How to Select and Size an Inverter and Batteries for Your Solar System
An inverter is a device that converts direct current (DC) from solar panels or batteries into alternating current (AC) that can be used by appliances or fed into the grid. Choosing the right inverter for your solar system is an important decision that affects the performance, reliability and cost of your system. In this blog post, we will explain the different types of inverters, their pros and cons, and the features that you should look for when selecting an inverter. We will also cover how to size an inverter and how to choose the appropriate batteries for your system and list the popular inverters in the South African market.
Types of Inverters
There are two main types of inverters: string inverters and microinverters. String inverters are connected to a series of solar panels and convert the combined DC output into AC. Microinverters are attached to each individual solar panel and convert the DC output of each panel into AC. Both types of inverters have their advantages and disadvantages, depending on your system size, layout, shading, and budget.
There are four main categories of inverter that are commonly used in solar systems: hybrid, off-grid, grid-tied and self-consumption. Each type has its own advantages and disadvantages depending on your needs and preferences.
Hybrid Inverters
A hybrid inverter is a combination of an off-grid and a grid-tied inverter. It can operate in both modes, depending on the availability of grid power and the state of charge of the batteries. A hybrid inverter can charge the batteries from the grid when there is excess solar power or when the grid power is cheaper than the battery power. It can also discharge the batteries to power the loads or feed into the grid when there is insufficient solar power or when the grid power is more expensive than the battery power. A hybrid inverter can also provide backup power to the loads in case of a grid outage.
The main advantages of a hybrid inverter are:
- It maximizes the self-consumption of solar power by storing excess energy in batteries and using it when needed.
- It reduces the dependency on the grid and lowers the electricity bills by optimizing the use of grid power and battery power.
- It provides backup power to the loads in case of a grid outage, enhancing the reliability and security of the system.
- It allows for flexible system design and expansion by integrating different sources of energy such as solar panels, wind turbines, generators, etc.
The main disadvantages of a hybrid inverter are:
- It is more expensive than a grid-tied or an off-grid inverter due to its complexity and additional components such as batteries, charge controllers, etc.
- It requires more maintenance and monitoring than a grid-tied or an off-grid inverter due to its multiple functions and modes of operation.
- It may have lower efficiency than a grid-tied or an off-grid inverter due to its multiple conversions between DC and AC.
Off-Grid Inverters
An off-grid inverter is a standalone device that converts DC from solar panels or batteries into AC that can be used by appliances. An off-grid inverter does not connect to the grid and relies entirely on solar power and batteries to supply electricity to the loads. An off-grid inverter usually works with a charge controller that regulates the charging and discharging of the batteries from the solar panels.
The main advantages of an off-grid inverter are:
- It is independent from the grid and does not require any grid connection or approval,
- It is suitable for remote areas where grid power is unavailable or unreliable,
- It is simple and easy to install and operate,
The main disadvantages of an off-grid inverter are:
- It requires a large battery bank to store enough energy for periods of low solar generation or high load demand.
- It may waste excess solar power if the batteries are fully charged and there are no loads to consume it.
- It may not be able to power some appliances that require high surge currents or stable voltages.
Grid-Tied Inverters
Grid-tied inverters are devices that convert direct current (DC) from solar panels or other renewable energy sources into alternating current (AC) that can be fed into the grid. They are also known as grid-interactive or grid-connected inverters. Grid-tied inverters have several advantages and disadvantages that should be considered before installing them. Here are some of the pros and cons of grid-tied inverters:
Pros:
- Grid-tied inverters can reduce or eliminate your electricity bills by selling excess power to the utility company. You can also take advantage of net metering programs that pay you for the electricity you generate at a higher rate than what you pay for the electricity you consume.
- Grid-tied inverters can provide backup power in case of a grid outage. Some grid-tied inverters have a feature called islanding, which allows them to disconnect from the grid and operate as a standalone system when the grid is down. This way, you can still use your solar power during blackouts.
- Grid-tied inverters are easy to install and maintain. They do not require batteries or charge controllers, which can be costly and complicated to manage. They also have fewer components and wiring than off-grid systems, which reduces the risk of fire or electrocution.
- Grid-tied inverters can improve the efficiency and performance of your solar system. They can match the voltage and frequency of the grid, which reduces losses and harmonics. They can also optimize the power output of your solar panels by using maximum power point tracking (MPPT) technology.
