What's the point in having access to solar electricity only when there is sunlight. Most of us want to access power 24 hours during every day. That means generating electricity during the day while there is daylight and saving some power for using later.

What types of batteries can you use for storing your excess solar electricity?

Many people invest in lithium-ion batteries for off-grid systems. Which solar batteries are the best for solar off grid use?

Solar power systems use deep cycle batteries. The design of battery is for charge and discharge over a long period of time thousands of times. The conventional car battery design delivers a large amount of current for a short burst. High current drawn in a short burst from the battery when starting the car.

Manufacturers of batteries recommend deep cycle batteries should not be fully discharged. They recommend that 30% capacity remain in the battery. Manufacturers say that discharging a battery more than this will reduce battery life.

​We rate batteries in Ampere Hours (Ah). That is the amount of current in Amps that the battery can supply over the specified number of hours. The solar batteries deep cycle rating usually indicates a discharge rate in hours; say 20 hours or 100 hours. A battery rated for 120Ah at the 100-hour rate could supply 120A over 100 hours or 1.2A per hour.

At a higher discharge rate, the battery’s internal resistance causes heating losses. That means the same battery could supply 110Ah at the 20-hour rate, or 5.5A per hour for 20 hours. There are more factors than rating that can affect the performance and life of a battery bank. Speak with your solar battery provider before purchasing your solar battery bank.

People know the benefits of harvesting power from the sun. Let's see what common types of solar battery are available and briefly look at their technology. This blog won't cover reused car batteries for solar storage. Solar batteries for home help us collect and hold more power from that radiant light source. Different types of battery use slightly varied technology to enable that to happen.

People often buy a solar battery or a bank of batteries to provide a power storage solution.  For some people that might be wanting a reliable regular power availability (free from drop outs) and for others that might extend to energy independence. Some people, after buying a solar PV (or a wind turbine), buy and install a bank of solar batteries. I hope I assist you find solar battery storage options.

Not everyone with irregular power has made the move to install a backup power source. That might be due to the high cost of buying a generator or they have a renewable solar power source at their home. Check your reasons that you haven't considered options to avoid the impacts of irregular power.

Householders want reliable price information to help them as potential buyers decide about their system options. Some householders will be early adopters. The potential buyers of solar energy storage batteries want reliable financial cost information that would give them assurances about the payback period.

Still, many will be cautious and wait to see what happens with prices. You may want to watch the early adopters to assess the effectiveness of solar energy panels and storage. You can validate their experience against the promised potential savings or benefits.

Few home owners know about solar battery storage. You might question whether these installations are safe. Potential solar storage customers want assurances that safety standards for batteries are in place. Solar battery owners want installers to adhere to safe practices and to know the installed battery systems will always be safe for them to use.

Few householders understand renewable energy or storage technology in much detail. You may want to make an informed decision and require information about what to look for when buying battery storage. 

The world is incrementally growing its solar power generation potential. We are far from harnessing the full potential of sun’s daily light and heat energy reaching earth.

The sum of harvested capacity of solar power generation on Earth was about 0.3 terawatts in 2014. That is small compared with electrical energy demand in 2014 at around 15 terawatts. That is tiny compared when compared to the sun’s energy reaching Earth. We are becoming more efficient at harvesting solar energy. We need to become more efficient at storing the excess daytime production for using later.

As householders embrace the idea of battery storage, they will see it as a wholesome way to cut electricity bills. There is an opportunity with battery storage to get some control of your solar power. You may want to stick it to the world because with solar panels and  batteries you have some level of energy independence.

The solar PV power incentives encouraged householders to install solar PV panel systems. People who had installed PV panels needed less convincing to add battery storage. Incentives were not needed for the uptake of solar batteries. The rationalisations of energy savings and energy independence were enough. Most battery buyers therefore had a level of motivation.

The government's incentives to have people consider solar energy appear to have worked. Incentives boosted the solar power adoption. The industry grew at about 60 per cent each year between 2014 and 2018.

If there is a level of uncertainty about the government’s position on renewable energy economic activity in that sector can stall. Better and clear information being available about renewables policies would reduce that general uncertainty encouraging more people to decide about buying renewables and batteries or staying with what they have.

