Our solar estimator answers all your solar questions

Our solar estimator answers all your solar questions

Solar Power FAQs

Solar Energy Basics
The United States currently relies heavily on coal, oil, and natural gas for its energy. Fossil fuels are nonrenewable, that is, they draw on finite resources that will eventually dwindle, becoming too expensive or too environmentally damaging to retrieve. In contrast, renewable energy resources - such as wind and solar energy - are constantly replenished and will never run out.
Renewable energy is important because of the benefits it provides.
The key benefits are:
  • Environmental benefits
  • Energy for our children and grandchildren
  • Jobs and the economy
  • Energy security
In some cases renewable energy systems may also save you money versus utility-provided power, especially in future years as utility power costs rises. Solar and renewable energy systems "fix" your energy cost in time. The cost to install a system divided by its expected lifetime output is what is called "levelized cost".
Renewable energy technologies are generally friendlier to the environment than conventional energy technologies, which rely on fossil fuels. Fossil fuels contribute significantly to many of the environmental problems we face today - greenhouse gases, air pollution, and water and soil contamination - while renewable energy sources contribute relatively little.

The increased use of fossil fuels has significantly increased greenhouse gas emissions creating an enhanced greenhouse effect known as global warming. Renewable energy technologies, however, can produce heat and electricity with a very low or no amount of carbon dioxide emissions.

Energy use from fossil fuels is also a primary source of air, water, and soil pollution. Pollutants take a dramatic toll on our environment.
Our national energy security continues to be threatened by our dependency on fossil fuels. These conventional energy sources are vulnerable to political instabilities, trade disputes, embargoes, and other disruptions.

U.S domestic oil production has been declining since 1970. In 1973, the United States only imported about 34% of its oil. In 2011, our country imported more than 45% of its oil.

Futher reading:

How much do solar panels produce?

Why is renewable energy important?

Solar Power Videos

Glossary of Terms


Solar Questions
The solar rating is a measure of the average solar energy (also called "Solar Irradiance") available at a location in an average year. Radiant power is expressed in power per unit area: usually watts/sq.meter, or kW/sq.meter.

The total daily Irradiation (Wh/sq-m) is calculated by the integration of the irradiance values (W/sq-m).

Click here for the Solar Radiance map of the USA

Shading: If your solar collectors experience any shading during the day the output of your solar system can be dramatically reduced. This is especially true of photovoltaic (PV) solar panels since a partially shaded PV panel can result in a loss of power across the PV array. Some solar incentive programs, such as the California Solar Initiative (CSI) reduce the incentive available to you if your solar system is impacted by any shading.
The wind rating is based upon the average wind speed at your location. We use average values for each month. It is measured in meters-per-second (m/s). 1 m/s is about 2.2 mph

We reference NASA Surface meteorology data from the Atmospheric Data Center. This data is based upon satellite-derived data over a 22-year period. The data is compiled for each degree of latitude and longitude (each degree represents about 69 ground miles).

Reference Height: The wind speeds are for a reference height of 50 m (164 ft) for USA locations and 10m (13 ft) for Canadian locations.

Note: Because wind varies, sometimes dramatically, from location to location the wind rating provided is only an estimate. Elevation, trees, mountains, valleys, thermal variations and other geographic and weather pattern factors will affect the actual wind you will realize at your location.
Buildings designed for passive solar and daylighting incorporate design features such as large south-facing windows and building materials that absorb and slowly release the heat of the sun. No mechanical means are employed in passive solar heating. Incorporating passive solar designs can reduce heating bills as much as 50 percent. Passive solar designs can also include natural ventilation for cooling.
There are three main types of concentrating solar power (CSP) technologies: trough systems, dish/engine systems, and power towers. These technologies are used in CSP plants that use different kinds of mirror configurations to convert the sun's energy into high-temperature heat. The heat energy is then used to generate electricity in a steam generator.

CSP's relatively low cost and ability to deliver power during periods of peak demand when and where we need it means that CSP can be a major contributor to the nation's future needs for distributed sources of energy.

For more information see Energy.gov
Concentrating solar power technologies use reflective materials such as mirrors to concentrate the energy of the sun. This concentrated heat energy is then converted into electricity.
For your estimate, we convert one Therm to 100 cubic-feet of natural gas.

A therm is 100,000 BTU. The average heat value of natural gas is 1000 BTU per cubic foot. A BTU (British Thermal Unit) is enough heat to heat one pound of water one degree (F). Natural gas is sold to the customer in units of 100 cubic feet (therm) or in a unit called MCF. A therm represents approx. 100,000 BTU of heating power, enough to heat a normal home for about 2 hours during colder weather.

