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How solar batteries work – The Complete Guide

21 December, 2023

How do solar batteries work - The Complete Guide

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Perhaps the most important tool in a renewable energy installation, solar batteries allow us to store energy captured from the sun (or the grid) for future use. The world is (at last) starting to understand the importance of sustainable power solutions, so understanding the essence and functionality of solar batteries is essential. This guide will help you understand everything about solar batteries, why they are important, how they are made, how to choose the right one for your needs, how to install and integrate them with a solar energy production system, how to maintain them and check their proper operation and how to troubleshoot common issues.

Let’s begin, shall we?

Solar Batteries - A Solar Battery for a renewable energy system

A Solar Battery for a renewable energy system

1. What Are Solar Batteries?

To understand more about Solar Batteries, we need to first identify their main purpose and importance in a solar energy generation system

1.1 Definition and Purpose

A solar battery is a device designed to harness and store electricity generated by an external source. We say “external source” because, even though their most frequent use is in conjunction with solar panels, these batteries can also be used to store energy from the grid too. At their most common set up, solar batteries enable the accumulation of excess energy that is produced from solar panels during peak sunlight hours. This energy is then utilised during periods of low solar activity or during power outages. This is a fundamental characteristic that makes solar batteries the most important components of both residential and commercial renewable energy systems.

1.2 The importance of Solar Batteries in Renewable Energy Systems

The basis of sustainable energy practices is to store the power produced by natural sources such as the sun or the wind in order to use it when necessary. The integration of solar batteries is a key enabler of such sustainable energy practices. Because the sun’s power is intermittent (only available during the day), the use of solar batteries allows us to have a consistent and reliable energy supply. This has several advantages which we will discuss later in this article, but the most prominent ones are the reduction of dependence on the conventional grid and the significant cost savings. And of course, let’s not forget the significant contribution to the global effort to mitigate climate change.

1.3 Are Solar Panels absolutely necessary in a renewable energy system?

Although you will benefit the most from a Solar Photovoltaic (PV) system, you may be surprised to learn that the existence of one is not absolutely necessary. To understand this better though, we need to explain the 3 main types of solar arrays first.

  1. The first type is called an Off-Grid Solar Array. In this type of array, the property where the array is installed is completely disconnected from the grid. This means that all the energy supply to the appliances comes 100% from the solar array. In this case, a solar battery is necessary as it allows us to have power available after the sun sets or on very cloudy days when the energy production from the solar panels is very low. If the array did not have a battery fitted, the sunset would immediately mean the property would be without any power.
  2. The second type is called a Grid-Tied Array. In this type of array, the solar panels produce energy during daytime and, after the night falls, all appliances are powered from the grid. The grid is also used in days when the solar panels don’t produce enough energy. A property with a grid-tied array doesn’t necessarily require a solar battery as it can cover its energy needs from whatever energy the solar panels produce, and then fallback to the grid for the rest.
  3. The third type is called a Grid-Tied Array with Solar Batteries. This is the same as the one above, but with the addition of a solar battery (or more). On days when the solar panels produce a lot of excess energy, this is stored in the solar battery. During the night, you make use of the energy stored in the battery and, if this gets all used up, then the property starts drawing energy from the grid.
Solar Batteries - Solar Panels installation

Solar Panels installation

Now that we understand the 3 main types of solar arrays, we can see that the answer to whether Solar Panels are absolutely necessary in a renewable energy system is that it depends on what you want to achieve with your array. If you want to become completely independent and fully isolate the property from the grid, then it is definitely recommended that you add at least one battery to your renewable energy system, although we would recommend more than one depending on your needs. If you want to rely less on the grid, but still have it as a backup for days when the solar panels don’t produce enough energy, then again it is useful to have a solar battery as this will allow you to store any excess energy to it, the cost of which will always be significantly lower than what the grid will charge per kWh. If you have a company that supplies you with electricity at different tariffs during different hours of the day, you can make use of the battery to store cheap electricity (usually overnight) and use that energy from the battery during the high tariff hours. Many people go for that solution, and use one or more batteries without a solar array at all. In that case, it’s not a renewable energy system, but it definitely helps minimise costs if you can find the right tariff.

