Frequently Asked Questions About Solar

Technical questions about solar…

When people start to think about solar, many of their first questions are technical: how does solar work, is my home or business a good candidate for adding solar, and so forth. Here are our answers to those questions (terms in italics are further defined in the glossary below)…

How does a solar power system work?

Glad you asked! At its most basic, a solar power system consists of a collection of individual solar panels (collectively called an array) connected to one or more inverters, which are then connected to your building's electrical service.
Let's look at each of these components in more detail.

Solar Panels (also called solar modules) — convert sunlight into electrical power. Not all solar panels are alike; at Run on Sun we use REC solar panels for their superior performance and reliability. You can click here to learn more about why we use REC solar panels.

Like a sun-powered battery, solar panels only produce power when exposed to light, and the power that they produce is Direct Current (or DC). (Which just means that the leads coming from the panel have polarity, plus and minus, just like a battery.)

However, the electrical loads in your home or business — like lights, computers, TVs, pool pumps, air conditioners, etc. — all operate on Alternating Current (or AC) and that is where inverters come into the picture.

Inverters or Microinverters — the job of the inverter is to convert DC into AC. If multiple solar panels are connected to a single inverter, then that inverter is referred to as a string or central inverter. On the other hand, if each solar panel has its own inverter, that device is called a microinverter, and microinverters have a multitude of advantages over string inverters, including greater reliability, better performance in shady areas, and more sophisticated monitoring abilities.
You can click here to learn more about why we use Enphase Microinverters.

Interconnection — in order to actually power your loads, the output from the microinverters has got to get connected to your electrical service, and that can be a bit of a limiting factor. We will install a disconnect switch (so the local utility or the fire department can shut the system off if they need to in an emergency) along with a performance meter (so you can tell at a glance that your system is working) and then connect to a circuit breaker in your main electrical panel.

Due to something known as the 20% Rule, the size of your electrical service (measured in Amps) can limit how big a system we can install.

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Will a solar power system work on a cloudy day?

Yes, but not as efficiently as it would on a sunny day. The important thing to keep in mind is that solar panels produce power by converting sunlight (i.e, photons) into electricity (i.e., electrons). The more photons hitting the solar panel, the more electrons produced and thus, more power.

On a cloudy day, the amount of sunlight is reduced, so less power is produced. But not all cloudy days are alike. Some days, particularly in the late spring, have a high overcast layer that tends to burn off as the day wears on. The bright overcast might actually produce a substantial amount of light, even though there is no direct sunlight. In that case, your solar system would produce as much as 70% or more of its rated capacity.

On the other hand, dark, stormy days (the sort we rarely see around here) will greatly reduce the output of your solar system.

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How can I know if my house is a good candidate for solar?

This is an important question to ask since, sadly, not all homes are a good candidate for solar. Putting a solar system on a house that is "bad" for solar will only result in an underperforming system and an unhappy consumer.

To really answer the question, check out our blog post: Assessing My Home's Solar Potential: Step-by-Step.

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How is the solar power system attached to my roof?

There are two main types of roof mounting for solar power systems based on the nature of the roof. On flat roofs a ballasted system is often used, whereas on a pitched roof your would use an anchored system.

By far the most common attachment method is to use bolted down achors on a pitched roof. Here one or two lag bolts (depending on the design of the anchor) are used to screw the anchor into the roof rafters. The rails are then attached to the anchors, and the panels are attached to the rails. Each anchor has to be “flashed” (sealed in some manner in conjunction with the roofing material), often with a metal piece much like what is used on vent pipes that penetrate the roof.

When done properly, the system will resist winds in excess of 100 mph, and last for the lifetime of your roof.

Ballasted systems, as the name implies, rely upon weight to resist the uplift force of the wind. The advantage of a ballast system is that you don't have lots of penetrations in your flat roof, thereby greatly reducing the possibility of a leak.

In California, however, we also have to account for seismic forces, so some number of attachment plates will be required (and must be properly flashed!) to resist lateral motion. The attachment system for ballasted systems cost 3-4 times as much as anchored systems.

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Will it leak?

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How long will a solar power system last?

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I heard that the technology is always improving — shouldn't I wait?

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Okay, I'm ready to start, how long will this take?

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Financial questions about solar…

Financing a solar power system is a key question for pretty much everyone before they can decide to go solar. How much does a solar power system cost? Should you buy it or (heavens forbid) lease it? Fear not, we've got you covered.