Please contact your utility if you have questions about your rate. Or, contact a renewable energy Professional who can help you develop a strategy to minimize your utility bills.
Electricity and CO2:

National average emissions factor for electricity is 1.64 pounds CO2 per kilowatt-hour. Source: The Cadmus Group, 1998. Regional Electricity Emission Factors Final Report.

Typical annual CO2 emissions of 20,000 pounds per household based on 1,000 kWh/month, which is the average used in most utility rate cases. Source: U.S. Environmental Protection Agency

Automobiles: Studies indicate that the average car produces about one pound of CO2 per mile driven. Source: Progressive Policy Institute
For a solar installation, you need a roof area with sun exposure. The amount we give you is a typical amount (10 watts per square foot), but the actual amount may vary based on roof angle, shade, type of PV cells installed, etc.
We use the Equifax Risk Level Indicator score.

The Equifax Risk Level Indicator Score ranges from 1 to 5, with lower scores indicating lower business risk. Variables used by Equifax to develop the RLI include:
  • Industry (SCI code)
  • Geographic region (state)
  • Years in business
  • Annual sales volume
  • Total number of employees
Risk RLI Score
Low 1-2
Medium 3
High 4-5
Prior to March 1, 2008, we used the PAYDEX Score from Dunn & Bradstreet. PAYDEX is a unique dollar-weighted numerical indicator of how a firm paid its bills over the past year, based on trade experiences reported to D&B by various vendors. The D&B PAYDEX Score ranges from 1 to 100, with higher scores indicating better payment performance.

Risk Paydex Score
Low 80-100
Medium 50-79
High 0-49
For more information, please go to Equifax.com or DNB.com

To remain Pre-Screened, a listed Pro must maintain a credit risk score indicating Low or Medium Risk. If no credit risk score is available for the listed Pro, they can remain Pre-Screened if they indicate to us they have no bankruptcies nor liens against them (as indicated on their company profile stored on our site). In this case the Credit Risk score defaults to Average/Medium.

Futher reading:

A guide to solar inverters for grid tied solar system

How does PV angle affect output?

Greenhouse Gas Reduction

Tesla's Solar Glass Tiles renew interest in Solar Shingles and building integrated photovoltaics


Solar Hot Water or Pool/Spa Heating
According to the American Water Works Association the average American home uses 45-65 gallons of total water (hot and cold) per day, per person. A little less than half of this would be for hot water uses.

Therefore, as a general guide, each person in your home would use 20-30 gallons of hot water per day. If your home is water efficient then you would be toward the lower end of this scale.

Your renewable energy Professional will make a more accurate assessment based on the number of people as well as the number of bedrooms and bathrooms.

Other helpful information is available at: Energy.gov and Florida Solar Energy Center
This calculation is based upon numerous assumptions and actual results will vary considerably. For this estimate we have assumed the solar collector for water heating is flat-plate glazed collector with 3 square-meters of surface area.

An actual site assessment by a renewable energy Professional is recommended to better determine your specific needs.
We assume a water heater operating on natural gas, fuel oil or propane is 70% efficient, and a water heater operating on electricity is 100% efficient.

For example, if your water heater is fueled by natural gas and your solar water heater produces 100 Therms of energy per year, the natural gas saved would be 100 Therms/0.70, or about 143 Therms of natural gas. This is our estimate for the amount of natural gas you would save on your utility bill in a year.

Please note: The actual efficiency of water heaters run on natural gas, fuel oil, propane, electricity or other fuels varies. We recommend you work with a renewable energy Professional who can better analyze your specific situation.
Solar hot water heaters use the sun to heat either water or a heat-transfer fluid in collectors. A typical system will reduce the need for conventional water heating by about two-thirds. High-temperature solar water heaters can provide energy-efficient hot water and hot water heat for large commercial and industrial facilities.
We use RETScreen to calculate the energy generated by a solar water or poo/spa heater. Several assumptions are made to create this calculation, as listed in the Assumptions.
For simplicity, we have assumed the solar collector for pool or spa heating is an Aquatherm Model SI-11001. This is an UNglazed (no glass cover) collector with 3.72 square-meters of surface area.

For Spa sizes less than 5 sq-meters, we assume one panel will be used. For pool sizes less than 24 sq-meters we assume 3 panels will be used. And, for pool sizes from 25-80 sq-meters we assume 8 panels will be used.
Solar Calculator
This estimate shows you both the size of system you would need to eliminate your bill and also instantly give you a rough ballpark of what it would cost and what rebates and incentives are available for your utility at your location.

However, often a ballpark estimate can be quite inaccurate and so we also have approximately 100 installation companies all around America that have agreed to share their real time pricing with users of this site.

