Valuing the Benefits of Insulated Battery Enclosures for Stand-Alone Photovoltaic Systems in Cold Climates

Transcription

1 Valuing the Benefits of Insulated Battery Enclosures for Stand-Alone Photovoltaic Systems in Cold Climates Michael Ross--CANMET Energy Diversification Research Laboratory Presentation from Dave Egles-- Soltek Solar Energy Ltd.

2 Outline umotivation: effects of cold on batteries uintroduction to thermal protection uvariables affecting cost-effectiveness of thermal protection uquantitative investigation ueffect of thermal protection on battery lifetime

3 Effects of Cold Temperatures on Lead-Acid Batteries Lower discharge capacity Decreased charge acceptance Danger of battery freezing Re duc tio n in Us e able Capac ity fo r Flo o de d Tubular Batte ry with no LVD Te mpe ra ture (C)

4 Motivation uin, large battery banks are used ubattery is significant part of system cost uif the battery bank could be kept warm throughout winter, a smaller battery bank could be used uif the cost of keeping the battery warm is less than the savings from a smaller battery, then system cost decreases

5 Thermal Protection for Batteries u Insulation uheating: Surplus power from the PV array uphase change material (PCM) uwater takes a long time to freeze, and will remain at 0 ºC until it is completely frozen ubut when does each of these make sense?

6 Variables-- Batteries ucost per unit capacity (high -> thermal protection) uvolume per unit of capacity (high->pcm) uvrla batteries -> thermal protection uenergy Density (low->pcm) ushape utemperature derating

7 Variables--Site udeg. sec. below freezing point of PCM (relatively low -> PCM) ushort, cold periods -> PCM uwinter solar availability (high -> heating) urime icing or mountain fog -> PCM

8 Variables--System Size and Design uload (large -> insulation) usize of the battery bank (large -> insulation) uarray-to-load ratio (high -> heating) udays of autonomy (low -> insulation)

9 Effect of Insulation Minimum Battery Temperatures for Various Insulated Enclosures in Montréal, Not Accounting for Battery Self-Heating Based on simulation for weather data from 1953 to Minimum ambient air temperature was ºC. Average January temperatures were ºC m of insula tion 0.3 m of insula tion 0.2 m of insula tion 0.15 m of insula tion 0.1 m of insula tion 0.05 m of insula tion Uninsula te d -35 Thermal conductivity of insulation W/ mk. C/20 Ba tte ry Ca pa c ity a t 25 ºC (Wh)

10 Reduction in Battery Size-- Insulated vs. Uninsulated Enclosure Va ncouve r Toronto Montré a l Ye llo wknife Ha ll Be a ch (Arctic) De s ire d Minimum Us e a ble Ca pa c ity (Wh a t C/20) Insulated enclosures have 15 cm of polyisocyanurate insulation.

11 Cost: Insulated versus Uninsulated Va ncouve r: Ave ra ge Ba tte rie s Va ncouve r: Abs olyte s Montre a l: Ave ra ge Ba tte rie s Montre a l: Abs olyte s Ye llowknife : Ave ra ge Ba tte rie s Ye llowknife : Abs olyte s Minimum Us e a ble C/20 Ba tte ry Ca pa c ity (Wh) Total Cost of Batteries and Enclosure: Ratio of Insulated to Uninsulated

12 Battery Temperature: Heating and PCM Enclosure with water as PCM: Min Temp is Approximate 0ºC Montréal, N = 35 Days, Array to Load Ratio = 16, 15 cm of polyisoc ya nura te insula tion Grande Prairie, Alta., N = 60 Days, Array to Load Ratio = 18, 20 cm of polyisoc ya nura te insula tion Surplus + Battery Self-Heating Accounting For Battery Self Heating Not Accounting For Battery Self Heating Surplus + Battery Self-Heating Accounting For Battery Self Heating Not Accounting For Battery Self Heating Ba tte ry Ca p a c ity a t 25 ºC a nd C/20 (Wh)

13 PCM Requirement Grande Prairie, Alta., N = 60 Days, Array to Load Ratio = 18, 20 cm of polyisoc ya nura te insula tion Not Accounting for Battery Self-heating Montréal, N = 35 Days, Array to Load Ratio = 16, 15 cm of polyisoc ya nura te insula tion Battery Self-Heating Not Accounting for Battery Self-heating Surplus + Battery Self-heating Battery Self-heating Ba tte ry Ca pa c ity a t 25 ºC a nd C/20 (Wh)

14 Cost per Unit Minimum Usable Battery Capacity-- Montréal Expe ns ive, Voluminous Ba tte ry Ave ra ge Ba tte ry Battery Self-Heating Surplus Heat + Battery Self-Heating Surplus Heat + Battery Self-Heating PCM with Self-Heating Battery Self-Heating PCM with Self-Heating Minimum Us e a ble C/20 Ba tte ry Ca pa c ity(wh)

15 Cost per Unit Minimum Usable Battery Capacity-- Grande Prairie Expe ns ive, Voluminous Ba tte ry Ave ra ge Ba tte ry Battery Self-Heating Surplus+ Battery Self-heating PCM with Battery Self-Heating PCM with Surplus+Battery Self-Heating Battery Self-Heating Surplus+ Battery Self-heating PCM with Ba ttery Self-Heating PCM with Surplus+Ba tte ry Se lf-he a ting Minimum Us e a ble C/20 Ba tte ry Ca pa c ity (Wh)

16 Effect on Lifetime uwill smaller battery banks cause deeper cycling and shortened battery lifetimes? uno: in systems with greater than 6 days autonomy, cycling is not responsible for ageing uthe battery stays fully charged for all but a short period during the winter

17 Conclusions uinsulation is generally cost-effective uwhen battery is costly, voluminous, and site is cold, PCM makes sense ureducing the battery bank through the use of thermal protection will not shorten battery life