Charge - A battery’s lifespan is affected by how deeply it is discharged before
getting charged back up, and how long it stays in that discharged state. A battery’s state
of charge is the amount of energy remaining in the battery. The lower the SOC is allowed
to drop, the shorter its lifespan will be.
Photo Courtesy: GNB Exide

9. Solar panel can be selected as per Performance, Quality, Durability (Proven track
record) and Warranty, Manufacturer’s reliability.
• Poly crystalline : Moderate, Cost effective, proven technology
• Mono crystalline : Good, Moderate cost, proven technology
• Thin film : Good, Moderate cost, New technology
BEST -Technology and Specification: SOLAR PV
Solar panel efficiency:- It quantifies a solar panel’s ability to convert sunlight into
electricity. Given the same amount of sunlight shining for the same duration with
different efficiency ratings, the more efficient panel will produce more electricity.
• Mono - 20% plus efficient
• Poly - less than 20% efficiency
• Thin - Up to 16%.
Photo Courtesy: India Mart

10. • Temperature coefficient - It is a matter of basic electrical physics that as
temperature increases in a semiconductor such as a solar cell, the voltage of the
cell drops and current may increase very slightly. Overall the power output falls,
as the temperature of the solar cell increases.
BEST -Technology and Specification: SOLAR PV
• Power tolerance - Power tolerance can either be expressed in watts or as a
percentage of the rated power. There are two values recorded in a specification
sheet in respect to power tolerance being the negative power tolerance and the
positive power tolerance.
• Solar Degradation - Solar energy is all about kWh, what ultimately matter. If every
day, more and more people across the globe invest in solar energy, it’s because of
the trust in future, where they self-produce the electricity. But investing in a PV
System is still a bet based on trust. Because one only buys the promise of future kWh.
Photo Courtesy: Kyocera Solar

11. BEST - Designing and Sizing: SOLAR PV
When measuring the output of a solar panel, we must consider below losses:-
• Module Soiling - One major problem in the UAE as dust often settles on solar panels,
affecting their performance. Need to be considered as 10%, while calculation.
• Shading - One must consider shading which may occur by high rise buildings/ trees.
However, this it can be neglected, if no obstacles are there.
• Module Temperature - High temperature can affect the performance of a solar system. This
must be taken into account, especially UAE summers are very hot. Normally, it is as 5%.
• Deviation From Efficiency - The efficiency of a solar module can decrease over time and
this also must be taken into account. The factor to be taken as 3% for calculations.
• Mismatching and DC Losses - This can also prevent some of the power from being available
in the output. Need to consider, as per selection of system components.

12. BEST - Designing and Sizing: SOLAR PV
• Inverter/AC losses - Can be considered as efficiency losses of inverter. Approximately total losses
could be around 15-20% and can be minimized further.
• Solar Insolation - It is a measurement of the cumulative energy measured over some area for a
defined period of time (annual, monthly, daily). Common unit of insolation is kWh/m2/day.
• Cables - Solar cables are designed to be UV resistant and weather resistant. They can be used
within a large temperature range and are generally laid outside.
• Array Junction Boxes - An AJB, is used to connect the photovoltaic strings in parallel. The
combined DC power is fed to the photovoltaic inverter. It includes photovoltaic string protection,
overvoltage protection and a DC output switch isolator.
Photo Courtesy: Evergreen Solar

13. BEST - Installation and Maintenance: SOLAR PV
• Solar module position - In the northern hemisphere, general rule of solar panel
placement is South, and towards North in the southern hemisphere.
• Inclination/tilt angle - Max performance is achieved, when panels are perpendicular
to the sun’s rays and thus it is to be tilted at certain angle depending on the longitude
and latitude of the site.
• Support Structure material - Aluminum, Steel- galvanized Solar Mounting Structures
for our UAE region is good to with stand salty-high temp humid climate in order to
avoid rusting.
• Protective devices - selection of proper isolators, DCMCB, fuses is to be installed to
protect the system against any electronic component failures.
• Dust & Bird droppings cleaning - On average, regular solar array cleaning will increase
annual solar energy production by 5 to 10%.
Photo Courtesy: Evergreen Solar