These installation companies require your phone number and email address as occasionally they have to call you and ask you questions (i.e often suggested system sizes do not fit on your roof, sometimes there are shading issues and sometimes rebate programs are put on hold because their annual budgets have been exhausted). These installers will email you accurate pricing for a system that will fit on your roof once they establish you are a real person and not a competitor simply trying to get their pricing.

Your data will not be used for any other purpose and will never be sold to other third parties. See "Privacy" section under Terms and Conditions
This is only an estimate: Installation costs vary considerably. We encourage you to contact a renewable energy Professional who can assess your specific needs and give you a competitive quote.

Please see the Notes, below the Estimate, for the many assumptions we have made for this simplified cost estimate.
Item Cost for less than 2kW Cost for more than 2kW
PV Panels $5.00 per watt $5.00 per watt
Inverter $1.20 per watt $1.20 per watt
Installation Cost $3.80 per watt $1.80 per watt
Total $10.00 per watt $8.00 per watt
This is a sliding scale between $5 per watt for a 1kw system, and $3 per watt for a 10kw system. These install prices are an industry average but will change over time.
The initial rate displayed represents a base residential service rate plus 50%. We add 50% to the base rate to accommodate expected over base rate use, surcharges and taxes. If no rate is available, reasonable default values are: Electric $0.15/kWh, Natural Gas: $1.40/Therm ($0.014/ft^3), Fuel Oil: $3.65/gal., Propane $3.00/gal

The actual rates, taxes and surcharges you pay are probably different. We suggest you review a recent utility bill and change the "Assumed Electric (or Gas) Rate" as needed to better match your situation.

Please reference your utility bill or contact your utility for more details on your actual rates.
We assume accelerated depreciation (5 year schedule) only applies to business installations. We attempt to provide direct links to incentive program information where possible.
We accommodate the main wind, solar electric (PV) and solar thermal (water, pool spa) incentives for each state and the major utilities in each state. Incentives changes and we may not cover all available incentives. For a complete list of incentives and programs that may be available, please consult with a renewable energy Professional.

See Energy.gov for more information on programs that may be available in your location.
We assume the state tax credit you receive, if any, will be taxed on your federal tax return at 28%.
Return on Investment (ROI) is calculated as sum of all returns over the system life divided by the energy system net cost (after all purchase incentives).

For residential (non-business) applications we assume utility savings are in Gross Income dollars ("pre-tax" or what you earned).

For business (commercial) applications we assume utility savings result a lower expense write-off against income tax liabilities.
Internal Rate of Return, or IRR, is the discount rate (%) that makes the Net Present Value of the system equal zero. Or, in other words, IRR is the amount of profit you gain by investing in a renewable energy system. It is a percentage. An IRR of 10% means you make 10% profit per year on the money invested in the project.

To calculate IRR, we take the Net Purchase Cost (after rebates and incentives) of your solar system, and the estimated annual utility savings or other cash in-flows, for each year, then find the rate of return on your money that makes the cash flow zero over the system`s life.

Utility Savings Assumptions: For residential (individual) situations we assume utility savings are in Gross Income dollars ("pre-tax" or what you earned).

Operating Cost Assumptions: For solar electric (PV) systems we assume the power inverter is replaced at year 15 in the systems life. No other operating or maintenance costs are assumed.

Futher reading:

About solar panels price estimates

The pros and cons of the PV Watts solar calculator

How do you calculate the solar system capacity?

How do you calculate my first year utility savings?

How do you calculate my energy usage?

How do you calculate renewable energy credit REC value?

How do you calculate the expected incentive or rebate?

How do you calculate the state tax credit deduction?

How do you calculate MACRS and CCA Depreciation?

What is a kilowatt (kW) and what is a kilowatt hour (kWh)?

What is a megawatt (MW) and what is a megawatt hour (MWh)?

What is levelized cost?

What is net present value?

What is the profitability index?

How does a solar feed in tariff differ from net metering?


Buying Solar Systems
When selecting a renewable energy Professional, look for a company that has experience installing (or other professional services you desire) the type of renewable energy system you seek. Ask them how many years they`ve been in business, ask what licenses they hold, and get (and check) references. Also ask if they have any specific manufacturer or industry training or certifications. Remember, renewable energy systems are an asset, that properly installed should provide many years of reliable service. You want a qualified professional. Get several bids, but picking the lowest bid is not necessarily the goal. Choose experience and quality too. Also compare warranty and service policies offered by competing bids.

Also use a service such as ContractorCheck.com to verify the company's status.

Check with your State or County to make sure your Professional is properly licensed or certified for the work (which can vary from local to local). If you plan to use any incentive programs to help pay for the cost of your system, check to make sure the Professional you choose qualifies for that incentive program.
Generally, yes. Contact your city or county building permit agency. If you have a home owners associaiton (HOA), you may also want to contact them to learn of any others requirements specific to your neighborhood.
If you are amongst the first in your community to install a grid-connected renewable energy system you and your installer can speed the process along by working closely and cooperatively with your local building officials to help educate them about the technology and its characteristics.

