Describe an off-grid solar setup, and someone 20 years ago would imagine a remote cabin in the woods, with lead-acid batteries and diesel generators used as backup power. But in the 2020s, off-grid homes might be closer than you think — like, right next door. Many neighborhoods, either because of their geography or restrictions on the existing grid, are flipping the script and using the grid solely as emergency backup.
“The newest thing is grid defection,” said David Norman, director of solar product and business development at lead-acid and lithium battery provider Discover Battery.
For example, in Hawaii, where utility prices average more than 30-cents/kWh and no new solar can be added to the grid, people are taking their power into their own hands. Often called total self-consumption or zero-export power, Hawaiian households are essentially working as off-grid homes with the grid as a backup.
In California where “public safety power shutoff” events have limited utility power for the last few years, homeowners are planning ahead for extended outages. In the best-case scenario, homes should now be designed to function off-grid for at least a month, while the other 11 months they can use the grid.
Doomsday bunkers aren’t present in either of these situations — off-grid setups already exist in many urban neighborhoods. Today’s power needs require battery technologies to keep up.
Lead vs. lithium in off-grid
An electric battery, by definition, is a device that stores energy that can be converted into electrical power. In that sense, all battery types are equipped to handle off-grid storage needs, but some are better than others at satisfying today’s electricity demands and cycling schedules.
“Off-grid is less about the battery and more about the use-case,” Norman said. “If you’re only doing backup power, lead-acid works. It’s not cycling regularly, and it’s primarily just sitting in reserve for a power outage or failure. But for demand charge applications, any lithium battery is better.”
Trojan AGM lead-acid batteries
Lead-acid batteries do work well for occasional, short-term backup needs. But if someone wants to switch power sources to take advantage of utility time-of-use rates or avoid the grid for an extended period of time, more frequent and deeper cycles are needed than what lead-acid can provide.
“Lithium is changing off-grid,” Norman said. “You still can live off-grid on lead-acid, but lithium is more efficient.”
This all boils down to the number of cycles a battery has and its depth of discharge — how many times the battery can be drained, and how much power can actually be used. KiloVault also offers both lead-acid and lithium-based batteries, and VP of sales and marketing Jay Galasso often explains the two chemistry-types’ charging specifications.
“Off-grid solar applications require batteries that can be discharged and charged every day,” Galasso said. “One cycle might be charging the batteries during the day, then discharging the stored energy for use during the evening. The more a battery is discharged, the ‘deeper’ the cycle.”
Lead-acid batteries degrade more with every cycle. Where a lithium battery may come with a 10,000-cycle guarantee, a lead-acid battery may peak at 2,500 cycles when discharged to 50%. Lithium batteries can be discharged to near-zero, or basically, all the juice in a lithium battery can be used in one cycle, where a lead-based battery can only use half of its juice before degrading even faster.
A modern off-grid setup using lithium batteries from Discover
“Lead-acid batteries are lower in cost for the same voltage and capacity but do not last for many cycles,” Galasso said. “[Lithium-based] designs can use fewer batteries for a given application because of the higher charge/discharge rates, resulting in lower initial costs.”
SimpliPhi Power was founded in the early 2000s and has always been a lithium battery provider. The company knows the value of lithium batteries in off-grid applications since its original market was remote power scenarios.
“Lead-acid is a legacy product used in off-grid. It’s where the solar industry originated. You couldn’t have a PV system without lead batteries in those early days,” said Sequoya Cross, director of global sales and business development for SimpliPhi. “Why we see more people scaling to lithium: you have more usable capacity in a smaller space, you can pull them to 100% depth of discharge.”
Physical space is another reason lead-acid is falling out of favor in today’s grid-detached setups in urban environments.
“Most people who build off-grid don’t have a separate mechanical room off their house where the batteries and inverter can go. Most people don’t have that kind of space,” Norman said. “In order to have enough energy storage to run your house as an off-grid home, just by volumetric space alone, you have to go lithium because you could never put that much lead in your house.”
When someone wants to take their active household off the grid today, that usually means they want the refrigerator to work, along with computers, internet, televisions, lights and everything else, all at the same time. Just backing up one emergency load can’t cut it anymore, especially in places like California where life must go on when the utility turns off the power. This requires larger battery capacity, faster charging rates and deeper depth of discharge — things lead-acid just can’t provide.
