Solar - Numbers

solar - What is U.S. electricity generation by energy source? - Number of countries that signed the Paris Agreement - Pollution caused by burning coal

How many panels you need
How much space is required
What they should cost

wind mills power plant: 1600 megawatts
solar panel power plant: ~ 100 megawatts

If it seems far-fetched to imagine millions of Americans becoming mini energy producers, just look at Germany, where 51 percent of the country’s clean energy production is owned by individuals or farmers, while major utilities control just 6.5 percent of it.

In 2015, more than 135,000 installations were done (out of 124 millions). See and

Rooftop solar panel mountings would need to withstand wind pressure building up under the panels during storms. This is an important consideration if you are located in a region prone to cyclones. Recent hurricanes in the United States and cyclones in many other parts worldwide have sensitised installers and rooftop solar owners to be more careful about the mounting structure materials and designs. The kind of mounting required for your location and type of roof should be discussed with the installer.

Rooftop Solar PV plants require 100-130 sq.ft (10-13 sqm) of shade-free roof area per kW of plant capacity. (show how much a 10kw system cost by state, the amount of electricity that a 10kw system will likely produce by state, and links to other important articles)

solar-goal - printed - done reading - California Solar Initiative - Annual Program Assessment - June 2010 - California Solar Initiative - Annual Program Assessment - June 2013 - California Solar Initiative - Annual Program Assessment - June 2014

Database of State Incentives for Renewables & Efficiency (DSIRE) (Roof Area Needed in Square Feet) - done reading - solar cheaper than coal - done reading - solar cheaper than coal - done reading - done reading - video - done watching - video - done watching - done reading - insolation measurement - a list of manufacturers, price, and other information - done reading - history - done reading - done reading - done reading - done reading - Subsidies - energy payback time is about 2 years - infographic - 0 down load versus leasing - done reading - infographic - done reading - infographic on zero-down loan versus leasing - done reading - infographic, solar compete with natural gas - done reading - infographic - done reading - infographic - done reading - infographic - done reading - done reading - done reading - history of solar panels - scroll to the middle of the page - infographic on average cost, payback period, etc - done reading - infographic on average cost, payback period, etc - done reading - done reading - Cost of module up to year 2013 - done reading - Tracking The Sun - Cost of module up to year 2013 - done reading - done reading (price per watt, manufacturing cost, etc) - done reading (amount of sunlight in some areas, some cost comparison) - done reading (Those solar systems add up to 3,440 megawatts of capacity, nearly as much as the largest nuclear power plant in the United States, Arizona's Palo Verde. But it still represents a tiny fraction of U.S. electric power plant capacity, 1.2 million megawatts spread through 19,023 generating stations.) Average Retail Price of Electricity to Ultimate Customers by End-Use Sector, - done reading - done reading - done reading (cost to upgrade the grid) - done reading (manufacturing capacity) (Some number on usage and price) - gives a breakdown by percentage of how much electricity is being produced by each method

1 SREC = 1 Mwh of solar electricity. A 10 kW facility generates around 12 SRECs annually.

How many SRECs does a typical solar system crank out a year? It’s usually about a 1 to 1 ratio between SRECs and the size of your solar system. For example, a 5kW solar system will pump out about 5 SREC credits a year.

Solar hot water heater costs around $2500, but saves $303 per year, paying for itself in about seven and a half year.

Heating and cooling account for 50 to 70 percent of energy used in an average American home.

Lyndon Rive, CEO of SolarCity, says that homeowners who enter into such arrangements pay two to three cents less per kilowatt-hour than the utility charges. Depending on the price of electricity where you live, that will cut your electric bills by 10% to 15%.

As you can see in the infographic, according to this research, it cost about $10,000 on average for a homeowner to go solar in California in 2011, while at the same time it cost about $25,000 on average for a homeowner to go solar in Florida, the Sunshine State! Again, this is because California has much better solar policies. Nonetheless, even the average Floridian would save $30,000–$39,000 over the course of 20 years by going solar. In California, New York, Nevada, New Mexico, and Arizona, those savings would actually reach beyond $40,000 (on average), but in almost every state in the country, the savings would at least be over $10,000, and would more often than not be over $20,000. Who wouldn’t want to cash in on such savings?

Regardless of what solar power’s detractors say, nearly all solar panel manufacturers guarantee that the panels they make will maintain above 80% efficiency by the end of a 25-year warranty. But those warranties are based on conservative estimates. The NREL study found that, for traditional silicon-based solar panels, the median reduction in efficiency is about 0.5% per year, which means that the panels operate at 88% efficiency, even after 25 years.