Cons:
- Grid-tied inverters depend on the grid for their operation. If the grid is down or unstable, your grid-tied inverter will not work or may shut down to protect itself and the grid. This means that you cannot use your solar power when you need it most, unless you have a battery backup system or a generator.
- Grid-tied inverters may not be compatible with all types of solar panels or grid standards. You need to make sure that your grid-tied inverter matches the specifications and requirements of your solar panels and your utility company. You may also need to obtain permits and approvals from your local authorities and utility company before installing a grid-tied inverter.
- Grid-tied inverters may be subject to regulations and limitations by your utility company or government. Depending on where you live, you may face restrictions on how much power you can export to the grid, how much you can get paid for it, or how long you can participate in net metering programs. You may also have to pay fees or taxes for using a grid-tied inverter.
Self Consumption Inverters
A self-consumption inverter is a device that converts direct current (DC) from solar panels or other renewable energy sources into alternating current (AC) that can be used by appliances or fed into the grid. A self-consumption inverter allows individuals or businesses to consume their own generated electricity, reducing their dependence on the grid and their electricity bills. In this blog post, we will discuss the pros and cons of a self-consumption inverter.
Pros of a self-consumption inverter:
- It can improve the self-consumption ratio up to 80%, meaning that most of the electricity generated by the solar panels or other sources can be used on-site, rather than exported to the grid.
- It can reduce the electricity bill by avoiding paying for grid electricity, especially during peak hours when the prices are higher. It can also generate income by selling excess electricity to the grid or participating in demand response programs.
- It can increase the energy efficiency and environmental benefits of renewable energy sources, by avoiding transmission and distribution losses and reducing greenhouse gas emissions.
- It can increase the energy security and resilience of the consumers, by providing backup power in case of grid outages or disruptions.
Cons of a self-consumption inverter:
- It can be expensive to install and maintain, depending on the size, quality and features of the inverter. It may also require additional equipment such as batteries, meters and controllers.
- It can be subject to technical issues such as power quality problems, voltage fluctuations and harmonics, which can affect the performance and lifespan of the inverter and the appliances connected to it.
- It can be subject to regulatory and legal barriers, such as grid connection requirements, permits, fees and taxes, which can vary depending on the location and jurisdiction of the consumers.
- It can be affected by external factors such as weather conditions, seasonal variations and demand patterns, which can influence the availability and reliability of the renewable energy sources.
Selecting the size of your inverter
The size of your inverter is measured in watts (W) or kilowatts (kW), which indicate the maximum amount of AC power that the inverter can deliver at any given time. The size of your inverter should match the size of your solar panel array, which is also measured in watts or kilowatts. For example, if you have a 5 kW solar panel array, you should have a 5 kW inverter. However, there are some factors that may affect this rule of thumb, such as:
- Oversizing or undersizing your inverter: Some people may choose to oversize or undersize their inverter relative to their solar panel array, depending on their needs and preferences. Oversizing your inverter means having an inverter that can deliver more power than your solar panel array can produce. This may be useful if you plan to expand your solar system in the future or if you want to have more flexibility in using power from the grid when your solar production is low. However, oversizing your inverter may also increase your upfront costs and reduce your efficiency. Undersizing your inverter means having an inverter that can deliver less power than your solar panel array can produce. This may be useful if you want to save money on your initial investment or if you have a high feed-in tariff for exporting excess solar power to the grid. However, undersizing your inverter may also limit your power usage and cause some power loss.
- Power factor and efficiency: The power factor and efficiency of your inverter affect how much AC power you can actually use from your solar system. The power factor is the ratio of real power (the power that does work) to apparent power (the power that is supplied). A low power factor means that some of the apparent power is wasted as reactive power (the power that causes voltage fluctuations). The efficiency is the ratio of output power to input power. A low efficiency means that some of the input power is lost as heat or noise. Both factors depend on the quality and design of your inverter, as well as the load characteristics and voltage conditions of your grid. A high-quality inverter should have a high power factor and efficiency, which means that you can use more of the AC power that it delivers.
