This educated suggestion will make it simpler to decide on the proper battery for off-grid residing. Examine all of the items it’s best to discover out about picture voltaic batteries for off-grid residing and the way in which they work.
I bought my first picture voltaic panel in 1989, a 50-watt Solarex photovoltaic module. Along with an earlier bike battery, some DC automotive lights, and a small radio, I created an off-grid room within the house I was renting. When the power was out, and even when it wasn’t, I had lights and music engaged on saved picture voltaic vitality.
As soon as I constructed my dwelling throughout the Nineteen Nineties, it was far ample from utility power that an off-grid system made monetary sense, partially because of I’ll do the work myself. Photograph voltaic panels had been dearer once more then, and the one accessible, moderately priced battery know-how obtainable was lead-acid. I’ve wanted to substitute my battery monetary establishment about every seven years since, no matter utterly completely different producers, sizes, and configurations. Within the meantime, enhancements in chargers, inverters, and PV panels have made lead-acid know-how actually really feel further antiquated.
This textual content compares a variety of the qualities of lead-acid and lithium iron battery utilized sciences for off-grid features.
Breaking Down Batteries
Lead-acid batteries haven’t modified loads in 100 years, and they also have an prolonged historic previous of dependability and affordability. They’re normally named in accordance with the electrode supplies used, and extra outlined by the electrolyte used. As an example, “flooded” refers to liquid electrolyte that should be replenished periodically by together with distilled water. Diversified types of maintenance-free, sealed, or valve-regulated lead-acid batteries exist.
Batteries are designed for specific features.
- Starting, lighting, and ignition (SLI)batteries utilized in cars are engineered to launch a variety of vitality in a quick time interval, after which quickly acquire a recharge.
- Deep-cycle batteries have thicker plates, allowing for bigger vitality storage functionality and deeper discharging.
- On this text, I’ll think about deep-cycle, flooded lead-acid (FLA) batteries, because of they’re probably the most actually lead-acid batteries to be used in off-grid features.
A relatively new know-how, lithium-based batteries are engineered for effectivity and characterize superior vitality storage. Numerous configurations are in use within the current day, each with utterly completely different electrode and electrolyte chemistry, value and discharge traits, specific vitality, costs, and safety parts. For this comparability with deep-cycle FLA batteries, I’ll think about lithium iron phosphate batteries (LFP). Lithium iron phosphate (LiFePO4) know-how, moreover referred to as “lithium ferro phosphate,” is known as after its cathode supplies. LFP batteries are gaining recognition for automotive, offshore, and off-grid use as a direct substitute for lead-acid batteries.
Safety is a broadly publicized concern with lithium batteries. Lithium-ion batteries are beneath inside pressure and embody a flammable electrolyte, in order that they should be durably packaged, and handled and charged with extreme care. Lithium-ion is simply not the similar as lithium iron phosphate, the LFP batteries referred to on this text. LFP makes use of an inherently safer, further safe design based on utterly completely different electrode alloys and electrolyte.
Lifetime
Battery lifetime is expressed as a result of the number of value and discharge cycles a battery can survive sooner than shedding a certain share of functionality. Deeper discharge results in fewer complete cycles and basic lowered lifetime. Deep-cycle batteries are considered sturdy ample to withstand repeated discharging of 80 p.c of their complete functionality, or 80 p.c “depth of discharge” (DOD).
Batteries utilized in off-grid features are generally carefully cycled at partial states of value, that implies that vitality is drawn out of them over the course of a day or further, adopted by some recharging, nevertheless it may be a variety of days, and even weeks, sooner than they’re completely recharged. That’s significantly laborious on lead-based batteries, and likewise makes it troublesome to interpret the producer’s battery cycle life chart to predict longevity. It may be tempting to predict that my frequent seven-year battery life expectancy (2,555 cycles) interprets to a median DOD of 35 to 40 p.c, nevertheless many parts are at play. Ultimately, lead will shed from the electrodes, depleting them quicker in durations of extreme discharge prices, partial value ranges, or elevated heat.
LFP batteries have a considerably bigger lifetime than FLA batteries, with far more value and discharge cycles obtainable, and fewer dramatic partial value degradation.
Functionality
Battery functionality is commonly expressed on the subject of what variety of amperes (amps) of current could also be delivered over a time interval. As an example, a typical deep-cycle lead-acid battery signifies that it may probably ship 75 amps for 115 minutes. A further important functionality time interval is the amp-hour (Ah), which expresses what variety of hours a battery can ship vitality until its specified end-point voltage is reached and the battery dies. Battery spec sheets current scores that replicate the potential at utterly completely different discharge prices over time. These scores are expressed as a amount adopted by the letter C. As an example, a “20C” charge signifies {{that a}} 6-volt battery can ship 225 Ah when discharged at a relentless charge over 20 hours. Doing the maths reveals that the 20C charge of this battery is 11.25 amps (225 Ah / 20 hours = 11.25 amps). That exact same battery used at a greater discharge charge would possibly want a functionality of 146 Ah, indicating that a lot much less vitality is available on the market from the battery at bigger discharge prices.