Householders and business owners need to rationally look at the existing economic information about their own energy costs and assess the benefits of renewables. Rather than rely on a government subsidy that could quickly change or feed-in tariffs that provide a return for excess solar power to justify their entry to renewables, people need to justify their solar or wind system based on total installed costs and savings from the system. Let the subsidies be a secondary consideration.

For most people the decision to buy solar panels and then add batteries are a big investment. That investment will impact their household for many years with repayments of the capital and savings from the expenses. 

Battery storage for roof solar systems are becoming a viable economic investment. Batteries give you security for your solar PV electricity supply. Solar battery storage ensures good system reliability when the sun is not seen and the PV cells are resting.

There are several reasons for the huge growth of the residential solar power:

• The solar industry becoming more efficient and accepted
• PV systems are more affordable
• Solar installations are a good investment for the average residential family
• Solar batteries are more efficient and their prices are reducing
• The introduction of peer-to-peer energy sales using blockchain technology

A price of fixed roof average solar PV power system for the residential home fell more than 50 per cent since 2010. During the same time frame the price of solar panels themselves has fallen 60 per cent. Solar battery costs are falling a decade later with growth in demand from solar battery adoption.

Generating electrical power from a solar resource is a clean renewable energy option. This electricity generation source is ‘cleaner’ than electricity generated from burning oil but it is only available while there is daylight.

Batteries are required for storing the electrical power that is needed later when the sun sets.

A side benefit of solar battery storage of electricity generated from solar panels, and using no other back up beyond the batteries, is that the environmental benefits will be recognised. They are acknowledged with renewable energy credits that go towards the government's renewable energy target.

There are many kinds of batteries available for storing home generated power, including:

• Lead acid batteries from cars that are 12volts. They are heavy; need space and ventilation (Hydrogen gas output is explosive). They have a relatively shorter life but cheap for larger power applications
• Use Lithium ion (Li-ion) batteries where high-energy and lightness is important. The technology requires a protection circuit to assure fire safety. They're used in laptop computers and mobile phones
• Nickel Cadmium (NiCd) batteries have low energy density. They have a long life with high discharge rate. They're used in two-way radios, large video cameras and power tools. These batteries contain toxic metals. They're not environmentally safe for disposal
• Nickel-Metal Hydride (NiMH) batteries have a higher energy density than the NiCd but low cycle life. NiMH batteries used in mobile phones and laptop computers contain no toxic metals
• Lithium Ion Polymer batteries have the attributes of the Li-ion. They are smaller and have slimmer packaging for mobile phone use
• Alkaline batteries are small dry cells labelled for general purpose use. They're used for cameras, toys, watches, and handheld electronics but contain no toxic metals
• Vanadium Redox flow batteries that use liquid electrolyte to hold electrical charge

When you buy solar batteries the cost of the total battery package is a factor for consideration. A low initial buy price is attractive, but low price might say low quality and a short battery life. That might mean having to replace the ‘cheap’ battery ahead of time.

You size your batteries bank for the solar PV energy system to match the system loads. Battery bank capacity in solar PV systems is routinely undersized. The size of your solar battery bank for home is a business investment decision. It's one overlooked by purchasers. That shortfall might be due to purchasers trying to keep their battery cost low. Sometimes people underestimate the system loads.

It’s important to know what loads to cater for and how much battery storage to buy. Many battery manufacturers provide online calculators for determining battery capacity. It can apply equally to off grid solar calculator excel spreadsheet workings or backup situations. 

The solar battery bank calculator helps you determine your electrical loads. It will assist with determining the solar battery bank set up and solar battery bank cost. Apply these to the residential system’s power needs. From that you can plan the system to fit your requirements.

We have chosen the Lead Acid battery, Lithium Ion battery and Vanaduim Redox Flow as three good battery types to consider for solar energy storage options.  

Those technologies are being produced in commercial sizes and quantities that target the commercial and residential market. The first two technologies have been used with success for a few decades and are the main products used in residential applications. 

The newer battery entrants to the residential market, like Tesla’s Power Wall, use Lithium Ion technology.

Lead acid batteries are widely available and used in most automobiles. It is reliable with a battery management system (voltage regulator or charger controller) for safe battery charging. The electrical storage cost for lead acid batteries is around $500 to $750 per kWh.

