Solar battery technology provides us viable ways to collect, save and store electrical energy that we generate from renewable solar power sources.
Five things to know about solar batteries:
The sun is a galactic sized store of energy, a solar generator that we can tap into. You know that the earth spins daily as it rotates the sun each year. Each day from dawn until dusk you can see the sun up there. There's potential to harvest abundant free energy from sunlight. Batteries help extend the free energy use to well after dusk.
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? Which solar batteries are the best for solar off grid use?
Many people invest in lithium-ion batteries for their off-grid systems.
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 is used 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 the 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 power from daytime sunlight 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 solar 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) kit, might buy and install a bank of solar batteries for power storage. This blog explores some storage options.
Some people with irregular power have made the move to install a backup power source. Not everyone is tempted to do that due to the high cost of backup; buying a generator or a battery for their solar PV renewable power source is not cheap. Maybe your reasons for not adopting alternative backup options to avoid the impacts of irregular power are similar: the cost of a bank of solar batteries or a generator.
Solar Battery Information Is Required
Householders want reliable price information to help them as potential buyers of solar energy storage batteries. Reliable battery cost information can help you determine the payback period.
Some potential buyers will be cautious and wait to see whether prices drop further. You can check the early adopters to assess the effectiveness of solar batteries for energy storage. You can validate their experience against the promised potential savings or benefits.
Not many home owners know a lot about solar battery storage and rely on the grid for back up. Are these solar battery installations are safe? Solar storage customers want assurances that rigorous safety standards for batteries are in place. Solar battery owners want installers to adhere to safe practices. They want to know the installed battery systems will always be safe to use.
This blog aims to help you understand renewable energy storage technology. You may require information about what to look for when buying battery storage.
Storing Potential
The world solar power generation is incrementally growing its potential. We use batteries for harnessing more of the sun’s daily light and heat energy reaching earth.
In 2014 the harvested solar power generation was about 0.3 terawatts compared with electrical energy demand in 2014 at around 15 terawatts. That is a tiny fraction of the sun’s energy reaching Earth. We are getting more efficient PV solar panels and need to find more efficient batteries for storing the excess daytime energy production.
Householders embrace the idea of solar power to cut their electricity bills. There is an opportunity with battery storage to get some control of your power autonomy. The cost of solar panels needs see a cost justified in the same way as installed batteries for storage also needs to be economically justified.
You may want to stick it to the world to have some level of energy independence, buying solar panels and batteries. That is fine but when you do, make sure you have checked the numbers and found the financial benefits are there.
The solar PV power incentives encourage householders to install solar PV panel systems. People who have installed PV panels need less convincing to add battery storage. Incentives were not needed for the uptake of solar batteries. There were no incentives available. The rationalisations of energy savings and energy independence were enough. Most battery buyers have 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.
For most people the decision to buy solar panels and then add batteries becomes one involving a big investment. That investment will impact their household for many years with repayments of the capital using anticipated savings from their energy expenses. Of course batteries for energy storage aren’t free. There are capital cost (buying it in the first place) and then running costs. The anticipated savings relate to the cost of electricity to charge the battery, then the round-trip efficiency . That means how much power is lost in the cycle of battery charging and discharging.
Take account of the size and performance of your current solar system, which has the most impact on the value you will get from your storage system. Solar systems under 5kW might use smaller rechargeable batteries of around 2.5kWh along with an energy management device. Anticipate paying around $5500 for a fully installed battery bank with controls. Look at around $13,000 or more for a larger 8 kWh battery for a larger solar array over 5 kW.
You want a level of certainty about the government’s position on renewable energy economic activity for the renewables sector to flourish. Good clear information about renewables policies reduces uncertainty, which encourages more people to decide to buy renewables and batteries, or confirms staying with what they have. The cost of grid power (kWh) is a determining factor in the purchase justification and payback period calculations of the initial solar installation and for the solar battery addition later. Let's remember the subsidies (that only apply to solar panels) should be a secondary consideration and subsidies might not apply to off-grid systems. You need to check this.
