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Why solar electric rooftop Photo-Voltaic ("PV") system? PV is non-polluting, once the panels are made, and give a good feeling when you watch your meter at times spinning backward, pumping electric into the grid, visible proof that you are part of the solution of our energy-independence problem. We've always had too much electric power, there's never been a shortage; the problem has been to make it when and where it's needed, because it's difficult to store. Electric is the cheapest and most efficient way of doing work and moving materials; producing it where it's used, at the house, and when, during the peak time of high electric use, is the most efficient and cheapest way of managing this resource. What does a residential solar PV cost, and why buy it? PV is a prudent investment. The bulk of the cost is the PV solar panels, which are guaranteed for 25 years and may last much longer, an enduring, visible asset. For each $20,000 in system cost, PV returns about $1000 in electric per year at an "average" utility rate, a 5% Return on Investment ("ROI"). But with rebates and tax credits, the price is reduced to about $10,000 and the ROI is 7% - 11%, even higher if applied to "tiered" rates or if Time Of Use (TOU) pricing is used. Never look at solar in terms of "payback", because it's an enduring asset like your home. You don't look for payback on your monthly payments to the utility company, or the house payment to the bank. A better way is RETURN ON INVESTMENT, the value returned to you from an investment in solar vs. other uses for the money. Renting a home seems cheaper than buying, if you just look at the monthly payment; but in the long run, home ownership has a much higher Return on Investment than does renting. Similarly, buying your electric, while a large investment, is cheaper in the long run than renting it from the utility company. It's even better than that, though, because: 1. Your money goes into hardware on your own rooftop that you get to keep, worth about twice what you paid for it. Instead of into monthly payments that just go to burn coal in the desert, or even support nuke power plants. 2. Your home value goes up by about $20,000 for each $10,000 you invest. 3. It's a large amount of money up-front, but solar is a home addition that returns you money. The amortized cost of solar power is less than the utility electric it replaces; if you borrow the money, not only is the interest deductable, but the payments are lower than the portion of the electric bill it replaces. 4. You're saving after-tax dollars you formerly sent to the electric company; solar frees up to 140% pre-tax income, depending on your tax bracket. Furthermore, you are protected against future electric rate hikes, your electric cost is "frozen" at less than current rates. 5. Panels are mounted about 6" above the roof; the portion of your home under the panels is shaded from fierce sunlight, and insulated to some degree in the winter. The panels cool the home, protect underlying roof, turn UV into power. Solar PV has the synergistic effect of shading the home while using the excess sunlight to make electric to run the A/C. 6. Tiered rates, which charge more for over-baseline usage and much more for profligate use, are the coming thing. Solar PV can reduce the highest tier, raising ROI to 20%, even if you don't want to "zero-out" energy usage. 7. Time of Use pricing, where available, can leverage a small system's on-peak production to allow a much larger off-peak drawdown, such as night-time charging of an electric car or weekend power tool use. 8. Plug-in hybrids and EVs, when available, can replace some gasoline with electric you make yourself, paying a much higher rate of return on the PV investment. The money not spent on gasoline can pay for your solar system. 9. Starting in 2011, the utilities will pay for excess solar production, although we don't know how much yet; if you lease a system, you won't get that benefit. 10. Leasing is always more expensive, because you are paying also the bank that loans the money; look out for escalator clauses in the lease arrangement. Just like the utility company, the seemingly low monthly payment really "nickels-and-dimes" you out of more money than if you can manage ownership. 11. Solar gives a feeling of "empowerment", visible proof of becoming part of the solution, not the problem. Your solar system may power 5 or 10 of your neighbors in the daytime peak period, you may see your meter run backward. 