Lead-Acid's Sweet Zone How to get more energy out of your Solar - PowerPoint PPT Presentation

Lead-Acid's Sweet Zone How to get more energy out of your Solar Batteries & Panels Presenter Mukesh Bhandari COO Author Kurtis Kelley Firefly International Energy Peoria Illinois Feb 2014

Lead-Acid's Sweet Zone How to get more energy out of your Solar Batteries & Panels Many off-grid installations operate below 50% efficiency but Can operate close to 95% efficiency

Lead-Acid's Sweet Zone Lowers your cost per kWh near 50%. Lower battery-array spec. amp-hrs needed for same functional cycling capacity More efficient use of panel solar power generated

Lead-Acid characteristics you need to know Charge and Discharge SOC changes Resistance some components increase & others decrease Chemistry goes through phases between easy and difficult Secondary Reactions such as gassing can become easier than charging All lead acid batteries share certain basic attributes Some lead acid have amazing Deep Discharge performance

Resistance vs. State-of-Charge Lead-acid batteries Charge Resistance (Rreg) and Discharge Resistance (Rdis) vary with the State-of-Charge (SOC) Rapidly rising charge resistance >80% SOC ( gassing) Rdis HPPC testing - typical lead acid cell Rreg Voc 1.4 2.2 2.15 1.2 2.1 1 2.05 Resistance 0.8 OCV (V) 2 0.6 1.95 0.4 1.9 0.2 1.85 0 1.8 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% DoD SOC

Storage Efficiency vs. SOC Battery efficiency changes with state-of-charge Above 80% SOC, battery efficiency is very low & Charge Cycling losses are high. This is also where most battery systems operate & where losses largely from gassing / electrolysis Typical lead-acid efficiency vs. SOC Round trip energy efficiency (%) 100 80 60 40 The Sweet Zone Gassing also 20 competes for energy at these higher voltages 0 100 90 80 70 60 50 40 30 20 10 0 Battery State of Charge (%)

Battery Efficiency Degrades with Cycle Life

Recharge Strategy is Important in Energy Efficiency - How you control current, voltage, and time have a big impact. - Float charging is almost never recommended. Note: Colored bands represent various common charging strategies. s s o L y g r e n E

How do these Battery attributes affect System Efficiency? Model Variables The Homer Model , originally developed by NREL, was used to find optimal system within the variable ranges listed. Every combination was analyzed Variables: 1. SPSOC – battery setpoint state of charge – 0% to 100% 2. PV array size – 0 to 40kW 3. back-up Generator size – 0 to 20kW 4. Battery storage system size – 0 to 96kWh 5. Converter size – 0 to 20kW 6. random 25% day-to-day variability allowed in load

Model Assumptions 1. System must meet all loads. 2. Generator operates at 100% efficiency or nothing. 3. Average 30 kWh /day – hourly load data from US home. 4. 38' North Latitude, approximate center of USA 5. One year of hourly data analysis 6. Lead-acid Batteries 7. Generator is cycle charging (CC) 8. 25 year system analysis

What is Set-Point-State-of-Charge? (SPSoC) quick definition - The SPSoC is used to tell the system when the batteries must be charged. - The SPSoC requires that the battery State-of-Charge be determined. - Below the SPSoC, the generator will supply recharge energy if other charging sources are absent. - Above the SPSoC, the generator will supply recharge only if it can operate near its peak operating efficiency (its maximum load capacity).

80% SPSoC Battery Array Use Summary for Traditional Lead-Acid Frequency Histogram 25 F re que nc y (% ) 20 15 10 5 0 0 20 40 60 80 100 State of Charge (%) Battery storage system spends most of it's life in higher states of charge Monthly Statistics 100 max 80 daily high SOC (%) 60 mean daily low 40 min 20 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec At 80% SPSoC there seems to be sufficient returns to a full charge Data generated with Homer Legacy software available from Homer Energy, LLC

20% SPSoC Battery Array Use Summary for Carbon Foam Lead-acid Frequency Histogram 10 Fre que nc y (% ) 8 6 4 2 0 0 20 40 60 80 100 State of Charge (%) Battery storage system SOC is a broad zone – much in the Sweet Zone Monthly Statistics 100 max 80 daily high SOC (%) mean 60 daily low 40 min 20 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec At 20% SPSoC the system rarely sees a full charge Data generated with Homer Legacy software available from Homer Energy, LLC

