Home Power Systems: Photovoltaics by L.K.O.

Home Power Systems: Photovoltaics by L.K.O.



　

[Editor's Note: This article is part of a series of feature articles by our Central Rockies Regional Editor about alternative/sustainable/renewable energy (RE) solutions for self-sufficiency. Previous related articles in SurvivalBlog that complement this one are: "Home Power Systems: Batteries," "Home Inverter Comparison: Off Grid and Grid Tied," "Home Power Systems: Micro Hydro", and "Energy Efficiency and Conservation." Upcoming article topics in this Home Power Systems series include: Wind Generators, Solar Water Distillers, Solar Ovens, and Solar Water Heating.]



Photovoltaic History: Maturing technology and infrastructure
Photovoltaics, or PV for short, is the technology that converts sunlight directly into electricity. PV has come a long way from the discovery of the photovoltaic effect in 1839 by French physicist Alexandre-Edmund Becquerel, the first practical silicon solar cell in 1954 by Bell Labs, commercial production by Western Electric at $1,785/Watt a year later, and Telstar’s power source in 1962. Early commercial uses included mountaintop radio repeaters, orbiting satellite power, and various experimental uses. Most of the early consumer adoption, starting in the 1960s and 1970s, was from off-grid pioneers who were challenged by high prices and unwieldy technology of not only the PV panels themselves but also the battery, inverter, and charge controller technologies needed to complete a practical home power system. In 1977, PV panels were first installed on the White House and world-wide production of PV cells surpassed 500 kW; a year later the first solar-powered calculators hit the market.

Even in those early days of PV, the simplicity of energy that comes directly from the sun, uses no moving parts and lasts for decades lured experimenters onward to refine and move towards perfecting the technology. There are numerous other reasons why one would want to switch from grid power to solar, including self-reliance/self-sufficiency/independence, reliability/stability, environmental, financial, maintenance and social/geopolitical ones; this article gives a quick overview of these motivations for PV use.

Home Power magazine, which started in the late 1980s, did much (and still does to this day) to chronicle, educate, and nurture the fledgling home energy market with PV as the flagship technology, adding inverters, home-scale wind turbines, and small hydro as complementary options that work best together to provide year-round energy coverage. Home solar electric systems were spurred onward in that era by surplus PV panels that still had significant useful life after their commercial and government lifespans had been reached; those PV pioneers showed that, even with the growing pains of an immature technology at the time, it still was a viable alternative. Inverters now put out better sine wave AC power than any utility company, leap-frogging over the early awkward days of modified square-wave systems that were buzzy, inefficient, and required a lot more technical savvy to install and maintain. Battery and other interconnection technologies and safety advances have moved home PV systems from home-brew and experimental status, a few decades ago, to mainstream appliance status today.

As the technology and momentum of economies of scale have improved, the cost per PV watt has continued to plummet, from over $70/Watt in 1977, to a mere 36 cents/Watt today, in 2014. Contrast this with the price of gasoline (the linked chart is adjusted for inflation) over about the same period of time, and PV looks more and more attractive all the time, compared with running a generator as a primary alternative energy source, for example. Nowadays one doesn’t have to go far to see PV panels used on traffic lights and equipment, on commercial buildings, and in ever-increasing numbers on residential buildings as well. A couple of decades ago, the prohibitive cost of PV panels and all the related gear (batteries still being one of the more expensive components, but advances are happening there as well) needed to complete a PV home power system stretched out the "break-even"– the time for a system to pay for itself– to spans of a decade or more. Now, with this time frame shrinking due to steadily declining costs of essential all-system components, more companies are manufacturing PV and more are sprouting up to offer PV home installations, sales, and maintenance service.