“Lead is dying in off-grid. You can get long lives out of lead-acid, but they require a lot of maintenance,” Norman said. “There’s no sense in selling a premium lead when I can sell lithium for only 10% more. Lead still works in automotive markets, but on the solar and stationary side, lead is dead.”
The off-grid lithium battle: NMC vs. LFP
The two dominant lithium battery types used in residential applications are lithium nickel manganese cobalt oxide (NMC) and lithium iron phosphate (LFP). The Tesla Powerwall, Generac PWRcell and LG RESU batteries all use NMC chemistry, while many more suppliers use LFP (including Discover, Eguana, Electriq Power, Enphase, KiloVault, SimpliPhi, sonnen). Although both battery types work great in demand arbitrage situations, LFP has an edge when it comes to off-grid. That may be why more companies are offering the cobalt-free chemistry.
“For on-grid applications where you don’t necessarily care about rapid recharge because you’ve got the grid there, NMC batteries are great,” Discover Battery’s Norman said. “The limitation with them for an off-grid scenario is that they can’t handle the high-current charge or discharge of demanding off-grid loads.”
SimpliPhi LFP batteries were used in a solar installation on former California Gov. Jerry Brown’s off-grid private residence in 2018
Aric Saunders, EVP of sales and marketing for NMC and LFP battery provider Electriq Power, explained the differing charge-rates for the two lithium chemistries. NMC batteries have a charge-rate of 0.5C while LFP batteries are 1C. If it takes an LFP battery one hour to charge, the NMC battery takes twice as long because it accepts current more slowly. LFP batteries can be charged in half the time as NMC.
“Because of [the faster charging rate], LFP batteries can provide a higher power output to the grid or home. This feature allows the battery to back-up larger loads with a smaller battery than would be needed with NMC,” Saunders said.
“Time is money. If I’m charging on solar and I’ve only got a six-hour solar day, I want to get as much into those batteries as I can,” Norman said. An off-grid solar + storage system would benefit most from the fast-charging properties of LFP.
While “off-grid” might be a loose term to describe using the main utility grid as backup instead of a primary power source, it may be an essential way-of-life for many more people in the near future. Homeowners should then choose the right battery chemistry for their situation.
“Off-grid is around us all the time. It’s not just people in the woods anymore,” SimpliPhi’s Cross said. “It isn’t necessarily possible to completely disconnect or pull your meter, but it is possible to design around an off-grid lifestyle.”
what about vanadium storage batteries? a lot less fire hazard, and a lot more recycling. now being used in australia. Are they available here? Reasonably priced or what?
Kelly,
Thank you for continuing to bring us timely and insightful information on the state of the solar industry and related areas.
It is much appreciated.
Michael
Quite interesting and handy.
I moved to the far southern end of Hawaii Island 5 years ago, and when building our house, designed and installed a 100% off-grid system charged by solar panels.
We use about 12kWH of electricity per day.
We use a gas fired inverter generator as backup power. Over 5 years, it has provided 7% of our power needs, including a year when Kilauea erupted, covered our area in a continuous ash cloud, and reduced solar radiation to roughly 30% of normal.
Last fall, we switched out our sealed lead acid battery for lithium ferrophosphate. It was a significant improvement in ease of maintenance and useable capacity. We rarely have need for our backup generator now, and since the switch, its usage has fallen to less than 2% of our consumption.
We could have easily hooked up to the local utility, and it likely would have been cheaper. But when a neighbor calls to ask if our power is out, answering “No”, is priceless.
Thank you for sharing your off-grid experience!
I totally agree with Steve_S. If you only think about the EV industry you can understand why until recent times they have preferred NMC, the higher current rates + the higher energy density.
Very timely message. Am in Nova Scotia Canads and actively exploring a solar PV system to run the house (6000 KWH annual load). Batteries seem to be the biggest concern and largest expense (2/3 of a $30,000 system). Off grid seems to be the most feasible as being grid tied could allow the utility provider to ‘borrow’ the energy in my battery bank when the grid needs it. Theoretically it would be replaced at a later time.