25 yr. Life costs vs. Set Point State of Charge (SPSoC) Cash Flow Summary 40,000 PV Generator 1 Trad P bA from 80-100SOC Converter 80% 30,000 Net Present Cost ($) SPSoC 20,000 10,000 0 PV Trad PbA from 80-100SOC Trad. PbA 40,000 30,000 20% 20,000 SPSoC 10,000 0 PV Generator Firefly Converter Oasis Data generated with Homer Legacy software available from Homer Energy, LLC

Cost of Energy vs. Battery SPSoC Levelized Cost of Energy vs. Setpoint SOC 0.7 Levelized Cost of Energy vs. Setpoint SOC 0.7 Fixed OR Solar = 25 % Levelized Cost of Energy ($/kWh) 0.6 0.6 Energy Costs increase as Setpoint SOC increases, Levelized Cost of Energy ($/kWh) representing increasing efficiency losses 0.5 0.5 approaching the 100% SP SOC 0.4 0.4 0.3 0.3 20 40 60 80 100 20 40 60 80 100 Setpoint SOC (%) Setpoint SOC (%) Data generated with Homer Legacy software available from Homer Energy, LLC

System Design & Energy costs based on SPSoC Set Point State-of-Charge SPSoC 20% 80% PV (kW) 15 20 6 3 Gen (kW) 4 4 Converter (kW) 19 77 Energy Storage Capacity (kWh) $21,349 $31,499 Initial capital 815 496 Diesel (L) Gen (hrs) 325 395 Operating cost $1,936 $3,309 ($/yr) COE ($/kWh) $0.33 $0.53 Data generated with Homer Legacy software available from Homer Energy, LLC

How It All Ties Together The total cost of Ownership Levalized Cost of Energy ( $ / kWh ) = O ∧ M Costs + Re ch arg eCosts + Disch arg eCosts + InstallationCosts O ∧ M Costs ⃗ Functionof : recombination efficiency ; ter min al design ; replacements ; cell equalization Re ch arg eCosts = Cost of Grid Energy Wh Re ch arg e Efficiency Total Energy Disch arg ed = ( Battery Capital Cost ) ∗ ( Energy Storage System Size ) Disch arg eCosts = BatteryCosts ( # cycles ) ∗ ( % DoD ) ∗ ( Capacity FadeQuotient ) ∗ ( Energy StorageSystem Size ) BatteryCapital Cost = ( ) = ( ) Pr oductionCost Pr oductionCost Gross M arg in Gross M arg in f ( η + ;η − ;η e ) Delivered Energy InstallationCosts ⃗ Functionof : power electronics ; HVACCosts ; systemvolume ( Wh / L ) HVAC Costs ⃗ Functionof : Whefficiency ; operating temperature ; Wh / L

Sulfation vs. Overcharge -The Quandary- Problem: PSOC operation causes Hard Sulfation (except in Firefly) Solution: Solution: Frequent recharge to Operate battery in 100% SOC PSOC (bad idea, but due to (easy in Firefly – poor PSOC in common since no hard cells, resort to this sulfation) wrongly) Problem: Frequent recharge to 100% SOC lowers cycle life & reduces efficiency, increases losses

What Really Matters? Attributes that don’t matter much: • Whr/kg • Wh/l • Cost of battery • Coulombic efficiency (Ah efficiency) Attributes that matter a lot: • Energy efficiency • Cycle life • Calendar life • Maintenance costs ( & cost of ownership) Okay, it all matters...we're just trying to make a point here.

Firefly Batteries the ONLY High-Capacity, PSOC, PbA Battery Technology

Firefly's Partial-State-of-Charge Battery All lead-acid batteries are not the same Firefly's Carbon Foam Battery: 1. Insensitive to PSOC operation range great PSOC performance, larger PSOC dynamic range with long life – better efficiency since avoiding the gassing “Knee” 2. No PSOC restriction ( recharge when convenient, not to avoid hard-sulfation issues) 3. No Float Charging (avoid gassing losses) 4. High Useful Capacity ( 50% to 100% larger cap w/o compromising lifetime excessively) 5. Deep Discharge 6. Exceptional Cycle Life Did you really think that you'd get through the entire presentation without a sales pitch?

Firefly Oasis Firefly Battery management module Thank You