Choosing the Right Size of Solar Power System: A Comprehensive Guide

Whether you are looking to build your solar power system for a home, business, boat, RV, camping, shed, or gazebo, you must choose the right size of solar power system size for your energy needs.

A solar power system is a technology that converts sunlight into electrical energy. It comprises components such as:

• Solar panel(s)
• Solar charge controller
• Solar batteries
• Solar inverter
• Wiring and cables
• Racking and mounting system

These components work together to produce electricity from sunlight.

Importance of choosing the right solar panel system size

Choosing the right size for a solar power system is important for maximizing the benefits of solar energy.

But what does size mean in this context?

The size of a solar power system may refer to the size of solar panels, battery system capacity, or size of solar inverter.

But, despite what you look for when deciding the size, note that the size of one component may directly impact the size of the other component.

For instance:

What size of solar battery, charge controller, and inverter should I use with a 450-watt 12v solar panel?

For a solar charge controller, A 400-watt solar panel may require a 20-amp solar charge controller and nothing less. What is this so?

Generally, a 400-watt solar panel has a current output of 10 amps and an open circuit voltage of 50 volts. Therefore, a charge controller size of 60 volts input and a current rating of at least 20 amps will be needed for a 450-watt solar panel.

For a solar battery, a 100Ah 12V lithium battery requires around 220 watts of solar panels to charge from 50% depth of discharge in 5 peak sun hours with an MPPT charge controller.

Therefore, a 450-watt solar panel can charge a 100Ah 12V lithium battery in less than five peak sun hours.

However, a larger solar panel may be required if the battery is larger or the peak sun hours are less.

For an Inverter: The inverter size should be determined by finding the home’s peak load or maximum wattage.

Assuming a typical home load of 1 kW, a 1.5 kW inverter should be sufficient for a 450-watt solar panel.

Considering this, here are some reasons why choosing the right size is important:

Maximizing benefits

Choosing the right size and capacity for a solar battery system is essential for maximizing the benefits of solar energy.

A system that is too small may need to provide more power, while a system that is too large may be more expensive than necessary.

Efficiency

Regarding solar panels, size is important because it affects their efficiency.

As solar energy technology advances, PV panels have been developed to collect more sunlight and provide more electricity while becoming physically smaller.

The more efficient and small solar panels grow, the more power they can produce with less space, making them more attractive.

Inverter sizing

The size of the inverter is also important in determining the overall electricity production of the solar panel system.

The size of the inverter should be appropriate for the size of the solar array, geography, and site-specific conditions.

An inverter that is too small may not be able to handle the amount of power produced by the solar panels, while an inverter that is too large may be more expensive than necessary.

Energy needs

Determining how many solar panels are needed is an important part of the solar research process.

The solar contractor should size and design the system for the homeowner’s energy needs.

Sizing a solar system can be tricky, especially if installed in a new home, RV, or mountain cabin or if the homeowner needs to know their energy needs.

The Benefits of Solar Power Systems

Here are some of the benefits you may enjoy from a solar power system:

• Renewable source of energy
• Reduced electric bills
• Solar power increases the value of your home
• Solar power system requires low maintenance
• Solar Power reduces your dependence on the grid
• It is energy efficient

In the next section, we’ll delve deeper into how you can evaluate your energy needs to choose the most appropriate size for your solar power system.

Assessing Your Energy Needs

Since you now understand the importance of selecting the right size for your solar power system and the importance of solar power systems, let’s discuss how you can evaluate your energy needs.

A. Assessing Your Current Energy Consumption

You’ll need to assess your current energy consumption to gather sufficient data. Here are some of the steps you can take to determine your energy consumption.

1. Gathering Your Energy Bills

Collect your energy bills for the past year to determine your average energy consumption.

Note the annual kWh you’ve used and the billing amount for each month.

For off-the-grid power consumption, you can determine how much you spend on fuel for your generator to power your appliances. This can give you a rough estimate.

2. Analyzing Your Average Daily Usage

Divide your annual kWh usage by 365 to determine your average daily usage. This will give you an idea of how much energy you use daily.

You can also look at the monthly variance to understand your high and low consumption throughout the year.

What if I don’t have energy bills?

In most off-the-grid lifestyles, one may not have the necessary energy bills that can be used to calculate annual and daily energy consumption.

In such cases, you can list your devices and appliances, including the wattage of each device and appliance.

To determine the peak energy usage, estimate how often you use each appliance and gadget.

A professional energy audit will thoroughly analyze your home’s energy use, including a room-by-room examination of the home and equipment, such as blower doors, infrared cameras, and moisture meters.

Note that you should consider your future energy requirements after assessing your current energy consumption. Will you add another fridge, TV etc.? 

You need to either determine the system size that can cover the future energy needs or set your system so that it will be easier to expand it to cover those needs. 

In other words, the possibility for an upgrade.

Factors to Consider When Choosing the Right Size

Several factors should be considered when determining the appropriate size of a solar power system for your energy needs.

These factors include

Available Roof Space

The available roof space plays a significant role in determining the size of the solar power system you can install.

