There is much to know about batteries and there are many myths to go with them, Here are RenewSolar we have put together a lot of information and carried out testing, so you know what your getting from us and how they should be used.
There are a few main types of battery that people use with solar, lead acid, LFP and Li-ion.
Lead batteries are fairly common as they are in cars, LFP is fairly new and highly popular, and Li-ion have been around a good while now in laptops, phones and EVs. Lesser known and up coming is Sodium batteries and no doubt there are others and new ones in development.
To have a home battery you will need to have a suitable inverter, this can be a primary inverter (hybrid) a DC or AC coupled inverter and or a retro fit. Solar Battery Storage — RenewSolar
Understanding Battery Technology
“Battery tech” refers to the specific chemistry of the battery (e.g., Lithium-ion, Lead-Acid, LFP), not its age or physical attachment. When evaluating battery options for solar systems, it’s crucial to consider:
- Pros and Cons: Performance, lifespan, cost, safety, environmental impact, and suitability for specific applications.
- Use Cases: The ideal applications for each battery type based on energy needs, charging frequency, and environmental conditions.
- Workarounds: Solutions to mitigate challenges such as temperature extremes or safety concerns.
Comparing LFP and Lead-Acid (LA):
- Temperature Sensitivity:
- LFP:
- Reduced charging efficiency and capacity at low temperatures (<10°C).
- Requires modified charging profiles in cold conditions.
- Performance degrades significantly above 50°C, a concern for installations in hot lofts or attics.
- LA:
- More tolerant of cold temperatures.
- Lifespan is significantly reduced at higher temperatures (e.g., 33°C).
- LFP:
- Cooling: Essential for both LFP and LA batteries to maintain optimal performance and extend lifespan.
Lead-Acid (LA) Considerations:
- Safety: Emits explosive gases during charging, requiring proper ventilation.
Lithium-ion (Li-ion) Considerations:
- Safety: History of fire incidents necessitates careful consideration for residential installations.
- Cell Format:
- Large Format Cells: Generally considered safer and more reliable than small-cell batteries used in some applications (e.g., some Tesla Powerwall models).
- Single Cell Failure: In large battery packs, the failure of a single cell can significantly impact performance and potentially pose safety risks.
Key Takeaways:
Consultation is essential for making informed decisions and ensuring proper installation and maintenance, and finding the right battery to meet your needs.
Selecting the right battery technology depends heavily on individual needs and circumstances.
Careful consideration of factors such as temperature, safety, and maintenance is crucial for optimal performance and longevity.
Battery life
Battery life is measured in Cycles, cycles which is where a battery is charged and discharged and charged again.
LA cycle life is around 800-2000,
LFP 2000-12000
Li-ion 800-2500
There is a lot of difference depending on how they are used and charged as well as discharge which relates to the rates this occurs along with temperatures.
The lower the current, the lower the capacity discharge, the longer the battery will last. Therefore Size matters.
Sizing Your Solar Battery:
Determining the appropriate battery size for your solar system depends on several key factors:
- Energy Consumption:
- Daily Energy Usage: Analyze your daily energy consumption to understand your typical energy needs.
- Usage Patterns: Identify peak usage times and periods of high demand.
- Backup Needs: Determine how long you need to power essential appliances during grid outages (if supported).
- Solar System Output:
- Production: Estimate the average daily energy production of your solar panels.
- Self-Consumption: Maximise self-consumption by aligning energy usage with solar production.
- Budget: Batteries are an affordable investment. Set a budget and explore options that fit within your financial constraints.
- Application:
- Buffering: For short-term energy storage (e.g., smoothing out peak loads), smaller batteries may suffice.
- Backup Power: Larger battery capacities are necessary for extended grid outages if your inverter supports this or if you are off grid.
- Off gird: power and extended capacity for winter with a shorter charge time window.
Key Considerations:
Professional Guidance: Consult with us to assess your specific needs and recommend the most suitable battery size and configuration for you.
Depth of Discharge (DOD): Aim for a DOD of 50% or less to prolong battery lifespan. Higher DODs can significantly shorten battery life which applies differently to the different types of battery.
C-Rate:
Charge Rate: The rate at which the battery can be charged.
Discharge Rate: The rate at which the battery can deliver power.
Ensure the battery can handle the required charge and discharge rates for your system this is typically around .4c. You should aim to charge the battery as slowly as possible with the timeframe.
Load Sharing:
Multiple Batteries: Consider using multiple smaller instead of a single large one.
Benefits: Load sharing can distribute the load more evenly, reducing stress on individual batteries and potentially extending their lifespan.