You need to rationally look at the existing economic information about your own energy costs. Assess the benefits and costs of the renewable energy option. Don't rely on a government subsidy (it could quickly change) or feed-in tariffs to provide a return on investment. You might still use the sale of excess solar power to justify your entry into renewables, but you need to justify your solar array (or wind system) choice on its total installed costs. You need to be sure about the savings from purchasing and installing a renewable energy system with a battery back-up.
Battery storage for roof solar systems are becoming a viable economic investment. Batteries give you reliability and security for your solar PV electricity supply when the sun is down and the PV cells are resting.
People have seen benefits from collecting radiant solar energy for heating water. You can apply solar thermal heating to your home, swimming pool water and solar hot water. Incentives apply to solar PV power and rooftop solar thermal applications. This encouraged growth in solar energy adoption. No government incentives apply to solar batteries but growth is expected. It seems the logic of storing excess solar PV energy produced for self-consumption rather than selling to the grid makes sense.
There are several reasons for the huge growth of the residential solar power:
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 used for storing the excess of generated PV electrical power for use later when the sun sets.
An indirect benefit for battery storage of solar electricity generated is that the environmental benefits are 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:
Battery Comparison Information
Battery Information
Characteristic notes for rechargeable batteries commonly used for storing solar panel power output:
- Internal resistance of a battery pack varies with cell rating, type of protection circuit and number of cells. Protection circuit of Li ion and Li-polymer adds about 100mΩ.
- Cycle life is based on periodic full discharge cycles.
- Cycle life is based on the depth of discharge. Shallow discharges provide more cycles than deep discharges.
- The discharge is highest immediately after first charge, and declines at about 10% every 30 days thereafter. Self-discharge increases with higher temperature.
- Internal protection circuits typically consume 3% of the stored energy per month.
- 1.25V is the open cell voltage.
- Capable of high current pulses.
- Applies to discharge only; charge temperature range is more confined.
- Maintenance may be in the form of ‘equalizing’ or ‘topping’ charge.
- Cost of battery for commercially available portable devices.
- Derived from the direct battery price divided by cycle life.
Source: https://www.leadingedgepower.com
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. That shortfall might be due to purchasers trying to keep their battery cost low. Sometimes people under-estimate 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.
Here are some things to consider when you decide about the batteries you buy for the solar storage.
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 Battery
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.
Lead Acid Battery Advantages
Lead Acid Battery Disadvantages
Lithium Ion Battery
Lithium-ion batteries are the most common storage technology. In 2017 the average unsubsidised 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.
Lithium Ion Battery Advantages
Energy density:
Discharge rate:
Low maintenance:
Many types available:
Lithium Ion Battery Disadvantages
Protection required:
Cycling Limit:
Transportation:
Expensive to Manufacture:
Relatively New Technology:
Vanadium Redox Flow Battery
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.
Making Vanadium Redox Flow Battery
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.
Improvements To The Vanadium Redox Flow Battery
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.
Advantages of Vanadium Redox Flow Battery
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.
Disadvantages of Vanadium Redox Flow Battery
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.
As VRFB technology is liquid based it is not mobile and the minimum size of around 8kW makes them more suited to commercial battery storage solutions, leaving them out of the residential market at the moment.
Click here if you want more information about this new battery technology.
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:
If you have a comment or question about this article feel free to add it to the section below.
References
https://www.power-eng.com/articles/2018/05/tesla-s-giant-australia-battery-lowers-electricity-prices-by-90-percent.html
https://www.digitaltrends.com/cool-tech/elon-musk-tesla-worlds-biggest-battery/
https://en.wikipedia.org/wiki/Flow_battery
http://energystorage.org/energy-storage/technologies/redox-flow-batteries
For an overview see respected Choice website last updated on 20 April 2018:-
https://www.choice.com.au/home-improvement/energy-saving/solar/buying-guides/battery-storage-buying-guide
Thank you, Paul,
A good summary on the topic of solar battery storage in Australia and generally. It covers the topics well. I appreciate your contribution.
Regards,
Barry
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