14. Inverter SPECIFICATION:-
• Nominal Voltage - As per Load/ Appliance – 230V/400V AC
• Frequency - 50HZ/60HZ
• Waveform - Sinusoidal preferred
• Efficiency - Above 95% preferred
• Surge capacity - Preferred - 300% for 10 seconds
BEST -Technology and Specification: INVERTER
All inverters have a continuous rating and a surge rating. Surge rating is usually specified
for specific Load (watt) for specific time (seconds). It may range from as little as 20% to
as much as 300%. Generally, Surge rating of 3 to 15-second is enough to cover 99% of all
types of load.
Photo Courtesy: ABB

15. Inverters are also available with in build charge controllers, CPU of the Solar System.
Charge Controller - To manage the power and ensure that batteries are not overcharged
and also ensure that power doesn’t run backwards to solar array from battery. At over
discharge condition, LVD gets activate to protect the battery life.
BEST -Technology and Specification: INVERTER
Major Technology available are:-
PWM - Pulse Width Modulation Controller.
a. Acts as a switch to connect solar array to the battery.
b. Voltage of the solar array is pulled down to nearer voltage of battery for charging.
MPPT - Maximum Power Point Tracking Controller.
a. MPPT harvest more power from solar array.
b. Acts as DC/DC voltage converter to convert excess voltage into current.
Photo Courtesy: Morning Star

16. BEST - Designing and Sizing: INVERTER
Below factors are very important, while designing the Inverter/Charge Controller: –
Cables - Single core/ Three core cables to be used depends on the size of the inverter in
order to avoid AC cable losses
AC and DC protective devices - External MCB, MCCB to protect from over current/ faulty
condition/ Manual isolation.
Inverter efficiency losses - It is important to be checked for considerations as per
equipment selection.
Cabinets - Selected inverter should work for out door application at ambient temperature
up to 50 Deg C. other wise temperature will reduce the efficiency of the inverter.
Photo Courtesy: Morning Star

17. BEST - Designing and Sizing: INVERTER
Cooling arrangements - Cabinets with cooling arrangements/ Air conditioner to maintain
ambient temperature within the limit of inverter operating temperature.
IP rating - Selected on the basis on environment. IP-65 is preferred for salty and humid
atmosphere.
Charge Controllers - Reliable, programmable charge controllers will ensure batteries do not
get overcharged, and a low-voltage disconnect (LVD) protects them from being overly
discharged. An inverter LVD can only protect the battery bank from AC loads.
Another common problem is a lack of adequate charging capacity. Batteries should be
brought to 100% SOC at least once a week—and more often is better.
Photo Courtesy: Morning Star

18. BEST - Installation and Maintenance: INVERTER
Wiring - Select the shortest path to avoid voltage drop & reduce cable length. Before
connecting DC input power cables, mark polarities on the cables to ensure safety.
Termination - AC output Power Cable should be terminated/ Connected to the respective
terminal by using crimped lugs with minimum number of cable joints and conduit bends.
Proper earthling - It is an important part of the protection of inverter against surges, which
may be caused by lightning discharge/ surges due to switching.
Protective devices - External input/ output MCB to protect from high current by source or
load to avoid any Abnormal/ Faulty conditions.
Periodic maintenance - A visual inspection should be done to ensure that all the indicators
such as LED lights are working and that the wires leading to and from this device are not
loose. The charge controller should indicate that the system is charging when the sun is ON…
Photo Courtesy: ABB

19. Common Engineering Mistakes
Courtesy: Off Grid Power Solutions, LLC
Awareness of IEEE
Standards
IEEE Std 1561 & 1562
for standalone and
hybrid solar power
systems
Engineering upon Watt
Hour Method as
Opposed to Amp Hour
Amp Hour, not Watt
Hours to be
referenced in system
engineering
Reliable Irradiance
Data
Data such as NASA is
extrapolated and may
be only 85% accurate
Proper Battery
Autonomy
Sufficient battery
autonomy is critical to
system operation,
battery life and
minimizing OPEX
Benefits of MPPT
Controls
MPPT benefits are
reduced in warm and
hot environments

20. THANK YOU
A wealth of presentations and reports from The Big 5 Solar are
available at www.thebig5solar.ae
Please don’t forget to collect your CPD certificate with PDU points
during the show from our CPD collection area.