Installing Solar Batteries to an Inverter: A Technical Guide — RenewSolar
Battery Charging
You can read this article about battery charging, Charging Solar Batteries — RenewSolar
Low and slow is best; You should avoid high currents and calculate the time you can charge to fill your battery, rather than higher current charging. Simply divide the Kwh needed to charge overt the time frame. For example 10kwh over 4hour low rate grid charge. 10/4=2.5kwh. 2.5kwh/48v (battery voltage) = 52 amps charge current.
Sizing the inverter
Battery and inverter matching is important if you want the system to work for you.
People are installing larger inverters which require more current from the batteries, however the important point here is that the battery current is correct for the loads and that your inverter can charge the battery, either from mains or solar at a suitable rate.
3kw 48v system voltage will load 62amps, for a 100ah battery (5kwh batteries) this is too high and you would require 2 batteries dropping the current to 31 amps.
Not all batteries are the same and this could result in having the rate too high.
And 8kw system with a 48v battery will draw 166 amps of current and you would need around 4 batteries to bring the current down. Typically the C rate will be between .3 and .4 for charge and discharge.
While sizing your inverter, or battery, you need to consider the size of the solar or AC charger to charge the battery. Read more on this topic here: Charging Solar Batteries — RenewSolar
How long should my battery last?
Battery life and cycles as well as the loads (current) and Temperature will effect the life of the battery.
We would say that an under sized battery would last less than 5 years, A suitable battery will last 16 years or more.
Low cost batteries vary on their life due to a wider range of circumstances, but most can be engineered out. The solutions are normally not costly, or fairly common place, such as the breaker may not be fitted to the battery, and you add an external breaker.
An issue could be low temp charging currents, or cell imbalance. It does depend on the how cheap and where corners have been cut to how well they will perform.
If you are buying a battery from us, you can ask questions or we may ask you questions to ensure that the item is suitable.
Our low cost range of batteries tend to have a life of around 15 years, and typically have a 5 or 10 year warranty, which is comparable to more costly batteries.
Some of the batteries we offer life is are around 5-6 years which is “the norm” for that type of battery.
Generally we like to just say the battery lasts 10 years when doing calculations on the higher range batteries which we offer.
Retro fitting battery storage
Having solar or not, for battery storage does not matter, you do need to have an inverter.
AC coupled inverters charge the battery from the grid – this is ideal for those with dual rate power.
Some installations allow for later solar additions.
BESS ( Battery Energy Storage System) can be hybrid or Ac coupled inverters, They are very much like a solar installation without the solar panels and work in a similar way. 40kWh Energy Trader — RenewSolar
Where you Retro fit, this is a AC coupled inverter, they detect excess power flowing from your home and then varies the charge rate to use that power to charge the battery. You would have this is you only have a grid tied inverter. and typically where you have FIT payments.
How to work out the savings and returns on a battery.
Buying a battery and installing solar is one of lifes choices, the matters which you look at and consider important will vary from person to person, some may be considering the environment and some may consider only the cost.
There was a time where installing your own solar made little to no financial difference, and the pay back time was the life span of the cost of the system. This is clearly not attractive and is a waste of time and effort.
RenewSolar has driven down the cost of solar and its hardware meaning that the value of solar installations is much better and of course the cost of power has increased making solar installations and battery more viable for more people.
Isolating the battery costs and return is fairly simple math. Here is the kWh costs at the standard rate charged by the grid.
Storage values:
5.1kWh Battery (budget) – £1.22
11.7kWh battery (budget) – £2.82
15Kwh Battery – £3.76
40kWh battery – £9.60
If you went for octopus energy, then you are likely to pay around £0.15 kwh, however our suggested provider charges just £0.04kWh.
Grid charge costs and savings per cycle – ROI – Annual saving:
5.1 £0.20 (£1.02) – ROI 1.54 years – Annual £372
11.7 £0.46 (£2.36) – ROI 0.89 years – Annual £861
15 £0.60 (£3.16) – ROI 1.45 years – Annual £1,153
40 £1.60 (£6.44) – ROI 3.1 years – Annual £2,350
With the figures provided above, you can set out your ROI time frame, or your annual savings, As you can see the budget battery 11.7kwh battery the ROI is less than one year making this seem very attractive for most buyers. Of course the 40kWh battery has the longest ROI but the highest savings.
For most homes the middle ground for capacity is going to be between the 11.7KWh and 15kWh batteries. More likely to be two of them.
Two 11.77kwh Batteries will give you 23.5kWh, store £5.64 of energy costing £0.92 to charge from the grid, saving annually £1,772. The ROI increases to just 1.04 years.
No responses yet