• They are used in millions of vehicles across the world and use a technology of over 100 years.
• Lead Acid batteries provide the lowest cost per unit capacity and lowest cost to manufacture of all rechargeable cells with many producers worldwide.
• This robust and portable battery provides large current capability.
• There are many applications for these batteries with a range of sizes and specifications available. 
• Lead acid batteries are tolerant of overcharging but use a charge controller to control current flow.

• Short lifespan – typically a few years or 300 - 500 charge/ discharge cycles.
• Liquid electrolyte limits the range of orientations and once the electrolyte is introduced into the battery it must be stored in charged state.
• The electrolyte is corrosive (acid can cause burns) and acid needs disposing of with care.
• Lead is not considered friendly to the environment.
• Lead Acid battery is not capable of fast charging and then charging efficiency up to around 70%.

Lithium-ion batteries are the most common storage technology. In 2017 the average unsubsidized levelized costs of energy storage using lithium ion batteries was $414/MWh. A levelized cost is the cost of installing a complete system (in this case a renewable energy storage system) divided by its anticipated lifetime output (in this case storing generated energy). The cost analysis accounts for all capital costs of the storage module, including the balance of systems, inverter system, engineering, approvals, procurement, construction, operation, maintenance and incidentals. The incidental costs includes interest payable, all taxes and cost of warranties, but it does not include the cost of the land used for the storage module or the cost of disposal at the end of the system life.

The average capital cost needed for a lithium ion battery storage system in 2017 was $650/kWh. In 2014 the cost of buying lithium-ion solar battery storage was between $750 and $950 per kWh.  One might consider the option of lithium ion solar batteries for remote home off grid use. It is also being considered as a grid tied battery backup. The average retail price of electricity in the United States in 2017 was $120/MWh so adding lithium Ion storage puts significant added lifetime cost to the peace of mind gained from stable power reliability.

The cost per kWh for a Lithium-ion solar battery is higher than for a lead acid battery. Li-Ion needs a more expensive battery management system (BMS) to watch the battery voltage and temperature. That's required to prevent excessive charging and discharging and overheating of the batteries.

The high cost BMS charge controllers aren't needed for all lithium-ion cells. It requires the system owner to use a correctly sized battery system. That reduces their initial price and lowering their life investment cost. Lithium can then compete with lead acid technology. Lithium-ion batteries typically deliver more cycles in their lifetime than lead-acid batteries.

There are advantages and limitations of every battery technology. Here are some advantages to using lithium-ion battery.

Energy density:

• Lithium ion battery cells have high energy density. That makes them ideal for electronic equipment that need to operate for a longer period between charges yet using power constantly such as with mobile phones, portable power tools and electric vehicles. With a higher power density lithium ion batteries can be more compact.

Discharge rate:

• Many rechargeable batteries have a self-discharge rate. The rate of self-discharge for Lithium ion cells is lower than most other rechargeable cells like Ni-Cad and NiMH. It is typically around 1 or 2% per month.

Low maintenance:

• Lithium ion batteries do not require and maintenance to ensure their performance. Ni-Cad cells gain a memory if not periodically discharged.

Many types available:

• There are several types of lithium ion cell available, meaning this technology can be used for many applications. Some lithium ion battery types provide a high current density and get used for mobile electronic equipment while others provide a higher current level and are used for power tools and electric vehicles.

Some lithium-ion battery disadvantages include:

Protection required:

• Lithium ion cells suffer from being over charged or discharged too far, plus they must have the current maintained within safe limits. That means a lithium ion battery requires protection circuitry embedded to keep within their safe operating limits. The battery management system (BMS) helps people to use li-ion batteries without a concern about leaving them on charge too long as after the battery is fully charged the BMS will cut the power supply.

Cycling Limit:

• Battery life is dependent on its chronological age, storage condition and the number of charge /discharge cycles that the battery has undergone. Li-ion batteries will have about 500 - 1000 charge/ discharge cycles before their capacity reduces and need replacing.
  
  When storing a lithium battery to extend the life it should be partially charged and put in a cool storage area.

Transportation:

• Airline travellers may be limited in how many lithium ion batteries they may take due to risk of overheating and fire. Lithium ion batteries may need to be in carry-on luggage, with lithium ion batteries carried separately in protective covers to reduce risk of short circuit or overheating.

