technical and economic assessment of solar photovoltaic...

Technical and Economic Assessment of Solar Photovoltaic and Energy Storage Options

for Zero Energy Residential Buildings

Pedro Moura, Diogo Monteiro, André Assunção, Filomeno Vieira, Aníbal de Almeida

Presented by Pedro Moura – [email protected]

Technical and Economic Assessment of Solar Photovoltaic and Energy Storage Optionsfor Zero Energy Residential Buildings


Introduction

• There is an increasing penetration of PV in buildings.

• Its generation profile presents significant temporal variability and cannot be reliably dispatched or

perfectly forecasted.

• In the context of residential buildings, the generation (usually PV) and consumption do not have the

same variation profile, leading to:

• High power flows between the household

and the grid.

• Impact on the grid management and on the

cost-effectiveness of the PV generation

system.



Introduction

• Several residential appliances can be used as a Demand Response (DR) resource:

• Washing and drying appliances can be rescheduled to periods of higher energy generation from

renewable sources.

• Its impact for achieving a high self-consumption level is very limited (about 10%).

• Energy storage can store the surplus of generation to be used later in the periods with high

consumption and small or null generation.

• The cost of the storage technologies is decreasing, and soon it is expected to become

economically suitable for small applications.

• Simultaneously, in EVs, the need of periodic

replacement of the battery will lead to a large

number of batteries available in the upcoming

years.



Objectives

• For the average Portuguese residential building, the achieved self-consumption level, as well as the

associated economic impacts were assessed for different sizes of PV systems,.

• To determine the optimum installed PV power for buildings without energy storage.

• The impact of energy storage is assessed for a zero energy building, considering lithium-ion batteries

with different sizes:

• New batteries and repurposed batteries from EVs.

• Different solutions were assessed regarding its impact on

self-consumption level.

• Cost-effectiveness assessed, considering the actual and

future costs of storage technologies.

• To determine the optimum size of energy storage.



PV Generation Sizing

Scenario 100% 75% 50% 25%Power (kW) 2.4 1.8 1.2 0.6Generation (kWh/year)

3673 2755 1837 918

10 Panels of 240 Wp

• It was considered the average consumption of electricity

per household in Portugal (3.67 MWh/year).

• Consumption profile from the REMODECE project.

• PV system sized (simulated in PVSyst) to ensure such

consumption, considering the solar radiation in Coimbra.

• 2.4 kW (10 Panels of 240 Wp).

• Additional scenarios to ensure 75%, 50% and 25% of the

average electricity consumption.



Energy Storage Sizing

Scenario 100% 80% 60% 30% 15%Required Capacity (kWh)

15.5 12.4 9.3 4.7 2.3

Standard Capacity (kWh)

16.6 12.8 10.2 5.1 2.4

• Effective energy storage capacity of 60% of the average

daily consumption (6 kWh).

• Minimum SoC of 30% (8.57 kWh);

• Lithium-ion batteries - efficiency of 92% (9.32 kWh);

• The default value in the market is 200 Ah (10.2 kWh).

200 Ah

48 V (51.2 V)

• Additional scenarios to ensure 100%, 80%, 30% and 15% of the average daily consumption.



Energy Storage Sizing

• For the repurposed batteries from EVs, a degradation up to 70% of the initial capacity was

considered.

• All the presented options, and their respective capacity for second life applications can fulfil the

storage needs of an average Portuguese household.

• For further analysis, the battery of a Nissan Leaf, due to its larger market share, and the battery of a

Citroen C0, due to its smaller capacity and yet capable of offering the storage needs of a

Portuguese household, were considered.

Electric Vehicle

Initial Capacity (kWh)

2nd Life Capacity

(kWh)Tesla Model S 85.0 59.5Nissan Leaf 24.0 16.8BMW i3 18.8 13.2Chevy Volt 16.5 11.6Citroen C0 14.5 10.2



PV Generation and Energy Storage System

• PV array connected to the DC bus by a boost converter with a duty cycle controlled to ensure the

MPPT (Maximum Power Point Tracking) using an Incremental Conductance algorithm.

• Lithium-ion battery charging and discharging ensured by the bidirectional DC-DC converter (buck

mode during the charging process and boost mode during the discharging).

• The system was modelled in MATLAB/Simulink and used to simulate the system operation.

PV PanelDC-DC

ConverterBidirectional

Inverter

Loads Grid

Bidirectional DC-DC Converter

Battery

DC Bus



PV Generation and Energy Storage System

• Minimization of Power Flows between the household and the grid:

• Only the energy generated by the PV system is stored.

• Priorities of the energy storage optimization:

• Minimization of costs:

• When energy has to be consumed from the grid, such energy is only consumed in off-peak

periods and stored.

Battery Generation > Demand Generation < DemandSoC = 30% 1. Needed generation to loads

2. Remainder generation to storage

1. Available generation to loads2. Remainder energy need

received from grid30% < SoC < 100% 1. Available generation to loads

2. Available stored energy to loads

3. Remainder energy need received from grid

SoC = 100%1. Needed generation to loads2. Remainder generation to grid



Self-Consumption – PV Generation

• The system was simulated for a typical

residential household in Coimbra, during

one year, using real data of solar radiation

and electricity consumption.

• The 4 scenarios of PV sizing were simulated,

as well as a baseline scenario without

generation.

• With 2.4 kW of PV power, 58.9% of the

generated energy has to be injected into the

grid (self-consumption of 41.1%).

• Decreasing the size of the PV system, leads

to an increase on the self-consumption.

