How does a solar battery bank work? | Pros and Cons

How does a solar battery bank work? | Pros and Cons

By Renogy marketing team
Renogy marketing team
renogys blog Feb 24th 2023

Buying a solar battery bank is one of the biggest investments you will make when setting up a solar installation. That’s why before you purchase your batteries you need to learn what to expect or avoid.

Our goal is to give you all the information you need to pick the right solar battery banks for your system.

In this article, we talk about:

Let’s begin.

What is a solar battery bank?

 

A solar battery bank can be one or several deep-cycle batteries connected in such a way that they function as one big battery in a solar installation. Think of a solar battery bank as a squad of soldiers that concentrates their efforts together to achieve a bigger goal.

A battery bank is an important part of any solar system. Why? Because battery banks store energy generated by your solar panels during the day for use during the night.

Without battery banks, all the energy generated by your solar panels during the day goes to waste and can’t be used at night.

How does a solar panel battery bank work?

Solar batteries store the power produced by your solar panels during the day. When the sun sets and your solar panels can’t continue working, that’s when the battery bank releases the stored power to be used by your devices.

During the charging phase, a solar battery bank can use other sources of power to charge besides solar panels. For example, you can use a generator, grid supply, or a vehicle's alternator to charge your batteries.

● To safely charge battery banks using solar panels you need an MPPT charge controller like the REGO 12V 60A MPPT Charge Controller for quick and effective charging.

● To charge your batteries using a grid supply or a generator, you need an AC to DC Battery Charger with the same DC output voltage as your battery bank.

● To charge your solar battery using an RV’s alternator, you need a 12V DC to DC On-Board Charger designed for use on vehicles.

● Always use battery chargers and charge controllers that are compatible with your battery type. Some Lead-Acid battery chargers are unsuitable for use on Lithium-ion batteries.

For the best results, we recommend using batteries of the same model, age, type, voltage, and size (Ah) in your solar battery bank. A battery bank with mismatched batteries is harder to synchronize and regulate, which may lead to a fire or damage to property.

 

Different systems of battery banks can be composed of different types of batteries. For example, you can have a battery bank composed solely of either AGM batteries, Gel batteries, or Lithium (LFP) batteries of the same model, capacity, and voltage.

Learn more about deep cycle battery types in What To Know About Deep Cycle Batteries For Solar Storage.

How are battery banks for solar interconnected?

Battery banks use two types of connections to output the required current or voltage:

1. Parallel Connection - Roughly speaking, parallel connections interconnect batteries by linking the batteries' positive terminals together using one line and negative terminals using another. In other words, one wire loops across all the positive terminals while another wire loops across all the negative terminals. The output voltage stays the same while the current of the battery bank is the sum of each battery's amperage.

2. Series Connection - In a series connection, one line connects the opposing terminals of closeby or adjacent batteries. The first battery's positive connects to the second battery's negative terminal. While the second battery's positive terminal connects the third battery's negative terminal and so on. The output voltage is the sum of the batteries' voltage while the current of the battery bank stays constant.

 

This knowledge about the battery bank connection types will come in handy when you are building a battery bank for your solar. It's also important to note that some battery banks can use a combination of both parallel and serial connections to meet the required voltage and current. You can find More information on solar panel connections in another article - A Guide Between Series And Parallel Connections.

Solar battery storage cost

The cost of solar battery storage depends upon four factors:

1. Battery Storage Capacity - Batteries that can store more energy typically cost more than batteries of the same type that store less energy. For example, a 12V 100Ah LFP battery will always cost more than a 12V 50Ah LFP battery of the same make. So the larger the battery capacity you need, the more it is going to cost.

2. Battery Type - This refers to the type of materials used in the battery's construction. Examples of battery types are Lithium-ion, Gel, and AGM batteries. Batteries made with better quality materials that are rare, safer, more durable, etc., tend to be more expensive than batteries made of common materials.

