Household backup batteries can provide backup power in case of an outage from your electric provider and they also can power your home or charge your car during your electric provider's more expensive "peak hours".
Backup batteries: Rack mounted solar batteries, Two Powerwalls, Assembly of 60 amp 12v battery, 24v 10 amp battery for solar storage, Jackery's 5000 plus with auto changeover, and mega 200 amp 1500 watt inverter camping system.
Some electric providers are now allowing willing particpants to send power to the grid through V2G or B2G (Vehicle or Backup to grid) programs. The electric provider can draw from the homeowner's vehicle or backup battery to add power to the grid at needed times (within parameters set [and modifiable] by the homeowner). We participated in Xcel’s test program but they never drew power just loaded the battery for us if it was low. They decided not to continue the program.
We added the Tesla Powerwall backup battery to our first solar install. There were a few other backup batteries available when we decided to add one to our solar panel project in 2017. But the Tesla battery had the largest capacity that we found when we researched. When we installed a Tesla roof there was a deal with Xcel for a second Tesla battery.
Each of these has a capacity of 13.5 kWh and about 11.5 of those is useable. Although at a peak rate of 5kw while on grid and 7kw when grid power shuts down. While on grid the charged powerwall batteries take over for direct solar power and will prevent the home from drawing power from the grid until a usage percentage set by the owner is met. After a sunny day with the batteries fully charged they will run during the late afternoon, a higher time of use power charge. Then when the set percentage left is reached, the grid takes over. Our two Powerwalls provide about half the total power used per month in summer but because our array mostly faces North that drops to less than 10% in the winter.
There are comparable alternatives to the Powerwall now. The Fortress Power 400Ah eForce 19.2kWh Stackable Lithium Iron Phosphate Battery is available from NAZ Solar for just under $9000. We saw rack mounted batteries in a solar tiny house this year. We asked them to be at our Metro Denver Green Homes tour but they were reorganizing. Maybe next year!
A new source of backup power can be found using electric vehicles. Some are specifically wired to perform as a backup (bidirectional) if a two way charger is installed. In some EV’s an internal inverter provides 120 and even 220 volt electricity. Several manufacturers offer V2X charging (vehicle 2 everything). My brother owns an extended range Ford Lightning and provided power to his essential appliances for a couple of days with extension cords and his onboard inverters after a hurricane in Florida. (An inverter converts DC power to AC which is what homes use.) That truck has 131 kw of power in its batteries and 3000 watt inverters including a 220 outlet! Besides Ford, some models of GM, Hyundai, Kia, Genesis and Lucid, the Nissan Leaf and the Tesla Cybertruck all offer V2X.
Our 2024 Tesla Y cannot provide power with an external inverter unless it was wired to the drive battery which would void the warranty. The model Y long range has a 75 kW battery. But the 12v outlets in the car are only 15 amps so they could only run a tiny inverter. Never deplete a lithium battery completely though. Stop at 10% at the lowest.
Many folks are purchasing what is sometimes called a “solar generator” for backup power. Brand names are Jackery and Bluetti. The largest Jackery was just released and it has an internal inverter. Tesla and Fortress require external inverters as typically used with solar panels. It advertises 5040 kw. It’s unclear to me whether 220 output requires an “expanded” unit. (More than one linked.) It also outputs up to 7000 watts of power. It provides 30 amps so could power a typical RV although the total run time depends on use. It can be wired into a home as an all in one backup power too. The company even provides an electrician in some markets. And one 5000 model includes an automatic changeover switch. If it senses there is no grid power it automatically switches to the battery. A home is typically between 100 and 200 amps total power so 30 amps is limited.
Smaller Jackerys have always seemed overpriced to me. It is relatively simple to set up a small power source from components and I have built two. The first was to power a trolling motor although I have used it with other 12 volt appliances especially inflators. It used three relatively inexpensive LiFePO4 12v 20 amp batteries wired together to provide 60 amps. That will run our small 12v trolling motor constantly for over an hour. I have a small 300 watt inverter but don’t use it with this system. The system has the required breaker, an on off dial, car battery posts, and two kinds of 12v connectors both Anderson and socket (cigarette lighter) and two USB plugs plus a battery meter. All packed into an inexpensive plastic toolbox and weighs about 24 lbs. (Very lightweight compared to a trolling motor battery.)
The second is a robust 200 ah battery with a 1500 watt pure sine wave inverter (for electronics). I put one together for our Tesla Y camping trip. I wanted hot water for the trip and can boil a full 128 oz electric carafe of water with this system. Although at 600 watts the electric boiler takes an hour to heat but also has a keep warm function. We also ran our 12v refrigerator from it and plugged it into the Tesla 12v outlet to recharge. The large and heavy 200 ah battery is in a purchased 200 ah battery vinyl case that has enough extra room to hold a 120 volt 20 amp lithium battery charger and the small DC outlet box. The inverter is in a separate canvas tool bag along with the battery screwdriver and other supplies. Both the inverter and 12v outlet boxes have built in fuses so I don’t have a separate fuse on this system. All 12v batteries should be fused to prevent dangerous power problems. The 60ah box cost about $300 back when lithium batteries were more expensive. Last summer the 200ah system cost about $400. A similar prebuilt system would cost over $1000. Putting the components together is relatively simple. A written description of the trolling box assembly is on my Twinsprings blog.
I also use a small 10 amp battery pack to power some 24 volt shades. This one connects to a solar controller and solar panel to charge the batteries.
Lithium batteries especially lithium ferric phosphate (LiFePo4) have made backup systems a practical approach to off grid solutions.
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