Download - 8 Export Limiting in Practice, James Hoare
Part of the BRE Trust
James Hoare CEng MIET MEI
BRE National Solar Centre -Associate Consultant LHW Partnership LLP - Partner
24th September 2014
Export Limiting in Practice
Export Limiting in Practice
• Grid Background
• Evolution Renewable & PV Development
• A Fictitious Application Example
• A Real Life Example
• Q&A
The UK Grid - Background
– Pre 1926 – Decentralised System with local generating supply companies
– 1926 CEGB established with a Nationwide synchronised 132kV network
– 1965 400kV Network established based around centralised power stations and decentralised demand customers
Statistics at Privatisation in 1990
11,500 kM 400 kV circuit, 9,800 kM 275kV Circuit, 5250 kM 132kV circuit. Essentially 1 GenCo (nearly no IPPs) 12 Regional Electricity companies
Purpose – with a centralised energy policy to get energy from
Generators Consumers
The UK Grid
1989 – The Electricity Act paved way for Privatisation in 1990
1990 CEGB (Central Electricity Generating Board) broken up into
National Grid (Transmission) & Powergen, National Power, Nuclear Electric with NGC controlling the Pumped Storage (principally Dinorwig / Ffestiniog) asset for emergency demand balancing.
12 Regional electricity Companies (now 6 DNOs) distributing from 132kV to 33/11 & LV customers.
To that point both the transmission & distribution networks had ben designed and evolved for centralised and not local power generation
The UK Grid
As part of 1989 Electricity Act introduced the NFFO (Non Fossil Fuel Obligation) a precursor to the RO (Renewables Obligation).
The first tranche was October 1990 with a number of projects mainly Wind, Landfill Gas, Straw/Poultry litter & Hydro. (No PV)
Local Cornwall projects were mainly wind
Connecting these to the distribution network was
uncomplicated, as though the network was designed for
consumers, (not prosumers) , the relative impact was
minor, and plenty of generation capacity.
Delabole Goonhilly Carland Cross St Breock
What is a Prosumer? A Prosumer is a term evolving in Europe to define an entity (domestic, commercial, public sector) that
Produces energy & consumes Energy
The UK PV Industry
– First Grid tied PV System(s) were connected in 1994
The UK PV Industry year 2000
– Total PV Connected Capacity c1MWp
– No FIT’s or ROC’s (nor in Germany)
– A large project was typically 12kWp
– G83 not in existence
Largest UK PV programme at the time
BP Solar Project Sunflower a 1098 kWp programme covering canopies on 76 UK petrol stations from 1996 to 2002
– Total PV Connected Capacity April 2015 c8GWp (8000 MWp)
– Circa 700,000 DNO grid connected Installations
– A large project is now 50-60 MWp
– At peak PV output in July 2015 a sunny weekend day will meet c15% of UK early PM national demand (UK demand data - source gridwatch.templar.co.uk)
The UK PV Industry year 2015
The move from Centralised to Decentralised (prosumer) power generation, and the rapid growth of the Renewable market, has started to put pressure on the Distribution network that is evolving from consumer based demand
system to a prosumer system.
Consequently there are now network constraints on connecting DG
The UK PV Industry year 2015
What is Network & Export Constraint? When the potential amount of locally generated electricity has reached a level when the DNO cannot accept any more without breaching its Licence conditions & ESQCR – a constraint may be needed
The solutions are
– impose an export constraint to limit the export of energy
– Upgrade the network to accommodate the requirement
Currently The Electricity Regulator Ofgem’s regulations means that the cost of network reinforcement for Distributed Generation Projects should be paid for by generator and not bill paying customers (DUOS). The DNO’s have to enforce this.
