I got bid from 2 different installers. One was SunPower panels; the other Canadian Solar. The SunPower bid (for a 5.2 kw DC system) was $21,000 and the Canadian Solar bid was $14,000 - why so far apart?

Great question. There could be many explanations why there is such a gap in the price. Generally, SunPower’s superior efficiency allows for it/ necessitates that it price its solar panels higher. (They have to pay for the best engineers to get the best efficiency, right?) Each installer may be giving you the best deal he can with both brands of panels. What you should check on both proposals is not the DC system size (in this case 5.2 kw DC), but the kilowatt-hours output. Ask your installer(s) how much energy (in kwh) each system expects to produce in the first year.

Then, divide the total cost of the system ($21,000, or $14,000) by the amount of energy produced. This will tell you how much money per kwh you’ll be paying. If money matters (which to most people it does), then choose the solar system with the best VALUE!

Another visitor asked:

Should I be looking for the panel that has the highest efficiency or for the panel that produces electricity at the lowest rate?

If space is a concern, meaning that you have very limited space and want to produce as much energy as possible, then look for the highest efficiency on the Top 40 Most Efficient Solar Panels chart. However, most people will consider price as an important factor. Therefore, for most people, I recommend choosing the panel that produces the most electricity (kwh) at the lowest cost.

It depends what is most important to you. If saving space is important (rarely the case), then choose the panels that have a smaller area. If saving money, while maximizing output (energy production) is important (usually the case), then choose the solar pv system with the best value.

Related Articles:

• Five Questions You Should Ask Before Installing Solar
• Five Financial Reasons to Go Solar Now
• Solar Panel Comparison Chart

Leave comments below.

1. Which panels should I choose? - Solar Panel Comparison Chart
2. What size solar system do I need? - Calculate your solar array size
3. How many panels do I need? - Calculate the number of solar panels
4. How much will it cost to install? - Calculate the cost of going solar
5. How much are the rebates? - Calculate California rebates

How Solar Works!

Simple diagram of how solar works

1. Solar panels collect the Sun’s energy and convert it into direct current (DC) electricity. The number of panels you need is determined by your electricity needs.
2. An inverter converts the electricity from DC to alternating current (AC) which is the typical type of electricity used in homes.
3. A bi-directional electric meter displays net power usage. When the solar system generates more electricity than you use, your meter spins backwards. When it generates some electricity but less than your are using, it spins forward, but more slowly.
4. You now produce your own electricity to be used throughout your home. Since there are no moving parts, your solar system is silent and virtually maintenance-free.
5. All excess electricity generated is, in effect, stored in the utility grid through the power lines for future use.

Solar Benefits!

• Reduce Your Electricity Bill
• Increase Your Property Value 10-15%
• Be Energy Independent
• Reduce Your Carbon Footprint
• Earn a High Return on Your Investment (ROI)
• Protect Your Children’s Future

Solar Basics from Other Sites

• Solar4Power - Learn the essential basics of using solar power so you can understand your solar PV project.
• Is My Home Right for Solar? - A good summary of factors that affect your solar potential.
• SolarPowerForum - Ask questions, browse explanations, and communicate with others involved with going solar.

• kWh/year = Average Kilowatt Hours of electricity that you use in a typical year.
• Your bill may tell you your kWh/month. If your bill is ~$100/month, you might use ~1,000 kWh/month. If your bill is ~$200, maybe closer to 1,800 kWh/month.

Step 2: Look at the US Solar Map below to get the number of hours per day the Sun shines on your house.



Step 3: What percent of your total electricity bill do you want to come from the Sun?

• If your budget is strong, 75- 100% is a good bet, but just realize that you’re still “on grid” which means you’ll likely still use the utilities electricity a little bit.
• If your budget is limited, start with 50% and talk to your solar installer about leaving room for expansion later.

Step 4: Array Size in kW = (Your kWh/year) / (365 days/year) / (Solar Hours/day) * (Percent you want to cover) / (75% efficiency constant)

• Example: My electricity bill is ~$110/mo and I use about 900kWh/month. I live in SoCal so I get about 5.5 solar hours/day and I want to cover 75% of my bill!
• (10,800 kWh/year) / (365 days/year) / (5.5 kWh/day) * (75%) / (.75%) = 5.38 kW Array
• Due to real world efficiency losses (irradiance, dust, temperature, and wiring), you should expect your system power output (AC power) to be about 75% of the system (DC power) size.

Step 5: Calculate solar array size!

Step 6: Now estimate the cost of installing a solar PV system of that size with our Solar Cost Calculator.

Step 2: Decide which solar panels you want to use, and enter the DC Watt rating of the specific solar panel model you want to use into the calculator below.

• Example: Suntech STP210-18/Ub-1 are rated at 210 DC Watts. Sunpower 230-WHT are rated 230 DC Watts.

