2. 2015 UK Power Networks. All rights reserved
Context
0
50
100
150
200
250
300
350
2008 2009 2010 2011 2012 2013 2014 2015
CumulativeMWConnected
Year
UKPN G83 PV Connections
SPN
LPN
EPN
3. 2015 UK Power Networks. All rights reserved
Improving how we assess new PV connections
Research
(LV network monitoring)
Design
assumptions
(derating, diversity, min load, no-
load volts, harmonics)
Voltage rise
assessment tools
(simple spreadsheet vs
spreadsheet tool)
Records of existing
generation
(G83, FiT registers)
4. 2015 UK Power Networks. All rights reserved
LV network monitoring
Source: “Validation of Photovoltaic (PV) Connection Assessment Tool – Closedown Report” bit.ly/ukpn-pvtool-cdr
Generation CT
Data Logger
(1min intervals)
Net Export CT
PV Inverter
Research
5. 2015 UK Power Networks. All rights reserved
Derating: efficiency / insolation
Source: “Validation of Photovoltaic (PV) Connection Assessment Tool – Closedown Report” bit.ly/ukpn-pvtool-cdr
Design Assumptions
Worst case
for thermal
constraints
Worst case
for voltage
constraints
Spike
Spike
6. 2015 UK Power Networks. All rights reserved
Diversity: panel orientation
Source: “Validation of Photovoltaic (PV) Connection Assessment Tool – Closedown Report” bit.ly/ukpn-pvtool-cdr
4kW panels and inverter
4kW panels / 3.5kW inverter
(flat 6 hour peak)
Design Assumptions
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Diversity: panel orientation
Source: “Validation of Photovoltaic (PV) Connection Assessment Tool – Closedown Report” bit.ly/ukpn-pvtool-cdr
Design Assumptions
No diversity
despite varying
panel orientations
8. 2015 UK Power Networks. All rights reserved
Derating: on-site consumption
Source: “Residential consumer responsiveness to time-varying pricing: Low Carbon London Learning Lab Report A3”,
Figure 5.29, http://bit.ly/1Lhllf0
Design Assumptions
Minimum load
200W
9. 2015 UK Power Networks. All rights reserved
Other Assumptions
Source: “Residential consumer responsiveness to time-varying pricing: Low Carbon London Learning Lab Report A3”,
Figure 5.29, http://bit.ly/1Lhllf0
Design Assumptions
Condition Assumption if unknown
No-load voltage 248V
Unbalance – Urban 1.43 : 1 : 1
Unbalance – Rural 2 : 1 : 1
Harmonics Ignored
10. 2015 UK Power Networks. All rights reserved
Simple Spreadsheet
𝐼 =
𝑃
3𝑉
∆𝑉 = 𝐼𝑍
Voltage rise assessment tools
11. 2015 UK Power Networks. All rights reserved
Spreadsheet Tool – Live Demo
Voltage rise assessment tools
12. 2015 UK Power Networks. All rights reserved
FiT vs G83 Registers: ≤4kW
Sources: FiT Installation Register Aug 2015, UKPN G83 Register Oct 2015
Records of existing generation
163 MW
205 MW
225 MW
369 MW
0 50 100 150 200 250 300 350 400 450
Missing
Registered in Both
UKPN G83 Register
Ofgem FiT Register
(UKPN MPANs)
Total capacity of ≤4kW installations (MW)
Only 41% have same
rating (within 0.1kW)
13. 2015 UK Power Networks. All rights reserved
Conclusions
Derating due to efficiency /
insolation
For thermal constraints: possibly yes
For voltage constraints: possibly not
Diversity due to varying
panel orientations
Potentially reduced or eliminated because of
undersized inverters
Derating due to on-site
consumption
Allow 200W per customer
Voltage rise assessment tool Ask me for a demonstration / copy
Records of existing
generation
G83 is incomplete and inaccurate.
DNOs can request Ofgem’s FiT data with full
MPANs.
0:30
2010: nothing
2011: huge uptake
Not well prepared
Project: look at the way we assess new PV connections
0:45 (1:15)
Project looked like this:
Orange:
Research – LV network monitoring
Analysed data – understand how PV impacts network - develop design assumptions
Red:
review tools (at the time = simple spreadsheet)
develop something better
Grey: all we had was G83, not accurate. Look at other sources of data
0:30 (1:45)
LV monitoring covered 20 substations and 10 PV installations.
