Lithium-ion solar batteries are the most popular option for home energy storage because they last long, require little maintenance, and don&#;t take up as much space as other battery types. Lithium solar batteries typically cost between $12,000 and $20,000 to install.
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When paired with solar panels, excess solar energy can be stored in the battery and used later, like at night or during a power outage. Depending on the area, lithium ion batteries can even help save extra money on electricity bills.
Let&#;s take a closer look at what you need to know about lithium-ion batteries before getting one installed.
Lithium batteries are rechargeable energy storage solutions that can be installed alone or paired with a solar energy system to store excess power.
Standalone lithium-ion batteries can be charged directly from the grid to provide homeowners with backup power in case of a power outage. They can also be used to avoid paying for peak electricity rates, by charging with grid power when electricity is cheap and discharging when it&#;s expensive.
Pairing a battery with solar will give you the most bang for your buck, especially if you don&#;t have access to net metering. The lithium battery can recharge with excess solar energy that is generated by your panels, so you can run your home entirely with solar even when the sun isn&#;t shining.
Lithium-ion solar batteries don&#;t come cheap, with installations ranging from $10,000 for a simple single-battery solution, to well over $30,000 for whole-home backup. This is significantly higher than that of installing lead-acid batteries, which typically run between $5,000 and $15,000.
Despite the price difference, people still tend to choose lithium-ion batteries over lead-acid because of increased performance and fewer maintenance concerns. The total cost of a solar battery installation depends on the battery brand you choose, the features it has, how many batteries you need, and labor costs.
Battery incentives can help lower costs. There are a number of solar battery incentives that help lower installation costs. The biggest is the federal tax credit, which is equal to 30% of the total costs of qualifying battery installations. There are a number of local battery incentives and rebates, pilot programs like Green Mountain Power's battery lease, and things like virtual power plant programs are becoming more popular, as well.
How much can you save annually with solar-plus-battery-storage?
High depth of discharge
Long lifespan
High energy density
High efficiency
Little maintenance
High cost
Thermal runaway
Lithium-ion batteries are the most popular option for homeowners looking for battery storage for good reason. Here are some of the benefits of lithium-ion home batteries:
The DoD of a battery is the amount of the stored energy in the battery that has been used compared to the total capacity of the battery. Most batteries come with a recommended DoD to maintain their health.
Lithium-ion solar batteries are deep cycle batteries, so they have DoDs around 95%. Compare this to lithium ion batteries, which have DoDs closer to 50%. Basically, this means you can use more of the energy that&#;s stored in a lithium-ion battery and you don&#;t have to charge it as often.
Because lithium ion batteries have a high DoD and don&#;t need to be charged and recharged as often, they have a long lifespan.
Most lithium-ion solar batteries have a minimum warrantied lifespan of around 10 years, or a cycle life of 10,000 cycles - whichever comes first. Lead acid batteries, on the other hand, only have warrantied lifespans of around 5 years.
The energy density of a battery is how much power the battery can hold relative to the physical size of the battery.
Lithium-ion batteries can store more power without taking up as much space as lead-acid batteries, which is great for homes where space is limited.
Lithium-ion batteries have a higher round-trip efficiency rating than other types of solar batteries on the market.
Efficiency refers to the amount of usable energy you get out of your battery compared to how much energy it took to store it. Lithium-ion batteries have efficiencies between 90 and 95%.
Not having to worry about regular maintenance is one of those advantages that you just can&#;t put a price on. Lithium-ion batteries require little to no regular maintenance - just make sure they&#;re clear of debris and. Some lead-acid batteries, on the other hand, require frequent off-gassing.
Although lithium-ion batteries have numerous benefits, there are still some draw backs.
Lithium-ion batteries tend to be the most expensive battery storage option, especially when compared to lead-acid batteries.
The good news is that solar battery systems qualify for incentives like the federal tax credit, which helps make lithium-ion batteries more affordable.