1.4 Advantages of Solar Batteries

You may think that free energy is the sole advantage of a solar battery, but there are more. Let’s see them all:

  • Solar batteries provide energy storage
    This is of course the primary advantage of solar batteries. The excess energy that your solar panels produce is stored in the batteries, and this allows us to use it when we want.
  • Partial or complete autonomy from the grid
    With the right amount of solar panels and solar batteries, one can partially or completely disconnect from the traditional grid. In properly configured renewable energy solar systems, one can also sell excess energy back to the grid, which helps minimise the return of investment period.
  • Significantly lower impact to the environment
    The world needs to urgently adopt a renewable energy policy in as many aspects of everyday life as possible. Using less energy produced by non-renewable sources aligns with a broader commitment to environmental sustainability. By reducing reliance on non-renewable energy sources, solar batteries contribute to lower carbon footprints and promote cleaner, greener energy practices. This, in turn, supports the global transition towards a more sustainable and eco-friendly future.
  • Lower utility bills
    By using the energy stored in a solar battery you use significantly less energy from the grid, which results in a lower utility bill.
  • Noise pollution
    Contrary to conventional power generators, solar batteries provide an almost 100% silent system, whether storing or providing energy. We say almost 100% as there may be an occasional hum, but this is insignificant and usually under detectable levels of noise detectors.

By carefully choosing your appliances (low energy ratings, high output, energy efficient lighting such as LED bulbs etc.) a house can be powered efficiently and at a low cost both for your pocket and the environment. A properly designed renewable energy system with an adequate solar batteries array will need very few, if any, compromises from your side in regards to powering a whole house.

Companies all over the world are switching to solar battery systems, connected to the grid or not, for their energy requirements. The cost of energy worldwide has risen a lot in the past few years, and this triggered an interest in more research and new innovations that benefit the companies financially but also the planet we call home.

2. How Solar Batteries Work

Understanding how solar batteries work is imperative in making the right choices for your own personal needs and energy requirements. This is a part that is often missed when people plan for a new solar energy system, because all the attention is usually drawn to the solar panels. Yes, they are essential and they are the main producer of energy, but without solar batteries to store that energy and use it when needed the system is not complete. Failing to understand the necessity and requirements of solar batteries in such a system usually results in improperly configured systems that are not well optimised and fail to give the maximum performance they can. We have the largest possible free and infinite source of energy, the sun. Why wouldn’t we want to take advantage of that?

Solar Batteries - A Renewable Energy system with an array of solar batteries

A Renewable Energy system with an array of solar batteries

2.1 Charging and discharging

During sunlight hours, the photovoltaic cells on your solar panels convert the sun’s radiant energy into electricity. Part of that electricity is used on the spot by any appliances in the property, whereas the surplus electricity generated is directed towards charging the solar battery. Conversely, during periods of low sunlight, the stored energy is discharged to power electrical devices, maintaining a seamless and continuous energy supply.

2.2 Conversion of Solar Energy to Electricity

There are two types of electric current: AC (Alternating Current) and DC (Direct Current). All solar panels create 12V DC electricity. That electricity can be used only by appliances that are made to be powered by 12V DC and is useless to any appliance that supports AC. This means that, in a solar energy system, the electricity coming from either the solar panels or the battery will only be able to power DC appliances, unless we convert that DC electricity to AC. To achieve that, we require a device that is call a converter. Converters receive DC power and convert it to AC, so that it can be used by lights, white goods and any other common household appliance that usually needs connecting to your wall socket to operate.

2.3 Do I need both?

In an optimised solar energy storage system, the answer is yes. You need the battery to store the excess energy your solar panels produce and, unless you are 100% confident you will only be using 12V DC appliances (which may be the case in a caravan or a shed in the woods with no appliances such as fridges, washing machines etc.), you also need the converter to produce AC current to power your home appliances. Keep in mind that some modern converters can also allow DC to come out of them (essentially operate as a pass-through), so you can power any DC appliances if you need to.

2.4 Are there any 12V household appliances?

You’d be surprised to hear that there are! We have seen 12V DC fridges, TV’s, water heaters, cookers, hair dryers, water pumps, toasters, kettles, blenders, battery banks etc.. Some of them are even better performing than their AC counterparts because a lot of attention has been given to make them as power efficient as possible. One of the best applications for domestic use is lighting. A 12V light bulb can be as efficient as its AC equivalent, and operates at a fraction of the energy cost. Unless you are lighting a concert or a theatre play or a stadium, there is no reason not to choose 12V DC lights.

