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BATTERY BACKUP WITH AND WITHOUT PV

SMA Sunny Pro Club Webinar April 10, 2013

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AGENDA

> Sunny Island Product Overview

> Definition of Terms

> Sizing Guidelines

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> Versatile grid-interactive battery based inverter designed for off-grid and backup power applications.

> Utilizes a 48 Volt battery bank.

> Not a typical charge controller that uses DC electricity from PV array to charge batteries!

> NO PV is connected directly to Sunny Island.

Sunny Island Overview

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Sunny Island – Basic Tasks

> Creates a “micro grid” when utility fails > Supplies and controls AC frequency and voltage

> Transfers and converts energy in both directions > AC to DC for battery charging > DC to AC to supply energy to loads

> Controls external loads and energy sources > Load shedding

> Power control of Sunny Boys, auto generator start /stop

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Grid Present: No Sunny Boy 120 VAC

120 VAC SmartFormer

120/240 Vac

State of Charge

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• Autonomy depends solely on battery bank size • Grid is used to charge batteries • SMA Smartformer converts SI 120Vac to 240Vac for larger loads.

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AC Coupling

> Use a solar inverter to directly power the loads > Excess power is sent to battery inverter to charge batteries and/or grid

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Grid

Batteries

Battery Inverter

Protected Loads Panel

PV Inverter

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AC Coupled Loads and Sources

Supp

ly B

reak

ers

AC1

Protected Loads Panel

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120/240

Smartformer

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Definition of terms

> Grid Dependent > Requires grid to function > No back up capability > That means, NO GRID =

NO POWER made, even if it is a sunny day.

Goal: Green or ROI Design Complexity: Easy

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Grid Dependent PV Array

> PV production powers loads in home, and if there is excess power, that backfeeds onto the grid (meter “going backwards”)

> If there is not enough PV power for the whole house demand, the grid provides the difference (meter is still going forward)

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Grid Dependent PV Array - Grid Failure

> PV inverter MUST stop providing power, EVEN if it is a sunny day, and the PV system is capable of producing power.

> This is done for safety. X X

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Definition of terms

> Battery Backup > Utility grid is available > Grid Interactive > “Bi-modal” > If there is PV, excess production

may be exported to Grid > May or may not utilize generator

Goal: Security Design Complexity: Medium

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Battery Back Up – Without PV

> Grid normally provides power to ALL loads, on main panel and on sub panel (protected loads panel)

> The grid is the only method of recharging the batteries.

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Battery Back Up – Without PV

> When grid is down, Sunny Island draws from battery bank to provide power ONLY to sub panel.

> Loads connected to the sub panel are “protected” from the grid outage and have power.

> What do you want to power when the grid goes down?

X

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Battery Back Up – With PV

> During normal grid operation, PV array can provide power to home, recharge batteries, and possibly back feed into grid.

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Battery Back Up – With PV

> If there is a PV array feeding into the protected loads panel, the Sunny Island will allow it to continue to produce power, while the grid is down!

> This is completely safe, as the Sunny Island is physically disconnected from the grid.

X

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Typical Grid Dependent design approach

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Read Date Days kWh kWh/Day 4/7/2009 29 578 19.93 3/9/2009 31 685 22.1 2/6/2009 31 683 22.03 1/6/2009 33 860 26.06

12/4/2008 31 702 22.65 11/3/2008 31 800 25.81 10/3/2008 29 1,115.00 38.45 9/4/2008 29 1,289.00 44.45 8/6/2008 29 1,189.00 41 7/8/2008 32 1,043.00 32.59 6/6/2008 31 723 23.32 5/6/2008 29 574 19.79 4/7/2008 31 587 18.94

27.47 Calculate average energy use per day for the year

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Typical Grid Dependent design approach

> In Sacramento, 5.5 psh/d. Using that, (27.5 kWh/d) / (5.5 h/d) = 5 kW

> Thus, a 5kW (AC output) array would on average meet the household energy demand.

> If we assume a 0.8 derate factor from PV to AC out, this yields 5/.8 = 6.25 kW DC

> Using PV Watts with a 18 degree pitch, a south facing array of 7 kW DC comes closer to averaging 27.5 kWh over a year.

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Battery Backup Sizing – no PV

> With no other energy source besides the battery, all energy used during an outage must be stored.

> Optimally, the battery bank is sized based on how much energy demand (kWh) is needed during the worst outage with buffer for whatever minimum SOC bank should see.