Recently a milestone was reached in a country not particularly notorious for having abundant solar energy. Germany is evidently producing over half of its electrical energy from photovoltaics! This related document has an interesting map/graphic on page 12, showing the theoretic space requirement to meet the electricity demand of the world, and it appears to be about half the size of Portugal; this is more evidence that the technology, infrastructure, and momentum is growing to make solar electricity a maturing option to our planet’s energy needs. So the obvious question arises: Why aren’t other countries, particularly ones like the United States that have significantly more solar potential, following suit, or better yet, leading the way in this regard? Instead of pondering this rhetorical question from a theoretical standpoint, a more relevant contemporary practical question might be to ask when, rather than if, is the best time to incorporate PV in a home energy system. Obviously location is important; as you can see from this solar map of the USA, if you live in the deserts of southern California, Arizona, New Mexico, or west Texas, your solar PV potential is superb, but if can make a go of it, why not other less sunny locations as well?

If you’ve eagerly followed this industry for decades, or even if you have not but are now curious, and have waited until PV systems are cost effective, your wait may be over. According to the "Trends in PV & Grid Residential Electricity Prices (U.S. Annual Averages)" chart (one of the clickable rotating slides on the page), it appears that last year (2013) the cost of Solar (which continues to drop) overtook the cost of Grid power (which continues to climb) at about 12 cents per kiloWatt-hour (kWh). What this means is that, in general, in the U.S., it’s now more cost effective to use solar than grid power, with everything being equal. What are we waiting for? If you live in a densely wooded area in Alaska with zero solar potential or have draconian CC&Rs in your neighborhood against solar, you might have other obstacles, but now, at least the overall cost issue should no longer be a primary deterrent to at least considering a PV-powered home.



PV System Types
To get a sense of the general categories of PV systems available and which might be suitable for a use you and your family might have, let’s explore four basic types of PV systems:

PV-Direct: The simplest of systems with the fewest components, a system of this type in simplified form consists primarily of a PV panel (or panels) and whatever load is being powered, along with whatever wiring is needed. Since there is no storage (e.g. batteries), this type of system will not work if the sun isn’t shining; the best uses for systems like this include ventilation fans and other efficient air-conditioning (since that’s usually when those loads are needed most anyway) and water pumping.

Off-grid: This type of system does not interface with utility (grid) power at all. These originally were most common in remote locations where the cost of bringing in power lines was prohibitive, and they were the only viable option in many cases. With today’s improvements in design, efficiency, and performance, combined with the low cost of newer systems, even locations with grid power available might consider an off-grid system because of the advantages of independence, which include a somewhat simpler system, since grid disconnects and switching aren’t required, to say nothing of the legal, regulatory, and financial hook-ups required; although, to be fair, these "hoops" are getting smaller and easier to jump through than ever, compared to the PV pioneer days. These systems need a battery (or bank of interconnected batteries) to store PV-acquired solar electricity for nighttime and/or overcast weather usage, a charge controller to protect the battery/bank from overcharging, and optionally (although nowadays this is the most common choice) an inverter to convert the Direct Current (DC) power from the PV array to Alternating Current (AC) for use with AC household appliances, and all the required disconnects, monitoring, and associated electrical safety gear. Fortunately, the equipment needed for a system like this is now easily and safely installed by certified professionals or any homeowners who will avail themselves of a bit of training, which can be found online for free.

Grid-tied systems with battery-backup: Similar to an off-grid setup, this approach is in some ways the "best of both worlds" approach, in that it provides grid backup for the local power (PV and/or wind, micro-hydro, generator, or other source/s) and local backup for the grid power. It’s also the most complex and hence, most expensive, but this might be worth it, considering the versatility, and particularly situations where reliable power is a must regardless of any other considerations. If you run life-sustaining biomedical equipment or run Internet servers or have other critical power-reliability requirements, this might be ideal for your situation. The additional components (above what is needed for a comparable off-grid system) include manual and/or automatic switching, often mandated, or at least regulated by the utility company and typically metering of both grid-supplied and locally-supplied power. Speaking of metering, an important consideration to make before deciding on a system of this type, is whether or not your location has net metering available and what the particular details are. For example, in some locations, e.g. Ashland, Oregon, will purchase excess power, if you generate more than you use in a given month, at full retail, rather than wholesale prices. Grid parity is a related topic you might want to look into. Even more fundamental than this, some locations still don’t allow full hybrid systems like these, so the point might be moot; always check with local, state, and other regulatory agencies and utility companies before making any significant investments in time or energy with a system like this to make sure it will be viable, not merely from a technological and financial point of view but also from a political one.

