When you consider the total ownership cost of solar panels – materials, installation, financing, and maintenance – they are now a cheaper electricity source than fossil fuels. However, since sunlight is not always available, solar panels cannot deliver power continuously. To use energy from the sun at night and on cloudy days, you need a solar battery.
via Sonnen USA
There are many types of energy storage systems, but batteries have many features that make them an ideal complement for solar panels. They are available in many sizes, ranging from compact home batteries to utility-scale systems that can power many buildings at once.
Just like you can install the ideal number of solar panels for your home, you can use a matching battery capacity that meets your energy needs.
In general, a battery system costs around $800 – $1,000 for every kilowatt-hour of storage capacity. For a 10-kWh home battery, you can expect to pay around $10,000.
However, battery prices have been decreasing during the last few years, and they will become even more affordable in the near future. The International Renewable Energy Agency (IRENA) has forecast that batteries could become over 66% cheaper by 2030.
How Are Solar Batteries Used?
Solar power systems reach their peak productivity in the hours around noon since they are getting maximum sunshine. However, homes are often empty at this time of the day, since a large part of the population is working or attending schools and universities.
Even now that many people are working from home or taking online classes, homes normally have their highest energy consumption in the evening. As a result, residential solar systems tend to have plenty of surplus production around noon.
You can export your extra solar energy to the grid, and a credit will be subtracted from your next power bill – this concept is called net metering. However, the energy price you’re paid is often lower than the price you’re charged, and there are some electric companies that don’t offer net metering.
With a battery system, you can store surplus energy from solar panels and use it later, which means you save the full value of each kilowatt-hour.
A solar battery can also be designed to operate as a backup power system during blackouts. This is not possible with solar panels alone – their energy output is variable, while a battery can provide a stable power supply while its charge lasts.
If your electricity provider charges time-of-use rates, you can configure your solar battery to provide energy when the highest kWh prices are being applied. This will maximize savings, increasing your return on investment.
As a quick example, assume that an electricity provider charges 35 cents/kWh during peak hours, and 15 cents/kWh the rest of the time.
- For every 10 kWh from your solar panels, you would normally save $1.50 in this case.
- However, if you store 10 kWh in a battery, and use them when the higher kWh price is being charged, you save $3.50.
- If your battery repeats this process for an entire year, you can get additional savings from 3,650 kWh of solar output – an extra $730 with the same energy production.
In other words, a battery system can increase the savings achieved by solar panels – you can use their electricity when it’s more valuable. This is not possible with solar panels alone: if you don’t use their energy output immediately, it gets exported to the power grid and you might not get full credit.
Types of Solar Battery Systems
There are many battery technologies, but two types are the most commonly used in solar power applications: lithium-ion and lead-acid batteries. Like in any engineering decision, each type has strengths and limitations, which means they are suited for different purposes.
Lithium-ion batteries have been used in cellphones and laptops for decades, but they have now evolved to a point where they can power homes and businesses. As you might guess from their name, these batteries use lithium ions to store energy:
- When the battery is charging, lithium ions accumulate on the anode – the negative end of the battery.
- When the battery is supplying electric power, lithium ions move from the anode to the cathode – the positive end of the battery.
The battery absorbs and releases charge with this back-and-forth movement of lithium ions. Outside of the battery, electric power is carried by electrons – the lithium ions only move internally between the anode and cathode, without leaving the battery.
Lithium-ion batteries are suitable for frequent charging and discharging. This makes them an ideal complement for home solar systems that are connected to the grid – batteries can be charged during the day and discharged at night.
Lead-acid batteries are an older technology. Instead of using the movement of lithium ions to absorb and supply charge, these batteries rely on chemical reactions that involve lead and sulphuric acid.
- A charged lead-acid battery has a lead dioxide cathode (+) and a pure lead anode (-), which are submerged in a sulphuric acid solution.
- When the battery provides electricity, these lead plates interact with the acid solution to form lead sulfate.
- When the battery recharges, the lead sulfate is dissolved, and it converts back into lead dioxide and pure lead.