Expensive to Manufacture:

• A lithium ion cell is about 40% more expensive to manufacture than their direct competitor, the Nickel cadmium cell, so cost may be a factor where consumer items are mass produced.

Relatively New Technology:

• Lithium ion batteries are considered as a developing technology as new lithium ion technologies are being developed all the time to find solutions to their current shortfalls.

Another battery technology that is driving the cost of solar storage down. That one uses vanadium and a different storage solution. Vanadium Redox Flow Battery (VRFB) manufacturers say they will reduce their battery costs. The stated timeframe is within ten years. Battery storage costs will fall from above $500/kWh down to $300/kWh. That's for commercial scale electrical plants. The VRFB’s design provides it with a unique advantage. Unlike with other energy-constrained systems VRFB's power and energy ratings are independent.

The principle behind the vanadium redox flow battery is not new. It's the principle of electrochemical reduction and oxidation (redox) reactions. The reactions occur in two liquid electrolytes. They both contain the vanadium metal ions. Connect both half-cells where the reactions occur to external vanadium solutions storage tanks. Each of the vanadium solutions circulate into the central cell using a pump (hence flow).

The VRFB provides a stable power storage solution. The pumps move fluids containing dissolved vanadium through the cell. In the cell the fluid stores electrical charge. The charged dissolved vanadium holds its energy performance over unlimited cycles of use. 

The vanadium flow batteries use dissolved vanadium solution. It's the same solution in the catholyte tank, anolyte tank and cell.  The VRFB battery storage system is large, heavy and is not intended to be portable. The electrolyte storage tanks use a lot of ground space. That makes these batteries fixed site energy storage solutions.

Vanadium is not found in huge mining reserves by itself. It has a source from fly-ash. Fly-ash is a waste product of coal-fired electric generating plants so it's available. Environmentalists are lobbying to phase out coal-fired power stations. That concern is coal burning pollutes with carbon emissions.

VRFB manufacturers say that vanadium electrolyte will not degrade over time. That means VRFBs last much longer than other technologies. VRFB developers say that the technology has no cycling limitations. These batteries can charge to full and discharge without impact on their lifespan. VRFB uses stable non-flammable aqueous electrolytes for electrical storage so it's thermally safe. That means there is no thermal runaway like some other battery types.

With VRFB architecture you can increase battery size by adding more electrolyte. Other battery technologies increase hours of storage is by adding more batteries. VRFB systems are starting to scale for domestic storage. VRFB matched with dedicated power electronic interfaces are promising plug in and play. That technology will revolutionize storing solar PV energy. Smart-grid applications the VRFB technology suit the intermittent power from residential renewable sources. 

Vanadium chemicals are safe for the environment and recyclable. The vanadium electrolyte in flow batteries is not toxic. At the end of the battery life reuse and recycle the vanadium in the electrolyte. Vanadium is also an additive used in making steel.

Vanadium holds a lower energy density. That is because of it's low solubility. This means the battery requires a larger system footprint (more tanks required). A scaled VRF battery can to store power for large grid scaled solar farms. Vanadium solution operates within a narrow temperature band. Manufactures of VRFB have improved electrolyte operational temperature range to above 50degC. This means using a simpler thermal management system. Such simpler system makes VRFBs suitable for warmer countries like Australia.

VRFB operating efficiencies were sensitive to dissolved impurities like Fe or Cr. Battery developers aimed for “zero” impurities. Recent VRFB technology improved storage efficiency and use of electrolyte. They achieved that by reducing sensitivity to slight electrolyte impurities of metals.

VRFB developers are evolving ways to boost power density. Newer improvements to VRFB’s technology include increased vanadium solubility. That improvement will benefit improved energy density. It also means the storage footprint for the VRFB will reduce. VRFB will store the same amount of energy in smaller tanks. They will reduce as the quantity of electrolyte solution required is almost halved.  

Manufacturers now integrate more power management electronics in VFRB. They combine the charging and discharging processes into the battery pack. That integration seeks to keep the battery ownership cost as low as possible.

Vanadium flow batteries have a predictable performance. There's no electrolyte degradation and have a life exceeding 20 years. Those batteries thereby outlast solid batteries like lithium ion and lead acid. The VRFB has an unlimited cycle life in both shallow and deep cycles.