3. Battery Lifespan - Longer-lasting batteries cost more than their short-lived counterparts. At first, long-lasting batteries, e.g. LFP batteries, seem to cost more. But then again, due to the need to often replace short-lived batteries, they may end up being more expensive. For example, suppose a $500 12V 100Ah LFP battery lasts for 10 years while a $150 12V Lead-Acid battery lasts for two years. Over 10 years, lead acid batteries will cost you $750.

4. Battery Depth of Discharge (DOD) - A higher depth of discharge on your battery allows access to more of the energy stored in the battery before being cut off. For instance, suppose a 100Ah battery has a 95% DOD. In that case, you can use 95Ah of the total 100Ah before the BMS cuts you off. In contrast, a 50% DOD only gets you half of the battery’s stored energy.

Other factors that influence the cost of solar batteries to some extent are:

● The Safety Level of the Battery

● Output Voltage of the Battery

● Level of Maintenance Needed

Here is a table listing different battery types, their price, and the cost to build a 4kWh and 10 kWh battery storage.

 

After comparing Renogy’s three battery types, you can see that at the same voltage and capacity, the Renogy Solar Lithium Battery with the longest lifespan always costs more than other Renogy deep-cycle batteries of the same voltage and capacity.

Determine Your Solar Battery Storage Sizes

To determine the optimal size of your solar battery storage, you need to answer two questions:

● Question 1: How much energy do you need from your batteries to power your electrical load/devices? This can be translated into how many devices you want to power each day with your battery bank.

● Question 2:The type of your solar installation. Is it an on-grid backup system, a cost-saving measure, or a completely off-grid solar system? Each type of solar installation needs a unique battery storage size. For example, a backup solar system that only powers mission-critical devices needs small-size storage. On the other hand, a cost-saving system or an off-grid system needs a large battery storage size to become as independent as possible from the grid.

Once you have answered these two questions, you can determine the optimal battery storage size that will give you the best performance, longevity, and cost savings.

For example, the average household uses around 30kWh of energy daily. The ideal solar battery storage size is 60kWh because it extends your batteries’ lifespan due to the 50% depth of discharge. That being said, due to the high cost of batteries, a 60kWh battery bank may be out of reach for some households.

In that case, you can work out a battery bank size that is more in line with your energy needs and budget. Renogy super power calculator, to some extent, may help you determine a suitable battery system size fast.

 

Pros and Cons of Solar Battery Storage

Here are the pros and cons of solar battery storage with solar panels.

Pros

1. Reduced Energy Costs - Solar is now the cheapest source of energy alongside onshore wind. Therefore, from the moment your solar starts working, whenever you use solar power instead of grid power you are saving money in terms of the cost of energy and reduced utility bills.

2. Income Source - You can feed excess power from your solar battery bank and PV system back into the grid. In return, your power utility will either pay you, reallocate the power back to you during the night, or give you another type of benefit.

3. Backup Power for Emergencies and Power Cuts – Suppose the grid goes down and there's no grid supply. In that case, solar batteries can keep your critical devices running during this period when everyone else has no power.

4. Self-Sufficiency and Independence from the Grid –- If you have enough solar panels and battery storage, you can completely break away from the grid and protect yourself from rising power utility rates.

5. Power Even in Remote Locations –- As long as there's enough sunlight, you can generate solar power and power your property away from the grid. For example, a certain Youtuber, who lives on a remote farm, realized that installing a gigantic 60 kWh battery bank ($50,000) was cheaper than bringing the grid to their property ($60,000).

6. Sustainable and Environment Friendly –- Generating solar energy and storing it in a solar battery does less harm to the environment than generating, transmitting, and distributing fossil fuel energy.

7. Enables Solar Power Storage for Later Use – Without solar batteries, a solar system cannot reach its full potential. Solar battery banks enable solar systems to store the excess energy produced during the day for use

Cons

1. High Upfront Costs - Investing in solar costs quite a penny in the beginning. For instance, just purchasing all the components needed requires thousands of dollars. In contrast, grid power usually has a lower upfront cost. The good news is the cost of solar products continues to fall steadily. Not only that, but you can leverage government tax credits to lower the cost by as much as 30%.