Scenario 100% 75% 50% 25% 0%Power (kW) 2.4 1.8 1.2 0.6 0Gene. (kWh/y)

3670 2760 1840 918 0

H2G (kWh/y) 2160 1370 533 22 0G2H On-peak

1290 1350 1470 1780 2570

G2H Off-peak

920 940 980 1040 1100

G2H (kWh/y) 2200 2290 2450 2820 3670Total (kWh/y) 4370 3650 2980 2840 3670



Self-Consumption – Energy Storage

• The system was then simulated for a PV

generation of 2.4 kW (able to ensure 100% of the

electricity consumption in average year) and

considering the five scenarios of energy storage.

• In different days, there are periods with energy

consumed from the grid (negative grid power) and

other periods with energy injected into the grid

(positive grid power).




• In winter months, energy is consumed from the grid and in summer energy is injected into the grid.

• For the smaller batteries, there are injection of energy and consumption during the same month.

• By decreasing the battery size there is an increase on the energy injected and consumed.




• With a 16.6 kWh battery, 12.4% of the

generated energy is injected into the grid

and 12.4% of the consumed energy

imported from the grid, leading to a self-

consumption of 87.6%.

• Decreasing the size of the battery leads to a

decrease on the self-consumption.

• The total exchange (H2G + G2H) increases

for smaller batteries.

• The smaller batteries do not have enough

capacity to avoid the consumption of energy

during on-peak hours.

Scenario 100% 80% 60% 30% 15%Cap. (kWh) 16.6 12.8 10.2 5.1 2.4H2G (kWh/y) 457 483 500 934 1540G2H On-peak 0 0 0 65 830G2H Off-peak 457 468 485 807 613G2H (kWh/y) 457 468 485 872 1440Total (kWh/y) 914 951 985 1810 2990




Scenario Large Reused Battery

Small Reused Battery

Capacity (kWh) 16.8 10.2H2G (kWh/year) 454 556G2H (kWh/year) 427 468Total (kWh/year) 881 1020

• The system was also simulated with a PV generation of 2.4 kW, but considering the two scenarios of

repurposed batteries.

• With a repurposed battery with 16.8 kWh of second life capacity, only 12.4% of the generated energy

is injected into the grid and 12% imported from the grid, leading to a self-consumption of 87.6%.

• Decreasing the size of the energy storage system, leads to a decrease on the self-consumption.



Economic Assessment

• A typical Portuguese household with an installed power of 6.9 kVA (in normal low voltage) and a

time-of-use tariff with two periods was considered.

• The Portuguese regulation for self-consumption allows for a paid price of the energy injected to the

grid of 90% of the average monthly price of the Portuguese spot electricity market.

• The economic assessment was done by calculating the Net Present Value and the payback.

• The benefit was calculated through the difference in the yearly energy cost between the

selected and the reference scenarios;

• Discount rate of 5%;

• Lifetime of 30 years for PV panels and 12 years for batteries.

Grid to House House to GridOff-Peak

(10 p.m. - 8 a.m.)On-Peak

(8 a.m. -10 p.m.) -0.03546 €/kWh0.1259 €/kWh 0.2437 €/kWh



Economic Assessment - PV Generation

• Lower yearly energy costs with larger PV

systems.

• Higher system costs with larger PV

systems.

• All systems are cost-effective (positive NPV).

• Smaller PV systems have a shorter payback.

• Shorter payback with a 0.6 kW PV system (25%).

• Higher NPV with a 1.2 kW PV system (50%).



Economic Assessment – Energy Storage

• Costs for the energy storage systems in

2017 were estimated considering a

battery cost of 480 €/kWh and an

additional cost of 15% for the BMS.

• Total cost of about 550 €/kWh.

• Only the two smaller batteries (2.4 and

5.12 kWh) are cost-effective.

• Shorter payback with a 2.4 kWh battery.

• Higher NPV with a 5.1 kWh battery.




• Forecasted costs for 2020 were

estimated considering a battery cost of

175 €/kWh and an additional cost of

15% for the BMS.

• Total cost of about 200 €/kWh

• The 10.2 kWh battery also becomes cost-

effective.

• The best solution is the 5.1 kWh battery

• Slightly higher payback

• Much larger NPV

• Higher technical impact




• Cost of 34 €/kWh for repurposed batteries

• Additional costs with the BMS, encapsulation

and installation.

Scenario Battery (€)

BMS (€)

Others (€)

Total (€)

16.8 kWh Reus.

571 1500 104 2180

10.2 kWh Reus.

345 1080 71.3 1500

• Cost of 34 €/kWh for repurposed batteries.

• Both batteries are cost-effective.

• The best solution is the 10.2 kWh battery

• Shorter payback.

• Larger NPV.



Conclusions

• Self-consumption:

• With a 2.4 kW PV system the self-consumption level is only 41.4%.

• With a 10.2 kWh battery the self-consumption level is 86.4%.

• Cost-Effectiveness :

• All PV systems are cost-effective.

• With the costs in 2017, only the 2.4 and 5.1 kWh batteries are cost-effective.

• With the costs for 2020, the 10.2 kWh battery also becomes cost-effective.

• With the repurposed batteries the two systems are cost-effective.

• Best economic indicators:

• 1.2 kW PV system.

• 5.1 kWh battery.

• 10.2 kWh repurposed battery.

Technical and Economic Assessment of Solar Photovoltaic and Energy Storage Options

for Zero Energy Residential Buildings


Presented by Pedro Moura – [email protected]

technical and economic assessment of solar photovoltaic...

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