HOW TO SIZE YOUR NET-METERED SOLAR PV SYSTEM Harsha Wickramasinghe
Net metering… closer to your home
Sri Lanka is one of the most progressive countries among the developing countries in this regard Complete
system now in operation in both CEB and LECO areas Facilities
up to contract demand or 10MW now connectable
Our
wronged energy mix has created a window of opportunity to a new industry Also
established a ceiling for penalising high end consumers
Why should we promote it..?
Policy intent
To increase the share of renewable energy in power generation by 10% by 2015 and 20% 2020
Reduce the level of energy consumption of 2010 by 10% by 2015 and 20% by 2020
Net metering fits into both
Many more answers to
increase green electricity generation in Sri Lanka
at
relatively low cost to utilities (private funds) to allow participation of large consumer group in green energy drive to stimulate further development in green energy
Grid-Connected System Layout
Limits of increasing domestic tariff Effective unit cost of electricity 60.00 50.00
LKR/kWh
40.00
30.00 20.00 10.00 0.00 0
100
200
300 kWh / month
400
500
600
Basic elements of the scheme 


Any customer who desires to use this facility, must get an import / export energy meter Electrical energy purchased by customer is considered as energy import electrical energy supplied to the grid is considered as energy export At the end of a billing month, the utility will read the customer's export energy meter and the import energy meter, and the bill will be for the difference between the import and the export energy readings.
Will this scheme alter load profile? 
High end consumers only 4.2%  Contribute
35% of the revenue Domestic Electricity Usage - January 2010
Percentage of Domestic Consumers
12% 10% 8%
6% 4% 2% 0% 0
30
60
90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540 570 600 Units of Electricity used per month
Who will benefit from the scheme..? Facilities up to contract demand or 10 MW now connectable Viable for the homes with higher electricity use Why? Viability matrix
Impact on revenue Electricity use and revenue distributions exhibit wide disparities Use and Revenue Profile 12% 10% Distribution

8% 6% 4% 2% 0% 0
300
600
900
1200 1500 1800 kWh/month consumed
2100
2400
2700
3000
System size: deciding factors How much can be invested Desired level of saving (down to LKR30..?) Use the sizing tool Future loads to be added (enhanced consumerism..!) The location of your facility
Understand
the present circumstances Worry about the future
Results from experiments 
Generation pattern during height of monsoons 350 300
Power (W)
250 200 150 100 50 0 06:00
07:00
08:00
09:00
10:00
11:00
12:00 13:00 Time of day
14:00
15:00
16:00
17:00
18:00
In sunny weather… 350
Tue 300
Power (W)
Wed 250
Thu
200
Fri
150
Sat Sun
100 50 0 06:31 07:31 08:31 09:31 10:31 11:31 12:31 13:31 14:31 15:31 16:31 17:31 Time of day
Avg
Location – a key concern Annual Variation - Kiribathgoda
Generation kWh/kW per month
140 120 100 80
60 40 20 0 Jan
Feb Mar Apr May Jun
Jul
Aug Sep
Oct Nov Dec
Solar potential
Results 
Averaged outputs 300
Active power (W)
250 200 Rainy days avg 150 100
Sunny days avg Avg
50 0 06:30 07:30 08:30 09:30 10:30 11:30 12:30 13:30 14:30 15:30 16:30 17:30 Time of day
Results 
Duration curve 300 Avg
Active Power (W)
250
Rainy day avg Sunny day avg
200 150 100 50 0 00:00
01:00
02:00
03:00
04:00
05:00
06:00
Duration (hours)
07:00
08:00
09:00
10:00
11:00
A glimpse of western province 
Even a very sunny area can have nasty surprises for solar power prospectors  Will
have to conduct ground studies to safeguard investments
Making the right decision
Know exactly what your roof can provide Orientation,
shading (present and future) Roof structure (slope, type of tiles, timber structure) Additional roof space (70 - 100 square feet / kW) Inverter sizing Over
sized inverters can be a real loss
Cabling Use
issues
the correctly rated DC cables (UV stabilized) Terminate properly
Effect of load growth 200 180 160 140 120 100
80 60 40 20 0 1
2
3
4
Generation kWh
5
6 2009
7
8
9 2010
10
11 2011
12
Time 0:30 1:30 2:30 3:30 4:30 5:30 6:30 7:30 8:30 9:30 10:30 11:30 12:30 13:30 14:30 15:30 16:30 17:30 18:30 19:30 20:30 21:30 22:30 23:30
Demand (MW)
If all high end users converted
Solar PV generation on daily demand
3,000
2,500
2,000
1,500
1,000
20% of demand
500
0
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 0:00

Demand (MW)
Altered load profile Likely improvement on a good sunny day Mid day load taken by solar PV
3,000
2,500
2,000
1,500
1,000
500
0
Other impacts
Net metering would feed in electricity during low load periods Same customer will draw electricity during high demand period Who
pays for the difference? Cost differential USCts10 vs. USCts.13 (30% more)
Will it displace other forms of RE plants? Only
if they are in the margin during sun shine hours
A fresh look at net metering needed Import / Export of Energy 500 400
200 100
-200
23:59
19:59
15:59
7:59
11:59
-100
3:59
0 0:00
Power (W)
300
THANK YOU..! more information‌
harsha@energy.gov.lk