This document summarizes a 3 kVA grid-supported residential solar energy system located in Pune, India. The system includes solar panels occupying 250 square feet that generate up to 3 kVA of power, 4 lead-acid batteries totalling 600 Ah of storage, and a power conditioning unit that interfaces the solar, batteries, and grid. Data from the system over sunny, partly cloudy and cloudy days shows how it charges and discharges the batteries and draws from the grid. Observations note the system could generate more power but batteries are too expensive, and more intelligent controls are needed to better optimize battery usage and minimize grid usage.

1. Grid Supported Residential Solar
System
A Real World Deployment

2. System Summary
System Summary

Located in a residential property at Pune, MH

3KVA Grid Supported Power Conditioning Unit (PCU)

3 KVA Solar Panels

12 x 250 VA. Vmax 35v

Connected in 2(series)x6(parallel)

Poly-crystalline

Occupying about 250 sq ft on the roof

Mounted on a 20 degree slope

Panels doubling as shade (custom fabrication mounting)

4 x 150Ah tall tubular batteries

More would have been better. But, than the system
becomes too expensive

3. Site Photographs

4. PCU
Power Conditioning Unit

PWM based controller

Takes solar, grid and battery as input

SBM and SMB priority settings

48 Volts

Battery charging control parameters

MAX main Amps (10-30 Amps)

Float volatge (~55v)

Boost charge voltage (~58v)

Fully charge voltage (~51v)

RS-232 serial monitoring

5. Data Graphs: Sunny Day
Boost
Float
Discharge
Grid
BV: Battery Volts
PV: Solar Volts
LdI: Load current
PI: Solar current
GrI: Grid Current

6. Sunny Day: Explained

Battery boost charge was over by 11:30 AM

Later battery maintained at float charge level

Changeover from boost charge to float charge clearly visible

Batteries lasted almost all night

Battery volt goes from 51v-45v during discharge cycle

At 45v, the system switches to mains

7. Data Graphs: Partly Cloudy
BV: Battery Volts
PV: Solar Volts
LdI: Load current
PI: Solar current
GrI: Grid Current

8. Partly Cloudy Day: Explained

Battery boost charge was over by 2:00 PM, with intermittent
drop of voltage below boost level

Later battery maintained at float charge level, again with
intermittent drop below float level, but above fully charged
voltage

Batteries were still fully charged

9. Data Graphs: Cloudy Day
BV: Battery Volts
PV: Solar Volts
LdI: Load current
PI: Solar current
GrI: Grid Current

10. Cloudy Day: Explained

Boost level only achieved momentarily

Batteries were not fully charged

The system still had an average output of 10amps (~500VA)

11. Data Graphs: Fridge
Grid switch
BV: Battery Volts
PV: Solar Volts
LdI: Load current
PI: Solar current
GrI: Grid Current

12. Fridge on the system: Explained

Compressor on-off cycles clearly visible

The compressor load spike made the switch to mains sooner
than it should have

13. Data Graphs: Washing machine
BV: Battery Volts
PV: Solar Volts
LdI: Load current
PI: Solar current
GrI: Grid Current

14. Data Graphs: Induction Heater
BV: Battery Volts
PV: Solar Volts
LdI: Load current
PI: Solar current
GrI: Grid Current

15. Washing machine/Induction heater: Explained

After observing data for few weeks, it was evident that we
have over capacity in the day time

Hence, it was decided to put more load on solar in day time

Washing machine worked fine

Induction heater was introduced to reduce LPG consumption
and fully utilize solar power

16. Observations

System capable of generating 15-20 KVAh/day. Power being
wasted due to

Batteries too expensive

Government not allowing connection to the grid

Starts to use grid once battery voltage falls to 46v (SBM) or
48v (SMB) – very simplistic logic.

Once it switches to grid, it charges the battery for longer than
it should. Most of the vendors have inverter/UPS pedigree

Even on a cloudy day panels output approx minimum 500 VA
(if possible – go for over capacity)

Heavy equipment like fridge, microwave etc. sometimes cause
the battery voltage (terminal) to fall resulting it to switch to
grid. Hence, best to use them in day time only when power is
drawn from panels and not batteries

17. Observations: Wish List

Government subsidy- limit of 1 KVA not very practical

Too much paper work

Government should allow to feed into the grid like many
counties/states do

Then we can minimize the batteries (the single most
expensive and toxic part of the system)

Lower cost

18. Observations: Wish List

Intelligent systems – system should learn the usage and
weather patterns. Currently the systems have very simplistic
logic to decide charging, grid usage etc.
Or/And

More control to the user. User should be able to set

MAX grid power consumption limit. This will vary site-to-
site and season-to-season

Timer based system by-pass (true SMB mode). For
example- to avoid battery degradation, may be a good idea
to use grid from 6pm-11pm

Better battery power monitoring. Momentary drop in voltage in
the systems should not cause it to switch to grid

GPRS based monitoring with real time SMS alerts