Installing solar panels on a home would require an estimated cost of $ 9,000 per 3 Kw installation. The system for heating by solar panels requires two service per year. The value USD 35 each. The cost of heating with such power pool average of 5 for 10 yards (the most common in the middle) is USD 6,000.

Your panels are guaranteed to be producing at at least 80% of their capacity at year 25. In actuality, they’ll be working for 40 to 50 years. However, your utility prices aren’t going anywhere but up. The 20x multiplier doesn’t even take that into account. The more your electric rates go up, the more valuable your investment becomes because you’re offsetting that much more power with your own power.

$40 monthly savings times 12 months in a year, and that equals $480 dollars saved annually. Now, multiply that by 20 and we’re at $9,600. So, your property will increase in value by roughly $10,000 and that’s a tax free property value increase.

"The amount of solar energy falling on the United States in one hour of noontime summer sun is about equal to the annual U.S. electricity demand," the Energy Department says in its SunShot Vision Study.

He now pays about $140 or $150 for electricity each month, down from about $220. And the total includes his $115 lease payment to SolarCity.

Depending on your pre-installation electricity usage, you can expect rates of return between 9% and 14% on your PV installation.

A south-facing three-kilowatt system installed at a 30-degree angle on a single-family home with a utility bill of $180 per month in San Francisco would cost a customer an estimated $19,282 with a payback period of 12 years.

As you can see in the infographic, according to this research, it cost about $10,000 on average for a homeowner to go solar in California in 2011, while at the same time it cost about $25,000 on average for a homeowner to go solar in Florida, the Sunshine State! Again, this is because California has much better solar policies. Nonetheless, even the average Floridian would save $30,000–$39,000 over the course of 20 years by going solar. In California, New York, Nevada, New Mexico, and Arizona, those savings would actually reach beyond $40,000 (on average), but in almost every state in the country, the savings would at least be over $10,000, and would more often than not be over $20,000. Who wouldn’t want to cash in on such savings?

Solar power is apparently going to be sold to Austin Energy for a tiny bit less than 5¢/kWh under a new 25-year power purchase agreement (PPA) with SunEdison. First Solar was selling electricity for 5.8¢/kWh. SunEdison project beat natural gas, coal, and nuclear on price. If you removed the ITC (a federal tax credit for solar), the cost would probably be about 8¢/kWh. Still, that’s not bad. Austin Energy’s 30-year LCOE estimate for natural gas was 7¢/kWh, while the estimate for coal clocked in at 10¢/kWh and the estimate for nuclear at 13¢/kWh. Only wind — 2.8¢/kWh to 3.8¢/kWh — was lower. US Department of Energy projected that the cost of solar would drop below 6¢/kWh before 2020. Keep in mind that this is the price that solar energy is being sold to utility. This is not the price that solar energy is being sold to end consumer by utility, but this is definitely exciting to see that solar energy is beating coal.

For the solar panels that typically sit on your roof to be really effective, they need exposure to direct sunlight for at least five hours a day. If there’s a lot of fog and rain where you live, or obstructions like trees or neighboring structures, then your solar system won’t be as efficient. But if your electric bills are high and your house receives sufficient sunlight, then solar panels might be a sustainable and energy-efficient alternative to consider. In general, systems are cheaper in places like Arizona and California, where electricity is expensive, sunshine is plentiful, and solar has gained wider acceptance.

A typical residential system should lower your electric bills by 25% to 50%, says Monique Hanis, a spokeswoman for the Solar Energy Industries Association. The average household pays about $110 a month for electricity, according to the Energy Department, so a solar-panel system should save you between $300 and $600 a year. The payback period will vary greatly depending on how sunny it is where you live, the size of your system, the cost of your system, and future swings in local electricity costs.

Conduct your own energy audit, seal windows and doors, and replace old appliances. Simply adding insulation to an attic can lower heating and cooling bills by 10% to 50%. A tube of caulk and a few rolls of fiberglass insulation cost a whole lot less than solar panels.

Taking out a loan to buy rooftop solar can save as much as 29 percent over lease arrangements, according to a new analysis from the National Renewable Energy Laboratory.

About 60 percent of U.S. households pay enough in annual federal taxes to take full advantage of the credit.

Without solar, air conditioning drives her summer electric bills as high as $575 a month. The lease offer just didn’t pencil out financially the way that purchasing it did with a credit-union offer on the table.

