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)…

More coming soon (like daily - check back often!)

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.

More coming soon (seriously, like every day - check back often!)

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!

Glossary

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.

Energy — Power 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 Rating.  Compare 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 EMT.  Cf. 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 Rating.  Compare 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.