What’s shown:
Monitoring setup – PV installation
Main points
Both generation and export
1 min intervals – see spikes and dips not visible with 30min measurements
2:30 (4:15)
What’s shown
Generation profile of same domestic PV installation, 2 different summer days, 4 days apart
LHS
Clear sunny day, with only a few dips (presumably) due to passing clouds
Peak = approx 3.2kW (80% of nameplate) – (efficiency / insolation) – great!
(click) Power spikes very briefly after dips
Hypothesis: solar panels cool down whilst shaded by cloud, so that when unshaded, they briefly work much more efficiently until they warm back up
RHS
Spiky output (presumably) due to scattered clouds
Peak = approx 4.0kW (100% of nameplate)
Note higher power, lower energy
Ambient temp lower and max solar rad higher, but not enough to explain 25% increase in peak power output
What this means (click):
For thermal constraints (depend on average power), worst case = clear sunny day, derate to 80% of nameplate reasonable
For voltage constraints (depend on peak power), worst case = scattered clouds, output=briefly 100% -> difficult to justify derating (at least in South of England)
1:00 (5:15)
Whether variations in panel orientation, which shift generation profiles, create diversity in the output of PV clusters
What this graph shows:
Maximum generation profiles for 6 domestic PV installations, over 3 weeks in middle of summer
Main points:
Most profiles flat at top, caused by undersized inverters
Look at purple and red, identical except for inverter size
0:45 (6:00)
What this graph shows:
Same as before, but all profiles scaled to per unit of peak output
Main points:
Profiles are shifted due to panel orientation, but
(click) At 10am, all profiles at peak
What this means:
Variations in panel orientation do not create any diversity in the output of PV clusters, if there are lots of undersized inverters.
0:45 (6:45)
Can allow more PV to connect by allowing for on-site consumption
What this graph shows:
Diversified demand for different demographics, summer weekday (worst case)
What this means:
We can effectively derate domestic PV installations by at least 200W per customer
Subject to enough customers for diversity
1:15 (8:00)
Also looked at No-load voltage, phase imbalance – key inputs in voltage rise assessment:
ideally use measurements
Difficult / impossible to measure
Need default design assumptions = have to compromise (protect network / facilitate DG uptake)
Decided on values shown - see these embedded into spreadsheet tool
Harmonics: no correlation between PV generation / THD
1:00 (9:00)
Pretty basic, enter generator kW, does ohms law, models feeder as single lump of impedance
Assume if multiple generators, they are all at end of feeder = worst case
Need something a bit more sophisticated – avoid having to use WinDEBUT or PowerFactory for relatively simple cases
6:00 (15:00)
Backup slide in case live demo doesn’t work
1 min (checked OK)
Works at LV, 11kV, 33kV. Can be easily customised to do other voltages
Enter actual no-load voltage if you have measurements. If not, we recommend 248V (ok for 84% of substations in trial)
Can do 1ph, 2ph, 3ph transformers/feeders
Strict data validation rules and prompts in place
Backup slide in case live demo doesn’t work
2 min (checked OK)
Worst case assessment – no load, all generators at the end of the feeder (new generator at end of service cable)
Enter new and existing generators separately (refer to Ofgem FiT data, google maps)
Select phase and unbalance
Red = no go
Click button (goal seek)
Green = OK
Backup slide in case live demo doesn’t work
2 min (checked OK)
Detailed assessment – if the worst-case assessment says no
Can handle up to 200 nodes, placed anywhere along the length of the feeder (can handle more – extend calculation sheet)
Allow for diversity due to minimum load
Graphical representation of voltage vs distance
Calculations all done using excel formulae – so easy to audit / reverse engineer. No VBA except to drive buttons
4:00 (19:00)
Background:
During project we found G83 not accurate
Site visits, google maps
Initial comparison G83-FiT registers = FiT register shows 50% more than G83
Public FiT register only has outbound postcodes - no good for voltage rise assessments
Since then, Ofgem has given us a copy of the FiT register for UKPN area with full MPANs -
What this chart shows:
SSEG installations ≤4kW (guaranteed to be in our G83 register. FiT doesn’t show 1ph vs 3ph)
Orange: total capacity according to FiT
Red: total capacity according to G83
Green: total capacity of installations that appear in both (matched by MPAN)
205W is according to FiT. Same installations in G83 = 194MW.
(click) Only 41% registered with same rating in both.
A lot of installations (5,287) 4kW in FiT and 3.68kW in G83
Grey: total capacity of installations we didn’t previously know about (44%)
What this means:
G83 register is incomplete and inaccurate
Ofgem can provide FiT register with full MPANs to other DNOs on request
Numbers:
Same rating = 26885
Different rating = 38177
Missing = 63821
