The Ultimate Guide to Choosing the Right Solar Panel for Your Roof

Choosing the right solar panels can help you enjoy a sustainable energy future and move towards a greener lifestyle. 

Not only is solar power good for the planet, but it can also be good for your pocketbook. Traditional on-grid electricity is increasingly expensive and unreliable. Over time the upfront costs of a PV solar array can be more than defrayed by reduced utility bills. 

But not every solar panel system will suit your specific needs. Read this guide to find out how to:

• Explore the different types of photovoltaic panels;
• Estimate the associated costs;
• Determine which solar panel is right for your roof.

How to Choose a Solar Panel

1. Understanding the Types of Solar Panels

There are three main types of photovoltaic panels: monocrystalline, polycrystalline, and thin film. Each panel has pros and cons regarding efficiency, cost, and form factor. 

• Monocrystalline panels consist of a single silicon crystal structure. They have a dark, sleek appearance and boast the highest efficiency of the three panel types. They’re more expensive than polycrystalline panels, but they’ll produce more power in less space. 
• Polycrystalline panels consist of multiple silicon crystal structures. They have a speckled blue appearance. They’re less efficient than monocrystalline panels but are usually cheaper as well. 
• Thin-film panels are lightweight and flexible, allowing them to adhere to curved and irregular surfaces. They’re the least efficient, but their unique construction makes them suitable for maximising available surface area.

2. Evaluating Solar Panel Efficiency

The conversion efficiency measures how effectively a panel converts sunlight into electricity. Higher efficiency requires less surface area for energy production, making it particularly valuable when space is limited. 

Factors that impact efficiency include temperature, shading, and orientation. Solar panels will perform better at lower temperatures and when angled towards the sun. Any partial shading across a panel — such as from overhanging tree branches — can drastically reduce the power output. 

Proper ventilation, minimising shading, and optimising tilt angles can enhance conversion efficiency, ensuring optimal performance and return on investment.

3. Determining the Size of Your Home Solar System

To determine the size of your home solar system, you first need to calculate your daily energy usage. Divide your electricity bill’s total kWh energy usage by the number of days it covers to find your daily energy usage.

Alternatively, suppose you’re primarily using your solar power system for backup power or to reduce your electricity bills by powering selected appliances. In that case, you can use the step-by-step process below to determine how much electricity you need.

1. Identify the wattage requirements of your appliances. Survey the starting and running wattage requirements of the appliances and devices you plan to plug into the generator. You can usually find the wattage requirements labelled on the appliance, but we’ve also compiled the starting and running watts of typical household appliances in the table below. 
2. Convert volts/amps to watts. If your appliance’s power requirements are in volts or amps, you can calculate an appliance’s running watts with this equation: 

Volts (V) x Amps (A) = ​​Watts (W)  

3. Count the running watts of your appliances. Add up the running watts of the appliances you plan to use — does the total exceed the running watts listed on your generator? If so, you should consider buying a generator with more output capacity.
4. Factor in starting watt requirements. Identify the appliance with the highest starting wattage. Add that appliance’s starting wattage to the running wattage total.
5. Calculate the sum. That final number is the total starting watts you need from your generator.  As discussed above, to avoid overloading your generator, do not exceed its starting watts rating.
   

Starting and Running Watts of Typical Household Appliances 

Next, look up your area’s average peak sun hours. A simple online search can provide you with this information. 

Then, figure out the rated power of your PV panels. Most residential rooftop solar panels will have a power rating of 400 watts. 

It is crucial to remember that the rated power of a solar panel indicates the maximum amount of electricity it can generate under ideal conditions. Depending on numerous environmental factors such as cloud cover and temperature.

Under real-world conditions, solar panels typically generate between 25% – 90% of their rated power wattage during daylight hours.

Finally, we can do a few simple calculations to determine how many solar panels it will take to power your house. 

Divide your daily energy usage by the average peak sun hours to calculate the kW output you require from your system: 

Daily energy use (kWh) / peak sun hours (h) = energy output required (kW)

Convert kW into watts by multiplying by 1000: 

Energy output required (kW) x 1000 = Energy output required (W)

Then, divide that required wattage output by the estimated output of your panels. For most locations, it should be safe to assume that your panels will output at least 75% of their rated power on average should be safe. For a 400W panel, that means you should estimate 300W of electricity production per daylight hour. 

