Valuation and Integration of Solar
Energy:
太阳能评价与并网
Early Results from the United States
美国初期研究成果
Ryan Wiser
怀瑞恩
Consultant to the Center for Resource Solutions
资源解答中心专家
Energy Foundation Workshop
能源基金会研讨会
Beijing, China
July 2, 1010
Motivation 研究动机
Increasing focus on solar as source of
electricity:
-
Growth in interest in large-scale plants: >50 GW
seeking interconnection in U.S., ~10 GW in later
stages of development
太阳能发电受到越来越多的关注
-
美国对大规模电站的兴趣在提升：
预期的并网需求超过50GW，约
10GW的项目处于开发的后期阶段
Decision-makers need to understand electric
决策者需要认识到太阳能电力在电
system value of solar electricity (PV/CSP, w/
力系统中的价值（光伏/光热，有无
and w/o storage):
储能）
-
Solar is variable/unpredictable: valuation will differ
from conventional gen.
太阳能具有波动性/不可预测性：其
评价方法将有别于常规能源
-
Output variability/uncertainty studied for wind;
little similar work on solar
针对风电出力变化/不确定性已有研
究；太阳能这方面的研究却很少
Two areas of particular interest:
-
两个主要研究方向：
-
Estimating the long-term electric system value
of solar without storage given displacement in
conventional gen. and optimal capacity expansion
-
Understanding the technical and economic
impacts of short-term variability and
uncertainty in PV output, and associated
integration costs
Current presentation does not include power
quality timeframe
-
估算无储能太阳能在电力系统中替
代常规电力的长期价值，及最佳容
量
了解光伏发电输出短期波动性和不
确定性带来的技术和经济影响及并
网成本
目前的报告并不包括瞬时电能质量
2
Long Term Valuation
长期价值
3
Value of an Electricity Generation Source Impacted By
Multiple Factors
电源价值受多种因素影响
发电成本
输电成本
并网成本
容量价值
能源价值
4
Central Solar in Western U.S. Currently >3 cents/kWh More
Valuable Than Wind Considering Energy/Capacity Value
考虑到能量/容量价值，美国西部集中式太阳能价值比风电高3美分/度
$140.00
Capacity Value
Energy Value
Transmission Cost
Economic Value ($/MWh)
$120.00
$100.00
$80.00
$60.00
$40.00
$20.00
$0.00
Solar
Load Sited CCGT Hydro
Biomass
Geothermal
Wind
-$20.00
-$40.00
Increased value due to coincidence with system peak, and therefore offset of
higher-cost resources; benefits likely to be lower in China
因与用电负荷高峰重合而增加了太阳能电力的价值，所以抵消了部分高成本；在中
国，这方面的价值可能要低一些
5
Marginal Value of Solar Energy Drops with Penetration, But At
Current Levels, Added Value Is Considerable
随着在总体电源中比重的增加，太阳能的边际价值会减少，但在目前的水
平下，增值仍相当可观
49
Load (GW)
120
Solar reduces peak load
(high capacity value)
100
45
Load
Net Load, 1% Solar
Net Load, 2% Solar
Net Load, 3% Solar
Net Load, 4% Solar
43
39
35
9 AM
80
2 PM
7PM
12 AM
5AM
Local Time Beginning 9/8/2004
60
Solar shifts peak load into night
hours (low/no capacity value)
40%
35%
30%
25%
20%
Solar increasingly curtailed
during peak production
10%
5.0%
4.0%
3.5%
3.0%
2.5%
2.0%
1.5%
-
1.0%
Wind: Long-Run Equib., no Storage
Solar: Long-Run Equib., w/ Storage - 10% peak, 168h
Solar: Long-Run Equib., no Storage
Solar: 80% Incumbent, no Storage
20
15%
40
-
Marginal Value of Renewable ($/MWh)
140
Renewable
basis)
RenewablePenetration
Penetration(%
(%energy
energy
basis)
可再生能源比重（发电量）
6
Incremental Wind or Total Analyzed (GW)
For PV (less so for CSP),
Lower Transmission
Needs Further Augment
Added Market Value
对于光伏（光热的情况不太
一样），较低的输电需求进
一步增加了它的市场附加值
Figure shows estimated
transmission cost for wind in
US for large number of studies:
> 1 cent/kWh
基于大量研究，数据表明美国风
电的输电成本高于1美分/度电
Solar PV is modular and does
not experience as strong
economies of scale, allowing
siting closer to load in many
cases
太阳能光伏是由一个个独立模板
组成的，规模经济效益不如其他
电源明显，并且很多情况下可以
建在负荷周边
0
5
10
15
20
PSCo
NYISO
MISO '03 - 1