The silicon from one ton of sand has the potential to produce as much electricity as 500,000 tons of coal. One medium sized solar system will save the earth from 6,000 lbs. of carbon dioxide pollution.

As a general rule, a 3-kilowatt-hour system will generate approximately 3,600 to 4,800 kwh per year; a 5-kwh system will produce 6,000 to 8,000 kwh per year; and a 10-kwh system will produce 12,000 to 16,000 kwh per year, depending on where you live.

According to Energy Star, the joint program of the Environmental Protection Agency and the Department of Energy, qualified solar water heaters can cut water heating bills in half and significantly reduce your carbon footprint. Though a solar water heater may take 10 years to pay itself off, homeowners can take advantage of federal and state tax credits to recoup the initial costs. Energy Star claims that a qualified solar water heater will prevent 4,000 pounds of carbon dioxide from entering the atmosphere. This is equivalent to not driving a car for four months every year.

Look at last year's utility bills and see how many kilowatt-hours you used (the national average is 10,000 per year). Then decide if you want to invest in a system to meet all or part of your needs. Typical residential systems range from 3 kwh to 10 kwh in size. As a general rule, a 3-kwh system will generate approximately 3,600 to 4,800 kwh per year; a 5-kwh system will produce 6,000 to 8,000 kwh per year; and a 10-kwh system will produce 12,000 to 16,000 kwh per year.

The most important factors affecting a solar photovoltaic system's effectiveness are orientation toward the sun and unobstructed access to sunlight. PV systems work best on a south-facing roof, and they must receive sunlight with no obstruction from trees or other shading. In addition to your own observations, consult solar resource maps available on such websites as the U.S. government's National Renewable Energy Laboratory.

4-kwh system requires 400 to 600 square feet of roof area, and a 10-kwh system requires 1,000 to 1,500 square feet.

American Solar Energy Society and the Seattle environmental group Cooler Planet.

The cost of solar panels is falling, down almost 100 percent since 1977 (see chart) and more than 50% since 2007 alone.

All this being said, the average price to install solar as of 2013 was $4.72 per watt, and an average-sized solar panel system is about 5 kilowatts. Those installation costs vary dramatically, though — the same size system costs between $3 and $7 per watt depending on where you live. So although it’s not a helpful ballpark, you can expect a turnkey solar system to cost anywhere from $10,000 to $35,000.

The Earth receives more energy from our sun in about one hour than humans consume in an entire year.,

The environmental cost of Chinese- made solar panels is about twice that of those made in Europe -

China has gone from being a relatively small player in photovoltaic production at the turn of the last century to the world’s leader today, manufacturing nearly 60 percent of the global total in 2012, according to the Earth Policy Institute. The next biggest manufacturers are Taiwan, Japan, Malaysia, Germany, South Korea and the United States.

NASA has been using solar-powered satellites since the 1960s -

If you only consume 600 kWh in a month, or 20kWh/day, you could supply all the energy you need with a 5-kW system.

New data from the Massachusetts Department of Energy Resources published last year suggests that state taxpayers that will pay (a lot) more to make solar easy to install for individuals and businesses, and to make solar energy lucrative for solar leasing companies. The report estimates the necessary production based incentive (in dollars per megawatt-hour of electricity produced) to support the development of solar. Specifically, the researchers priced a “10-year levelized incentive…that allows system owners to achieve their target economic rate of return.” The analysis notably focused on ownership structures, either 3rd party ownership (solar leasing) or host ownership (owned by the home or business owner). The following chart shows the difference in state incentives necessary to support a small-scale (15 kW or less) solar array that is either owned by a 3rd party or the actual electric customer.

A host-owned solar array is expected to get financing at 4% interest and have a return on equity expectation of 4%. A solar leasing company is expected to pay 6% interest on shorter-term debt and to require 15% return on equity.

Complicated tax incentive, interconnection, and contract policy makes solar cost more to install than in mature markets like Germany. Solar leasing middlemen simplify the complications, but at a price premium to (complicated) individual ownership. Even though sunshine is free, no kind of solar power is a free lunch.

Should we blame Vote Solar for the high price?

We’ve previously discussed why tax credits make for lousy renewable energy policy. In 2009 and 2010, however, changes to the federal tax credits allowed people to take a cash grant instead, reducing the need for third party ownership. That ends in December.

California's renewable energy mandate is one of the most ambitious in the country. By 2020, state utilities have been ordered to generate at least 33% of their electricity from clean power sources. Gov. Brown has called for an even higher renewable energy mandate. By 2030, he wants the state to generate at least 50% of its electricity from green power sources.