Ah tells us what variety of amps a battery can ship over time at a certain charge, nevertheless it doesn’t completely quantify the vitality saved in a battery. Vitality is power (watts) delivered over time (hours). Watts are calculated by multiplying volts by amps. The 225-Ah, 6-volt occasion above could also be wired in assortment to achieve the required battery monetary establishment voltage. Since Ah already has a time challenge inbuilt, all we have to do is multiply 6 volts by 225 Ah to get 1,350 watt-hours (Wh). Divide Wh by 1,000 to particular vitality storage functionality throughout the further acquainted time interval of kilowatt-hours (kWh), which is how electrical companies bill us for {the electrical} power we devour. For perspective, a 100-watt lightbulb that’s lit for 10 hours consumes 1,000 Wh, or 1 kWh.
Every kind of sizes and capacities will be discovered for LFP batteries. Case configurations make direct substitute of FLA doable. As a result of higher value and discharge prices doable with LFP, you would possibly even see fractional C-values (akin to 0.5C), which level out a value or discharge interval of beneath an hour.
Explicit vitality
Generally called “vitality density,” specific vitality is vitality per unit of weight. Our occasion FLA battery retailers 1,350 Wh and weighs 67 kilos, so it has a specific vitality of 20.1 Wh per pound (1,350 ÷ 67 ). For perspective, a gallon of gasoline weighs 6.3 kilos and retailers the equal of roughly 36,000 Wh, with a specific vitality of about 5,714 Wh per pound.
The actual vitality of LFP batteries is over 40 Wh per pound, twice that of FLA.
Value and discharge dynamics
Value and discharge dynamics in FLA batteries are pushed by lead-based electrode plates immersed in a sulfuric acid and water electrolyte decision. As a result of the battery is charged, lead oxide builds up on the optimistic plates, and the electrolyte turns into stronger. All through discharge, the electrolyte decision grows weaker as every electrodes turn into lead sulfide, having absorbed sulfuric acid from the electrolyte. All through discharge, the voltage drops predictably. The state of value of an FLA battery could also be determined by finding out the resting voltage of the battery. Battery voltage together with a hydrometer finding out of the exact gravity of the electrolyte in each cell can reveal a lot in regards to the state of value and basic properly being of an FLA battery.
The fee and discharge dynamics in LFP batteries differ from FLA on the subject of the electrochemical course of, nevertheless could also be described in an identical technique. All through discharge, positively charged lithium ions switch inside lithium salt electrolyte from the unfavorable electrode to the optimistic electrode. Electrons are carried from the unfavorable electrode, by means of {the electrical} circuit, and once more to the optimistic electrode. One large distinction between FLA and LFP batteries’ reactions is that FLA chemistry happens on the ground of the lead electrodes, whereas ions throughout the nonliquid electrolyte of LFP batteries are completely absorbed into the crystalline development of the electrodes.
You can’t merely resolve the state of value of LFP batteries with a voltmeter, because of the battery voltage stays fairly mounted over quite a lot of discharge depths. Those who change from FLA to LFP would possibly uncover this, as I did, a bit flummoxing. When the voltage lastly drops, it means the battery should recharge. The simplest strategy to know and deal with value biking is to utilize a accurately calibrated monitor that tracks vitality going in and out of the battery monetary establishment. As a result of delicate nature of LFP chemistry and tight limits on value and discharge parameters, producers current an digital battery administration system (BMS) to help forestall charge- and discharge-related battery hurt. The BMS might embody a functionality monitor.
Charging
Charging should be carried out using the precise “value profile,” which means the right voltage and current for a prescribed time frame to rejuvenate a battery’s chemistry, assure most lifetime, and steer clear of most likely catastrophic failure. Voltage and current requirements change over the course of the fee cycle. As a battery fills up, the fee current should decrease to steer clear of overheating. If the current is just too extreme, the battery heats up. When the battery heats up, it accepts a value sooner and heats up far more. Shortly, the battery is in “thermal runaway,” and its life may be significantly lowered in a very transient time.
Normally, FLA value current shouldn’t be moderately greater than 10 p.c of the potential rating, though bigger current could also be tolerated if the temperature is intently monitored. Periodically, FLA batteries must be “equalized,” which is a managed overcharge that helps reverse sulfation (lead sulfate crystal growth) on the plates. Most fashionable battery chargers are refined ample to deal with a flowery three-stage value profile routinely.
In LFP batteries, charging is the reverse of discharging on the subject of ion and electron swap. Most fashionable off-grid battery chargers (picture voltaic and inverter-integrated) are adjustable to accommodate the exact LFP value profile. That’s mainly a two-stage value consisting of bulk and float prices. Commonplace FLA charging schemes don’t belong throughout the LFP world. That is, no equalizing, trickle charging, or temperature compensation must be used. LFP batteries have a very low inside resistance and should accept very extreme value currents, resulting in sooner recharge events. An LFP battery’s BMS is designed to cease hurt as a consequence of overcharging and over-temperature operation.