The more unshaded roof area you have, the larger the system you can accommodate.

However, alternative options, such as ground-mounted systems or solar canopies, are available even with limited roof space.

Daily Energy Consumption

Understanding your average daily energy consumption is crucial for sizing your solar power system.

By analyzing your electricity bills and identifying your peak usage periods, you can estimate the energy you need to generate to meet your needs effectively.

Location and Climate

Your area’s geographical location and climate also impact the sizing of your solar power system.

Areas with higher solar irradiation levels require smaller systems to generate the same amount of energy as areas with lower irradiation levels.

Additionally, climate conditions, such as extreme temperatures, may affect the performance and efficiency of your solar panels.

Budget and Financial Considerations

Your budget and financial considerations play a vital role in choosing the right size of a solar power system.

While larger systems can generate more energy, they come at a higher upfront cost.

It’s essential to balance your energy needs and the investment you’re willing to make.

Solar Panel Sizing

Solar panels are the primary components of a solar power system and are responsible for converting sunlight into electricity.

Sizing your solar panels correctly ensures you generate enough energy to meet your needs.

Here’s how to determine the appropriate solar panel capacity:

1. Calculate your average daily energy consumption in kilowatt-hours (kWh).
2. Consider solar panel efficiency. Higher-efficiency panels generate more electricity per square meter. For the efficiency of each solar panel type, read this post.
3. Determine the solar panel capacity by dividing your average daily energy consumption by the panel efficiency. This calculation gives you an estimate of the number of panels you need.

The most common types of solar panels are:

• Monocrystalline Solar Panels: Efficiency range of 15-25%.
• Polycrystalline Solar Panels: Efficiency range of 13-16%.
• Bifacial Solar Panels:  Efficiency range of 20-30%.
• Thin-Film Solar Panels: Efficiency range of 10-13%.

When selecting solar panels, consider their durability, warranty, and compatibility with your system.

Additionally, look for certifications and reputable manufacturers to ensure the panels meet high-quality standards.

Additionally, look for certifications and reputable manufacturers to ensure the panels meet high-quality standards.

Charge Controller Sizing

A solar charge controller is an important component of a solar power system. It regulates and controls the flow of electric current between the solar panels and the battery bank.

Considering this, you must choose your solar charge controller properly. Here are some steps to follow when sizing a solar charge controller:

1. Start by determining the type of charge controller you need. The two basic types are PWM and MPPT.

Feature	PWM Charge Controller	MPPT Charge Controller
Efficiency	Less efficient than MPPT controllers	More efficient than PWM controllers, up to 30% more power generation
Cost	Cheaper than MPPT controllers	More expensive than PWM controllers
Technology	Older technology	Newer, more advanced technology
Suitable for	Smaller systems (vans, RVs, tiny homes), those living in warmer climates	Larger solar systems with multiple panels or high-voltage panels
Voltage Matching	Solar panels and batteries have to have matching voltages with these controllers.	Can match a battery system with solar panels of higher voltage
Power Output	You cannot charge batteries with higher-voltage solar panels	You can charge batteries with solar panels of higher voltage

1. Determine the maximum output amps from the controller. Add up the total watts of solar panels and divide by either 14.4 for 12-volt systems, 28.8 for 24 volts, or 58.8 for 48-volt battery banks. This will give you maximum output amps from the controller.
2. Size the controller: If you don’t want to waste output in heat, size the controller at around two-thirds of the rated output of the controller. Charge controllers are sized depending on your solar array’s current and the solar system’s voltage. You typically want to make sure you have a charge controller that is large enough to handle the amount of power and current produced by your panels. Charge controllers are typically available in 12, 24, and 48-volt varieties. Amperage ratings can be between one and 60 amps and voltage ratings from six to 60 volts. The rating of the charge controller should be at least 40A.
3. Introduce a safety factor: Multiply the value you have found by 1.25 to account for variable power.
4. Exceed the minimum: It is a good practice to exceed the minimum, as environmental factors can cause surges and spikes.

Solar Battery Sizing

Batteries are essential to off-grid and hybrid solar power systems, storing excess energy for later use.

Proper battery sizing is crucial to ensure enough storage capacity to meet your energy requirements during periods of low or no sunlight.

Here’s how to determine the right battery size:

1. Calculate your average daily energy consumption in kilowatt-hours (kWh).
2. Determine the number of days of autonomy you desire. Autonomy refers to the number of days you want your system to run solely on battery power without relying on sunlight.
3. To determine the required energy storage, multiply your average daily energy consumption by the desired number of autonomy days.
4. Consider the battery’s depth of discharge (DoD) and round-trip efficiency when selecting a battery. DoD refers to the capacity of a battery that can be discharged without causing damage, while round-trip efficiency accounts for energy losses during charging and discharging cycles.

Lithium Nickel Manganese Cobalt Oxide (NMC) and Lithium Iron Phosphate (LFP) are the most popular types of lithium-ion batteries used in solar systems. They are known for their:

• High efficiency,
• Long lifespan,
• Low maintenance

Other types of solar batteries include lead-acid, nickel-cadmium, and flow batteries. Lead-acid batteries have been around for many years and are dependable, but they take longer to charge and have a shorter lifespan than lithium-ion options.