MISO '03 - 2
Xcel - BRIGO
ISO-NE - Low
SCE - ISM - MP
ERCOT - C3
CapX - CBED
IAP - 2010T
SPP - 1
SPP - X
RMATS - 1
CDEAC
SCE - ISM - K
ERCOT - Cb3
SPP-CRA
MATL
Xcel - BR - Proj
JCSP
SSG - WI
SCE - ISM - V
SWAT
CapX - 1
CPUC - 2017
ERCOT - M2
SCE - ISM - P
CapX - 2
CPUC - 2010
IAP - 2020
SPP - 2
ERCOT - CW3
ERCOT - Cb1
Xcel - BR - Actual
CAISO - A1
ERCOT - Cb2
SCE - ISM - I
SCE - IR
ERCOT - TOS - 4
ERCOT - P4
SCE- LA/Kern
SPP - EHV
ERCOT - TOS - 3
RMATS - 2
SCE - ISM - EDM
CLRTPG - N1
SPP - OK - 2020H
Tehachapi
ERCOT - TOS - 2
EPTP - 1
SPP - OK - 2020N
MSTI
NTAC - 2A'
CAISO - A2
SunZia
CAISO - A6
SPP - OK - 2010H
ERCOT - TOS - 1A
ISO-NE - High
SPP - OK - 2010N
EPTP - 2
NorthWestern
ERCOT - TOS - 1B
MPC
TWE and GS
NTAC - 2A
NTAC - 2B
Frontier - B
Frontier - A
CAISO - A4
HPX
C/PNW-NorCal
NTAC - 1
25
30
Unit Cost (Capacity-weighted)
Wind Analyzed (GW)
Total Analyzed (GW)
236 GW wind
analyzed
$0
$500
$1,000
$1,500
$2,000
Unit Cost of Transmission ($/kW-wind)
$0
$24
$49
Unit Cost of Transmission ($/MWh-wind)
$73
7
$98
But, Solar without Storage Is Also Variable and, to a Degree,
Unpredictable
但是，无储能太阳能仍然是波动性较大的，某种程度上，不可预测
Two key assumptions in previous
analysis
- Perfect foresight (did not evaluate forecast
error)
之前分析的两个关键假设
- 完美预测（预测误差未评估）
- 不存在小时内波动 (需要平衡小
时内波动)
- No sub-hourly variability (changes within
hour require balancing)
Costs for dealing with imperfect forecasts 预测误差带来的成本/ 小时内波
动= “并网成本”
/ sub-hourly variability = “integration
- 大量研究表明，风电并网成本 <
costs”
- Wind integration well studied: cost <
$10/MWh
$10/MWh （10美元/千度电）
- 但对太阳能并网成本认知还太少
- Integration costs for solar poorly understood
Note: Focus here is on large-scale PV; CSP
with and without storage a much smaller
concern due to thermal inertia and storage
注意: 此处关注的是大规模光伏; 有
储能或无储能的光热因其热惯量和
储存问题，受关注更少
8
Short Term Integration
短期并网
9
Clouds Can Produce Rapid Ramps
in PV Output
阴云会导致光伏出力锐减
PV plant output can change by 70% in five minutes at single site
一个光伏电站的发电出力，在五分钟内变化可达70%
Clear Day (May 1)
Cloudy Day (May 3)
100%
80%
80%
Solar Output
(% Maximum Output)
Solar Output
(% Maximum Output)
100%
60%
60%
40%
40%
20%
0%
7:00
20%
9:00
11:00
13:00
15:00
17:00
19:00
0%
7:00
9:00
11:00
13:00
15:00
17:00
19:00
Timeplant
(hh:mm)output on a clear and cloudy
Actual PV
day
for a
Time
(hh:mm)
plant in the Southwest United States
10
Operational Impacts Vary
with Time Scale
针对不同时段运行影响有所不同
Regulation: Automatic
adjustments to
conventional generation
output to maintain balance
between supply and
demand
调节：自动调整至常规发电
输出保持供需平衡
Load Following: Periodic
operator dispatch of
generation to follow trends
in load
负荷跟踪：分时段运行调度
以配合负荷变化趋势
Scheduling: Commitment
of generation units based
on forecasted need for
generation
调度计划：基于需求预测的
发电约定
Source: Milligan 2009
Concerns that Rapid Fluctuations in Output Are a Potential
Roadblock to PV
对光伏出力快速波动的担忧有可能阻碍光伏的发展
 Market operators / utilities have expressed
concern
 市场运营商/电力公司表示这样的担忧
 Numerous early studies found potential
limits to increased PV penetration
 大量早期研究给出了光伏电源整体占比的可
能极限
 But… many of early concerns did not
account for geographic diversity and
forecasting
 然而 …许多的担忧并未基于全面考虑，分
散的地理分布因素和预测贡献的因素都未考
虑
 Solar PV’s characteristics allow for ready
use of site diversity and forecasting
 太阳能光伏的特征允许分散式布局和利用预
测技术
12
Solar Plants Are Variable, But Output Smoothing from
Geographic Diversity
太阳能电站有波动性，但分散的地理分布可以平滑这种出力波动