Grid-tied systems without batteries: Similar to the grid-tied systems with batteries, these systems provide power from both local and off-site sources, but if the off-site (grid) power goes down, you’ll be without power for the duration of the outage. If you have a reliable grid utility with minimal outages, this type of system might work for you. (A bit of phone research a decade ago revealed that the home I bought was on the same sub-grid as the local hospital, which had multiple backup sources and explained why outages were so rare, compared with other places I had lived; this home would have been a good candidate for a system like this.) The "grid-outage-becomes-my-outage" disadvantage is somewhat mitigated by the advantage of reduced system cost, since batteries (and to a lesser extent charge controllers) are non-trivial expenses in systems that store excess power in batteries, with or without the grid-tied connections. Systems like these can be installed by companies, such as RealGoods Solar, SolarCity, SunRun, Trinity Solar, and others. If you opt to go with a system like this (and all of the siting, regulatory, zoning, CC&Rs*, legal, financing and other issues have been addressed), most likely you won’t need to be directly involved in the selection of PV panels and other components, since an installer would likely guide your family through this process, but you might still want to familiarize yourself with the technology, which the remainder of this article will address.

* If your Home-Owner’s Association (HOA) has Covenants, Conditions & Restrictions (CC&Rs) you might want to check their rules first, since their local jurisdiction might constrain the nature and scope of your proposed solar project, even if city, county, state, and federal particulars are all a "go". For example, if you’re on 40 acres with no visible neighbors for miles, there’s not likely to be much in the way of issues in this regard, but if your suburban neighbors "view" looks directly at your roof from 50 feet away, getting "buy-in" from the neighbors and the HOA is well advised. Also, if you’re considering a grid-tied system, make sure you check into your home’s specific net-metering and the wholesale/retail particulars with your electric utility, and get all pertinent details before calculating any financial figures, such as budgets and/or break-even/payback analyses.



Enlist Expertise Before Starting Your PV Project
For all of these system types, it is vitally important that you do your research first; research technical requirements, such as power budget, anticipated loads and peak demand, system sizing, and so forth, and all the safety, regulatory, and utility requirements, which will vary by location, type of system, and what sources you plan to use (e.g. PV, small/micro-hydro, wind, et cetera). Even if you plan to do much of the design and/or installation yourself, it is always a good idea to have a licensed solar professional review your proposed PV (and/or other alternate energy) system before you begin and certainly before you invest your hard-earned time and money into a new system. Also, make sure to check if there are Renewable Energy (RE) Incentive programs and/or Net Metering policies in effect.



Molecular Nitty-gritty
Most solar cells that comprise PV solar panels are made of silicon, which is not any different, in principle, from the sand on your favorite beach or the silicon in SiO2 (Silicon Dioxide, a.k.a. quartz) in your favorite hiking mountain, but those silicon atoms are obviously a bit more sophisticated after they’ve been made into PV solar energy cells. The two primary categories of PV cells are crystalline silicon or thin-film. Crystalline silicon modules, which enjoyed earlier widespread adoption in the history of PV, can use monocrystalline, multicrystalline, or ribbon silicon. Here’s an article with more details on The Difference Between Thin-Film And Crystalline-Silicon Solar Panels. Thin film includes amorphous silicon and a variety of other semiconductor technologies, such as Copper Indium Gallium Diselenide (CIGS), Cadmium Telluride, and other compositions. While these newer approaches to making PV cells garner a lot of media attention, they only comprise about 20% of of the installed base of PV systems, with the crystalline modules doing the majority of the planet’s current PV solar workload.