It&#;s also important to remember that while lead-acid batteries may be cheaper upfront - they have to be replaced more often, increasing your overall storage costs.
Lithium-ion batteries run a higher risk of thermal runaway, AKA overheating and catching on fire. While the risk is technically there, the chances of this happening with a properly installed lithium-ion battery is slim to none.
There are many lithium-ion solar batteries on the market. Some of the best solar battery brands include Enphase, Panasonic, and Tesla.
The following table outlines some other popular lithium-ion solar batteries on the market:
At $682 per kWh of storage, the Tesla Powerwall costs much less than most lithium-ion battery options. But, one of the other batteries on the market may better fit your needs.
There are two main types of lithium-ion batteries used for home storage: nickel manganese cobalt (NMC) and lithium iron phosphate (LFP).
An NMC battery is a type of lithium-ion battery that has a cathod made of a combination of nickel manganese and cobalt. When people say &#;lithium-ion batteries&#; they&#;re often referring to NMC batteries. These batteries are what shot lithium-ion to the mainstream, with better performance than that of their lead-acid competitors. The Generac PWRcell, LG RESU Prime, and Tesla Powerwall 2 are NMC batteries.
LFP battery cathodes are made of lithium irone phosphate (LiFePO4) and are still considered lithium-ion batteries. The iron and phosphate used to make the cathode are more abundant and less expensive than some of the materials used in NMC batteries - mainly cobalt. The Enphase IQ, Panasonic EverVolt, and Powerwall 3 use LFP technology.
More battery manufacturers have been switching to LFP batteries because they dont contain expensive, toxic cobalt. LFP batteries are easier to recycle, a little bit cheaper, longer lasting, and ,most notably, safer. Aside from having fewer toxic metals, LFP batteries are better at handling temperature fluctuations and are even less likely to experience thermal runaway than their NMC competitors.
Batteries are recycled by being shredded and mixing all of their components. Once all of the metals are mixed into a powder, they need to be separated by either being liquified or dissolved in acid so that the desired metal can be retrieved.
Since the process of recycling batteries is still in the early stages, the United States has suggested an enhancement to the Defense Production Act. The goal is to put money towards securing the metals we need for a clean energy transition while also researching and investing in recycling lithium-ion batteries.
Alternatively, instead of shredding old batteries, sometimes batteries within an EV can be reused. Lithium-ion batteries have a very long lifespan, and while they will lose their ability to power a car, they can still be used for less intense energy storage needs, like backup power.
Currently, when you replace technology such as your EV or storage battery, recycling the old one is a chore. You can find certified electronics recyclers through the EPA website. Alternatively, some manufacturers like Tesla will take back their lithium-ion batteries at the end of their life to be recycled.
At this stage, current recycling methods are not sophisticated enough to extract most of the key metals that can be reused in a way that is more cost-effective than mining.
It is cheaper to mine most metals found within a lithium-ion battery than recycle them. Perhaps ironically, cheap lithium mining is one of the many reasons we can invest heavily in batteries. Unfortunately, if we build cheap lithium batteries that are not recycled, we will end up with landfills full of electronic waste.
While recycling batteries may require some extra work and additional cost, the metals within the batteries are durable and usable. Recycling needs to become economical to reduce our dependency on freshly-mined lithium.
Since lithium mining emits a high amount of CO2, using lithium and other metals from recycled batteries is a more environmental and sustainable alternative.
Additionally, a potential shortage of metals that are used in batteries is looming. Discovering a way to reuse all the metals within old batteries will help meet supply needs.
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Lithium-ion solar batteries are the best solar energy system for everyday residential use because they take up little space while storing a substantial amount of energy. They last longer and provide more usable energy than lead-acid batteries, plus they require little maintenance.
However, sometimes a lead-acid battery might be the better choice. If you&#;re only using a solar battery for backup storage and not daily use, or if you&#;re looking for storage for an off-grid solar project, lead-acid batteries will get the job done and won&#;t break the bank.