Every minute of every day, enough of the suns energy reaches the earth to meet the world's energy demand for an entire year.

Because PV technologies use both direct and scattered sunlight to create electricity, the solar resource across the United States is ample for home solar electric systems. (look on the left hand side)

First used in about 1890, "photovoltaic" has two parts: photo, derived from the Greek word for light, and volt, relating to electricity pioneer Alessandro Volta. And this is what photovoltaic materials and devices do—they convert light energy into electrical energy, as French physicist Edmond Becquerel discovered as early as 1839. Becquerel discovered the process of using sunlight to produce an electric current in a solid material. But it took more than another century to truly understand this process. Scientists eventually learned that the photoelectric or photovoltaic effect caused certain materials to convert light energy into electrical energy at the atomic level.

Systems rated between 1 and 5 kilowatts are generally sufficient to meet most of the needs of home and small business owners.

PV modules should be oriented geographically to maximize the amount of daily and seasonal solar energy that they receive. In general, the optimum orientation for a PV module in the northern hemisphere is true south. However, your modules can face up to 45 degrees east or west of true south without significantly decreasing its performance.

Most PV modules are mounted flat on the roof, and so have the same tilt as the roof. Although the optimal tilt angle for your modules is an angle equal to your latitude, fixing the PV modules flat on an angled roof is generally not a problem. However, because most roofs are pitched at an angle less than the latitude, you and your contractor will need to factor your roof angle into the performance calculations when sizing your system.

The average household uses 64 gallons of water a day. Water heating accounts for 14%-18% of utility bills!

The U.S. Department of Energy's Lawrence Berkeley National Laboratory released a study last year that found homes with solar systems sell for a premium over homes without solar systems, specifically about $17,000 more for a relatively new 3,100-watt photovoltaic system.

From just 31 gigawatts of new worldwide solar installations in 2012, Bernstein’s analysts predict that will grow to 300 GW a year by 2020. That would be a very material annual addition equal to 1.5% of global energy demand.

This despite the fact that NRG still generates 98% of its power from big fossil-fuel burning power plants. NRG has invested about $1 billion in solar, including about $300 million in the brand new $2.2 billion Ivanpah solar project (392 MW) in California, a 50% stake in the 290-mw Agua Caliente project being built in Arizona and a 50% stake in solar outfitter Sunora, which has developed easily erected solar canopies. In July NRG even raised nearly $500 million in the IPO of a new subsidiary called NRG Yield (NYSE: NYLD). The idea behind NRG Yield is for it to own NRG’s cash generating renewable energy assets and pay solid dividends. And it gives NRG a low-cost financing mechanism to keep acquiring more of those assets, from the likes of Sunnova.

The solar panels and associated supplies cost about $8,000 for a typical 4,000-watt residential system. A qualified solar specialist or electrician should be able to install these panels for about $2,000 given that it’s only about a day of work. The total installed price should be about $10,000, without any tax credits or incentives. That is about the price of a comparable system in Germany. But the average price of a residential system in the U.S. is about $20,000. So where does the extra $10,000 go? I can assure you that it is not the result of greedy installers, paranoid utilities or greater German installation efficiency. Studies by the National Renewable Energy Laboratory and by the University of California, Berkeley both confirm that these higher prices are almost exclusively related to the paperwork it takes to “officially” install a standard rooftop system in the U.S. That’s right, government red tape -‐ local, state and federal.

Each additional $1 in energy bill savings (from your solar installation) adds $20 to your home’s total value.

Average increase in resale value being $5,911 for each 1 kilowatt (kW) of solar installed. In a state like California, for example, a small 3.1-kilowatt (kW) system can add an average of $18,324 to the value of a medium-sized home. The property value advantages of solar energy only increase as you scale up. Installing 5kW of solar panels adds an average of $29,555 to the retail value of a medium-sized home.

Installing solar panels not only helps you fetch a higher asking price, but it can also help your home sell 20% faster.

EPA/DOE studies indicate that the value of a home increases from $11 to $25 for every $1 reduction in annual utility bills

Code requirements for PV systems vary somewhat from one jurisdiction to the next, but most are based on the National Electrical Code (NEC). Article 690 in the NEC spells out requirements for designing and installing safe, reliable, code-compliant PV systems. If you are one of the first people in your community to install a PV system, your local building department may not have experience in approving one of these systems. If this is the case, you and your PV provider can speed up the process by working closely with building officials to educate them on the technology.

