Updated battery choices for today’s power needs
Describe an off-grid solar installation, 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 may be closer than you think – like, next door. Many neighborhoods, either because of their geography or because of restrictions on the existing network, flip the script and only use the network as an emergency backup.
“The latest is grid failure,” said David Norman, director of solar products and business development at a lead acid and lithium battery supplier. Discover Battery
In Hawaii, for example, where electricity prices average more than 30 cents / kWh and no new solar energy can be added to the grid, people take their energy into their own hands. Hawaiian households are often referred to as total self-consumption or zero-export power and essentially operate like off-grid homes with the power grid as a backup.
In California, where “public outage” events have limited power in recent years, homeowners are planning ahead for extended outages. Ideally, homes should now be designed to operate off the grid for at least one month, while being able to use the grid for the other 11 months.
Doomsday bunkers are not present in any of these situations – off-grid setups already exist in many urban neighborhoods. Today’s power needs require battery technologies to keep up.
Lead versus lithium in the off-grid
By definition, an electric battery is a device that stores energy that can be converted into electric current. In this sense, all battery types are equipped to meet off-grid storage needs, but some are better than others to meet current electricity needs and cycling schedules.
“Off-grid is less about the battery and more about the use case,” said Norman. ‘If you only do backup power, lead acid works. He doesn’t cycle regularly, and he’s just in reserve for a power outage or outage in the first place. But for on-demand charging applications, any lithium battery is better. “
Lead-acid batteries work well for occasional, short-term backup needs. But if someone wants to switch power sources to take advantage of utility life 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,” said Norman. “You can still live off-grid on lead acid, but lithium is more efficient.”
This all comes down to the number of cycles a battery has and the 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 batteries, and Jay Galasso, vice president of sales and marketing, often explains the charging specifications of the two chemistries.
“Off-grid solar applications require batteries that can be discharged and charged every day,” said Galasso. “One cycle could be to charge the batteries during the day and then discharge the stored energy for use in the evening. The more a battery is discharged, the ‘deeper’ the cycle. “
Lead-acid batteries deteriorate with each cycle. Where a lithium battery may come with a 10,000 cycle warranty, a lead acid battery can peak at 2,500 cycles when discharged to 50%. Lithium batteries can be discharged to near zero, or really all the juice in a lithium battery can be used in one cycle, with a lead battery only being able to use half of its juice before deteriorating even faster.
“Lead-acid batteries are cheaper for the same voltage and capacity, but don’t last many cycles,” said Galasso.[Lithium-based] designs can use fewer batteries for a given application due to higher charge / discharge rates, resulting in lower initial costs. “
SimpliPhi power was founded in the early 2000s and has always been a supplier of lithium batteries. The company knows the value of lithium batteries in off-grid applications as the original market was external energy scenarios.
“Lead acid is an old product that is used off-grid. It’s where the solar industry originated. In those early days, you couldn’t have a PV system without lead batteries, ”said Sequoya Cross, director of global sales and business development at SimpliPhi. “Why we see more people scaling up to lithium: you have more usable capacity in a smaller space, you can pull them up to 100% depth of discharge.”
Physical space is another reason why lead acid is falling out of favor in current grid-disconnected setups in urban environments.
“Most people who build off-grid don’t have a separate mechanical room next to their house where the batteries and inverter can go. Most people don’t have that kind of space, ”said Norman. “To have enough energy storage to run your home like an off-grid home, just because of the volumetric space alone, you have to start using lithium because you could never put that much lead in your home.”
Today, when someone wants to take their active household off the grid, it usually means they want the refrigerator to work, along with computers, the Internet, televisions, lights, and everything else, all at the same time. Backing up one emergency load can’t cut it anymore, especially in places like California, where life has to go on when the utility cuts the power. This requires greater battery capacity, faster charging speeds, and a deeper depth of discharge – things that lead acid just can’t provide.
“Lead dies off-grid. Lead acid provides a long life, but they require a lot of maintenance, ”said Norman. “There is no point in selling a premium lead when I can only sell lithium for 10% more. Lead still works in the automotive markets, but on the solar and stationary side, lead is dead. “
The Off-Grid Lithium Battle: NMC vs LFP
The two dominant types of lithium batteries 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, Enphase, KiloVault, SimpliPhi, Sonnen). While 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 fast charging because you have the power grid there, NMC batteries are great,” said Norman of Discover Battery’s. “The limitation with them for an off-grid scenario is that they cannot handle the high current charging or discharging of demanding off-grid loads.”
Aric Saunders, EVP of sales and marketing for NMC and LFP battery supplier Electriq Power, explained the different charge rates for the two lithium chemistries. NMC batteries have a charge rate of 0.5C while LFP batteries are 1C. If an LFP battery takes an hour to charge, it takes twice as long for the NMC battery because it draws power more slowly. LFP batteries can be charged as NMC in half the time.
“Because [the faster charging rate], LFP batteries can provide higher power output to the utility power or home. This feature allows the battery to back up larger charges with a smaller battery than would be needed with NMC, ”said Saunders.
“Time is money. If I’m charging on solar power and I only have a six-hour solar day, I want to get as much as I can into those batteries,” said Norman. from LFP.
While “off-grid” may be a casual term to describe using the main grid as a backup rather than a primary power source, it could be an essential way of life for many more people in the near future. Homeowners then have to choose the right battery chemistries for their situation.
“Off-grid is all around us. It’s not just people in the woods anymore, ”said SimpliPhi’s Cross. “It is not necessarily possible to disconnect or remove your meter completely, but it is possible to design around an off-grid lifestyle.”