Solar Batteries - 12V Fridge Freezer by Montpellier

A 12V Fridge Freezer by Montpellier

3. What Chemistry do Solar Batteries come in?

Currently, we have 3 prevailing chemistries but there is also a new type emerging.

3.1 Lead-Acid Solar Batteries

Lead-Acid batteries are a chemistry that has been around for several years. In fact, they’ve been around since the 19th century (you can read more about them in our Lead Acid Batteries article). They don’t display as advanced characteristics as newer chemistries, but they are and always have been very reliable, which is the reason why they’ve been used non-stop for decades. Compared to Lithium-ion batteries, they are much more cost effective. There are two sub-categories of Lead-Acid batteries:

Flooded Lead-Acid Solar Batteries (FLA)

The plates in FLAs are submerged in water, therefore the water level must be checked and filled when needed to keep them working. Forget to do that and you will be looking at a shorter overall battery life, which will make your return of investment period extend significantly. Another critical factor is that these batteries need to be installed in areas with good ventilation, as gases are produced by them that need to escape somehow.

Sealed Lead-Acid Solar Batteries (SLA)

Contrary to FLAs, SLA batteries don’t require any maintenance at all. They are spill proof and completely sealed. They come in two different types, AGM (Absorbent Glass Mat) and Gel, which share similar properties. They require little to no maintenance, they are spill-proof and don’t require refilling with water. The way they do that is by keeping the water of the electrolyte either via fibreglass separators which are made to be absorbent, or by turning the electrolyte into a gel. The first ones are called AGM batteries, and the second ones are called GEL batteries. AGM batteries are faster to charge and can output more power than gel batteries.

To recap:

  1. Lead Acid is the most effective Solar Battery option as they are cheap.
  2. They are very reliable.
  3. Easy to dispose of and recycle.
  4. Flooded lead acid batteries must be maintained and monitored.
  5. Due to the liquid, they cannot be placed on their side.
  6. They have a low depth of discharge (DoD), which means they need to be charged more frequently.
  7. They have a short life cycle that ranges anywhere between 5 and 10 years, if maintenance is optimal.

They would be the best fit for an off grid solar system or as an emergency backup when there is a power cut from the grid.

Solar Batteries - Renogy Deep Cycle AGM 12 Volt 100Ah Solar Battery

Renogy Deep Cycle AGM 12 Volt 100Ah Solar Battery

3.2 Lithium-Ion Solar Batteries

The Lithium-ion chemistry is more recent (you can read more about its history in our Lithium-Ion Batteries article) but it is the prevailing chemistry in hundreds of every day applications. From phones and cameras to electric vehicles and anything in-between, they can be found anywhere and everywhere, so it’s no surprise that they are also used in Solar Energy Storage systems.

Out of all the sub-chemistries, the most suitable for solar batteries is Lithium Iron Phosphate (LiFePO4) which we have already analysed in our LiFePO4 article. They last way longer than Lead Acid batteries, they do not require any ventilation, refilling or maintenance and they are much more efficient. The only issue is that they are more expensive to buy, but their efficiency (if set up on a well designed system) outweighs their cost. In fact you can actually make up for the higher initial cost if these batteries are used every day, but we wouldn’t recommend them for a holiday house that is only used and powered infrequently (go to Lead Acid for that).

To recap:

  1. Lithium ion batteries are zero maintenance.
  2. They have high battery energy density compared to Lead Acid. This means you need fewer and smaller batteries to store the same energy than Lead Acid.
  3. They last longer. Their average life is a guaranteed minimum of 10 years. The more a battery lasts for, the quicker your return of investment.
  4. They discharge slowly, so you can pull out more energy from them before they need a recharge.
  5. They are expensive.
  6. They are known to catch fire due to thermal runaway, so we strongly recommend that you go with reputable manufacturers that follow high production standards, and not just buy the cheapest batteries you can find. Price does reflect quality in Lithium-Ion batteries, so don’t go cheap, neither on the batteries, nor on the certified installers that will fit them to your system. A proper installation of a good quality Li-ion battery essentially eliminates any chance of fire under normal operation.