A tax credit can provide significant savings. It reduces the amount of income tax you have to pay. Unlike a deduction, which reduces the amount of income subject to tax, a tax credit directly reduces the tax itself.

Photovoltaic (PV) systems convert sunlight directly to electricity. They work any time the sun is shining, but more electricity is produced when the sunlight is more intense and strikes the PV modules directly (as when rays of sunlight are perpendicular to the PV modules). Unlike solar thermal systems for heating water, PV does not use the sun's heat to make electricity. Instead, electrons freed by the interaction of sunlight with semiconductor materials in PV cells are captured in an electric current.

PV allows you to produce electricity without noise or air pollution from a clean, renewable resource. A PV system never runs out of fuel, and it won't increase U.S. oil imports.

The basic building block of PV technology is the solar “cell.” Multiple PV cells are connected to form a PV “module,” the smallest PV component sold commercially. Modules range in power output from about 10 watts to 300 watts.

PAYS: Pay As You Save.
TIPs: Tariffed Installation Programs (TIPs)

"tariff" is imposed on the utility bill each month to pay for the costs of the retrofits and associated costs. The reason why it is called "tariff" instead of a "loan" is because the obligation to pay loans are usually connected to individual customers, while the obligation to a tariff can remain with the meter.

“Panel prices make up about 20 percent to 25 percent of the cost of a solar system, compared with as much as 70 percent in 2010 and 2011,” (as of July 18, 2013)

What is tier rate?

The lowest rate in your territory is about 11 cents per kilowatt hour (kWh) for the “base tier.” Everybody, including you, get this rate for a certain amount of usage. When you use energy above this level, the utility charges you HIGHER rates. The next rate tier above 11cent is 25 cents/kWh–more than double. If you use even more, the rate jumps even higher to 35 cents/kWh. The utilities do this to penalize energy hogs like you and to encourage you to conserve.

If you buy enough solar panels to offset your usage by say 50%, you’re sort of tricking the utility into thinking you use a lot less energy. In reality, your solar panels are generating enough to get you out of the higher tiers back into the lower tiers.

How much electricity is being produced by solar panels in the US?

About 5.7 gigawatts. Need to compare this against the total amount of electricity being generated.

How much electricity is consumed by your iphone?

Charging up a smartphone or tablet takes relatively little electricity, but watching an hour of streamed or internet video every week for a year uses up about as much power as running two refrigerators for a year because of the energy powering data centers elsewhere. See

What is the world total manufacturing capacity?

The IHS report also noted that total global solar PV shipments hit 38.7 GW in 2013 — roughly a 24% increase over the previous year.


How can we estimate the desired size for your system?

  1. Look at your utility bill to see how much electricity you are consuming
  2. Decide how much of that you want to be coming from your panel. For example, I consume about 470 kwh per month
  3. 470 kwh per month / 30 days per month = 15.6 kwh per day
  4. Assume that your location receive approximately 5 hours of sunlight per day: 15.6 kwh per day / 5 hours per day = 3.1 kwh

How can we determine the price per watt?

If you were quoted $14,699 for a 3.3 kwh, your price per watt would be: $14,699 / 3.3 = $4899 per kw or $4.899 per watt.

How can we determine the payback period?

If the price for your system is $14,699 and the saving from your electricity bill is $80 per month, the payback period is 183 months or 15.3 years (without the 30% federal tax credit)

Another way to calculate the payback period: If the average electricity rate is $0.20 per kilowatt hour and your installed cost was $4.00 per watt, your payback time would be just over 15 years.

A typical solar panel produces around 200 watts of power. There’s a little bit of variation on this, based on the size and efficiency of the solar panel you choose; you’ll see panels that produce 205, 210, even 230 watts. More efficient panels are a little more expensive, and are usually only needed if you have limited space on your roof. It won’t matter as much how much each panel is producing as the whole array. A typical installation might be about a 5 kWh array, or roughly 25 panels.

To get a very rough estimate of how big a system you need, look at your electric bill and figure out how many kWh you use per day. The average home in the United States uses about 900 kWh every month, or about 30 kWh per day [source: DOE]. Multiply that by 0.25 [source: GE]. We come up with 7.5, so we need a 7.5 kW system.

A typical solar panel produces a maximum of 120 watts, or 0.12 kW, in a day [source: Richards]. For a 7.5-kW setup, then, you'd need about 62 panels. A single panel might measure about 56 by 25 inches (142 by 64 centimeters), so a 62-panel solar setup would measure roughly 700 square feet (65 square meters).