They are also bulkier and heavier. Due to their high cost and toxicity, nickel-cadmium batteries are not commonly used in solar systems.

Choosing batteries from reputable manufacturers offering warranties and sufficient energy storage capacity for your needs is important.

Inverter Sizing

Inverters are responsible for converting the direct current (DC) electricity generated by solar panels into alternating current (AC) electricity used in your home.

Sizing your inverter correctly is essential for optimal system performance.

Here’s how you can determine the appropriate inverter size:

1. The DC rating of your solar panel system. As a general rule of thumb, the size of your inverter should be similar to the DC rating of your solar panel system. For example, if you are installing a 6-kilowatt solar energy system, the chosen inverter should be about 6,000W, give or take a few watts.
2. Geography. Geographical factors are vital in sizing your solar inverter due to their impact on solar energy production. Locations with high temperatures are expected to have a large amount of solar radiation, thus generating more electricity compared to areas with low temperatures.
3. The size of the solar array. The size of the solar array is another factor to consider when sizing a solar inverter. The manufacturers usually indicate the sizing instructions on the product sheet for inverters showing which array capacity they can handle.
4. Specific conditions of the site. Specific site conditions, such as shading or orientation, can also impact the solar inverter size needed.
5. Oversizing calculations. Oversizing calculations always optimize the string inverter size. A PV-to-inverter power ratio of 1.15 to 1.25 is optimal, while 1.2 is considered the industry standard.
6. Under-sizing vs Oversizing. Under-sizing your inverter will mean that the maximum power output of your system will be dictated by the size of your inverter while over-sizing your inverter can lead to higher costs.

When selecting an inverter, consider its efficiency, reliability, and compatibility with your system.

Some inverters offer additional features like data monitoring and grid interaction capabilities.

Wiring and Electrical Components

Proper wiring and electrical components are crucial for your solar power system’s safe and efficient operation.

Following local electrical codes and regulations is important when installing and connecting your system.

Some key considerations are:

1. Use appropriately sized wires to minimize voltage drop and maximize system efficiency.
2. Install disconnect switches and surge protection devices to enhance safety and protect your system from power surges.
3. Incorporate charge controllers to regulate the charging of batteries and prevent overcharging or undercharging.
4. Utilize grounding systems to ensure electrical safety and protect against lightning strikes.

Working with a professional solar installer can help ensure that all wiring and electrical components are installed correctly and meet the necessary safety standards.

Solar Power System Installation

Installing a solar power system requires careful planning and consideration. While some homeowners may opt for a DIY installation, hiring professionals can ensure a safe and efficient setup.

Here are the key steps involved in installing a solar power system:

1. Conduct a site assessment to evaluate the suitability of your location and roof for solar panel installation.
2. Obtain the necessary permits and approvals from local authorities.
3. Design the system layout, including installing solar panels, inverters, and other components.
4. Install solar panels securely on the roof or other mounting structures, following manufacturer guidelines and local regulations.
5. Connect the panels to the inverter and electrical components, ensuring proper wiring and connections.
6. Test the system to verify its functionality and safety.
7. Set up monitoring systems, if available, to track the performance of your solar power system.

Remember to consult local regulations and enlist the help of professionals to ensure a smooth and successful installation process.

Financing Options for Solar Power Systems

When investing in a solar power system, various financing options are available to make it more affordable.

Here are some of the most common financing options:

1. Purchase: Buying a solar power system outright allows you to benefit from long-term cost savings and ownership of the system. It may require a larger upfront investment but can provide a quicker return on investment.
2. Lease: Leasing a solar power system involves renting it from a third-party provider. This option typically requires little to no upfront cost but may result in lower long-term savings than purchasing.
3. Power Purchase Agreement (PPA): With a PPA, a solar energy provider installs and maintains the system on your property, and you purchase the generated electricity at a predetermined rate. This option can provide immediate cost savings without the need for upfront investment.

When considering financing options, assess the financial incentives and tax credits available for solar installations in your region.

Additionally, conduct a cost-benefit analysis to determine the most suitable option for your budget and energy needs.

Personal loans, home equity loans, and HELOCs are the most common types used to finance solar panel systems.

There are also financing partners available through EnergySage, such as  LightStream Financial and GreenBiz.

Solar loans are unsecured personal loans with fixed interest rates and terms from two to seven years.

The best way to finance solar panels is with a loan with the lowest annual percentage rate.

Frequently Asked Questions (FAQs)

Choosing the Right Size of Solar Power System: Final Thought

Choosing the right size of a solar power system is a crucial step in maximizing the benefits of solar energy.

You can select the appropriate capacity for solar panels, batteries, and inverters by considering available roof space, energy consumption, location, and budget.

Remember to work with a professional solar installer to ensure a safe and efficient installation.

Embrace the power of solar energy and take a step towards a sustainable and environmentally friendly future.