The ideal application of Lithium-ion solar batteries would be a home. Their ability to hold more power in a smaller space makes them perfect for your domestic renewable energy system.

3.3 Flow Solar Batteries

A relatively new battery chemistry/technology is that of flow batteries. The technology consists of external tanks that store liquid electrolytes. By making the electrolytes flow, energy is produced, which is then stored for reuse. Even though they are significantly more expensive that the above mentioned chemistries, they are very promising and research is ongoing to produce them in a format that will be suitable for home use.

Their main characteristics:

  • Amazing longevity, with an estimated life cycle of 30 years with over 10,000 charging cycles.
  • They can be scaled up very easily: just by changing the size of the tanks for a bigger one immediately produces more energy.
  • 100% depth of discharge. Which means you can use all of the energy they store before recharging without destroying the battery.
  • The liquid that the tanks contain is actually fire retardant, so no risks of thermal runaway like Li-ion batteries.
  • They are very quick in power output, which makes them ideal for applications where high output is required quickly. They are also very quick to recharge.
  • Large size, which is a problem for domestic applications.
  • Lower energy capacity compared to Li-ion. This is a significant con, as it makes them impractical when combined with their already big size.
  • They require some maintenance. Due to the movement of liquid, filters (membranes) are included in the tanks that need replacing periodically. The actual electrolyte liquid also needs replacing, even though not that frequently.
  • They are expensive.

We are aware of Redflow, an American company that are doing extensive research in producing flow solar batteries of more manageable size. You can see their page here. We are closely monitoring their progress which we find promising, especially since they introduced their domestic battery called ZCell.

Solar Batteries - Zcell Domestic Flow Battery

The Zcell Domestic Flow Battery

If you are planning to have a large scale installation where space is not an issue, these are the best solar batteries to go for. We do not recommend them for any domestic setting due to their size.

3.4 Other technologies of Solar Batteries

Apart from Lead Acid, Lithium-ion and Flow solar batteries, scientists and companies around the world continue researching materials and methods to produce more energy density in smaller footprints. One of the most promising technologies we see is that of solid-state batteries. Read more about them on our Solid State Batteries article.

3.5 So which Solar Battery type or chemistry should I choose?

We know you hate that answer, but it depends on your specific use case. Let’s see the options you have:

3.5.1 Solar Batteries Cycle Life considerations

How often will your battery be charged and discharged? If you are planning to add a renewable system in a holiday house that you visit only a few times a year, you should go for Lead Acid and they will last you for many, many years.

If, on the other hand, you plan to use your renewable energy system in your main house where each year would mean probably 250-300 charge and discharge cycles every year, then Li-ion is a no brainer.

3.5.2 Solar Batteries Depth of Discharge considerations

The depth of discharge in a battery measures how much of the battery’s capacity you can use before the battery needs to be charged again.

Why does that matter? Can’t I use all the energy stored in my battery? No, you cannot. All batteries have a recommended discharge level (that’s the depth of discharge), after which you should not keep discharging them but you should charge them instead. Remember that dead car battery you experienced in the past? Most probably that battery ended up in a recycling facility because it could never be recovered after losing more charge than what the manufacturer recommended. So the battery, for whatever reason, went under the recommended Depth of Discharge. By the way, we have an excellent article about battery savers, battery maintainers and trickle chargers that we recommend you read.

Back to our comparison. So, due to their Depth of Discharge, Lead Acid batteries should only be discharged to around 45-55% of their capacity. Any lower than that and you risk permanent damage to them. On the other hand, Lithium-ion batteries can be discharged all the way down to 80-85% without any permanent damage. So, again, if you are in a house located in a sunny country and with lots of solar panels, then a Lead Acid battery will be quickly recharged by the energy the panels will produce before its charge drops under 45-55%. But if you are in a country with less sunshine, then a Lithium-ion battery would be much preferred.