To determine the cost per watt for any system, simply take the quoted price for the system before incentives and divide that price by the DC wattage of the system Example: Price of system before incentives $15,000 divided by the size of the system 5,000 watts (or 5kW) equals $3.00 per watt.

When it comes to pricing, the bottom line is this: For a standard 5 kW or larger, grid tie solar system with a name brand string inverter (no micro inverters or power optimizers) on a composition shingle rooftop with no barriers to installation, you should not be paying more than $3.00 per watt before incentives. Of course there are higher performance systems with extra bells and whistles available at a higher price, but for most residential applications a standard system at the $3.00 per watt before incentives price, mentioned above is sufficient. To determine the cost per watt for any system, simply take the quoted price for the system before incentives and divide that price by the DC wattage of the system Example: Price of system before incentives $15,000 divided by the size of the system 5,000 watts (or 5kW) equals $3.00 per watt. The leasing and PPA companies typically quote their systems at about $5.00 to $6.00 per watt. Which is much too high in today's market.

Always add the amount of the 30% federal tax credit and any cash rebate and the 20 years worth of lease payments and any annual payment escalator together to determine your actual lease or PPA cost when comparing to the cost of a purchase. Never, ever sign a solar lease or PPA without comparing your total rental cost to at least 3 separate purchase quotes.

Look at your utility bill to determine the average consumption per month. Divide that by 30 days to obtain the daily consumption (DC: daily consumption). Look at the solar map to determine the number of hour of sunlight that your roof receive (SH: sunlight hours). Divide DC by SH to determine the desired system size.

How can we determine the amount of roof space that you need?

Refer to for the amount of roof space required.

You size your system by examining previous utility bills. You need to determine the number of kilowatts-hour that you consume annually. Divide this number by 12 to arrive at the monthly average. You then divide this number again by 30 to determine the daily average, and then divide by the average number of hours that your roof. If you have a good location, your annual utility bill should be 0. To determine the payback period, divide the cost of the solar system (including cost for installation and permit, etc) by your previous annual energy bill.

How can we calculate electric bill saving for a net-metered PV system?

Determine the system's size in kilowatts (kW). A reasonable range is from 1 to 5 kW. This value is the “kW of PV” input for the equations below.

Based on your geographic location, select the energy production factor from the map below for the “kWh/kW-year” input for the equations.

Energy from the PV system = (kW of PV) x (kWh/kW-year) = kWh/year

Divide this number by 12 if you want to determine your monthly energy reduction.

Energy bills savings = (Energy from the PV system) x (Residental Rate) = (kWh/year) x (Residential Rate) = $/year saved

Obviously, the amount of saving (in term of dollars) is equal to the amount of kilowatts that your system produce times the rate that your utility company is charging you per kilowatt.

(Residential Rate in this above equation should be in dollars per kWh; for example, a rate of 10 cents per kWh is input as $0.10/kWh.)

For example, a 2-kW system in Denver, CO, at a residential energy rate of $0.07/kWh will save about $266 per year: 1,900 kWh/kW-year x $0.07/kWh x 2 kW = $266/year.

See (page 11)

How can we determine the appropriate size for our system?

Look at your utility bill to determine the number of kilowatt/hour that you consume per year. Divide this by the number from the map.

See the map on (page 11)

To calculate the payback period for the project, first find out the final installed cost per watt, the electricity cost per kWh in the area, and the average number of sunlight hours in the location. Cost per watt install divided by cost per kWh charged by the utility company is equal to the number of watt that your system must produce. Take this number and divide by the average number of kWh that you consume monthly is equal to the number of month that your system must function. Divide this number by 12 to determine the number of year that your system must function.

The less expensive the system was to put in and higher the electricity rate is in the area, the shorter the payback period is.

How can we calculate ROI?

This is dependent the amount of sunlight that you receive, and your current electricity consumption. In my case, my family currently spend about $80 per month on average, or $960 per year on electricity. This would be $24000 assuming that the rate that you pay for electricity, and the amount of electricity that your family use does not increase or decrease much. In my case, I pay $10,289. I am not an investment expert, so you can look at these numbers and compare that to the ROIs that you receive from your other investments. If solar provide a higher ROI, then perhaps you should consider liquidating your other investments and investing in solar.

How can we calculate the cost per watt?

This can be determine by the total cost divided by the size of your system. In my case, I pay $10,289 (with incentive) for a 3.36kw system (1kw == 1000 w), so it is $10,289 / (3.36 * 1000) = $3.06 per w.

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