Unfortunately, some lead sulfate crystallizes permanently each time the battery is discharged. This gradually reduces the energy storage capacity, and an excessive accumulation of lead sulfate can burst the battery open. This effect is more severe when lead-acid batteries are not charged completely before their next use.
Lead-acid batteries are reliable and cost-effective as backup power systems, and they are also suitable for off-grid solar systems. However, lithium-ion batteries are a better option when you need frequent charging and discharging.
Lithium batteries from leading manufacturers now come with a rated service life of 10 years, while a lead-acid battery normally needs a replacement in around 500 cycles – less than two years with daily charging and discharging.
Lithium-ion batteries also have much simpler maintenance needs that their lead-acid counterparts, making them a much better option for homes.
The following are some of the most popular home batteries as of 2022, and all use lithium-ion technology:
|Home Battery||Energy Storage Capacity||Rated Power Output|
|Tesla Powerwall||13.5 kWh||5 kW|
|LG Chem RESU 16H Prime||16 kWh||7 kW|
|sonnenCore||10 kWh||4.8 kW|
The storage capacity indicates how much energy the battery can hold, while the power output gives you an idea of how many appliances can be powered at once.
- For example, a 13.5 kWh battery like the Tesla Powerwall can deliver 5 kW of power during 2.7 hours (5 kW x 2.7h = 13.5 kWh).
- As the workload decreases, the battery charge lasts longer. With only 2 kW of electrical load, 13.5 kWh of storage will last for 6.75 hours.
Pros and Cons of Solar Battery Systems
Solar battery systems offer many benefits for homes and businesses, increasing the electricity savings achieved by solar panels. The following are some beneficial applications of home batteries:
- You can use solar power even when there is no sunlight: You simply need a solar panel system that is large enough to charge the battery, while producing enough electricity to meet your daytime consumption.
- A solar battery can provide backup power: You only need to make sure you purchase a battery that is designed to continue operating when disconnected from the grid, combined with a suitable inverter.
- You can avoid the highest electricity prices with a battery system: If your electricity provider charges higher kWh prices at certain times of the day, you can rely on your solar battery during those hours.
Depending on where you live, it may be possible to join a virtual power plant or VPP. Since batteries can supply power to the grid at times of peak demand, electric companies benefit when many homes and businesses have them.
A smart platform can coordinate battery systems in multiple properties, adding up their storage capacity and power output to keep the grid stable – if your electricity provider manages one of these programs, you may be offered incentives for connecting your solar battery.
Currently, the main limitation of battery systems is their high price. Each property has unique energy needs and site conditions, and a professional assessment is recommended to determine the ideal battery capacity for your home (and its cost).
Solar Battery FAQ – Frequently Asked Questions
Can I add a battery to an existing solar panel system?
Yes, if you have a suitable inverter. Traditional inverters are designed for solar panels operating on their own, while hybrid inverters can be connected with solar panels and batteries simultaneously.
If you have a traditional inverter, you must upgrade to a hybrid unit before using batteries, but there is no need to replace the solar panels. However, you can consider adding more panels to your system, since now you can store surplus energy.
Does a solar battery qualify for the 26% federal tax credit?
Yes, but you must meet certain requirements. The benefit is only available for batteries that operate along with solar panel systems that are eligible for the tax credit – not for battery systems that operate on their own without solar generation.
- If the battery is used by a home, it must get 100% of its charge from solar panels to qualify for the tax credit. In other words, you cannot charge your battery using the grid, only solar panels.
- If the battery is used by a business, it must get at least 75% of its charge from solar panels to qualify. In this case, the tax credit amount is reduced in proportion to the solar charging percentage. For example, a battery that meets the minimum charging percentage also gets 75% of the available tax credit.
Can I go off-grid with a solar battery?
Yes, but staying connected to the grid is generally a better option. To go completely off-grid, you need a solar battery with enough capacity for high-consumption devices like air conditioners and electric stoves. This will make your system much more expensive.
You can get a better return on investment with a smaller solar battery that powers your most important devices. You can continue using the grid as backup, since the productivity of solar panels is reduced during winter and on cloudy days. The grid can also provide the extra kilowatts needed by power-hungry devices, without having to use a large and expensive battery.
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