3.5.3 Solar Batteries Efficiency considerations

Efficiency is the measure of how much energy we can get out of a battery compared to how much energy we stored in it. Due to the Law of Conservation of Energy, there is no battery that has 100% efficiency, but some battery chemistries are more efficient than others. For our article, Lead Acid batteries have an energy efficiency of approximately 70%, whereas Lithium-ion batteries have a much higher efficiency at over 90%. So one could say that Lithium-ion batteries win in this case and should be the preferred battery, but that’s not 100% accurate.

If your house has a large enough surface area to install many solar panels, it would be beneficial to go for Lead Acid batteries as you would have more than enough electricity to charge them to compensate for their lower efficiency and the overall cost would be lower. If, on the other hand, you are restricted by the area where you can put panels on (for example on a roof), then it makes sense to go for the more expensive Lithium-ion batteries as you would need to take advantage of every little bit of energy your solar panels produce, albeit at a higher cost for the batteries. Furthermore, the use of the house itself also is a deciding factor here, depending on whether it is your permanent residence or a holiday house.

3.5.4 Solar Batteries Charge Rate considerations

Charge rate measures how quickly a battery can be charged. In this characteristic, Lithium-ion batteries are clear winners. Lead Acid batteries require low amperage to charge and if you attempt to increase it, that will result to the battery overheating. Also, the closer they get to 100% charge, the slower the charge rate becomes. Lithium-ion batteries have no such issues.

3.5.5 Solar Batteries Energy Density considerations

The last critical difference between the two battery chemistries is Energy Density, but it’s definitely not the least. Energy density measures how much energy we can get within a specific weight or volume. Let’s get an example of two batteries, A and B, identical in size and weight. If one can produce more kWhs than the other, then we say is has a higher Energy Density.

Energy Density is measured in watt-hours per kilogram (Wh/kg) or watt-hours per liter (Wh/L) and it depends greatly on the materials used to produce the battery. For our two contestants, Lead Acid batteries have an average density of 32-50 Wh/kg and Lithium-ion batteries go much higher at 110-255 Wh/kg. The advantage of higher energy densities is that you need fewer and smaller batteries to achieve the same energy output, so the higher the energy density a battery has, the better. Lithium-ion batteries are clear winners here, and there is no case where Lead Acid would have any advantage at all.

3.5.6 Lithium vs. Lead-Acid: Which Solar Battery chemistry should I choose?

Their long-term cost throughout their useful life is similar. The difference is that Lithium-ion batteries have a higher upfront cost, but make that cost up due to their longer life and higher efficiency. Another factor is the actual use. If you are looking to power a house that has already got a grid connection and is your main residence (meaning the renewable energy system will be used daily), then an array of Lithium-ion batteries is the best choice. If we are talking about a cabin in the woods that isn’t connected to the national grid and is used a few days at a time every year, then the lower cost of Lead-Acid batteries makes them a much better choice.

A good installer will provide you with calculations that will help you decide which option is best for your specific needs, as there isn’t a catch-all formula.

Solar Batteries - A domestic solar batteries array ready to be connected

A domestic solar batteries array ready to be connected

4. Solar Batteries and Inverters

As mentioned earlier, solar panels produce Direct Current (DC). In order to use this in a common AC domestic appliance, the current needs to be inverted from DC to AC. This is the job of a device called an inverter, which is essential if you want to use your stored energy to power any AC appliance.

Solar Batteries - Victron Energy Phoenix Inverter 245000 24V 5000W

Victron Energy Phoenix Inverter 245000 24V 5000W

What is not known about solar batteries is that there are actually two different types, depending on where the inverter is installed. The two types are DC-Coupled and AC-Coupled.

4.1 DC-Coupled Solar Batteries

DC-Coupled solar batteries connect to an inverter directly. This allows the electricity produced by the solar panels to flow and get stored directly to the batteries.

The advantage of DC-Coupled batteries comes from the fact that they get charged directly from the solar panels with DC power that the panels produce. When the time comes to use the stored energy, this gets converted to AC only once. Each conversion from DC to AC or vice versa comes at the expense of some energy loss. This means some energy is unavoidably lost during that conversion. So the whole process with DC-Coupled batteries is more efficient as there is only one conversion, from DC (solar panel) to AC (battery output). Furthermore, if you are planning a brand new solar panel renewable energy system, a DC-Coupled battery is cheaper to install, because you won’t need an inverter that is specific to your battery. The disadvantage of DC-Coupled batteries is for when there is an existing system with solar panels. In existing installations, unless your panels are already connected to an inverter, these batteries are not ideal.