- Peak demand and surge capacity: The peak demand and surge capacity of your inverter affect how well it can handle sudden spikes or drops in your power consumption. The peak demand is the maximum amount of power that you use at any given time, which may vary depending on the time of day, season, weather, and number and type of appliances and devices that you use. The surge capacity is the maximum amount of extra power that your inverter can provide for a short period of time, usually a few seconds or minutes, to start up or run appliances and devices that have high startup or running currents, such as air conditioners, refrigerators, pumps, motors, etc. A good-quality inverter should have a high surge capacity, which means that it can handle these spikes without tripping or shutting down.
To sum up, selecting the size of your inverter is not a simple matter of matching it with your solar panel array. You need to consider various factors that may affect your power usage and production, such as oversizing or undersizing your inverter, power factor and efficiency, peak demand and surge capacity, etc. You also need to compare different types and models of inverters based on their features, performance, reliability, warranty, price, etc. You may consult a professional solar installer or an online calculator to help you choose the best inverter for your solar system.
Choosing and sizing a battery for your inverter
Inverters are useful for backup power, off-grid living, camping, RVs, and more. However, choosing and sizing a battery for your inverter can be a challenging task. Here are some tips to help you make the right decision.
The first thing you need to consider is the power rating of your inverter. This is the maximum amount of AC power that the inverter can deliver at any given time. It is usually expressed in watts (W) or kilowatts (kW). For example, a 1000 W inverter can power up to 1000 W of AC load at once. The power rating of your inverter determines how much battery capacity you need to run it.
The second thing you need to consider is the energy rating of your battery. This is the amount of energy that the battery can store and deliver over time. It is usually expressed in watt-hours (Wh) or kilowatt-hours (kWh). For example, a 12 V 100 Ah battery can store and deliver up to 1200 Wh of energy. The energy rating of your battery determines how long you can run your inverter before the battery runs out.
The third thing you need to consider is the depth of discharge (DoD) of your battery. This is the percentage of the battery’s energy that you can use before it needs to be recharged. For example, a 50% DoD means that you can use half of the battery’s energy before recharging it. The DoD of your battery affects its lifespan and performance. Generally, the lower the DoD, the longer the battery will last and the better it will perform.
The fourth thing you need to consider is the efficiency of your inverter and your battery. This is the ratio of the output power or energy to the input power or energy. For example, an 80% efficient inverter means that it converts 80% of the DC power from the battery into AC power for the load, and loses 20% as heat and other losses. The efficiency of your inverter and your battery affects how much power or energy you actually get from them.
To choose and size a battery for your inverter, you need to do some calculations based on these factors. Here is a simple formula to estimate the minimum battery capacity you need:
Battery capacity (Wh) = Inverter power rating (W) x Run time (h) / Inverter efficiency (%) / Battery DoD (%)
For example, if you have a 1000 W inverter that you want to run for 4 hours at 80% efficiency and 50% DoD, you need a battery with at least:
Battery capacity (Wh) = 1000 W x 4 h / 0.8 / 0.5 = 10,000 Wh
This means that you need a battery with at least 10 kWh of energy rating. You can choose any voltage and amp-hour combination that gives you this rating. For example, you can use a single 48 V 208 Ah battery, or four 12 V 208 Ah batteries in series, or eight 6 V 208 Ah batteries in series-parallel.
However, this formula is only an estimate and does not account for other factors such as temperature, aging, load variations, etc. Therefore, it is advisable to add some safety margin to your calculation and choose a slightly larger battery than what you need. For example, you can choose a 12 kWh battery instead of a 10 kWh one.
Choosing and sizing a battery for your inverter is not an exact science, but rather an art that requires some trial and error and experience. However, by following these tips and using this formula as a guide, you can make an informed decision that suits your needs and budget.
Popular Small Capacity Inverters
If you are looking for a small capacity inverter to power your home appliances or electronics in South Africa, you might be overwhelmed by the number of options available on the market. How do you choose the best one for your needs and budget? We review some of the most popular small capacity inverters in the South African market and compare their features, pros and cons.
What is a small capacity inverter?
A small capacity inverter is one that has a power output of less than 2000 watts, which is enough to run devices such as laptops, TVs, fans, lights, fridges, etc.
Why do you need a small capacity inverter?
A small capacity inverter can be useful for several reasons. For example, you might want to have a backup power source in case of load shedding or power outages. You might also want to reduce your electricity bill by using solar energy or other renewable sources. Or you might want to have more flexibility and mobility by being able to use your devices anywhere without depending on the grid.