How much does a solar power system cost?

The short answer is, it varies - depending on the size of the system that you need, the nature of your roof, the condition of your electrical service, and so on. As a general proposition, larger systems benefit from economy of scale, whereas smaller systems are made more expensive by fixed costs that are not tied to system size (such as engineering or permitting). Steep roofs, tile roofs, or arrays far from the electrical main service panel will all cost more for the labor needed to build them.

There are two ways that the cost of systems are described: cost per Watt, and the Levelized Cost of Energy (LCOE). Sadly, cost per Watt is the most common way to talk about solar system costs, but it tends to be misleading since it is nothing more than the total system cost divided by the power (nameplate) rating of the system. So, a system with fifteen 300 Watt panels that sold for $18,000 would have a cost per Watt of $4.00 ($18,000 ÷ (15 * 300)). The problem with that calculation is that it tells you nothing about the quality of the components used (e.g., how well do those panels perform at temperature, or how efficient are the inverters being used?), nor does it take into consideration site factors that affect the yield of the system (such as shading or orientation). LCOE takes all of those factors into consideration and gives you a much better understanding of what a proposed system will actually save you compared to the energy you are buying from your utility.

All of that being said, we are currently installing residential systems that range from $3.90 to $4.75/Watt, with an LCOE of 9¢/kWh to 12¢/kWh.

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Should I buy or lease my solar power system?

We really do not like solar leases! Check out our Top 5 Reasons to Stay Away from that Solar Lease!

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What is net metering? I heard it's changing (Net Metering 2.0), will that affect me?

Net metering allows the owner of a solar power system to earn credits when their system generates more power than is needed by their home or business at that time. That credit is then used later when the building demands more power than the solar system is producing. And yes, it is changing (at least for SCE customers).
We've laid it all out in our post: Net Metering 2.0 Explained.

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How many bids should I get — and how do I compare them?

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Will installing a solar power system increase the value of my house? And if so, what will that do to my property taxes?

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Will the solar power system pay for itself? How long will that take?

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Environmental questions about solar…

Solar power, we are often told, is clean, renewable energy — but is it? Maybe you've seen those random posts on the Internet claiming that solar is actually dirty (it isn't), and all the environmental claims are false (they're not).
Let's set the record straight!

I heard that it takes more energy to create solar panels than they will ever produce. Is that true?

No, not even close. The National Renewable Energy Laboratory (NREL), which probably knows more about solar than anyone else, looked at this years ago and concluded that with solar panels that were only 12% efficient, the payback on energy occurred in just 4 years! The REC solar panels that we are installing today have efficiencies greater than 21% so their payback is even faster. ( You can read the NREL analysis on solar energy payback here.)

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What happens to solar panels when they no longer work? Can you recycle solar panels?

Solar panels that are being taken out of service need to be properly handled, and not simply dumped into the nearest landfill. We are pleased that a growing number of solar panel manufacturers, including REC, are ramping up a recycling program for "retired" solar panels so that they can be disposed of in a responsible manner.

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20% Rule — According to the National Electrical Code, the sum of the sources of current on a service panel cannot exceed 120% of the rating of the service panel bus bar. What does that mean? On a typical residential service rated at 200 Amps, both the bus and the main circuit breaker are rated at 200 Amps. Applying the 20% rule means that we can install a solar source breaker that is 20% of the bus rating, or 40 Amps, bringing the total of current sources to 240 Amps, or 120% of the bus rating. A recent development are so-called solar ready service panels which allow for higher solar connections, either by way of a dedicated connection that bypasses the bus, or by having a bus with a higher rating than the main breaker.

3-Phase — A type of AC Power delivered by the local utility over three “hot” wires, each one phase shifted by 120°. Commonly used in all but the smallest commercial sites. Compare with Single-Phase.

AC (or Alternating Current) — Electrical power where the polarity alternates (meaning that the flow of electrons reverses direction) so many times per second. In the United States AC powers operates at 60 Hertz (or cycles per second). Common appliances are designed to operate on AC.

Amp — An Amp is a measure of electrical current flow. Your electrical service is rated in Amps, with a 200 Amp service being the most common.

AHJ — Authority Having Jurisdiction, the governmental entity responsible for approving various aspects of a solar project.  Frequently includes both the local building and safety department as well as the local utility.