Temperature
Temperature impacts the chemical reactions inside a battery. Higher temperatures suggest sooner value and discharge performance. Nonetheless, if the temperature is just too extreme, the battery will deteriorate shortly. Lead-acid batteries operate best spherical 80 ranges Fahrenheit. Rather a lot colder than 70 ranges, and functionality is noticeably lowered; loads hotter than 90 ranges, and longevity is negatively affected.
Temperature consistency is important for LFP battery operation, nevertheless to not the similar diploma as FLA batteries. The operational temperature range for charging is between 32 and 113 ranges, though colder temperatures are acceptable for discharge and storage.
Effectivity
FLA batteries frequent about 75 p.c effectivity, which means 25 p.c further vitality should be put into an FLA battery than was taken out to utterly recharge it.
LFP effectivity is throughout the range of 95 to 98 p.c, resulting in shorter charging events and higher current provide to the load with loads a lot much less heat. Further surroundings pleasant charging means a smaller, less expensive PV array, fewer hours on the generator, and reduce vitality worth in case you value batteries from the grid.
Off-gassing
Off-gassing occurs when lead-acid batteries launch hydrogen gasoline on the unfavorable plates and oxygen on the optimistic plates all through charging and heavy discharge. This generally is a most likely explosive combination, which can be exacerbated by the manufacturing of hydrogen sulfide gasoline boiling off the electrolyte whereas the battery is charging. Storage batteries are generally enclosed in packing containers throughout the basement or utility room of an off-grid dwelling; it’s important to seal and ventilate the battery area with a fan ducted to the skin whereas drawing up to date air into the battery area.
Off-gassing is nonexistent in LFP batteries, because of they’re sealed and the electrolyte doesn’t boil off.
Maintenance
Together with appropriate value and temperature administration, FLA batteries should have their electrolyte checked and refilled month-to-month. You’ll probably wish to scrub corrosion off a variety of the terminal connections as correctly; making use of anti-corrosion grease or spray will help. Do not forget that when FLA batteries are in {{a partially}} discharged state for any dimension of time, or if the electrolyte dips low ample to indicate the plates to air, sulfation will occur shortly, insulating the plates in the direction of the required chemical reactions. Sulfation is troublesome, if not unattainable, to reverse if the battery isn’t accurately maintained.
Maintenance for LFP batteries portions to checking and tightening connections as needed. There’s no electrolyte to look at, and corrosion isn’t a problem for LFP batteries.
With regards to repairs, one issue to ponder is that lead-acid batteries have been spherical a really very long time, and technicians have a great deal of experience with them, nevertheless I can’t say the similar for comparatively new lithium-based batteries.
Recycling
Recycling lead-acid batteries is fairly simple and really important. Lead is a toxic supplies that should be handled safely and saved out of landfills. Take the earlier battery to an auto parts retailer or salvage yard for recycling.
LFP batteries must be recycled, though they’re considered unhazardous and every landfill and incinerator nice.
Worth and effectivity
I found disparity in how LFP battery effectivity is reported amongst producers, and even by the similar producer, significantly relating to the connection between functionality and DOD. Most LFP producers current a cycle life worth analysis that, not surprisingly, favors LFP over FLA. Their analyses are truthful in that they put values on FLA repairs labor and grid charging costs, nevertheless the information used doesn’t always look at apples to apples. So I’ve decided to present a comparability of 1 FLA battery to 1 LFP battery of comparable dimension and functionality made by the similar producer to take away some uncertainty.
I’ve compiled the information into comparability tables. These tables don’t embody costs to handle and substitute FLA battery banks, as most off-gridders actively participate in these actions. As well as they don’t take into consideration the related charge to buy grid power or to operate a fossil gasoline generator to value batteries. Till you rely 100% on renewable vitality for charging, this can be a vital take into consideration determining lifetime cost-effectiveness.
Discover that these figures replicate glorious circumstances of value and discharge regime, temperature, and maintenance.
Primarily based totally on my experience, lead-acid batteries in off-grid homes present moderately priced storage with acceptable effectivity. Nonetheless, I can’t say I ever sit up for together with water, cleaning terminals, exposing myself to toxic and explosive gases, or lifting and transporting 100-pound anchors every seven years, and I’ve really misplaced my share of garments by way of the years to dripping electrolyte.
In the event you occur to’re considering LFP batteries, ask the vendor, installer, or vitality information a great deal of inquiries to confirm apples are compared with apples and likewise you get the evaluation you need. And regardless of which battery type you choose, be certain you completely understand the assure, which is commonly prorated based on age for every FLA and LFP, nevertheless would possibly change based on how the batteries are used.
I’m due for a battery monetary establishment substitute this summer season, and haven’t however decided which know-how I’ll end up with. If upfront worth weren’t an issue, lithium will be the winner based solely on longevity and lack of repairs. Each battery type has execs and cons; take some time to utterly evaluation every, and ponder your vitality desires and personal preferences sooner than making a name.
Paul Scheckel is an vitality effectivity and renewable vitality information, and author of The Home proprietor’s Vitality Handbook.