How to size your net metered solar pv system

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