Why Use Solar Cell Storage | Backup Power, Savings, Efficiency

Install 10kWh solar cells, through opening peak-shaving valley-filling mode nighttime use electricity, can photovoltaic self-use rate raise to 80%, yearly save 30% electricity bill, power outage time can even provide 12 hours backup power.

Backup Power

Calculate calculate can carry what

Single piece 13.5 kilowatt-hour mainstream household cell, system set standard continuous discharge power is generally 5 kilowatts. Facing carrying physical motor equipment's instant start, the system is able to provide maintain 10 seconds around's 7 kilowatts peak output power. One piece cooling capacity is 2 tons central air conditioner, start instant will produce up to 3.5 kilowatts to 4 kilowatts surge instant load, enter stable run state after consuming electricity power only will slowly fall back to 1.5 kilowatts around.

If the cell currently already carries a total of 3 kilowatts of basic household electricity load, again forcefully start this air conditioner, the 7 kilowatts peak load upper limit will trigger the inverter's overload protection mechanism, leading to the whole house within 5 seconds to be forced to power off. Install personnel usually will separately set one 60 amperes or 100 amperes backup load distribution box, take the whole house's 200 amperes main distribution box in's oven, electric water heater etc. super large power appliances physically removed, only keep total peak not exceed 5 kilowatts life necessary circuits.

Appliances consume electricity

In the 13.5 kilowatt-hour theoretical available electricity pool, different appliance equipment's consume rate difference extremely large, according to cell depth of discharge parameter set as 95% calculate, system actual available for dispatch output electricity amount is about 12.8 kilowatt-hours.

· One piece capacity is 600 liters household inverter refrigerator, compressor average run power at 150 watts to 200 watts fluctuates, according to every day's run cycle, occupies whole day 25% time calculate, 24 hours cumulative actual electricity consumption amount is 1.2 kilowatt-hours to 1.5 kilowatt-hours.

· Gas heating furnace's blower fan power is usually calibrated at 400 watts to 500 watts, at minus 5 degrees Celsius air temperature, fan every day cumulative run 10 hours, will consume off 4 kilowatt-hours to 5 kilowatt-hours cell reserve electricity amount.

· Take 8 pieces of 10-watt LED ceiling lights and 2 pieces rated power is 65 watts laptop computers same time open, per hour joint consume electricity amount is 210 watts, continuous use 5 hours only need consume 1.05 kilowatt-hours reserve electricity amount.

· Basement's accumulated water pump work power is usually 800 watts, every time it starts running for 5 minutes, every day it starts 12 times, one whole day consumes a total electricity amount approximately equals 0.8 kilowatt-hours.

Side charge side use

Power outage time extends to 3 days, even 5 days. The cell at first night consumes 60% of the electricity amount, and the second day morning remaining electricity amount will drop to 40% around. Morning 9 o'clock after, the roof's 8-kilowatt photovoltaic array at solar radiation amount reaches per square meter 600 watts time start produce significant direct current.

Morning 10 o'clock photovoltaic end's real-time output power climbs to 4 kilowatts. This time, the house's inside appliances total consume electricity amount maintains at 1 kilowatt, the inverter will take the remaining 3 kilowatts of direct current, with about 55 amperes current charge into rated voltage is 51.2 volts lithium iron phosphate cell pack in. According to 98% direct current to direct current charge efficiency, about need 2.5 to 3 hours, the system can take the cell from 40% low valley state and re-push back to 100% full charge threshold.

When the cell reaches 100% full charge and the house consumes electricity, the amount still stays at 1 kilowatt hour, the inverter will actively take the output alternating current's frequency from 60.0 hertz to 60.5 hertz above. Micro inverter detects 500 millihertz frequency shift data after, immediately through limit output current's way, take photovoltaic panel's generate power from 4 kilowatts forced press drop to 1 kilowatt, achieve generate electricity and use electricity at millisecond level data match, prevent cell overcharge lead to single cell voltage exceeding 3.65 volts.