4.2 AC-Coupled Solar Batteries

AC-Coupled solar batteries on the other hand have their own inverter within the battery itself.

AC-Coupled batteries are simpler to add to any installation because they come with their own inverter. They can be charged either through the existing AC circuit (for example using energy from the grid), or through an inverter that has already been connected to the solar panels and gives out AC. Of course, in such case the disadvantage is reduced efficiency, because the current is converted twice: once from the solar panels to the inverter (DC to AC) and once from the inverter to the batteries (AC to DC). This results in an efficiency drop of approximately 2% for each conversion, which is essentially energy produced by your solar panels that is lost.

4.3 DC-Coupled Solar Batteries vs AC-Coupled Solar Batteries. Which type should I choose?

If you are in a very sunny country, this difference may be negligible, but if not, you should consider DC-Coupled batteries instead of AC-Coupled, even if they are a bit more complicated to install. Of course, a specialist installer should always be consulted, even if you are experienced in such installations.

5. How long do Solar Batteries last for? What is their life expectancy?

There are several factors that affect the longevity of solar batteries. First and foremost comes the frequency of use. Batteries have a limited number of discharge/charge cycles, so the more a battery is charged and discharged, the less it will last. That is not to say you shouldn’t charge your solar batteries, after all that’s what they’re there for! It’s to help you understand that when you buy solar batteries, one of the specs you need to check is the number of charge cycles the manufacturer claims their batteries support. It’s always a good idea to check online for reviews or ask others for their experience, as manufacturers can sometimes be overoptimistic with their claims.

Solar Batteries - Time to replace these

Time to replace these…

All solar batteries lose a small percentage of their capacity every year. The average time they can still be usable is between 5-15 years, but this figure varies among manufacturers. If you consider that solar panels usually last for more than 20 years, you will probably need at least one new set of solar batteries throughout their life, if not more.

Another factor that reduces a solar battery’s life is the storage location and the temperatures the battery is exposed to at that location. This is why it is always recommended to store batteries indoors, in a well-ventilated area. You should avoid storing batteries outside as exposure to the elements decreases their active life and may cause technical issues.

The last thing to mention is that you need to avoid is leaving the battery discharged, or leaving it at full charge for long periods of time. Both approaches will make the battery lose its ability to charge and therefore render it unusable sooner or later. That of course doesn’t happen if you do it once or twice, but long periods of battery inactivity will eventually cause irreparable damage. The best approach is to leave your batteries half charged, or charge them according to the manufacturer’s instructions. Oh, and if they are full, avoid leaving them on charge constantly, this also affects their lifespan. This applies to all lithium batteries, whether we are talking about solar batteries or your phone or tablet or laptop.

6. How much energy can be stored in a Solar Battery?

Solar batteries come in different capacities. We measure the storage capacity in kilowatt hours (kWh). To explain that in simple terms, a battery with a capacity of 1kWh can provide 1kW (or 1000 Watts) for 1 hour. So, for example, if you have a light bulb that uses 1W to light up, a battery with a capacity of 1kWh will provide enough power to keep the light bulb on for 1000 hours. Of course, we need to clarify that this is the theoretical figure because there is always some power loss (for example due to converting the electricity from AC to DC or loss due to heat), so this figure should not be taken as an absolute number but rather as a guide.

Solar Batteries - Generac Pwrcell, one of the champions in battery capacity

Generac Pwrcell, one of the champions in battery capacity

Today you can find batteries with capacities from 2kWh to 14kWh. Please note that these figures are referring to batteries intended for domestic use; industrial batteries come in much larger capacities. This is due to the restrictions in size for domestic batteries, that don’t apply to industrial settings as there is usually much more space available.

Solar Batteries - Industrial size Solar Battery array

Industrial size Solar Battery array

A simple way to increase the battery capacity in a renewable energy system is to simply add more batteries. How many more? Well, that depends on how much energy you want to store and are planning to use, as well as how much energy your solar panels can provide. Even if cost is not a factor, there is no point in adding more batteries to store more energy in your array if your solar panels cannot produce that much energy in the first place.