Azimuth — The orientation of a Solar Array relative to true North.

DC (or Direct Current) — Electrical power where the polarity is fixed, plus and minus, like with a battery or a solar panel.

EMT — Electrical Metallic Tubing, is thin-wall steel conduit used as a raceway for electrical conductors.  Compare with Rigid Metal Conduit.

EnergyPower consumed over time. Standard units are the Watt-hour (Wh), kilowatt-hour (kWh), Megawatt-hour (MWh), or Gigawatt-hour (GWh). One kilowatt of power (say from lighting ten, 100-Watt light bulbs) used for an hour equals one kilowatt-hour of energy.

Energy Yield — The amount of available solar energy converted into electrical energy by a solar power system. Energy Yield is affected by many factors including: Solar Module used, Inverter(s) used, Azimuth, Pitch, Shading, Soiling and whether the array is a Fixed-Plate or Tracking Array.

Fixed-Plate Array — A solar power system consisting of Solar Modules mounted in such a way as to share a common, unchanging Azimuth and Pitch (e.g., fixed to the roof of a house). Compare with Tracking Array.

Inverter — a device that converts (inverts) DC into AC power. Solar power systems use one or more inverters to convert the DC power from the solar panels to AC power for your home or business.

IOU — Investor Owned Utility, a utility that is owned by shareholders.  Cf., Municipal Utility.

IRR — Internal Rate of Return, a common measure of the value of an investment.  Technically, it is the interest rate for which the Present Value of all of the future cash flows associated with a given project is equal to the cost of the project.  The higher the value, the more desirable the investment.

Kilowatt (kW) — One thousand Watts, the most common measure of electrical power.

Kilowatt-hour (kWh) — One Kilowatt of power consumed over one hour of time, it is the most common measure of electrical energy.

Levelized Cost of Energy (LCOE) — is the cost in $/kWh for the energy produced by your solar power system. It is calculated by adding up your final cost for the system over its lifetime (purchase price, financing charges (if any), maintenance costs (if any)) and dividing that by the total amount of energy that the system will produce over that same lifetime.

Line-Side Tap — A means of connecting a solar power system to a utility-provided electrical service on the “line” (as opposed to the “load”) side of the main electrical disconnect. A Line-Side Tap is required if the current being delivered by the solar power system exceeds the 120% of busbar-rating rule in the NEC, or if there simply is no place to install an appropriate circuit breaker on the load side.

Loads — anything that requires electrical power to operate is considered a load. Electrical loads in a home include lights, computers, TVs, pool pumps, air conditioners, etc. The higher your total load the higher your electrical usage will be, and so to your bill!

Microinverter — a sophisticated form of inverter, designed to match up with one solar panel. Enphase microinverters are more reliable than conventional inverters, provide superior performance in shaded locations, and allow for comprehensive performance monitoring.

Municipal Utility (Muni) — A utility owned by a city, county or other governmental entity.  Compare with IOU.

NABCEP — North American Board of Certified Energy Practitioners, the preeminent certification entity in the solar industry.

Nameplate Rating — See STC Rating.

NEC — National Electrical Code,  guidelines governing all aspects of electrical work, including solar power systems, that can be adopted by a local AHJ, and once adopted, become the basis for permitting and inspection.

Net Metering — A billing arrangement between a solar customer and their local utility whereby energy in excess of that needed by local loads is exported to the grid for credit that is “netted” against energy drawn from the grid.

NREL — The National Renewable Energy Laboratory in Golden, Colorado.

PACE — Property Assessed Clean Energy, a means of paying for a solar power system through the site owner’s property taxes.

Performance Meter — A meter of varying degrees of accuracy that measures the output of a solar power system.  Performance meters can be as simple as a refurbished analog meter or as sophisticated as a Revenue-Grade Meter.

Pitch — The inclination of a Solar Array in degrees relative to horizontal.

Power — The ability to do work.  Standard units are the Watt (W), kilowatt (kW), Megawatt (MW), or Gigawatt (GW).

Present Value — The value, as of a specified date, of future economic benefits and/or proceeds from sale, calculated using an appropriate discount rate.

PTC Rating — The measure of a Solar Module’s power output based on Photovoltaic Test Conditions.  It is always lower than the module’s nameplate or STC RatingCompare with STC Rating.