Contact your Homeowners' Association, if your community has a homeowners association (HOA), you will want to contact them to ensure you file the proper architecture request forms and obtain approvals. They cannot prevent you from installing a PV system.
The Florida Department of Business & Professional Regulation has online tools to help you verify contractor licenses for the State of Florida: Go to Verify FL Licenses
To remain Pre-Screened, a listed Professional must pass ("Checks out") criteria established by Experian's ContractorCheck.com service. A checklist and score of points is compiled to determine the contractor`s overall ContractorCheck rating. Among items that provide points are the presence of License, Bond, and Insurance information. Some items that can negatively affect the overall rating are delinquent and past due credit items, liens and judgments, and missing license, insurance or bonding information.

If no ContractorCheck report is available for the listed Professional, they can remain Pre-Screened if they indicate to us they have no bankruptcies nor liens against them and have listed licensing details (as indicated on their company profile stored on our site).

For more information, please go to ContractorCheck.com
We pre-screen our listed Professionals. A listed Professional with a Pre-Screened insignia has indicated, through their profile information, that they meet the following screening criteria:
  • Their business has been in operation at least 3 years, or they have equivalent professional experience.
  • Good professional and customer references: The firm has provided a minimum of three (3) customer references, and those references resulted in a minimum of an AVERAGE ("OK") overall rating (2 is considered average on a rating scale from 1 to 4). To remain Pre-Screened the listed Pro is asked to update its references at least every 12 months.
  • The business has passed criteria established by ContractorCheck.com. This service verifies such things as licensing, bonding, and financial health. If not listed with ContractorCheck.com, the listed Pro has certified to us that they have not had liens or disputes with creditors in the past 5 years, nor filed for bankruptcy in the past 7 years, and has listed their licensing details.
  • The listed Pro has certified their Profile information is true and correct as of the date of application.
Insurance Note: For any firm that you are considering hiring, we recommend that you obtain a copy of its general liability insurance certificate directly from its insurance carrier. Most responsible Professionals carry both general liability and workers' compensation insurance. Be sure to ask your Professional about this coverage as well, because if a third party is injured by a contractor working on your home improvement project, or if one of the contractor's employees is injured, you may be liable. Your homeowner`s insurance policy may give you some coverage. You should, however, check the exclusions listed on your policy and your coverage limit. Even if your policy provides secondary coverage, the limits of your policy may put you at risk.

Note: Any person or business may be listed on our site. For the Pre-Screened insignia we rely upon a "self-certification" process (the Pre-Screened listed Professional has, by signing an agreement with us, warranted to us that the information is correct). We screen listed Professional profiles to see if they match our screening criteria to gain the Pre-Screened insignia. Wherever possible, we provide links and references so you, as a consumer, may verify the information yourself, and we encourage you to do so. We reserve the right, but not the obligation, to verify/screen selected information provide by a listed Professional through third-parties services such as ContractorCheck.com local and state licensing agencies, and customer references.
How much are the grants? The grants are awarded on a competitive basis and can be up to 25% of total eligible project costs. Grants are limited to $500,000 for renewable energy systems and $250,000 for energy efficiency improvements. Grant requests as low as $2,500 for renewable energy systems and $1,500 for energy efficiency improvements will be considered. At least 20% of the grant funds awarded must be for grants of $20,000 or less.

Who is eligible? The program is designed to assist farmers, ranchers and rural small businesses that are able to demonstrate financial need. All agricultural producers, including farmers and ranchers, who gain 50% or more of their gross income from the agricultural operations are eligible. Small businesses that are located in a rural area can also apply. Rural electric cooperatives may also be eligible to apply.

What types of projects are eligible? Most rural projects that reduce energy use and result in savings for the agricultural producer or small business are eligible as energy efficiency projects. These include projects such as retrofitting lighting or insulation, or purchasing or replacing equipment with more efficiency units. Eligible renewable energy projects include projects that produce energy from wind, solar, biomass, geothermal, hydro power and hydrogen-based sources. The projects can produce any form of energy including, heat, electricity, or fuel.

Futher reading:

Efficiency of solar panels

Solar lease vs buy

Top 5 tips for buying solar panels for your home

How to work out how many solar panels you need?

How many square feet of roof space do I need to install solar panels?

How much do solar panel kits cost?

What do you want to know about buying cheap solar panels?

What maintenance is required?

Are solar systems exempt from property tax in Wisconsin?

Solar installer training and certification

Is there a directory of green building professionals in Kentucky?

Your guide to buying the right solar panels kit



Solar panels cost by system size?