Step 3: Calculate!

• Formula: Number of Panels = (Array Size in kW * 1,000 W/kW) / Solar Panel DC Watt rating.

Hint: Now you’re wondering how much roof space that many panels will need. Well a general estimate is 17-20 sqft per panel. So if you need 20 panels, you’ll need 340-400 sqft of unobstructed (mostly South-facing) roof space.

There are a nerve-wracking number of solar manufacturers and installers out there, so I caught up with Shawn Roe of SRoeCo Solar, a solar advice service, and asked him to share five questions that all consumers should ask before purchasing a system. I hope you’ll find his insight as helpful as I did:

1. “How many systems has your company installed?”
Due to the recent spike in solar panel installations, and the decrease in other construction-related businesses, many roofers, fencers, and builders are attempting to start solar installation companies with no solar experience and without proper solar installation knowledge. Look for a reputable installer with at least 50 installations and a few references.

2. “Is the warranty on my solar panels 25 years?”
Most solar panels on the market are high-quality and will have a guaranteed output of not less than 90% after 10 years and no less than 80% after 25 years. Any panel should have this warranty, whether it’s made in Germany, China, or America.

3. “Is the warranty on your labor 10 years or longer?”
Some states require installers to warranty their labor for 10 years in order for the system to be eligible for state rebates. Any good installer should have no problem including this.

4. “What is the total output of the solar panel system in kWh/year?”
This is arguably the most important factor in comparing solar electric systems (other than price, of course). If you have solar panels warranted for 25 years, and labor guaranteed for 10, then the brand of solar panel – whether Canadian Solar, SunPower, Suntech, or any other – doesn’t matter. The only thing that matters is how much energy they are expected to produce in a year. Many times the cheaper, “less efficient” solar panels will produce more energy in a year at a better price than the pricier, “more efficient” solar panels. When warranties are the same, output is the money-maker, not brand or efficiency.

5. “What is the final cost after parts, labor, installation and rebates?”
Don’t compare the cost of the panels exclusively, or the labor exclusively. Compare the bottom-line cost after rebates. Whoever can give you the most output (kWh/year) at the best price, is the company you should chose.

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If you found this article helpful, you might like these:

How to Calculate What Size Solar System You Need

How to Calculate Solar Cost

Most Efficient Solar Panels

Step 1: Know Your Electricity Usage

Gather your old electricity bills for the past 12 months. Contact your utility company if you don’t have them and your electricity provider should gladly send you a printout with your past electricity usage. You’re looking for 2 things: (1) your monthly kW/h usage, and (2) your monthly cost.

Step 2: Know your Roof Direction

Grab a compass (maybe your car navigation, or check Google Maps) and figure out which way is South. Go outside, look at your roof and see how much roof space is facing South, Southwest, East and West. The more South the better, but West is actually okay.

Step 3: Measure Roof Area

Measure your available roof space facing South, SW, and/or W. There are several ways to do this, but I think the easiest is to go to www.roofray.com. Type in your address, and measure your roof. You can also use Google Earth, or simply get out on your roof with measuring tape.

Step 4: Calculate Array Size

Step 5: Calculate How Many Solar Panels Will Fit

Now that you know how much roof you have available for solar panels and how big of a system you need, you need to determine what size panels you will need to cover your electricity usage while staying within the space you have available.

Determine the number of panels you can fit on your roof by dividing your roof area (maybe 600 sq ft for a 2,000 sq ft home) by 16 square feet (500/ 16 = 31.25). Round down, as you cannot fit partial panels on your roof. So I can fit a maximum of 31 panels on my roof.

Step 6: Calculate What Size Panels You Need

Now divide the array size (of the solar electric system) you need, by the number of panels you can fit. For example, let’s say you need a 6 kW solar system to cover 90% of your electricity usage and you can fit a maximum of 31 panels on your roof. So 6,000 kW / 31 panels = 193 kW/panel. So to meet your needs, you need to use solar panels rated above 193 kW (PTC)/ panel. This means you’ll probably use panels advertised as 220 kW (STC) or higher.

Next, use our Solar Cost Calculator to estimate the cost installing a solar PV system.

Or Calculate How Many Solar Panels You Need.

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All of these solar modules are Monocrystalline clearly proving that this type of solar panel is the most efficient - more efficient than Polycrystalline and Thin Film. The panels listed at 290 kW and above all take up more than 17.5 square feet per panel. The solar panels rated at 230 kW and below take up less than 13.5 square feet.

(click for a larger image)

So, for the most efficient solar panels - choose one of these Top 40. Remember: the best efficiency doesn’t necessarily mean the best panels. Check out the Solar Panel Comparison Chart for an explanation on how to choose the best solar panels.