2. Maintenance Requirements - A solar battery bank is not the type of system you can just install and forget about. A solar system needs constant monitoring, cleaning, and maintenance to ensure it keeps performing at optimal levels. That being said, the maintenance activities are simple and won't take too much of your time. Examples of maintenance activities are cleaning, dusting, debris removal, tightening connections, etc.

3. Shorter Battery Life Spans — Solar batteries do not last as long as the rest of your solar panel system. As a result, you will probably need to replace your batteries before the rest of your system. For example, if your batteries last around 10 years while your solar panels can easily withstand over 25 years of use. You will probably have to replace your solar battery bank at least twice depending on the type of your batteries.

So is solar battery storage worth it?

Generally speaking, solar battery storage is a good investment for residential and commercial use. Without solar battery storage, you can’t enjoy all the advantages your solar installation offers.

Here’s what you need to know before you decide if solar battery storage is worth it for you:

● If you live off-grid, away from any power lines, solar battery storage is something you cannot do without.

● If you’re connected to the grid and your state has favorable net metering plans, solar battery storage is not absolutely crucial for your solar system. This is because all the excess energy you don’t use can be fed into the grid. At night, when your solar panels are down, you can claim the power you fed into the grid for your use. In other words, the grid will serve as your battery storage.

While you can use the grid to store power, we advise against it. We recommend using solar batteries because, if the grid shuts down during an emergency or fault, you can rely on the batteries as a backup power source.  

To conclude, solar battery storage is worth it if:

● You live off-grid away from any power lines.

● You live in a state with unfavorable net metering policies.

● You need a backup power source to tide you over emergencies and power cuts.

How to build a battery bank for solar?

So we have covered much of the theory about solar battery banks, but we haven’t talked about the practical aspect of assembling a battery bank.

To build a battery bank for solar, you need to have all the required cables, connectors, and batteries in one place.

Once you have everything ready, follow these steps:

Step 1: Create shelves or space to place your batteries. The area needs to have normal temperatures and not be exposed to extreme heat or cold.

Step 2: Place your batteries in a manner that gives the interconnecting cables easy access to your batteries.

Step 3: Securely connect all the positive terminals of your batteries using battery interconnect cables.

Step 4: Connect together all the negative terminals of your batteries using the respective interconnecting cables.

Step 5: Add the cables from the inverter and charge controller to the first and last battery bank. The positive cables should go to the first battery's positive terminal. While the negative cables go to the last battery’s negative terminal as demonstrated in the image below.

If you need a visual step-by-step demonstration, check out the video below.

Important note: Do not connect both of the cables coming from your inverter to the same battery. Instead, connect the inverter’s positive cable to the positive terminal of the first battery. And connect the inverter’s negative cable to the last battery’s negative terminal.

For more info on how to safely work with Renogy batteries watch this video:

 


Best solar power banks in 2023

We genuinely believe that Renogy products are the best solar products on the market. Our products go through strict testing to ensure they perform at a high level and comply with all safety standards and certifications.

For power banks, we have two types of power banks on offer – The first offering is the range of portable power banks and solar generators. Renogy portable power banks are the best portable power banks and are highly suitable for use in RVs, campsites, and as an emergency power supply for your home. We recommend buying

the Renogy 1000 Portable Power Station that can be used in tandem with another Phoenix 1000 for more power.

In contrast, our second offering, the less portable but more powerful Lycan PowerBox power banks are the best power banks for homes and off-grid construction sites. The flagship product in this range, the LYCAN 5000 PowerBox boasts one of the biggest, expandable battery capacities on the market. It comes in at 4.8kWh, which can be expanded seamlessly to a whopping 19.2kWh of capacity.

If you are looking for the best power banks, look no further than Renogy. We have the best portable power banks to suit any budget, place, or purpose.

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