7. How much do Solar Batteries cost?

The cost varies, depending on the battery’s capacity and its energy rating. A rough estimate is that you can expect to pay anything from £420/kWh ($535/kWh) upwards, with the top brands costing up to £850/kWh ($1,083/kWh). Why such a wide range? Because of different capabilities. Batteries can have varying life cycles and storage capacities, and they can be produced with less or more expensive materials. Another factor is the actual usable capacity of the battery as mentioned above. Some batteries come with management software that allows you to fine-tune their operation, or are second life batteries coming from recycled electric car batteries. These are in fact the best bargains you can get. One of the most known companies worldwide that offers these batteries is Nissan, the automotive manufacturer.

8. What is a Charge Controller and do I need one for my Solar Batteries?

We mentioned earlier that a critical component on a renewable energy system is an Inverter, but that’s not all. There is also another device that is very beneficial to your Solar Batteries, and it’s called a Charge Controller.

Solar Batteries - MPPT Charge Controller by Epever

MPPT Charge Controller by Epever

This controller functions as crucial regulator, and its job it to coordinate the flow of electricity between your solar panels and your solar batteries in the most efficient way. Its main objective is to prevent overcharging, which is a serious threat to your batteries’ health and longevity. By optimizing the charging process, a charge controller ensures that the batteries receive precisely the required energy, safeguarding them from the adverse effects of excessive voltage.

There are two types of charge controllers:

  • Pulse Width Modulation Charge Controllers (PWM), and
  • Maximum Power Point Tracking Charge Controllers (MPPT)

Let’s see what each one does.

8.1 Pulse Width Modulation Charge Controllers (PWM):

They work by intermittently interrupting the current flowing between the solar panels and the battery. They regulate the charging process by controlling the voltage sent to the battery. While they are effective and work great, PWM controllers are not as efficient as MPPT controllers, especially in situations where there is a significant difference between the voltage of the solar panels and the battery.

8.2 Maximum Power Point Tracking Charge Controllers (MPPT):

These are more advanced and efficient. They continuously adjust the electrical operating point of the solar panels to extract the maximum power available from them. This is particularly useful when environmental conditions (clouds) or the angle of sunlight change. They are significantly more efficient than PWM controllers, especially in scenarios where the solar panel voltage and battery voltage differ significantly. They can provide a higher charging efficiency and harvest more energy from the solar panels.

In summary, PWM controllers are simpler and cost-effective, but they may be less efficient in certain conditions. MPPT controllers, on the other hand, are more sophisticated and tend to be more efficient, making them preferable for situations where optimization of power harvesting is crucial. The choice between the two depends on factors such as system size, your budget, and the specific requirements of the solar power setup. For a domestic use where you want to maximise the efficiency of your whole renewable energy production, we would definitely recommend that you buy an MPPT Controller.

9. Installation and Maintenance of Solar Batteries

Although not necessarily rocket science, the proper installation of Solar Batteries will need to be done by a certified professional. Perhaps a small scale installation just to power a few garden lights is something you find really easy to do, but for a full scale domestic setup you should definitely use the services of an experienced installer. This will ensure all necessary precautions are taken to protect your investment, but also that everything is configured in such a way that the energy output is maximised. Let’s see the steps involved.

9.1 Risk Assessment in Solar Batteries installations

A solar battery installation is usually accompanied by a solar panel installation. A professional installer will account for the specific needs of the property, but will also adhere to building regulations and safety protocols that need to be followed both for your and your system’s safety. After all, let’s not forget that this is electricity we are talking about, and you don’t want to take risks, do you?

9.2 Mounting of Solar Panels and wiring them to the controller, inverter and Solar Batteries

The process starts with mounting the solar panels to the area that has been decided during a survey as the most beneficial in order to take advantage of as much sunlight as possible. After mounting is complete, all panels must be wired together and to the charge controller, the inverter and the solar battery (or batteries) you have bought. This is precision work that follows certain protocols to maximise efficiency and minimise energy losses so that you can make the most of your investment. Once again, a certified professional is recommended as they know what to do and how to do it.

