Q: What is photovoltaics?
A: Photovoltaics, or PV for for short, is the process by which sunlight, when it shines upon a properly designed light-sensitive semi-conductor material, generates electrical power in the form of DC voltage and current.
Q: How much power can I harvest using PV?
A: How much money do you want to spend? Seriously, although systems of any size can be designed, we need to know the power flux (power per unit area or power density) that can be reaped. The standard known as "1 sun" corresponds to 1000 Watts/sq meter at sea level. If the panel is facing perpendicular to the sun on a clear day at sea level, that will be the power available. However panels are only 13-15% efficient, and system inefficiencies reduce that number further to about 10-12% overall. So at sea level a 1 square meter panel facing the sun would yield (conservatively) about 100-120 Watts of net power. Note that at higher altitudes such as the Front Range of Colorado and the mountain communities the solar intensity is greater than at sea level, by 10-15%. This increase will show up in the energy harvested by the system, so this is an excellent free benefit for high altitude users. Furthermore, the panels are more efficient at lower temperatures, so the cool mountain air will make the panels more productive. Finally, any reflections from snow, water, etc. will directly increase panel output in proportion to the reflected energy.
Q: How large is a typical PV system?
A: For a residential installation, typical sizes are in the 2-5 KW range. Commercial installations vary considerably, but are usually 10 KW and up. In terms of size, a conservative estimate would be made by taking 100 Watts/sq. meter net output value and dividing that into the size of the array. So a 3 KW array would require 30 sq. meters of space. This comes out to about 16 x 20 ft. Arrays of other sizes scale linearly, so double the power = double the area (and double the $$). Commercial systems vary, but typically exceed 10 KW.
In September 2006, Xcel, Colorado's largest utility, announced that it have awarded Baltimore-based SunEdison a $60 million contract to install 8 megawatts of PV, enough to power 2600 homes. That comes out to about 3.1 KW/home.
Q: How big of a system will I need?
A: To answer this question, many other questions must be answered first. For starters, we should note that there are two general types of PV systems: "off-grid" and "grid-tied." An off-grid system is one which is not served by an electric utility company. These systems typically get there power from PV and/or generators, and battery banks are used for electrical storage, thus assuring 'round-the-clock service. These are stand-alone systems, usually found in remote areas where the cost of running power lines is prohibitive. Sizing these stand-alone systems correctly can be a somewhat complicated affair, with many trade-offs and decisions. An undersized off-grid system will be a source of heartache for the owner, and an oversized one will waste money. Grid-tied systems are, as the name implies, integrated with the power supplied by an electric utility company. This is the standard case in 2006 and beyond. Sizing grid-tied systems is usually much less critical since any undersizing will automatically and seamlessly be compensated for by simply drawing more power from the utility. Oversizing is also less critical if the utility is buying back the excess power (this policy is known as "net metering"), since that credit will help offset (but in no way financially justify) the cost of the extra size. Delibrately oversizing the solar system with the intent of selling excess power back to the utility is not generally a good investment strategy.
For our usual case of grid-tied designs, the size of the system will be determined by many factors, including:
1. How much power must I (or do I want to) produce?
2. How much suitable (south-facing, or south-facing mountable) area do I have on the structure's roof? On the ground?
3. What is my budget?
4. Can I or am I willing to reduce my present usage?
Sizing the system should be done only in conjunction with an experienced solar company or consultant, to assure that all the variables are accounted for and correctly addressed, but here is a simple example: Assume that the homeowner wants to attain "net zero" status. (This means that the homeowner wants to produce as much electricity as she consumes.) Furthermore assume that that average monthly electrical usage is 600 KWh, or 20 KWh/day. (Note: if sizing an off-grid system, the peak monthly usage would be the design figure of merit instead.) Finally, we need to know in what geographical region the system will be installed, so that we can reference the average amount of sunshine available there. For Colorado, we can use 5 hours/day of "peak sunshine." The rest is easy: we divide the 20 KWh of daily use by the 5 hours of sun, and see that we need a 4 KW system. That would (conservatively) require 40 square meters of panels.
Q: What is "peak sunshine?" I thought every place on earth averaged 12 hours per day of sun, minus a small amount for clouds?
A: While it is true that every square inch of earth is in the sun's view an average of 12 hours per day over the course of a year, that time is reduced to account for clouds and more importantly, for the fact that the sun is often at an inefficient angle for generating solar power. (Perform a web search on "heliodon" to get a better understanding of sun angles.) To account for the effects of poor solar angles as well as local weather, every spot on earth has a condensed "peak sun" value that represents the average number of hours per day that the sun would have to be shining square to the array to equal the actual amount of sun the is received on average. For Colorado, that number is approximately 5 hours/day year 'round.
Q: How much does PV cost?
A: Although every system is individually designed and bid, barring any exotic mounting requirements, as a first estimate systems can be ball-park priced at $8/Watt (installed). For systems up to 10 KW in the XCEL service area, there are rebates and credits of up to $3.50/Watt available, which is typically slightly more than 50% of the system cost. Furthermore a federal tax credit of 30% can be claimed be homeowners as well as commercial users.
Q: Are building permits required?
A: It depends on the jurisdiction, but they are required in most cases. All work is done to all applicable building codes and subject to inspection as required locally. Typically the installing firm will acquire any needed permits.
Q: Will GeoStar Solar install the system?
A: No, we are an educational consulting firm only. That means that we will assess your readiness for solar, answer your questions, and then, if you wish to proceed, we will engage an established installation vendor in the area.
Q: I live in a covenant-controlled community. What about my HOA architectural design committee?
A: Alternative energy systems enjoy an exemption from HOA vetoes much the same as satellite dish receivers do. However that does not mean that one may do anything that one wishes. The recommendation is to inform your HOA architectural control committee of your plans and work with them to achieve a mutually satisfactory result. But the bottom line is, HOA’s cannot prevent PV systems from being added. For more information see: http://www.solarbound.org/HTML/for_builders/q6.htm
and http://www.dsireusa.org/library/includes/printincentive.cfm?incentive_code=CO01R
Q: Will the system cause my property taxes to increase?
A: No. Unlike many other improvements, alternative energy additions do not cause a reassessment. They do however add to the value of the house. That is expected to become even more true as energy prices increase and alternative energy systems become more commonplace.
Q: Is solar electricity the best choice?
A: This depends in one’s situation, location, and values. In most cases however, the “best” choice far and away is simply to reduce one’s usage. This is so because it is usually the easiest, cheapest, and quickest option, and it has the advantage that conservation is slightly easier on the environment than generating renewable energy is (and certainly far easier on Mother Earth than using fossil fuel power). PV is good for generating 10-20 KWh/day of power, for general use. Heating water or living space is a poor use for PV. If any type of heating is required, the preferred alternative energy method is passive solar (sun shining in through south-facing windows) followed by solar thermal – systems that heat water via sunlight - or geothermal systems that pump heat out of the earth.
Q: How do I know if solar is right for me?
A: If you are considering a PV installation for your home, business, or mountain cabin, you can start by confirming that your property has a sufficient amount of south-facing roof or other suitable mounting space that is free from shade all day at all times of the year. Remember that the sun is low in the winter, so trees and structures to the south might shade the panels in December but not in June. Next, if you are in the Xcel service area, consider a rough budget of $4/W (after credits and rebates) for systems up to 10 KW. If these two factors are in place (clear southern view and budget) then contact GeoStar Solar and we can perform a complimentary site visit, discuss particulars, and answer any questions.