However, if we&#;re being totally honest, most homeowners probably don&#;t need a battery at all. Solar batteries do provide numerous benefits, but their substantial upfront costs means they don&#;t quite make sense as a financial investment in most cases. It depends largely on local policy, utility rates, battery incentive programs. and how frequently you expertience power outages.
The best way to figure out if a solar battery is worth if for you is by speaking with multiple solar installers. Solar companies can give you an idea of how much a lithium-ion battery can save you (if anything) and if it&#;s something you should consider for your home.
Get lithium-ion battery quotes from local trusted solar companies
Main Post #2 - Battery Options - Capacity & Cost
In post #1 I covered the (current!) economic case for solar-free battery storage, as a quick aside I thought it worth mentioning that there is also an environmental case despite the lack of on-site generation.
The UK electricity grid uses a variety of energy sources, some clean/renewable, others polluting/finite. The mix of clean to polluting sources constantly varies, but generally speaking, polluting fossil fuel sources are at a maximum during periods of peak demand (e.g. 4pm to 8pm). By importing the bulk of my electricity overnight, I'll be using a cleaner mix of energy sources and helping to reduce peak demand; wind energy tends to be particularly dominant during the off-peak 00:30-04:30 period:
(UK Grid Generation for 24 hours 16/11/ - 17/11/)
Battery Options - Capacity & Cost
I'd like to cover as reasonably close to 100% of my 'peak-time' usage as possible with battery supplied power (that is, everything outwith of the Octopus Go off-peak 00:30-04:30 hours).
My annual house usage is ~kWh, which averages out at 8.2kWh/day (EV charging is not included as that will be done off-peak). Some days will be higher, some will be lower, I estimate I'll need ~10kWh of battery storage to safely cover the vast majority of days. It's also considered good practice for longevity not to let lithium batteries discharge below 10% or charge above 90%. Following that guidance, 12kWh of battery storage would look to be the ideal size.
Ideal capacity in hand, my first port of call was to price up 'plug-and-play' branded battery storage. Note that all options also require an inverter to act as interface between battery and grid.
Two of the most commonly recommended brands of battery are PylonTech and GivEnergy. Pricing changes regularly so it's always worth doing your own checks.
PylonTech produce a 5.1kWh peak capacity battery (US), I could source two of these for ~£ including VAT (note that batteries are VAT free if being installed at the same time as solar panels, not relevent in my case). That would give me 10.2kWh of storage, or 8.1kWh (£432/kWh) usable capacity with the 10/90% rule.
GivEnergy produce a 9.5kWh battery pack for a similar price to the PylonTech option, ~£. I contacted GivEnergy to ascertain exactly how much 'peak' capacity was within their 9.5kWh usable battery but they simply repeated that it was possible to discharge 9.5kWh (£379/kWh). Hmm...I suspect their peak capacity will in reality be closer to the PylonTech offering.
Then there's the option that I've settled on. A DIY battery.
So, how does the capacity and cost compare to the off-the-shelf options?
Shockingly well - ~£ (broken down during this and a following post) for 14.3kWh of peak storage, applying the 10/90% rule, 11.4kWh (£230/kWh) of usable capacity.
That's 20-40% more usable capacity at roughly 75% of the price &#;.
A DIY battery is composed of battery cells (that store the electricity), a battery management system (BMS) to monitor and manage the cells, and an enclosure/storage area in which to safely locate the cells and BMS. In this post I will consider only the cells, the other components will be discussed in a future post. There are some other bits and pieces to purchase in order to safely assemble a DIY battery but we've a hefty margin to play with.
Battery Cells
For UK grid-tied domestic energy storage you'll generally opt Lithium Iron Phosphate (LFP or LiFePO4) cells; these are the present industry standard, offering longevity and safety for use in the home.
