For this week’s entry in the Solar Basics series, we’re revisiting the topic of efficiency. Everyone spanning installers, manufacturers, online commenters and industry experts will stress that efficiency is one of the most important drivers in the solar purchase process. But few resources provide a clear explanation of what efficiency is, how efficiency is calculated and what factors influence efficiency. Today we’ll try and clear up the confusion.

For starters, here’s an informative interview with SunPower Founder and President Emeritus Dick Swanson in which he explains solar panel efficiency and how it benefits homeowners:

Dr. Swanson touches on two key areas that influence the efficiency of solar power systems. First is the rate at which the solar panels convert the energy in sunlight into energy that will power your home. This is basic efficiency. To use a concept that most consumers are familiar with, it’s analogous to fuel efficiency in a vehicle, or that rate at which fuel converts into miles traveled. Just like with a car, a solar panel with high efficiency levels is more favorable (although sunlight is free while gas prices are volatile!).

Second are the barriers to efficiency that residents experience due to the physical location and setup of their homes. Key among these barriers is usable roof space. Certain roof areas might be unsuitable for solar panels due to their size, the direction they face and the ability of the roof to support panels. Sources of shade, especially trees, can also affect usable roof space.

When homeowners compute all these factors, they’re left with a specific tract of their roof that is suitable for solar. In many cases, homeowners want even fewer panels than possible due to cost or aesthetic reasons.  In making the solar purchase decision, it’s in the best interest of any owner to ensure that they can deliver the most energy per square foot of solar panels installed. For space-constrained owners, this ensures they can achieve maximum output. For owners worried about aesthetics, they can generate the same amount of power in a smaller amount of space. Taking into account reliability factors from our last Solar Basics post, highly-efficient and reliable solar power systems allow homeowners to generate the most electricity over the lifetime of their system.

At SunPower, we aim for transparency. On our website, you can find listings of our residential panel offerings and how their efficiency levels stack up against the competition.  Here’s a video detailing how SunPower’s solar power systems are the most efficient in the world:

If you have any additional questions about solar panel efficiency or the efficiency of SunPower products, please post them to our Facebook page or leave them below.

For today’s installment of Solar Basics, we’re going to discuss the importance of system reliability. SunPower solar technology delivers the highest reliability in the industry, so our dealers and salespeople talk a lot about reliability with prospective customers. But for customers who are comparing many different manufacturers at many different price points, they want to know how to measure reliability and why it matters. Those are very fair questions. Here’s one video from SunPower dealer Independent Power Systems of Boulder, CO, which demonstrates one type of reliability:

SUNPOWER HAILSTORM VIDEO:

Solar system reliability is best summed up by three metrics:

1.    The functional lifetime of the panels - All dealers should share the functional lifetime of the panels. This is the number of years the panels are expected to produce power (as set by the manufacturer).

2.     How well the panels perform over their lifetime - Just like a computer processor or a rechargeable battery, solar panel production degrades over time. Some panels maintain higher levels of production over the course of their lifetime.

3.     Energy production continuity - Since solar panels need to face the sun, they are subject to the elements. Over a 25-year lifetime, the panels are exposed to a lot of rainstorms, hailstorms, snowstorms and even the occasional hurricane. All of these factors represent risks that could knock a panel offline. All panels differ on how well they can handle extreme weather and maintain consistent uptime. Be sure to ask your dealer for more details.

Reliability is important when you take into consideration the total cost of ownership over the lifetime of your panels. You are not receiving the full value of your investment whenever your panels aren’t functioning properly. A standard 25-year warranty may not cover you for everything. In addition, imagine having to go through the hassles of dealing with the company to replace the panels and the loss of energy production - and, what if this happened every two years or less? The losses can add up quickly…

To make sure you are investing in a reliable solar energy system, we’d recommend you to get answers to the following questions before you buy:

1.      How much experience does the company have installing and manufacturing solar panels?
2.      How extensively do they test their panels?
3.      What certifications do they have? Do they settle for the industry standard or go beyond it?
4.      How much of the design and manufacturing process does the company control

At SunPower, we take reliability very seriously. Check out this video detailing how we build and test our solar panels to provide the highest level of reliability in the industry:

Today on the blog, we're unveiling a new series of ongoing posts called 'Solar Basics'. These posts are intended to answer frequent questions we receive about solar power, ranging from how solar works to some tips for finding the right solar solution for you. If you have any questions you’d like answered, please post them to our Facebook page or leave them in the blog comments for any Solar Basics posting.

