Buffering PV Output during Cloud Transients with Energy Storage
Yacouba Moumouni
Mechanical Engineering, UNLV, 4505 Maryland Pkwy, Box 454027, 702-895-4160
THE PROBLEM
• A high concentration PV unit manufactured by Amonix
(model CPV 7700) will be the basis for this study,
using actual 15-minute output data for one summer.
• The unit puts out 38 kW of power maximum.
• In the beginning a generic type of battery is assumed,
and then costs will be compared for three different
types of batteries.
• An attempt will be made to determine the constant
power level that could be put out over the period by a
system of this sort using an electrical storage battery.
• Perhaps used electric vehicle batteries might be used
for this application because they will have several
years of life left at a lower power level when they
need to be replaced in the car. This could be a less
expensive solution for this application.
Average Electric Vehicle (EV) price/kWh = $775
Total Energy capacity of the CPV 7700 = 18.36kWh
Total price = 18.36kWhx$775/kWh = $14,229
Amonix CPV 7700 Power output curve (Cloudy Day)
45
PV
40
40
35
35
30
25
20
15
20
5
300
400
500
600
FIGURE 2 An electric vehicle battery is shown mounted in the vehicle.
15
5
200
This is what Amonix would pay for each unit if they
were to put an ESS on to smooth out any transients.
25
10
100
For 2nd EV battery life; price is halved to $7,114.5
PV
30
10
0
0
Amonix CPV 7700 Power output curve (Clear Day)
45
Power delivered in kW
A POSSIBLE SOLUTION
ECONOMIC ANALYSIS
Power delivered in kW
• Photovoltaic output power can be affected by
many factors including clouds passing
overhead.
• Utilities in generally prefer a guaranteed power
delivery level over some specified power
delivery period.
• Power delivered during peak demand hours is
generally more valued by utilities. For the
Desert Southwest this is in the summertime
afternoons. For the local area this will be
defined as 1-5 pm for the three summer
months.
• While battery power can be adapted to this
problem, large batteries to be expensive.
CER: Center
for
Energy
Research
0
CONCLUSIONS
8400
8500
Time step in minutes
8600
8700
8800
8900
Simulations started with power of constant 15kW with
an ESS of 30kW for the period of 1pm to 5pm (summer)
9000
Time step in minutes
•Simulation findings matched the calculated values
FIGURE 1 Amonix CPV 7700 unit above with its output on two different days (Right clear and
Left cloudy )
•Constant power of 20kW throughout peak times periods
of the summer is achieved !
•Estimates of the cost-effectiveness with current prices
were not positive
7
9
•Could be if battery pack prices drop to $375/kWh or
below
8
6
•Performing an experiment on an actual system is
desirable to see if the estimates made here would be
reasonable.
7
5
•Set the size of the battery, both in power and energy.
•During a full summer season assume that power
generated off-peak is used to charge the battery unless
the battery is fully charged.
•Power generated on-peak is sent to the grid and battery
power supplements this when the power is not constant.
•Numerical experiments are performed holding the
output power constant during peak times at a given
value.
•If the system does not have enough energy to supply to
the constant load during the summer peak, the desired
constant load is lowered.
•The numerical calculation/iteration is continued until the
desired constant load is met.
•Another rating for the battery is set and the calculation
sequence is performed again.
Deficit in kW
THE STRATEGY
Deficits in kW
6
5
4
CONTACT
4
Yacouba Moumouni
University of Nevada, Las Vegas
Mechanical Engineering
Masters student, Solar Energy
UNLV, LAS VEGAS,NV USA
Email 1: yacoubam@unlv.nevada.edu
Email 2: yakedz@yahoo.fr
Cel:480-390-7309
3
3
2
2
1
1
0
0
0
5
10
15
20
Level of Constant Power desired in kW
25
30
0
10
20
30
40
50
60
Energy storage Capacity in kW
70
80
90
FIGURE 3 Graph showing deficit equals zero at desired power of 20kW
FIGURE 4 Graph showing decreasing deficit as ESS is increased
Constant battery (54kW) vs Variable power supply (20,21,22,23,24,25kW)
Constant power supply (25kW) vs Variable ESS capacity (60,65,70,75,80
kW)