9.3 Cleaning

Believe it or not, yes, solar panels need cleaning every now and then. The reflective surface can gather dust and debris from the environment and this will affect the energy production negatively. If your solar panels are in an area that is easily accessible, this is a job that you can do yourself. If not, then you may need to hire someone who can access hard to reach areas such as the roof of your house. This person will also need to inspect for wear or damage to the connectors, the panels and the wiring.

Solar Batteries - Dirty Solar Panels

Dirty Solar Panels

9.4 Maintenance of your Battery Management System (BMS)

The Battery Management System (BMS) is a circuit that monitors and balances the cells of each battery. Most modern solar batteries are built in such a way that allow you or a professional to monitor their performance and make adjustments if necessary. The main things to look out for are overheating (especially in warm countries) and overcharging or even undercharging that may not be justified. For example, if on a sunny day you usually get 1kW from your panels but you see only 0.5kW instead, it’s time to start troubleshooting. The tool that will provide you with that information is the BMS, so it’s important that it is in good shape and fully operational.

Solar Batteries - A Solar Battery BMS

A Solar Battery BMS

10. Troubleshooting common issues in Solar Batteries operation and performance

As with everything, Solar Batteries may at some point present issues in their operation. Even though technically there aren’t many things that can go wrong with a properly installed and configured renewable energy system, and they are considered to be low maintenance, issues do arise sometimes. Below we discuss the most common ones and how to resolve them.

10.1 A drop in Solar Battery capacity

This is a common issue but not necessarily one that implies a malfunction. As we explained earlier, all batteries degrade over time. This means they gradually lose their ability to store energy, resulting in less energy coming out of them to power the appliances of the house. This degradation is usually slow, but it depends on the battery’s depth of discharge, how frequently the battery is charged and discharged (cycles), and its age. Usually batteries are expected to last at least 5 years, some a lot longer (depending on their chemistry), so if you start seeing a degradation in the first year or so, then something is wrong. If you notice that degradation say 7 years after the batteries were first put to use though, then this is a perfectly normal process and it’s just a sign that your batteries will need to be replaced at some point soon.

10.2 Solar Batteries not charging enough

This can be a result of several factors or a combination of factors. For example, if the weather is not sunny enough, it makes sense that the batteries don’t receive enough energy from your solar panels, and therefore don’t charge in full of as quickly as you expected. But if the weather is nice and sunny, a low charge may be the sign of a problem with your solar panels, the wiring, the connectors or the charge controller. A professional will be able to pinpoint the origin of the problem and advise on the best course of action. An easy thing to do is a visual inspection, starting with the solar panels. Are they clean? Are there any cracks? Are their connectors or wiring loose or damaged? What do the charge controller’s diagnostics show?

10.3 Charged Solar Batteries fail to output power

This is most probably the result of either a faulty connector or a failed inverter. Replacing the connectors is not that difficult, and should be your first port of call when troubleshooting. If the connectors are new or show no apparent damage, then the inverter is either malfunctioning, badly configured, or needs replacing.

Solar Batteries - An array of two Tesla Powerwall 3 Solar Batteries

An array of two Tesla Powerwall 3 Solar Batteries

11. Conclusion

Solar Battery technology has seen significant advancements in the last 10-20 years, and as the world is trying to reach net-zero it’s only bound to see more.

Researchers and engineers have been working on improving the energy density of solar batteries. This means that batteries will be created that will be able to store more energy in smaller and lighter packages. An immediate benefit will be the ability to store more energy in even smaller spaces, which means more households will adopt them.

Innovations in battery materials, such as new cathode and anode materials, have the potential to enhance the efficiency, lifespan, and safety of solar batteries. This will also result in cost reduction, something we are seeing slowly but steadily in the past decade. This is a key focus in the solar energy industry because the main obstacle for many people who understand the benefits of renewable solar energy systems and solar batteries is the high initial investment cost. As technology advances and more players get into the game, competition will eventually make prices drop, and adoption will increase.

One of the most promising technologies we look forward to are Solid-state batteries. By using solid electrolytes instead of liquid electrolytes, their potential to offer higher energy density, faster charging times, and improved safety compared to traditional lithium-ion batteries will be crucial in further adoption, which should be the main goal towards a cleaner environment for everyone.

We are very excited to see what the future of Solar Batteries will bring.