Frequently Asked Questions
| Assumptions

Why does the Energy chart show “Excess from Solar” providing more electricity than I use?

During sunny summer months, your solar system will often produce more electricity than you consume. This excess electricity is typically carried over as a credit on your account to make up the difference in future months when days are shorter and your solar system is producing less.

What is included in the upfront cost of my solar system?

The upfront system cost represents what you can expect to pay initially to get your system up and running. Depending on how you finance your system, the upfront cost can be a portion or all of the net system cost. The net system cost is the complete cost of your system after incentives. Solar panels, balance of system components (wiring, mounting hardware, inverter, etc.), and labor for installation are all taken into account in the upfront cost.

Why don’t my energy savings match my bill savings?

Most utilities include “fixed charges” on your bill, which are charges that are the same no matter how much energy you use. Since your solar system can only be used to offset energy related charges (charges on a per kilowatt-hour basis), your bill savings will not exactly match your energy savings. Other times your solar system may offset energy from higher tiers that is expensive. This energy may represent a small portion of your total electricity consumption, but a large portion of your electric bill. In this case your electric bill savings will be greater than your electricity savings.

Does Energy Trust offer incentives for non-solar renewable energy projects?

Yes, Energy Trust offers incentives for non-solar renewable energy installations. Incentives are available for wind power, hydropower, biopower and geothermal electricity projects. Full list of incentives for renewable energy projects.

What rebates or incentives are available for solar?

Energy Trust of Oregon provides solar electric cash incentives for Oregon customers of Portland General Electric and Pacific Power.

Some public utility districts and electric co-ops also offer solar rebates.

Tax credits, which may be combined with Energy Trust incentives, are available from the federal government.

Do I have to use an Energy Trust trade ally for my project, or can I use my own contractor?

We strongly encourage you to work with Energy Trust trade allies, as they are trained on our offerings and requirements, and we frequently verify the quality of their work.

If you hire a contractor who is not a trade ally, you are able to receive cash incentives for most projects. Your contractor must have a current Oregon Construction Contractors Board license or, for NW Natural customers in Washington, a current Washington contractor’s license in order for your project to be eligible for Energy Trust incentives.

You must work with an approved Energy Trust trade ally to receive a cash incentive for solar projects. To receive a customized list of referrals to trade allies that work in your area, visit Trade allies are familiar with Energy Trust’s standards and quality control requirements. However, it is your responsibility to interview and select your contractor carefully.

Are Energy Trust cash incentives available to all Oregonians for renewable energy installations?

No. Energy Trust cash incentives for renewable energy installations are only available for residential customers of Portland General Electric or Pacific Power in Oregon, or for businesses that deliver power to PGE or Pacific Power.

What is the lifespan of a solar system?

Solar panels carry 20 to 30 year performance warranties. That means they will continue to produce at least 80 percent of their original power output through the end of the warranty period. Some of the first solar panels made in the 1950s are still producing electricity today. Inverters carry a 10 to 15 year warranty but can last as long as 20 years.

How much roof space do I need for a solar electric system?

An average size, five kilowatt residential solar electric system will have 16 to 20 panels and require about 400 square feet of roof space.

How much does solar cost?

For a solar electric system, the cost depends on the size of the system and the ease of installation. To receive a customized bid from trade allies that work in your area, visit

How much power does a solar electric system produce?

An average five kilowatt solar electric system will produce between 5,000 and 7,000 kilowatt hours of electricity each year, depending on where in Oregon it is located. That’s 50-70 percent of a typical Oregon home’s electrical load.

Can I receive an Energy Trust incentive or tax credits if I install my own solar system?

Self-installed systems are not eligible for Energy Trust incentives or Oregon state energy tax credits.

What resources are available if I want to install solar myself?

We don’t have recommendations for buying your own solar panels, but there are many online resources available. Solar Energy International offers installation classes in several western states, including Washington.

What is a solar inverter?

The inverter is the “brains” of the solar electric system. It changes the DC (direct current) electricity into AC (alternating current) or “household” electricity. This power is then fed directly into a double breaker in your home’s main electrical panel.

What direction should solar panels face?

South is the best orientation, but east or west can work, too. Your solar contractor can assess the best orientation for your site. To receive a customized bid from trade allies that work in your area, visit

Can I heat my house with solar?

If you heat your home with electricity, a solar electric system will help offset the energy you use to power your heating system. Homes can also be designed to absorb heat passively through the sun. Only systems that generate electricity are eligible for Energy Trust cash incentives.

What is net metering?

Oregon’s net metering law allows utility customers to generate their own electricity and reduce their electricity bills. If you install a solar electric system, your electric utility will replace your existing utility meter for a bidirectional “net” meter. This meter keeps track of how much electricity you use from the utility and how much your solar systems supplies to the grid. Each month, the power you used from your utility is offset by the power you send to the utility. You are only charged for the difference or the “net.”

If you generate more power than you use in a given month, your electric bill will have no charges, and you will receive kilowatt hour credits that will be applied to your future bills. Unused credits will accumulate in your account, so what you “save” during sunny summer months can be applied to charges during cloudy winter months. This eliminates the need for batteries to store your excess energy.

Do I need batteries with my solar system?

You don’t need to install batteries unless you want to have backup power during a utility power outage. Solar electric systems have no way to store power without battery backup and for safety reasons cannot produce power during an outage.

Will my solar electric system work if there’s a power outage?