Air temperature and electricity amount

Lithium iron phosphate cell's best charge discharge temperature range is at 15 degrees Celsius to 35 degrees Celsius, external environment's temperature change will cause internal electrochemical reaction rate and internal resistance's linear change. Garage or outer wall temperature at winter drop to 0 degrees Celsius time, cell's available discharge capacity compared to 25 degrees Celsius time's nominal value will physically shrink 15% to 20%, originally 13.5 kilowatt-hours capacity, actual only can release out about 11 kilowatt-hours effective electricity amount.

The system built-in cell management module will start rated power is 200 watts to 300 watts silicone heating pad, continuous heat 40 minutes to 60 minutes, consume about 0.2 degrees to 0.3 degrees electricity, take cell surrounding physical temperature forcefully pull raise to 10 degrees Celsius above. Complete heating program after, system only allows external inverter with greater than 20 amperes current toward internal cell charge, prevents low temperature large current charge trigger lithium ions at graphite negative pole surface precipitate crystal, avoid cell nominal life appearing 5% to 10% permanent data decay.

Savings

Hide high price electricity

One piece nominal capacity is 13.5 kilowatt-hours cell pack immediately with highest 5 kilowatts continuous output power take over house internal all loads. Assume in this 5-hour discharge cycle, the indoor air conditioner compressor, dryer heating wire, and whole house lighting equipment cumulatively consume 10 kilowatt-hours of electricity. If from the power grid, full amount buy electricity, the single day cost is 5.50 US dollars; utilize photovoltaic panels in the morning flat valley period to charge into the cell's free electricity amount, single day then can lower about 5.10 US dollars electricity bill expense. According to the summer 120-day cycle, single peak shifting operation's cumulative amount can reach 612 US dollars.

In winter's 245 days inside, the peak valley price difference average narrows to 0.15 US dollars, and every day's cell releases 8 kilowatt-hours of electricity, which can produce 1.20 US dollars of deviation profit. Winter cumulative savings amount is about 294 US dollars. Whole year single piece cell's peak shifting profit book total is 906 US dollars.

Store for own use

One set installed capacity is 7.6 kilowatts roof system at clear weather, under produce about 35 kilowatt-hours of total electricity, the house at daytime only consumes 10 kilowatt-hours, the remaining 25 kilowatt-hours under no cell intervention's situation will be forced to push into the power grid. The power company provided grid-connection purchase electricity price only is per kilowatt-hour 0.04 US dollars to 0.05 US dollars, 25 kilowatt-hours output can only exchange for 1.12 US dollars bill points.

Arrived at night, lack illumination's stage, house needs power grid re-buy back 15 kilowatt-hours electricity, according to the average retail price of 0.30 US dollars/kilowatt-hour, need pay 4.50 US dollars, produce 3.38 US dollars bill deficit. If merged in two pieces, the total capacity is 20 kilowatt-hours lithium iron phosphate cell pack, the inverter will take 25 kilowatt-hours excess electricity amount in's 20 kilowatt-hours intercept, with an average 4.2 kilowatts power charge into the cell inside, the cell's physical charge discharge Coulombic efficiency maintains at 96% above.

Arrived at night, the ambient temperature drops, and the cell releases 15 kilowatt-hours of electricity to cover all nighttime load. Originally, with 0.045 US dollars sold electricity amount converted into offset 0.30 US dollars high price electricity's internal asset, per kilowatt-hour's value amplify coefficient reached 6.6 times, making system's actual self-generate self-use rate from insufficient 30% forcefully pull raise to 85.7% peak value.

Receive subsidy

Buy one piece nominal capacity is 13.5 kilowatt-hours, built-in hybrid inverter's AC coupled cell, equipment factory average price distributes at 6500 US dollars to 7500 US dollars range. Add on local licensed electrician about 6 to 8 work hours' install labor fee (average hourly wage range at 120 US dollars to 150 US dollars), as well as various level municipal departments charged 300 US dollars to 500 US dollars grid-connection review fee, initial total install capital expense reaches about 9800 US dollars.

At the next year's annual personal income tax form time, this sum expense's 30% (namely 2940 US dollars) will be with tax reduction quota's form proceed return. Net hardware obtain cost subsequently is diluted to 6860 US dollars.