Or if you want to see modules of more brands check out the Most Efficient Solar Panels

Many people ask, “Which solar panel should I choose? Which panels are the best?” Though any salesman is going to tell you his panels are the best, the truth is that it is not easy to compare solar power panels and to firmly state that one brand stands out among the rest as the best.

The solar panel comparison chart I created below shows how difficult it can be to compare panels and brands. Listed are common panels between 190 and 230 watts of 5 common solar panel manufacturers (Canadian Solar, Kyocera, Sharp, SunPower, and Suntech).

At first glance you can see that there isn’t even a standard DC watt rating. 200, 210, 220 etc. seems obvious, but then there’s 205, 208, 216, 225. What does all this mean?! It simply means that the panels produce at slightly different outputs.

I’ve attempted to standardize the comparison by including “Cost per Watt” and “PTC Watts per Sqft”. I’ve also included “True” factors, which simply means numbers based in reality as opposed to theory. Though a panel may have high efficiency, you can’t use 5.65 panels; you have to put 5 or 6 panels on your roof. And the sqft of 6 panels is going to be more than that of 5.65 panels.

(Red means bottom 5 of the category and Green means Top 5 of the category).

(Click on the chart to view larger image.)

As you can see on the chart, some panels are top 5 in some categories and bottom 5 in others. No specific panel is top 5 all the way across. It looks like SunPower solar panels score high in several categories, but does that mean they are worth the extra money? Maybe not, actually. The difference between a less efficient Kyocera, and a more efficient SunPower panel is negligible in terms of performance. You might get an extra $3 of energy per year for the same system.

Though hopefully helpful, the chart still doesn’t include other factors such as the environmental efficiency of the manufacturing process of the panels, how “green” the company is, or how the panels look.

So, how does one decide which solar panel to use? As a consumer, make sure the panel has at least a 25 year warranty and then let the installer make the decision.

The two most important numbers in comparing solar PV systems are 1) the AC kWh output/year, and 2) the cost. Whichever complete system can give you the most yearly output at the best price is the system to choose. Read that again.

When you are comparing panels or installation proposals, make sure the panels are warrantied for 25 years, the inverter for 10, and the installer warranties his work for at least 5 years. Then compare the yearly kWh output (in AC) and the price. All other factors equal, the most bang for the buck is the best deal.

Ultimately, the most important thing is to install solar! The difference between using non-renewable coal, gas and nuclear energy and using renewable solar, wind, and geo-thermal is the one thing everyone should be comparing!

If you enjoyed this article, please share it with your friends. Thank you!

Chart Key

• DC = direct current
• PTC = PVUSA Test Conditions (realistic test conditions)
• sqft = square feet
• True = real world
• True # of panels = the rounded number of panels it would take to get closest to a 1 kW array. (1,000 / PTC rating, then rounded to the nearest whole panel)
• Cost per DC and PTC may vary. Numbers given are general estimates and vary depending on many factors.

Calculations behind the “Solar Electric Cost Commercial” after the break.

See the “Solar Car Commercial” for an explanation of system rebates and net cost calculations.

A California resident spending an average of $200 per month on electricity bills to Southern California Edison (SCE), will spend $2,400 over the course of a year. Since 1980, the annual electric rates for SCE have increased an average of 2.91% and can reasonably be assumed to continue to rise at least that much over the next 25 years.

I calculate the cost and savings over 25 years because this is the guaranteed warranty for most solar panels. Therefore, $2,400/yr at a 5% annual increase will total $114,707 over 25 years.

The net cost after rebates of a 4 kW solar electric system for an SCE customer is $16,700. To view the specifics of this calculation use my SCE solar cost calculator and type in “5940″ as the kWh/year usage. You will see that I have conservatively rounded up from $16,690.80.

Using NREL’s PVWatts calculator, a 4 kW solar electric system located in Long Beach, CA at the default setting will produce 5,795 kWh of electricity. A similar system in Orange, CA will produce 6,123 kWh of electricity according to the CSI-EPBB calculator. For my savings calculations, I have conservatively used 5,700 kWh as the expected output.

Based on SCE’s 5 tier residential rate schedule of $0.12, $0.14, $0.24, $0.28, and $0.32 tiers, a customer would consume 11,750 kWh/year to average a monthly bill of $200. Using this rate schedule and consumption pattern, a 4 kW solar electric system producing 5,700 kWh/year would save $1,533/year in electricity costs. The annual savings being counted against the net cost of $16,700 would result in a system payback of 8.91 years, meaning that every every dollar saved after 8.91 years is money in the pocket.

Including the cost of replacing the inverter for $4,000 in year 15, the payback chart for this example 4 kW solar electric system would be as follows:

I hope you enjoy this solar promotion video. Please share it with your friends by using the convenient buttons below.

Michael Kanellos, Editor in Chief of Greentech Media, gives a short tour of the conference asking the question, “what’s the solar panel of the future - silicon or thin film?” View the video after the break…