Energy output required (W) / PV estimated output (W) = Number of panels needed

4. Calculating Solar Panel Costs for Your Roof

A complete residential array will come with upfront costs in the thousands. However, the return on investment (ROI) usually exceeds these initial costs. 

You determined how many PV panels your home might require in the previous step. The panels are the highest cost in a solar system. Factors that impact the cost include construction quality, power rating, conversion efficiency, and type.

However, the savings you experience will pay you back over the system’s lifetime, usually around 25 to 30 years. Here is a simple ROI calculation: 

Lifetime Utility Costs – Lifetime Cost of Solar = Solar System ROI

If your expected utility costs over your system’s lifetime exceed your system’s price, you’ll receive a return on your investment. Often a substantial one! 

5. Comparing the Price of Different House Solar Panel Systems

There are a few different payment schemes for purchasing solar panel systems, each with its pros and cons: 

• Cash Purchase: Paying cash upfront will provide the most significant long-term savings. You’ll own the system from the get-go, and you can avoid interest payments. Purchasing a PV system outright will also give you access to rebates, tax credits, and other incentives that leasing can’t offer. 
• Financing: As with other large purchases, financing your system can be enticing. A loan lets you pay for your system over several months or years, lowering your upfront costs. However, the interest on the loan will reduce the savings you could experience with a cash purchase. 
• Leasing: Some companies allow you to lease a solar system. They own and maintain the system, but you enjoy immediate savings on your electric bill. Leasing a system will have few upfront costs, but you won’t be eligible for tax credits and other incentives. Your long-term savings will also be lower than with cash purchases or financing. 

There are many factors to consider when comparing the costs of different systems. Consider these factors to determine the best value for your budget: 

• System Size
• Equipment Quality
• Incentives and Rebates
• Warranty
• Installation Costs (DIY vs Professional) 

6.  Understanding the Quality of Different Roof Solar Panels

The quality of solar panels is usually measured by their efficiency. Manufacturers determine PV efficiency by testing the photovoltaics in Standard Testing Conditions, which specify a room temperature of 25° Celsius (77°F) and 1000W/m2 irradiance.

Monocrystalline panels have efficiency ratings above 20%, while polycrystalline panels are around 15%. Even with the cost savings of polycrystalline panels, the higher efficiency of monocrystalline panels makes them worth it over the long term.

7. The Importance of Solar Panel Temperature Coefficient

The PV temperature coefficient indicates how temperature change affects a panel’s efficiency. It is expressed as a percentage per degree Celsius and represents the decrease in power output for every degree above a reference temperature (usually 25°C). For example, a temperature coefficient of -0.3% / °C would mean that the panel’s output decreases by 0.3% for every degree above 25°C.

As photovoltaics heat up, their efficiency decreases due to increased electrical resistance within the cells. A lower temperature coefficient means the panel’s performance is less susceptible to temperature increases, making it a desirable characteristic when comparing different panels. 

8. Durability of Home Solar Panels

Solar panels generally last around 25 to 30 years before diminishing in output capacity by about 20%. Any panel you purchase should be resistant to harsh weather — an IP68 waterproof rating indicates durability. Solar panels rarely require maintenance, as there are no moving parts. 

It is a best practice to keep your panels free of dirt and debris. Inspect and clean them at least every six months with a soft, lint-free cloth and gentle soap. Never clean PV panels with harsh chemicals.

9. Solar Panel Installation on a Home Roof

Rigid solar panels are permanent installations mounted on rooftops. They’re the best solution for residential systems where it would be impractical to repeatedly set up and take down 10-12 portable PV panels.

If you wish to forego installation costs, you can also learn how to install solar panels on a home roof. 

EcoFlow’s Portable Solar Panels are an alternative to rigid systems that don’t require installation. They’re best suited to smaller builds or situations like camping, hiking, etc. They provide the same power output as a rigid panel but fold up for easy transport and setup. 

Conclusion

Once you know what to look for, choosing the right solar panel for your roof is straightforward. Most homeowners will appreciate the efficiency and cost-effectiveness of monocrystalline panels, and with EcoFlow, you have your choice of rigid, portable, and flexible designs. 

Frequently Asked Questions