ESQCR
Electricity Safety Quality & Continuity Regulations
Principal Stakeholders
Reportable by Members of public, Meter operators, distribution and transmission companies , generators and suppliers
Key aspect in context
The DNO is licenced and legally bound to provide phase voltage to customers at 230V +/- 10% (ie between 207 & 253V)
Demand Customers reduce voltage with increased demands ,
Prosumers can raise grid voltage with increased generation
(G83/2 is 262V to allow 3% volts rise between DNO connection and inverter)
White Goods are built to work within ESQCR limits
For European Harmonisation all electrical appliance are designed to work between 207 & 253V
For European Harmonisation all electrical appliance are designed to work between 207 & 253V
A DNO can be prosecuted if for example was found to be caused by providing to a voltage outside ESQCR regulations
White Goods are built to work within ESQCR limits
When is Export Limiting Network Reinforcement Required?
The DNO may propose an export constraint or network
reinforcement for 2 principal Reasons when you apply to
connect a PV (or other DG system)
1. The voltage rise may put the network out of ESQRC
compliance
2. The thermal capacity of the network has been reached
If the network fault level has been reached, export constraint
will not resolve the issue.
A Fictitious Worked Example to demonstrate the impact of export constraint, and options of how to manage the impact
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
Assumed Annual Electricity Consumption c50,000 kWh
Initial idea
Install a 50kWp array to match annual consumption with
a combination of onside consumption with some export
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
System Size 50 kWp System
Annual generation 47,000 kWh
Estimated On Site use 50%
Export 50%
Revenue from
FITs, Export, Import offset
Decent ROI & IRR
To Proceed with project - No Planning needed, just DNO approval…..
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
ENA Connection Application sent to DNO
for 50kVA PV connection
A few days later the DNO responds outlining
You can connect a system to export 50kW
– Due to the level of existing DG connections in the
area, network network upgrade costs in the order of
£500,000 will be required , or you can connect a
system that can export 20kW (KVA) with no additional
reinforcement needed.
NB Figures Entirely fictitious and fabricated
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
What do you do?
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
✔
What do you do?
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
But what do you do?
✔
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
The 2 key things you need to assimilate are
1. Relationship between kWp and real time kW system
yield quantum.
1. On Site Energy Demand profile (if any)
In context of
Exported Energy = Generated energy – onsite demand
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
Do annual / monthly yield and other such models help
when there is an export constraint?
Yes a bit , but in reality not very much
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
Generation
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
Generation
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
Generation
PV Syst can output
modeled Hourly generation
data sets in CSV/Excel
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
Key Graph – derived from PVSyst Hourly Generation
Key Graph – derived from PVSyst Hourly Generation
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
Max output 50kW
Area under line
Hours x % of max 50 kW
= total kWh
Mean operating output 11kW
Key Graph – derived from PVSyst
Findings
• PV System will be generating for 47% of year
• Max output is 50kW
• Average operating generation output is 11 kW (22%)
(This is not generic and is project / location specific)
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
0
50
100
150
200
250
300
1 4 7
10
13
16
19
22
25
28
31
34
37
40
43
46
49
52
55
58
61
64
67
70
73
76
79
82
85
88
91
94
97
10
0
Ho
urs
of
Op
era
tio
n
Annual Hours of Unconstrained Outputs as a Percentage of Max 50kW Output
Unconstrained Output
5 Periode gleit. Mittelw.(Unconstrained Output)
Point for the example 50 kWp
System where a 20kW export
constraint will need to limit
the outputs to keep within
20kW export
20 kW Export limit total export
Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh none 0 100%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh none 0 100%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh none 0 100%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 49kW 0 99.99%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 48kW 0 99.9%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 47kW 0 99.9%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 46kW 0 99.90%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 45kW 0 99.9
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 44kW 0 99.9%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 43kW 0 99.9%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 42kW 0 99.9%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 41kW 0 99.9%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 40kW 0 99.9%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 39kW 0 99.8%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 38kW 0 99.5%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 37kW 0 99.4%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 36kW 0 99.3%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 35kW 0 99.0%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 34kW 0 98.6%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 33kW 0 98.2%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 32kW 0 97.6%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 31kW 0 97.0%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 30kW 0 96.3%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 29kW 0 95.5%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 28kW 0 94.6%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 27kW 0 93.7%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 26kW 0 92.6%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 25kW 0 91.4%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 24kW 0 90.2%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 23kW 0 88.8%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 22kW 0 87.3%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 21kW 0 85.8%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 20kW 0 84.0%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 20kW 0 84.0%
Conclusions from Model
• 84% of max yield in Cornwall with a 20kW export
constraint on a 50kWp system is still probably higher
than yields in North of England with no constraint
• There are lots of variables, so allowing sensitivity and
contingency are important.