VRFB uses the same base electrolyte material in the catholyte and anolyte. So, it can be electrochemically reversible. But you need controlled operation. You are balancing the catholyte and anolyte levels for the battery to operate. This battery operates at a large range of energy storage levels. You can scale up by adding electrolyte the storage capacity the system.

Vanadium redox-flow batteries currently exhibit low energy storage density, so the active electrolyte volume sets the battery’s capacity.

Because vanadium is a relatively abundant material and is recyclable, its cost of may be acceptable, but the flow system uses expensive ion-exchange membrane material, which is responsible for just under half of the battery cost.

In another ten years, the nation’s solar battery storage capacity is predicted to double. Some of the added battery storage will go into solar farms. Most of the new battery storage will be installed into homes and businesses and will be going on the customer’s side of the meter. Some of that outcome will depend on energy consumers finding information and pricing that demonstrates a bottom line benefits for them from making the solar battery investment.

If people are going to be encouraged to buy solar panel generators and then invest in renewables battery storage in a big way, they want to know about their costs. Solar battery bank costs have been a moving target. You can obtain quotes for what the costs are to install solar panels, but less know what’s the cost for battery storage. For many purchasers batteries are there in the future and many don’t consider if there are added rules and requirements. Battery buyers tend to have less confidence in the energy market not changing to their detriment. Prices of power trend upwards and after they invest in panels more people are considering add on benefit of batteries.

The people who are planning to buy a solar battery storage solution want accurate information about its cost. If you are connected to the grid and have solar panels, installing a domestic scale solar battery storage system for back up requires a significant capital outlay. It might be an emotional decision that prompts the purchase rather than a good understanding of economic benefits. Householders who seek predictive market information from battery system installers may be disappointed as rarely can they provide the financial justification to install.

Solar battery energy storage costs will fall as more people buy batteries and these items become a relatively common residential commodity. In locations with reliable power, regardless of its unit cost, while there are good financial returns for converting from mains power to solar power, the add on of batteries might take more time. Using a totally rationalist economic approach to the decision to buy solar batteries, you are likely to be persuaded to hold off longer. You may be persuaded by convenience and reliability arguments. Frequent power outages, unreliable mains power and fluctuating power level that impact your electronics will probably make a decision to buy batteries an easier one.

This article has been about solar battery technology. It’s more than providing new ways to store electrical energy. Most solar battery storage is used for holding on to  excess energy from renewable solar power sources. Solar battery storage can be added to a house to provide the option to use off peak power during the more expensive times of each day. Also, for those occasions where the power fails, the batteries can become your uninterruptible power supply.

Using batteries as a current filter provides a safety mechanism for brown-outs and spikes and for periods of no power. The battery storage bank would then be a backup in place of a fuelled generator but without the pollution, noise or excessive need for maintenance or fuel.

If you were going to buy a solar battery bank, consider the option of using lithium ion batteries. They are more expensive initially yet they have comparable life costs to the cheaper lead acid, but Li-ion cells have three times the life and a deeper charge/ discharge.  

Maybe ask yourself; “Why would you consider putting batteries on our solar system?” It might not be viable if you live in a residential area using a grid tied solar power system. Maybe the grid is reliable; you get the free daytime solar power from the panels and maybe a feed-in tariff payment accompanies the benefits of free daytime power. You might argue the off peak power rates at night makes the added investment in batteries too high.

Here are some things you could look at before leaping to buy solar batteries:

• Cost – even lithium ion batteries provide a very long payback period if you add them after the solar panels and the grid is efficient (and expensive). The bank of batteries is nice to have from a discussion point, and from the self-reliance angle, but probably not yet economically justified. That is entirely different if the power line to your rural retreat has not been installed so, rather than mains power, adding batteries is definitely cost effective. Solar and batteries is a cheaper option than paying to bring in a mains power line and connecting to the grid.
• Value – the added reliability and security of power that you get from an autonomous system come at a cost. Cost is not the same as value. In places that need power to keep lights on and appliances or machines running all day every day then a back up is a valued add on. Batteries and/or generators will provide that back up. It’s a risk assessment decision as to whether you need to make that level of investment. You will find very few hospitals that rely solely on mains power.
•  Life span – buying batteries is a long-term investment so buy batteries that provide a longer no maintenance life or ones that are easily replaced as they expire. The battery bank set up will need a monitoring system and easy access to permit you to replace failing batteries

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