At our recent dealer conference, one of our dealers said he gets a lot of customer questions about the terminology associated with the power and electricity output of SunPower solar systems. Specifically, customers are confused about when to use the term 'kilowatt' and when to use ‘kilowatt-hour’ (and what both terms even mean). So here’s a simple explanation you can use when talking with a potential dealer or explaining your system’s output.

Kilowatt (kW) is a measure of power. It’s important to understand that power is a rate statistic that measures the flow of energy conversion within a system (and not the energy itself). When describing a solar installation, kilowatts provide a measure of system capacity. For instance, a 10 kW system acting at full capacity will have 10 kW of energy flowing through at any singular moment.

Kilowatt-hour (kWh) is a measure of electricity. Unlike kilowatts, kilowatt-hour is not a rate statistic and is cumulative. In fact, kilowatt-hours represent the amount of power (in kilowatts) used over a period of time (hours).

One useful example is to think of a stomach, which is a kind of engine that we all have within our bodies. The stomach gets fuel in the form of food, which uses food energy (otherwise known as calories) to power the body. Imagine that you have a completely full stomach beginning the process of digestion. At full capacity, the stomach will digest food and power the body at a specific rate (say 120 calories per hour - a rate statistic similar to kilowatts). Over three hours, your somewhat-less-full stomach will have produced 360 calories of energy (a counting statistic similar to kilowatt-hour). That's enough to power an hour of moderate exercise, so there's a good excuse to burn those calories.

Now back to solar. Let’s say you have a guest over who wants to know how much energy you're producing with your SunPower rooftop installation. You have a 'perfect' 10 kW AC power system that includes all system and module level losses, meaning that at peak production the system is producing exactly 10 kW of power. From 10 am to 4 pm, your system is running at full capacity (a perfect solar day!) with peak sun hours of 5.8 hours. And thanks to SunPower’s market-leading panel efficiency, less roof space is required to capture the 10 kW system output and feed it into your home. To compute the energy output of those six hours, follow this simple calculation:

10 kW AC x 5.8 peak sun hours = 50 kWh from 10am to 4pm

That’s a lot of energy! We hope this helps clear up any confusion around kilowatts and kilowatt-hours. And if you’re a SunPower customer, be sure to check out our in-home monitoring tool to get up-to-date readings of how many kilowatt-hours your system is producing each day.

If you have any further questions or comments, please post them to our Facebook page or leave them below.

Today on the blog, we're unveiling a new series of ongoing posts called 'Solar Basics'. These posts are intended to answer frequent questions we receive about solar power, ranging from how solar works to some tips for finding the right solar solution for you. If you have any questions you’d like answered, please post them to our Facebook page or leave them in the blog comments for any Solar Basics posting.

Kilowatt (kW) is a measure of power. It’s important to understand that power is a rate statistic that measures the flow of energy conversion within a system (and not the energy itself). When describing a solar installation, kilowatts provide a measure of system capacity. For instance, a 10 kW system acting at full capacity will have 10 kW of energy flowing through at any singular moment.

Kilowatt-hour (kWh) is a measure of electricity. Unlike kilowatts, kilowatt-hour is not a rate statistic and is cumulative. In fact, kilowatt-hours represent the amount of power (in kilowatts) used over a period of time (hours).

Now back to solar. Let’s say you have a guest over who wants to know how much energy you're producing with your SunPower rooftop installation. You have a 'perfect' 10 kW AC power system that includes all system and module level losses, meaning that at peak production the system is producing exactly 10 kW of power. From 10 am to 4 pm, your system is running at full capacity (a perfect solar day!) with peak sun hours of 5.8 hours. And thanks to SunPower’s market-leading panel efficiency, less roof space is required to capture the 10 kW system output and feed it into your home. To compute the energy output of those six hours, follow this simple calculation:

10 kW AC x 5.8 peak sun hours = 50 kWh from 10am to 4pm

That’s a lot of energy! We hope this helps clear up any confusion around kilowatts and kilowatt-hours. And if you’re a SunPower customer, be sure to check out our in-home monitoring tool to get up-to-date readings of how many kilowatt-hours your system is producing each day.

If you have any further questions or comments, please post them to our Facebook page or leave them below.