> Also must ensure that largest power draw can be handled by the Sunny Island

> POWER demand will determine size (and number) of Sunny Island(s). > ENERGY demand will determine size of battery bank.

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Average Power Demand of Household items

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Space heater 1500 watts Clothes dryer (electric) 7200 watts Light bulb (100w) 100 watts Fan 100 watts Television 70 watts Microwave oven 1200 watts A/C (12,000 BTU) 3250 watts

Vacuum cleaner 600 watts Sump pump (1 hp) 700 watts Refrigerator (EnergyStar) 60 watts Deep freezer 35 watts Circular saw 6" 800 watts Coffee maker 1200 watts Water heater 3000 watts

This is instant power, not the total amount of energy consumed

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Example – Battery Backup Power Demand

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Fan 100 watts Refrigerator (EnergyStar) 60 watts Television 70 watts Lights (LED 3x40W) 120 watts Microwave oven 1200 watts Sump pump (1 hp) 700 watts Running all the devices at the same time requires 100+60+70+120+1200+700 =

2250 Watts of needed power capacity.

- Sunny Island 4548 has nominal 4500 Watt capacity - Sunny Island 6048 has nominal 6000 Watt capacity

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Example – Battery Backup Energy Demand

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Running the fan for 4 hrs uses 400 Watt-hours (Wh), or 0.4 kWh Running the fridge for 24 hrs uses 1440 Wh, or 1.5 kWh Running the tv for 4 hrs uses 280 Wh, or 0.3 kWh Running the lights for 5 hrs uses 600 Wh, or 0.6 kWh Running the microwave for 15 min uses 300 Wh or 0.3 kWh Running the pump for 3 hrs uses 2100 Wh, or 2.1 kWh Total for one day is 5.2 kWh FOR THIS CASE: Battery bank size determines how long the system can power these loads.

Fan 100 watts Refrigerator (EnergyStar) 60 watts Television 70 watts Lights (LED 3x40W) 120 watts Microwave oven 1200 watts Sump pump (1 hp) 700 watts

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> Assume that worst case outage is 6 days.

> Each day requires 5,200 Wh, so need 31,200 Wh to cover those 6 days.

> If we want SOC never to go below 30% (this parameter is enforced in the SI automatically), then the energy required is only 70% of the battery capacity.

> So, we would choose a 31,200/.7 = 44,570 Wh battery bank.

> This means the system needs a 930 Ah (44570 Watt-hr/48 V) battery bank.

Example – Battery Backup Energy Demand

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Example – Battery Backup With PV

> Now the PV array can contribute power for loads, or to recharge the batteries.

> From PV Watts, that 7 kW array yields: > 12 kWh/d in December > 39 kWh/d in July

> Even in December, the array would be able to more than meet the daily energy demand. Thus, the battery bank could be smaller. (4800 Wh storage = 100 Ah battery)

> Leave some capacity to allow for loads at night and periods of no sun.

> Design with multiple energy sources becomes harder, but system is more resilient.

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Sizing Guidelines

> For backup, recommend 1W of Sunny Island for 1W of load

> Without PV, size battery bank to satisfy energy demand for longest outage without exceeding maximum depth of discharge limit

> With PV, recommend no more than 2W of PV per 1W of Sunny Island

> With PV, recommend 100Ah per 1kW of PV

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Case Study: Residential Battery Backup System

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Treasure Island, FL House can withstand 220 mph winds Poured concrete walls 500 gallon cistern: irrigation/potable water All LED lighting Battery bank can power house for a WEEK

8 Sunny Islands – up to 40kW power 4 Sunny Boy 5kW PV inverters 20 kW array: Uni-Solar mats and Kyocera panels glued to metal roof.

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Battery Backup With Sunny Island can be modular

> Sunny Island is based on AC coupling – the other sources of energy are AC coupled into the home wiring. Many advantages to this: > Use readily available AC appliances > Avoid efficiency hit by forcing PV energy to go into and then out of battery to power AC loads > PV array can be retrofit into battery backup system, or vice-versa!

> For budget constrained customers, the can start with Sunny Island and “too small” battery bank and add PV later, or purchase array first and later add Sunny Island.

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Sunny Island Equals Energy Security

> “My Sunny Island system powered me and neighbor for our two week outage” – David J Morrison, via Facebook from New Jersey

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