According to previously calculated, every year 906 US dollars peak shifting price difference profit, add on about 650 US dollars to avoid low price transmit electricity's bill reduction amount, system annual average comprehensive cash return is about 1556 US dollars. Adopt straight-line depreciation method and static return model calculate, 6860 US dollars divided by 1556 US dollars/year, investment payback cycle shortens to 4.41 years.

Cell's warranty agreement generally promises 10 years within remaining cycle capacity not lower than initial nominal capacity's 70%, within the remaining 5.59 years effective life period, according to annual electricity amount decay rate 2% calculate, energy storage equipment still can continue produce about 7800 US dollars cumulative net monetary positive profit.

Earn dispatch fee

When the summer environment temperature soars to 38 degrees Celsius, millions of air conditioners run at the same time at 100% full load, the substation's instant load pressure approaches its rated physical capacity's 95% red line, and the power grid AC frequency might drop to 59.9 hertz, even lower, into a dangerous range. The public utility company will through a cloud server toward a networked household energy storage system send frequency is per second 1 time dispatch data packet. Users at terminal applications inside agree to specific commission rate participate in power grid peak-shaving valley-filling.

One single high voltage load demand response event usually lasts 2 hours to 3 hours. The power company offered purchase price often reaches per kilowatt-hour 1.50 US dollars to 2.00 US dollars. Set cell keep 20% bottom-most depth of discharge as run bottom line, remaining 80% available capacity (about 10.8 kilowatt-hours) with 5 kilowatts maximum safe discharge rate toward power grid reversely transmit alternating current.

In one time, it lasts two hours, and the power grid support event lasts two hours, and the system injects 10 kilowatt-hours of electricity, and a single time can earn about 20 US dollars in cash exchange commission. This kind of extreme load event happens every year in extremely hot or extremely cold climates, and the frequency of occurrence is about 20 times to 35 times. If the system is set as fully automatic response, a single unit cell at one year can cumulatively output about 280 kilowatt-hours of electricity, produce about 500 US dollars of subsidiary monetary cash flow, and take equipment's overall capital yield rate again push high 3 to 4 percentage points, same time assist stabilize main power grid about 3% local voltage fluctuation variance.

Efficiency

Charge discharge loss small

Roof on 20 pieces rated power 400 watts monocrystalline silicon photovoltaic panels, at noon 12 o'clock receive per square meter 1000 watts of standard radiation time, will produce about 8 kilowatts of continuous direct current. The current through the cross-sectional area is 6 square mm pure copper cable, and it transmits downward. The cable's internal physical resistivity is about 3.4 ohms per kilometer, leading to transmission processes in which about 1.2% of the line heat loss appears.

Direct current rated conversion capacity is 10 kilowatts hybrid inverter end time, built-in silicon carbide power module will with 99.5% internal switch efficiency, take photovoltaic panel outputted 350 volts to 450 volts high voltage direct current, step-down to 51.2 volts cell match voltage. Nominal capacity is 13.5 kilowatt-hours lithium iron phosphate cell pack, immediately receive up to 80 amperes continuous charge current.

In the whole complete charge discharge cycle back and forth test model, high quality energy storage system's alternating current to alternating current (AC-to-AC) round trip physical efficiency stably maintains at 90% to 92.5% range. Take the deposit of 10 kilowatt-hours of electricity as an example, pass through AC-DC conversion, cell internal resistance heating, and inverter standby loss, finally can at 240 volts alternating current end toward household load release out at least 9.1 kilowatt-hours of effective run electrical energy.

In the United States, the California Energy Commission's (CEC) equipment test database, the mainstream household energy storage inverter's weighted conversion efficiency indicator has been forcefully required to reach 96.5% above. System at 20% light load, 50% half load, and 100% full load three kinds of test working conditions under's weighted average value, determined from direct current converted to 60 hertz, 240 volts standard alternating current time's electrical energy physical evaporation proportion.

Control temperature more save electricity

When the garage inside environment air temperature at midsummer soars to 45 degrees Celsius, the cell with 5 kilowatts maximum continuous power toward outside discharge, the single cell internal 0.5 milliohms alternating current internal resistance will produce about 150 watts to 200 watts of waste heat. If not proceed physical intervention, sealed chassis inside temperature will in 40 minutes within break through 55 degrees Celsius safe extreme value.

