Solar + Storage for Homeowners
Storage Value Proposition in VA Bac ackup up Save ve money or g r get et pa paid d to Power er help t p the Gri rid for or you ou
Batteries Similar to Generator Source: alarmcentralsecurity.com Source: Sonnen
Other Applications of Storage Peak demand reduction, grid support (mostly non-residential) Time of use (arbitrage)
How Does Storage Work With Solar? • On grid/off grid • Solar charges batteries for later • Grid can charge batteries too (ac coupled) • batteries “topped off” • Batteries ‘kick in’ automatically “Islanding” with grid connected
What Can Batteries Power? Duri ring ng an outage ge • Seamless backup power • Critical loads Subpanel • “Loads” consume power • “Critical loads” consume power- are vital to functioning” • Essential lights, medical equipment, well pump
Sizing a System: 2 Considerations Power and Energy Power: er: • Instantaneous Watts (Measured in KW) • What are you powering at any given instant • Difference between 100 W light or 2,000 W HVAC • “Surge power” Energy rgy: • Quantity of power used/available over time • Measured KWh • Do you need to run load for 1 hour or 24 hours? (data center example) Source: SimpliPhi
Terminology: Power and Energy Energy (kWh) Power (Watts/KW)
Solar Battery Backup Example Batt ttery y Bank: nk: (P (Power wer 5 KW/ Ene nerg rgy y 6 KWh) ) Fully re-charged by solar daily • • No solar = 1 day of backup power • (days of autonomy) Cri ritica ical Loads ds The Johnsons lose • Refrigerator; small microwave power several times a • Some lights; some outlets year. • Cable modem Each time the power is What they chose not ot to po power wer: out for at least a day. Stove; dryer; electric water heater • .
How is storage priced? Tot otal al cost t = hardware costs + installation costs + lifetime maintenance costs Hardware are (battery, , inver erter) er) Install stallation ation + Lifetim time e maint intena enanc nce • Price per kW (power) • Cost of design, • Battery replacement OR installation, and • Associated labor cost • Price per kWh (energy) permitting • Additional equipment (Charge Controler AC/DC coupling) $$$ $$$ $$ $$ $
Federal Tax Credit for Storage 30% federal tax credit available for storage systems that are 100% charged by solar • Value: 30% % of the e total otal system em co cost st (hardware + installation) for fully solar-charged batteries • Storage systems that are at least st 75% % charged by solar are eligible for a portion of the full tax credit • Storage system that are less than n 75% % charged by solar are ineligible for the tax credit
Common Battery Technologies ”Deep Cycle” Lead Acid/AGM Lithium ium Ion Bu But w t wait, t, there’s more! Pros: Pros: • Lower upfront cost • High energy density • Tried and true • Lower lifetime costs Cons: • Longer lifespan • Maintenance requirement • Small space requirement There are other chemistries used in battery applications, • Slower energy discharge • More usable energy per cycle but their deployment is much uch (power) Cons: le less common ommon • High space requirement • Higher upfront cost • Shorter lifespan • Newer to market • Less usable energy per cycle • Losses for heating/venting
Operations and Maintenance Space Requirements Lead d Ac Acid • Small, shoe box-sized battery • Wired together in a group • Can sit directly on floor or shelf • Requires more space Lithiu thium m Ion Source: Fire Mountain Solar • Single, larger box Source: Clean Technica • Wall-mounted or floor-mounted • Can often also be wired together
Operations and Maintenance Siting Considerations • Batteries function best in cont ntro rolled lled envir ironm nments ents • Specific conditions depends on chemistry: • Lead-acid • Stable temperatures (ideal: 50 ℉ – 80 ℉ ) • No extreme heat or freezing air • Often installed indoors (garage/basement) • Special ventilation required for unsealed batteries • Lithium Ion • Wider temperature range (~32 ℉ - 100 ℉ ) • Some can be installed outdoors in stable climates
Operations and Maintenance • Installer’s labor should be warranted (wiring) • Note: Solar panels are warranted for 25 years Source: https://blog.pickmysolar.com/home-battery-backup-comparison-tesla-sonnenbatterie
Basic cost estimates (example) Hardware are co cost st (examp amples les) ) + Installatio tallation n co costs sts + Maint intenan enance ce co costs ts Equipment Cost Size $3,000 - $5,000 for Varies between installers Powerwall 2 (Li-ion) $6,200 13.5 kWh retrofit installation and and battery chemistries Powerwall 1 (Li-ion) $3,000 6.4 kWh additional equipment LG Chem (Li-ion) $6,000 6.6 kWh Sonnen Eco 4 (Li-ion) $10,000 4 kWh Sealed Lead Acid $5,200 12 kWh Pri ricing ing for r our r small ll 6 kW kWh h batt ttery y example: xample: ~$6,000 + $4,000 + $1,000 = ~$11,000
Check out our Residential Storage Guide!
Installing Storage with Solar vs. Later Lat ater With Solar ar • Solar now and wait for battery • Immediate backup power benefits prices to fall further • May reduce some shared labor • AC-coupled or retrofit existing and admin costs by paying a solar array contractor once instead of twice • Inverter replace or add • Eligible for solar Federal Tax Credit • Uncertain eligibility for solar Federal Tax Credit
The value of resiliency Losing power does have a cost
Latest update from the IRS In Marc rch 2018, the IRS issued a private-letter ruling clarifying: • Adding storage to an existing rooftop solar array will qualify for the 30% Federal Tax Credit • Solar charging stipulations still apply
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