PTO — Permission to Operate, an official notice from the local utility that a solar power system has been approved to begin regular operations connected to the grid.

PVWatts — A computer model created and maintained by NREL for analyzing the performance of solar power systems.  PVWatts is the model commonly used for creating system performance projections used by utilities in determining solar Rebates.

Rebate — A payment from a utility to a solar customer as an incentive to install a solar power system.  As of this writing, the only utility still offering rebates in the Run on Sun service area was LADWP.

Revenue-Grade Meter — A Performance Meter designed to measure the output of a solar power system to a level of accuracy deemed sufficient by the local utility.

Rigid Metal Conduit — A thick-wall steel conduit used as a raceway for electrical conductors and providing greater conductor protection than EMTCf. EMT.

ROI — Return on Investment, a calculation that determines how soon a particular investment will be paid back (the “payback period”) based on a series of anticipated cash flows.

Shading — The amount of sunlight blocked from reaching the solar array due to obstructions such as trees, buildings, power poles, etc.  Ideal sites have no shading; acceptable sites will be 90% shading free.  Sites with shading values below 90% should not be built without the use of Microinverters or other comparable technology.  See also, Shading Analysis.

Shading Analysis — An analysis that determines the degree of Shading at a site.  Typical output of such an analysis is a month-by-month assessment of how much of the available sunlight will actually reach the array.  (An unshaded site would be at 100% for each month.)

Split-Phase — A type of AC Power supplied by the local utility where power is delivered over two “hot” wires, 180 out-of-phase with each other.  Commonly used in residential electrical systems or very small commercial sites.  Compare with 3-Phase.

Site Plan — A series of drawings that shows where a solar power system is located at a given site and may include detail drawings showing how various system components are mounted or connected together.

SLD — Single-Line Drawing, a simplified schematic view of the electrical components involved in a solar power system,  typically also includes specification of conductors and conduits to be used in the system.

Soiling — Term for the dirt, debris and other deposits that accumulate upon Solar Modules over time, thereby reducing their Energy Yield.

Solar Sub-Array — A collection of Solar Modules with a common Pitch and Azimuth.

Solar Array — A collection of Solar Sub-Arrays.

Solar Cell — A semiconductor device that converts light (photons) into electricity.  Multiple Solar Cells are combined together to produce a Solar Module.

Solar Module — Also referred to as a solar panel, an integrated electronic device consisting of multiple Solar Cells, arranged in an interconnected grid, encapsulated against moisture and other environmental agents, and held together by a rigid frame for mounting.

Solar Noon — The moment in the day when the Sun is at its highest point in the sky.

Solar Pathfinder — A device used to perform a solar Shading Analysis.

STC Rating — Also known as the Nameplate Rating, the measure of a Solar Module’s power output based on Standard Test Conditions.  It is always higher than the module’s PTC RatingCompare with PTC Rating.

Tiered Rate — a term used to describe Utility Rate Schedules that charge a higher rate as total consumption increases. The purpose of a Tiered Rate is encourage energy conservation by making heavy energy users pay more.

TOU Rate — Time-of-Use, a term used to describe Utility Rate Schedules that charge different amounts for energy consumption and/or peak power demand, based on the time of day. In SCE territory the amount charged is also dependant on the season of the year. The purpose of a TOU Rate is to encourage load shifting so that peak power demand from the utility is reduced.

Tracking Array — A solar power system consisting of Solar Modules mounted on a frame that can change its Azimuth over the course of a day to track the Sun, and its Pitch over the course of the year to account for variation in the Sun’s path.  A Tracking Array that only changes Azimuth is called a single-axis tracker, whereas one that also changes Pitch is called a two-axis tracker. Although Tracking Arrays can increase annual Energy Yield by as much as 45% over a comparable Fixed-Plate Array, they are not commonly used in rooftop solar power systems due to space and maintenance constraints.

Transformer — An electrical device used with AC Power systems that can increase (“step-up”) or decrease (“step-down”) the voltage in a circuit.  Transformers are commonly used with an Inverter to match its output voltage to that of the electric service provided by the local utility.

Usage — The most common component of electric utility bills, based on the total amount of grid-provided energy consumed during a billing cycle.

Utility Rate Schedules — The formula by which a utility calculates a customer’s bill.  Utilities, especially IOUs, have many, many rate schedules, some of which will be more or less advantageous to solar power system owners.