Most UK on-grid approved inverters (the device that transfers electricity to and from batteries) only work with '48V' batteries. LiFePO4 cells are typically 3.2V each and it takes 16 cells to create a '48V' battery, although in reality 3.2V x 16 = 51.2V (apparently the widespread use of 48V labelling somehow relates to lead acid batteries &#;).
Cell Capacity
Cells are available in different capacities ranging from 105Ah to 304Ah. To convert Ah to Wh you multiply the Ah capacity by the cell voltage, e.g. 304Ah x 3.2V = 972.8Wh.
Remember, you need 16 cells to produce a '48V'/51.2V battery. When calculating the Wh capacity of multiple cells the Ah variable remains the same but the voltage increases by 3.2V for every 3.2V cell added, e.g. 304Ah x (16 x 3.2) = 15,565Wh = 15.5kWh.
By changing the Ah capacity of your chosen cells you can tailor the battery capacity to best suit your needs. You can also build two seperate batteries and link them together in parallel to add their capacity together but this will not be covered here.
I decided on 280Ah cells as they seem to have the wide availablility and would give me a battery of 280Ah x 51.2V = 14.3kWh peak capacity. Applying the 10/90% rule that gives me 11.4kWh usable capacity. That'll handle my daily usage and builds in a bit of headroom for battery degredation over time and small manufacturing inconsistencies between the battery cells.
Grade A or Grade B?
Grade A cells are cells that meet a range of strict testing parameters and are generally destined for 'high performance' uses. Grade B cells have failed one or more of these tests but can still be perfectly suitable for home energy storage where the demands are relatively gentle.
This write-up by Fogstar provides opinion on the different grades of cells available:
The REAL difference between EVE Grade A and Grade B LiFePO4 Prismatic Cells
From that write-up and numerous threads over on the DIY Solar forum ( SEE HERE ) I decided quality-controlled 'genuine' Grade B cells would be absolutely fine for my use case. (Also, do you think that branded off-the-shelf battery providers are using premium Grade A 'automotive' batteries when, with good QC and cell matching, the end user almost certainly can't tell the difference between Grades?&#;)
Where to buy?
LiFePO4 battery cells are manufactured exclusively in China and I considered two options for purchasing them:
Option 1) Order from a 'reputable' Chinese reseller (you cannot buy from the battery manufacturer's directly) through Alibaba.com
I sourced quotes from Docan and Luylan, Alibaba resellers considered trustworthy by users on the DIY Solar Forum, they were very similar in price at around £ (16 x 280Ah cells) delivered to the UK DDP (i.e. including all import fees/duty). The initial price was significantly cheaper but Alibaba adds both a transaction fee and a payment fee to the quoted cost. Also, prices are quoted in USD and the British pound unfortunately plumetted around the time I was looking to order.
As a side note, Luylan were up front that their cells were Grade B and offered Grade A cells for a more expensive price. Docan claimed their cells were Grade A but it's common practice for even reputable Chinese suppliers to sell good Grade B cells as Grade A. As such I believe I would receive much the same cells from both suppliers. Less reputable sellers may supply used or borderline defective Grade B cells but still advertise as Grade A.
Option 2) Order from a domestic reseller (e.g. Fogstar)
Fogstar is a UK company, they offer 280Ah Grade B cells for £150 incl. delivery. They have seemingly always available 15% off codes on their Twitter/Facebook, taking the price to £128.50/cell, or £ for a set of 16. Fogstar have been in the battery business for several years and have an excellent reputation. Also, as a UK company, there are comparatively straight forward options for recourse should the cells prove problematic (ever tried shipping something heavy back to China? &#;).
With less than £100 seperating the two options, I decided it was worth paying a bit extra for the UK based reseller and ordered from Fogstar with delivery expected in mid-late December (in the 3 weeks since I ordered the exchange rate has shifted such that Alibaba is now £200 cheaper so it's always worth getting up to date quotes).
Next Post - Battery Management System (BMS) & storage solution
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