Clouds cause rapid changes in output of individual plants

就单个电站而言，阴云会引发快速的出力波动

Multi-MW plants can change by > 70% in less than 5-min

兆瓦级电站在五分钟内变化可达70%以上


Aggregation dramatically reduces variability; even within-plant variability at < 1 min reduced with
plant size due to smoothing
将众多电站作为整体考虑，则波动会大幅降低；同理，即便是单个电站范围内，一分钟内波动也
随电站规模扩大而减少
Source: Wiemken 2001
Actual 5-min data from 100
PV plants in Germany.
Aggregate output (P) is
normalized by installed
capacity (P installed)
13
Aggregation Decreases Relative Variability When Sites Are
Less Than Perfectly Correlated
整体优势在电站分布不是非常集中的情况下可以降低相对波动性
Deltas: step
changes from one
averaging interval
to the next
Clear Sky Index:
ratio of insulation if
no clouds were
present to
measured
insolation
Data: 1-min
insolation data from
23 timesynchronized sites
in the U.S.
Source: Mills and Wiser 2009
Forecasting for Solar Still Developing, But Is Much Better for
Geographically Diverse Sites
太阳能预测技术仍在发展，针对地理上分散分布的电站来讲预测效果更佳
Clouds lead to forecast errors, and errors are greatest on partly cloudy days
Forecast errors for geographically diverse sites smoothed by aggregation
阴云导致预测偏差，多云/晴转阴的天气会加大误差。不同地区多电站形成的整体优势可以降低预测误差。
Source: Lorenz 2009
Forecasts of solar output based
on forecasts from the European
Centre for Medium-Range
Weather Forecasts
15
Longer Forecast Horizon Increases Error
远期预测误差增大
Assuming that current cloud conditions will not
change (persistence forecast) is reasonable for
short forecast horizons (<1 h)
Satellite or numerical weather model based
forecasts are better for longer forecast horizons
对短期预报来说，假设当前云的条件不变
(持续性预报) 是合理的（一小时内)
卫星或数值天气模型预报，对长期预测更为
合适。
Multiple Sources of Reserves Can Mitigate
Variability
多种类型备用电源可以减轻出力波动
Source
Description
Timescale
Mechanical inertia
Rotating mass of generator
Instantaneous, sustain for 10s
Thermal inertia
Steam pressure in boiler
10s, sustain for mins
Storage/hydro
Turbines not currently used
10s to 10 min
Gas turbines
Peaking and backup turbines
5 min to 20 min
Thermal plant
overrunning
Run station above max rated
capacity
Can run 3-10% over for few min without
added stress
Industrial load
management
Voluntary interruptable loads
Fast response but need to make
provisions ahead of time
Domestic load
management
Automatic interruption of some
loads (i.e. water heating)
Instantaneous with proper equipment
installed
Voltage reduction
Low voltage reduces loads
Instantaneous, but degrades supply
Imported power
Additional flow on tie lines
Instantaneous, need to arrange/warn
Spinning reserve
Spare capacity on committed
units
Large thermal units can provide 24%/min reserve up to capacity
Banked/prescheduled plant
Units on hot standby or
scheduled early
Available in 1-2 hours
Source: Grubb 1991
Additional Reserves Have Modest Cost for
Diverse Solar Sites
太阳能电站分散分布可以大大降低备用电源成本
Source: Mills and Wiser 2010
5 close sites: ~ 7,000 sq. km
25 site grid: 5 X 5 Site array with 40 km spacing between sites ~ 40,000 sq. km
These costs do not include cost of day-ahead forecast
error. EnerNex (2009) estimated day ahead forecast
costs to be $4-7/MWh for 800 MW PV/CSP combination,
depending on assumptions for fuel costs
这些成本不包含一日前预测误差。EnerNex (2009) 估
算一日前预测成本，800兆瓦的光伏/光热组合规模
下，大概是4至7美元每千度电， 这个成本也取决于对
燃料成本的预期。
Conclusions from the United States
美国经验总结
 Solar energy without storage, at low levels  太阳能在整体电源中占比较低
情景下，无储能太阳能发电在
of penetration, can be quite valuable within
美国电力系统中较有价值，值
the US energy system, supporting higher
得给以高电价和政策支持
tariffs and policy measures
- 与负荷高峰的重叠增加其能源
- Peak coincidence increases energy
价值
value
- 资源量充足/ 容量价值高
- High resource adequacy / capacity value
- 输电成本相对低
- Lower transmission costs compared to
- 对中国的借鉴意义尚不明晰
less-modular technologies
- Implications for China less clear…
 无储能太阳能的短期出力波动
 Short term variability and uncertainty in
性和不确定性带来相关的并网
solar without storage creates integration
问题，增加了成本，这点和风
issues that appear to be relatively similar to
电相似
wind in terms of cost implications
 鉴于技术进步和成本下降的速
 Given rapid pace of technology and cost
度较快，有必要提前考虑大规
developments, important to start thinking
模太阳能发电的评价和并网问
about large-scale solar valuation and
题
integration at an early stage
19