Built-in cell management system (BMS) will immediately wake up rated power is 60 watts direct current exhaust fan or micro liquid cooling circulation pump, with per minute 3000 revolutions rotation speed proceed active heat dissipation, take box inside heat with per hour 800 BTU rate toward outside draw away. Active heat management module's parasitic power consumption per hour will consume off 0.06 kilowatt-hours of reserve electricity.

In the up to 5-hour peak shifting discharge cycle, the heat dissipation system total consumes 0.3 kilowatt-hours, only occupies 13.5 kilowatt-hours of the total capacity's 2.2%, but yet successfully takes cell physical work temperature forcefully pressed at 32 degrees Celsius below, avoiding high temperature lead to's internal resistance multiplied surge, recovered about 8% physical discharge capacity loss.

When the ambient temperature drops to minus 10 degrees Celsius, not configured heating module's lithium iron phosphate cell forcefully proceeds 0.5C rate's charge action, will trigger severe lithium ion precipitate effect. Deposited at the negative pole surface's metal lithium dendrite will pierce through the thickness of only 16 micrometers polymer separator, leading to single time violating low temperature charge then can cause irreversible capacity decay rate up to 3% to 5%.

Calculate accurately decay rate

Adopt square aluminum shell packaged 100 ampere-hours lithium iron phosphate cell, at standard laboratory environment under, with 0.5C charge discharge rate (namely 2 hours full charge, 2 hours empty discharge), 100% depth of discharge (DoD) proceed continuous cycle test. Complete 6000 times physical cycles after, capacity retention rate (SOH) still able to maintain at initial nominal capacity's 80% red line above.

According to the ordinary family, the daily cycle consumes 10 kilowatt-hours of electricity. Calculate, one year 365 days cumulatively produces 365 complete cycles. Experience 10 years total 3650 times cycle baptism, cell pack's internal equivalent series resistance (ESR) increase margin less than 20 milliohms, its actual available capacity from factory state's 13.5 kilowatt-hours, slowly present linear decline to about 11.8 kilowatt-hours. Depth of discharge's software limitation to equipment overall efficiency life cycle's extension played an extremely large leverage role.

Take inverter end's backup electricity amount threshold set at 20%, limit daily peak shifting discharge only at 100% to 20% range within proceed, take actual depth of discharge from 100% narrow to 80%, can make cell's theoretical cycle life extreme value from 6000 times largely leap to 8500 times above, physical service age easily cross 15 years mark.

Commercial grade cell factory before will proceed up to 180 days accelerated aging test, in a 45 degrees Celsius constant temperature box, apply 1C large current high voltage shock. Test data shows, take charge upper limit cut-off voltage from 3.65 volts fine tune lower to 3.55 volts, although lost about 4% single time charge top end physical capacity, but can effectively delay positive pole material structure's crystal lattice collapse rate, make long cycle capacity retention rate additionally raise 12%.

Millisecond level follow load

Install at the main distribution box, incoming line end's two pieces 200 amperes split-core current transformers (CT), with per second 100 times ultra-high frequency continuous collect power grid bidirectional current's instant ampere value. When the house is open, the rated power is 1800 watts microwave oven, CT induction coil in 10 milliseconds within capture to load end newly added 7.5 amperes current demand.

Inverter inside DSP digital signal processor at receive sampling signal after, only needs 20 milliseconds to complete closed-loop calculation, immediately instruct bidirectional DC-DC converter to take cell end's discharge current from standby state's 2 amperes instantly pull raise to 38 amperes. Whole load tracking process in 50 milliseconds within thoroughly complete, speed far faster than AC power grid 60 hertz (single cycle 16.67 milliseconds)'s three complete sine wave cycles.

Extreme millisecond level dispatch algorithm ensured at microwave oven run's 5 minutes within, from external power grid absorbed supplement electrical energy is strictly controlled at 0.001 kilowatt-hours below, take optical storage system's self-sufficiency response accuracy maintain at 99.8% high position.