What are some of the popular small capacity inverters in the South African market?
Based on our research and online reviews, here are some of the popular small capacity inverters in the South African market:
– KODAK Home Inverter: This is a modified sine wave inverter that has a power output of 1000 watts and a peak power of 2000 watts. It has a built-in solar charger that can charge your battery from a solar panel. It also has an LCD display that shows the battery level, input voltage, output voltage, load level, etc. It is compatible with most appliances and electronics, except for sensitive ones such as medical equipment or audio systems.
– KRIEGER 1100 Watt 12V Power Inverter: This is a pure sine wave inverter that has a power output of 1100 watts and a peak power of 2200 watts. It has a heavy-duty casing that protects it from overheating, short circuits, overloads, etc. It also has an LCD display that shows the battery level, input voltage, output voltage, frequency, etc. It is compatible with all appliances and electronics, including sensitive ones such as medical equipment or audio systems.
– Builders Inverters: These are modified sine wave inverters that have different power outputs ranging from 300 watts to 1500 watts. They have a simple design that does not have any display or solar charger. They are compatible with most appliances and electronics, except for sensitive ones such as medical equipment or audio systems.
If you are looking for a reliable and efficient way to power your home with renewable energy, you might want to consider investing in a larger inverter.
We have compiled a list of some of the most popular and best inverters in the South African market. Here are our top picks:
1. KODAK Home Inverter
The KODAK Home Inverter is one of the most affordable and versatile inverters on the market. It is based on a tried and tested Voltronic system that offers high efficiency and reliability. It has a built-in MPPT solar charger that can handle up to 4500W of solar power. It also has a fast power source switching feature that can automatically switch between grid and battery power in less than 20 milliseconds. It has a user-friendly LCD display that shows the status and settings of the inverter. It also has a low noise design that does not require a fan. The KODAK Home Inverter comes with a 2-year warranty and can be easily installed by an electrician.
2. Growatt SPF 5000TL HVM-WPV
The Growatt SPF 5000TL HVM-WPV is a high-performance hybrid inverter that can work with both grid and off-grid systems. It has a dual MPPT solar charger that can handle up to 6000W of solar power. It also has a built-in battery management system that can protect and extend the life of your batteries. It has a smart load control feature that can automatically adjust the output power according to the load demand. It has a remote monitoring function that allows you to monitor and control the inverter via Wi-Fi or GPRS. It also has a parallel operation function that allows you to connect up to 6 inverters together for more power. The Growatt SPF 5000TL HVM-WPV comes with a 5-year warranty and can be installed by an electrician.
3. Victron MultiPlus-II GX
The Victron MultiPlus-II GX is a premium hybrid inverter that offers advanced features and functionality. It has a powerful AC output that can deliver up to 5000VA of continuous power and up to 10000VA of peak power. It also has a high-quality MPPT solar charger that can handle up to 4400W of solar power. It has a unique PowerAssist feature that can supplement the grid or generator power with battery power when needed. It also has a built-in GX device that provides system monitoring and control via the VictronConnect app or the online portal. It also supports various communication protocols such as CAN-bus, VE.Direct, VE.Bus, USB, RS485, and RS232. The Victron MultiPlus-II GX comes with a 5-year warranty and requires professional installation.
What about mecer inverters you might ask? A Mecer inverter is actually a rebranded version of the Voltronics Power Axpert MKS series of inverters – Just like the Kodak and many other brands of inverter sold in South Africa. Voltronics Power is a Taiwanese company that specializes in power electronics and renewable energy products. They manufacture the Axpert MKS inverters, which are hybrid off-grid inverters that can work with solar panels, batteries, and grid power. We will soon post a full article on the various mecer models.
These are some of the best inverters in South Africa that you can choose from depending on your budget and requirements. However, before you buy any inverter, make sure you do your research and compare different models and brands. You should also consult an expert or a qualified electrician for advice and installation.
Installing a solar system involves a lot more than simply choosing an inverter and battery. Roof integrity inspections need to be carried out, to determine the load baring capacity – so that the roof doesn’t collapse under the weight for example, electricity consumption readings and more need to be carried out – we invite you to fill out the free assessment form on any of our sites and a professional consultant will attend and advise you.
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