I’d be surprised if neighborhoods didn’t get together and co-op 1Mwh containered (20′) flow batteries and single point micro-grid when that tech finally comes down to it’s projected Levelized Cost of Storage. Possibly contracting with grid to provide some parker power access where that micro-grid also has EV V2H capacity.
Slight Correction, you inverted some info.
“differing charge-rates for the two lithium chemistries. NMC batteries have a charge-rate of 0.5C while LFP batteries are 1C.”
I use & BUILD LFP systems, have written documents & manuals on LFP Assembly, BMS’s and more.
I am also a Long Term offgridder in Northern Ontario Canada who started off with heavy Rolls Surette Lead and have now migrated fully to LFP that can provide 10 Days of Runtime before charging is required.
Standard LFP has a 1.0C Discharge Rate and a 0.5C Charge Rate.
Feel free to verify that with any spec sheet from CATL, EVE, LISHEN, BYD, ETC and others.
Other Lithium Chemistries are capable of higher than 1C Rate and pending on Pack Assembly & Cell Spec, that can easily support up to a 5C Burst Rate (which also heats up the cells quite a bit). Such high Discharge Rates are not required in a Residential ESS Application. (ESS = Energy Storage System)
Also not mentioned why there is a greater preference for LFP (LiFePO4).
– LFP is Cobalt Free,
– considerably LESS Costly than other Lithium Chemistries,
– Is not as Volatile as other chemistries and as such much safer.
– Does not suffer the High Thermal issues of other chemistries at the 1C Discharge Rate
– The LFP Voltage Curve is also the closest to Lead Acid Battery charging/discharging profiles, therefore making it much easier to integrate with Solar Charge Controllers, Inverters & Chargers.
* CAVEAT * Standard LFP cannot be charged below 0C/32F but can be discharged up to -20C Temps.
IF in Cold Environment, battery packs must either be equipped with a Warmer OR the battery packs should be assembled with Yttrium Doped Cells (LiFeYPO4) which tolerate the cold to -20C for charging.
– LFP Batteries also do NOT offgas Hydrogen (Like Lead Acid) and in many jurisdictions can be installed within a residence unlike Lead Acid battery banks.
“Many neighborhoods, either because of their geography or restrictions on the existing grid, are flipping the script and using the grid solely as emergency backup.”
The interesting part is the late 1990’s and early 2000’s the IOU utilities laughed at those putting in solar PV as a grid tied system. When enough solar PV was installed even without battery backup, at around 2% to 3% penetration of grid tied, the utilities started to complain that at least in some places a “duck curve” was being created cutting into the utility’s assured revenues. Many price gouging electricity programs later, the utilities have managed to push the grid tied adopters to accept smart ESS as their next purchase. New adopters will more than likely step right into large solar PV arrays, smart energy storage and home chargers for BEVs. Grid agnostic is becoming a (real concept) for homeowners to consider. The down side for the utilities former grid tied can actually use an A.C. charger and use more solar PV generated A.C. to charge a smart ESS and with it’s interactive inverter could charge from a D.C. source like solar PV panels directly and also auxiliary A.C. to D.C. charger to take what would have gone out into the grid and cycle this back to the battery bank for after hours self energy generation. I would submit, the utility death spiral is picking up speed once again.
“This all boils down to the number of cycles a battery has and its depth of discharge — how many times the battery can be drained, and how much power can actually be used. KiloVault also offers both lead-acid and lithium-based batteries, and VP of sales and marketing Jay Galasso often explains the two chemistry-types’ charging specifications.”
The (LTO) lithium titanate battery is low energy density, but at only 90Wh/kg can charge and discharge to 85% to 90% for something like 15,000 to 20,000 cycles. Get this technology down to $100/kWh and keep smart ESS installed systems costs at the $400/kWh installed, folks would be looking for a 20 to 30kWh solar PV array and 100kWh to 200kWh to meet their daily energy needs completely. One entity Kilowatt Labs says it’s technology is super capacitors and can fully charge and discharge 1,000,000 times. One You Tube video I ran across was from a foreign country and the engineer stated if you put super or ultra capacitors in front of lithium ion battery chemistries you can (double) the useful life of the lithium ion batteries. True? False? Perhaps hybrid with super capacitors in front of lithium ion batteries would be the proper partnering of technologies to create the minimum 25 year warrantied system and very possibly the legacy energy generation system to the grandkids.