Model With on site Energy Demand • 50kWp Array
• 20kW export Constraint
• On site Consumption
If Site Demand is added to the 50kwp system
with an export constraint of 20kW max
Assumption for model
5kW – continuous at weekends (Sat & Sunday)
Weekday model graded in incremental steps of 5kW
(Historic HH consumption data is desirable if available)
January sample HH Consumption Data
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 20kW 0kW 0kW 84.0%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 20kW 0kW 0kW 84.0%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 20kW 5kW – 5kW 88.1%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 20kW 10kW – 5kW 90.5%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 20kW 15kW – 5kW 92.5%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 20kW 20kW – 5kW 94%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 20kW 25kW – 5kW 95.1%
Max PV Gen Export Constraint
On Site Demand (5d/weekend)
% of Max
47 MWh 20kW 30kW – 5kW 95.9%
Key Factors
• A Degree of sensitivity / contingency is required as
both solar radiation and on site demands are
intermittent and will vary year on year
• PVSyst estimates hourly outputs in kWh, so need to
be careful when matching to on site demand as 1
kW for one hour = 1kWh (as does 0.5 kW for half
an hour and 1.5KW for half an hour) – Sensitivity
needed
• The more consumption information the better – Half
hourly data, and a thorough energy consumption
profile is helpful. (The more demand info the better)
Conclusions from Modeling
• The impact of network constraints is probably less than
anticipated, and a larger array than anticipated may be
possible.
• Choose a conservative and least optimistic solar
dataset. Maybe use P90 irradiance data
• If you are modeling with historic Half Hourly
consumption data remember this is historic and not
assured year on year
• Allow contingency, and be cautious with energy yield
projections – the level of yield risk is higher than total
export.
• If in doubt Ask BRE NSC for modeling assistance !
Export Limiting Case Study – a 1.2 MWp Zero Export Rooftop – Vegetable Storage Cambridgeshire 2013
Export Limiting Case Study – a 1.2 MWp Zero Export Rooftop – Vegetable Storage Cambridgeshire 2013
• Large provider of parsnips to supermarkets
• Large onsite energy use for refrigeration
• DNO could not allow any export due to large wind
farm on same circuit
Export Limiting Case Study – a 1.2 MWp Zero Export Rooftop – Vegetable Storage Cambridgeshire
• Undertook Modeling of 2 years historic consumption data
• Modeling showed 1.2MWp would provide 95% of
maximum projected generation output with zero export
constraint.
• System installed
• DNO Witness test on G59 & export limiting system
• Learning experience solar gain reduction on roof reduced
energy consumption by a few %
Export Limiting Case Study – a 1.2 MWp Zero Export Rooftop – Vegetable Storage Cambridgeshire
Commissioned March 2013
• 1.2MWp 4,400 PV Modules
• 9 x 100 kW Inverters
• G59/2 Switchgear
• PLC based Export sensing Actuator & Controls
Export Limiting Case Study – a 1.2 MWp Zero Export Rooftop – Vegetable Storage Cambridgeshire
• Subsequent application to DNO for variable export
allowance successful
• Site can export 97% of time, so nearly 100% of
projected yield is attainable
• Ultimately Active Networks will prevail