Efficiency and System Sizing
Start here, with a conservation and efficiency overhaul, even if you end up postponing or even abandoning a RE (Renewable Energy) project. You’ll be glad you started with the essential conservation/efficiency audit, since you’ll save money and minimize your exposure/dependency on external sources of power, while reducing your family’s carbon footprint. Since PV systems (purchased outright at least) are still typically more expensive than several years worth of grid utility bills, the most important first step is almost always to do some serious-but-fun analysis, and often re-thinking, about the home energy budget. It’s fun, because if you stick with it even partial implementations can sweeten your pocketbook while reducing energy consumption. A prior article in this series details important conservation and energy efficiency considerations; a thorough review and elimination of energy wasters from small to large, including replacing watt-guzzling appliances and lighting and just plain old mindful, common sense (free!) lifestyle adjustments to one’s daily energy usage, plus (where appropriate) low-cost upgrades. Also, if remodeling or designing for new construction, solar and efficient home planning can all make a tremendous difference in the sizing of a PV system. If, for example, you can go from four dozen PV panels to two or even one dozen, that can make a tremendous difference in system cost and break-even/payback timing. Another factor to consider is that PV modules in some cases can be added to or subtracted from an installation if one’s energy budget changes, e.g. kids that take marathon showers and leave lights on 24/7 go off to college.



How Much to Hire Out?
If you have a bit of technical aptitude, possess some mechanical prowess, and like to learn new skills, you might want to consider doing some of your own solar design and/or installation with guidance from a seasoned, licensed solar expert. Since we’re talking about electrical wiring and potentially-lethal voltages and other safety considerations, an unguided installation should be out of the question. At minimum, one should enlist a licensed, solar installer with reputable credentials and references from the beginning of a PV project to, at least, double-check (reality check) your energy budget, array sizing calculations, array location, thermal factors, wiring sizing, and diagrams, component selection, safety considerations, parts list, technical skills, planning, et cetera. This will minimize expense, delay, re-work, and other costly and/or hazardous pitfalls. If you find you really enjoy this sort of work, careers in this industry are burgeoning.



PV Panel Selection
Obviously, PV panels are just one component in a Renewable Energy (RE) system, so they must be considered in the context of an overall, well-thought-out design that considers the specific home’s energy budget, array location and sizing, battery sub-system sizing, wiring and safety considerations, geographic and climatic factors, et cetera. Having made that caveat, however, one can select from an ever-growing array (pun-intended) of solar PV manufacturers, models, sizes, and other variables. Here is an extensive chart (Excel spreadsheet) of their 2012-2013 PV Module Buyer’s Guide, prepared by the folks at Home Power Magazine (currently the 2nd link on their Web Xtras page), which lists over 900 PV Manufacturer/Model combinations in the spreadsheet rows, and over two dozen parameters/specifications in the spreadsheet columns, such as rated power per square foot, module efficiency, maximum power voltage, open-circuit voltage, short-circuit current, various temperature coefficients, fuse Amperage ratings, connector types, length, width, depth, frame color, weight, overall warranty, power warranty, and more. Here’s a general overview article on Choosing PV modules from the same folks. If some of these terms don’t ring a bell, ask your solar installer or PV consultant to explain them to you, what to look for, and why.



Digging in Deeper
Since each system design is generally fairly unique, it would take volumes to cover even fairly generalized details of specific classes of PV systems; this is yet another reason to contact a solar PV pro ASAP in your design process to save you time looking into minutiae that might not apply to your particular situation. However, if you spend a little time familiarizing yourself with PV jargon, technology, systems, components, and approaches, you might find you will be better equipped to ask the right questions. If this article has piqued your interest to learn more, Home Power Magazine (among numerous online resources) in addition to helpful overviews of general subject areas, has superb coverage of both general and specific topics, such as Professional Load Analysis & Site Survey, ENERGY BASICS: Shading and Solar-Electric Systems, Free Tools for Estimating PV System Output, Successful PV Site Evaluation, Solar Equipment and Products, Optimizing a PV Array with Orientation & Tilt, iPhone Apps for Solar Geeks, PV Array Mounting Options, numerous examples of first-hand accounts and project profiles of those who have used off-grid PV systems for decades, such as this one, small, medium, and large PV systems, solar home tours, and many more.

Another excellent resource is the National Renewable Energy Laboratory (NREL), which has resources such as this Consumer’s Guide: Get Your Power from the Sun and other resources for solar and other RE topics.

Happy PV solar explorations! – L.K.O. (SurvivalBlog’s Central Rockies Regional Editor)





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