12. The Edison system consists of large, central generators that power substations at very high voltage; each substation powers a string of pole-mounted transformers that step the voltage down to 240 volts. Each pole-mounted transformer powers 8 to 12 residences (businesses sometimes get their own). During periods of high demand, when the voltage drops, substations jack up the voltage; that sometimes blows up superannuated pole-mounted transformers during a "heat storm". Each solar system lowers the load on ancient transformers, prolonging their life and lowering the chance of outages from the heat storm event. 13. Solar rooftop power puts the electric generation on thousands of already-developed rooftops, instead of plans to build new power plants in the desert. Why tax the wilderness when we already have unused sunny rooftops? What does a solar PV rooftop system consist of? Lightweight (3 lbs. per square ft.) solar panels mounted on racks affixed via watertight, hot-mopped bolts to roof joists, which generate DC current. Wires in conduit bring the DC to an inverter, which changes the current to familiar AC house-current. Each system must be permitted and approved under building codes and by the utility, which must allow it to feed excess electric into the local grid. Each grid-connected PV is a "co-generator" with the utility. Weight: any roof that is up-to-code can easily stand solar without new "engineering", because it must be strong enough to support a 300 lb. person -- even one who jumps -- which is over 100 times the weight of a solar panel. Furthermore, while you can walk on the panels, they distribute the weight over more rooftop. The panels weigh 3 lbs. per s.f., one layer of composition; if you replace a tile rooftop with solar, you actually lower the weight. Roofs are allowed 3 layers of composition, so one layer of solar is comparatively light. Some fun electric facts Volts and Amps: Electrician-talk. Suffice it to say that "Watts are equal to Volts times Amps", and wires have to be thicker with low voltages (like your car's battery cable) and high-voltage systems are more efficient than lower-voltage systems. Watt: Measure of electric POWER consumption-rate. 30 Watt light bulb, 300 Watt computer, and 2000 Watt hair dryer. kilo-Watt: 1000 Watts, like ten 100 Watt light bulbs turned on at the same time. Also, about what a refrigerator uses when its motor goes on, and less than a hair dryer when it's turned on. Abbreviated "kW". kilo-Watt-hour: 1000 Watts of appliances running one hour. This is the normal unit of work that the electric company charges from 8 cents to 50 cents to deliver to your electric meter. Abbreviated "kWh". This is the standard unit of electric ENERGY. kW: POWER or potential to do work kWh: ENERGY or work actually done over a period of time PV size: Measured in Watts. A 1000 Watt system is needed, as a rule of thumb, for each resident. So the "average" home (2.5 persons) needs, as a rule of thumb, 2500 Watts, or 2.5 kW. So if every home had a 2500 Watt solar system, we'd have a chance of producing almost as much energy as we used, overall. Such a system would, on the average, produce about 12 kWh per day (360 kWh per month) assuming the rule-of-thumb number of about 5.5 hours of full sun equivalent per day, valid at our latitude. Energy efficiency conservation can lower usage closer to this number. Battery backup optional PV requires hookup to the grid to get the rebate, pumping excess electric into the grid in the day, but drawing down at night. But these "grid-tied" systems stop producing electric if the grid goes down, or if the utility voltage varies from what it should be (120v on each of lines one and two) by more than 10%. For safety, when the grid is unstable or fails, all solar systems are required to "island" and shut off until the grid comes back to normal. Battery backup systems can also be connected to the grid, but in addition can stay on if the grid fails. These systems require a place to put the battery, a special inverter, and rewiring of the main panel so that the inverter can detect grid failure. If this happens, the inverter temporarily breaks the connection to the grid and draws on the stored power of the battery. Service is uninterrupted on the backed-up circuits as long as the batteries last. Hooking such an inverter up to a solar PV system means that you only have to last on the battery pack until the next sunny day, when the batteries can be recharged by the PV. If the grid were to fail for a long time, you could still have power and would be, in effect, "off-grid". When the grid comes back up, the inverter detects it, locks into it, and restores your full power to all circuits. Battery backup systems use an inverter that operates at a much lower voltage and lower efficiency. Battery backup systems sacrifice some efficiency in exchange for the benefit of backing up the home.