For safety reasons, your solar electric system will stop generating electricity during a utility power outage unless you have a battery system. While batteries can be installed for backup power, they increase installation cost and complexity. As a result, most homeowners choose not to install battery backup.

Will I be disqualified for an incentive if my sun exposure reading does not meet Energy Trust requirements?

To receive an Energy Trust incentive, your solar energy system must have access to at least 75 percent of the sun available to that spot. Your solar trade ally contractor must conduct the sun assessment at the worst location of the future array or collectors and is responsible for ensuring that your system meets this requirement.

Some contractors may be more conservative with sun assessments than others. However, as long as they take measurements from the worst location and document a reading that is better than 75 percent, your system should pass inspection and qualify for an incentive.

If a trade ally’s assessment is discovered to be untrue when an installation is inspected, the trade ally is responsible for the lost incentive.

Do I need to install a new roof before installing solar on my home or business?

Your roof must have at least 10 years of remaining life in order to qualify for an Energy Trust solar incentive. This requirement protects you from having to remove solar panels for roof replacement just a few years after you install them.

Most solar contractors can estimate the age and life expectancy of your roof. If needed, they may consult with a roofer or home inspector.

Where can I learn to install solar?

If you are not a licensed electrician or plumber and want to become a professional solar installer, you must complete a licensing program. For a summary of licensing and apprenticeship programs in Oregon, visit the Oregon Solar Energy Industries Association website.

If you are already a licensed professional, you can gain solar experience through installation training course at an IBEW training center, Oregon community college or the Oregon Solar Energy Industries Association website.

If you are not a professional and would just like to learn how to install solar, consider enrolling in a class through Solar Energy International. They offer classes in several western states, including Washington.

Can I get incentives or tax credits if my solar electric system isn’t connected to the grid?

Only grid-tied systems qualify for Energy Trust incentives. However, off-grid systems may be eligible for a federal tax credit.

Are there tax credits for installing solar panels at my home?

There is a federal personal income tax credit for homeowners who install a solar energy system. If you receive an Energy Trust incentive for your solar system, your eligibility for federal tax credits is not affected, but it may impact the total amount of credit you are qualified to receive. Consult your tax professional for guidance.

The federal government offers an Investment Tax Credit for solar energy systems. If you lease your solar electric system, you are not eligible to claim this tax credit. Consult your tax professional or solar trade ally for current information about the credit.

Are there tax credits for installing solar panels at my business?

The federal government offers a Business Energy Investment Tax Credit and a special, accelerated depreciation schedule for businesses that install solar. Receiving an Energy Trust incentive does not affect your eligibility for either of these tax benefits. In general, nonprofit organizations and public entities are not able to use these benefits because they do not pay taxes.

Consult your tax professional or solar trade ally for more information about these tax benefits.

Are there any special grants available for renewable energy projects?

There are several local, state and federal grants available to promote the installation of renewable energy systems at farms or businesses. Grants are typically awarded through a competitive application process and may not be able to be combined with Energy Trust incentives. For current information, contact one of the following grant programs.

Bill Savings Calculation

To calculate utility bill savings, WattPlan calculates a before-solar and an after-solar bill, and compares the bill details. The after-solar bill is calculated by modifying the before solar load profile based on the estimated output of the proposed solar system.

Customer Energy Usage

When consumption data is not available, WattPlan generates an hourly consumption profile from the user provided average monthly bill. WattPlan uses statistical average profiles published by utilities to synthesize an hourly consumption profile for the user based on their electric rate plane and average monthly bill amount. This assumption will be reasonably accurate for the majority of users, but those with unique profiles, such as users with time - of - use rates, may experience notable differences.

Derate Factors

The solar system derate factors used in WattPlan are as follows:

ComponentDefault Derate Factor
Standard Test Conditions rating to PVUSA Test Conditions rating10%
Wiring losses, module mismatch and module soiling10%
Annual system degradation0.5%

Environmental Savings

Environmental impact figures for CO2 are computed using EPA regional emission rates derived from the fuel mix used to generate electricity within the region. These savings are then displayed as equivalent measures(trees planted or miles not driven) using EPA approved conversion factors.

Operation and Maintenance

In the course of this analysis, WattPlan assumes an annual maintenance cost of $10/kWdc, and a one-time inverter replacement cost of $400/kWdc, halfway through the life of the system. These costs can be seen in the cash flow details and lifetime cost breakdown.

PV Module Temperature

The solar production simulation process uses a module’s rating under PVUSA Testing Conditions(PTC). Because ambient temperature, and not cell temperature, is specified by PTC, a cell reference temperature of 45°C is assumed in the calculation of temperature derate.

Solar Data Source

To calculate solar system production, WattPlan uses SolarAnywhere® Typical GHI Year satellite data where GHI stands for Global Horizontal Irradiance. More info can be found at

System Size

The system size is calculated dynamically to offset 80% of the user's annual electricity use. Depending on the user’s electric rate plan, the annual bill savings may be greater than, or less than, the percentage of electricity that is offset.

Tax Implications

WattPlan makes several assumptions about the tax impact of owning a solar system. Residential customers can receive income tax credits and depending on financing, may be able to take tax deductions due to loan interest payments. Commercial customers are classified as taxable or tax exempt entities. WattPlan assumes tax exempt customers have no tax benefits, as they do not pay any taxes. Taxable customers can have tax benefits or costs related to investment tax credits, depreciation and change in expenses, etc. WattPlan makes no guarantees about tax benefits, and users should check with their tax advisor with regard to any tax treatments.