In order to defectively use of solar energy using solar module panels. This is square one in your quest for a supply of renewable energy. Let’s start the ball rolling with a question: How much energy do you need? If you skipped over the chapter on energy efficiency, it’s quite likely that you are consuming significantly more electricity than necessary, resulting in equally high generation system requirements and costs.
Remember the rule of thumb: for every energy dollar you put into energy efficiency, you reduce electrical generation capital costs by between three and five dollars. You cannot afford to sidestep the energy efficiency process. Sorry!
Start by checking your electrical.. bills over the last few months or call your utility to find your average monthly electrical consumption. A figure of 20 to 40 kilowatt-hours per day (kWh) is average and may be considerably higher if you have electric heat, electric hot water, or central air-conditioning.
If your current electrical consumption is a bit on the high side you will quickly find out that you need pockets as deep as Bill gates in order to generate enough electricity to power your house.
To quickly recap, let’s consider the case for compact fluorescent light bulbs one more times. As discussed earlier, a compact fluorescent light bulb uses approximately 4.5 times less energy than a standard incandescent bulb. Assume for a moment that your home requires 600 W of lighting in the main floor area. If this light is generated using incandescent bulbs, we need 600 W of PV panels to power them. If PV panels are selling for $4.00 per watt, the cost is $ 2400. With compact fluorescent lamps, however, we need only 130 W of bulbs to create the equivalent brightness, for a PV module cost of $520. Efficiency is ALWAYS cheaper than additional generation.
Another factor in determining the size of your PV generation system is any grants or low-interest loans that may be available in your jurisdiction. The California reneuwables buy-down program provides the homeowner with a grant of up to 50% with a maximum dollar limit. Political realities being what they are, it is always wise to get onto the gravy train while you have the chance.
Lastly, discuss this decision with your dealer. Get advice about system sizes for your roof area, equipment package prices, and other market variables that are impossible to define in this book.
As there is no standard or typical system size, we will assume an electrical energy-generation objective of 4,000 Watt-hours ( 4 kWh) per day.
To give you a bit of guidance on this value, Lorraine and I run our house-hold on between 3 and 5 kWh per day, less if we traveling, more if we have friends over for a late-night party. If you have teenagers who stay up all night, maybe you should stay grid-interconnected. To define “typical” is pretty hard, but here are some values that I can share from other installations:
- Weekend cottage running a few lights, small T.V., boom-box stereo, and no fridge: a 12 Volt D.C. system is fine with two to four solar module panels and a small battery Bank with solar battery charger. This system will generate 200 Watts peak power and 1,000 Watt-hours per day energy.
- Full-time, seasonal cottage with four people, requiring refrigeration and limited water pumping: a 12 Volt system is fine, possible using a mix of direct current and alternating current outlets for various loads. If the cottage will “grow” over time, wire for 120 Volts A.C now. Use a small inverter for 1,500 Watts peak power and up to 2,000 Watt-hours per day of energy. The system will require a PV array of approximately 500-Watts peak output.
- Full-time residence with four people, large energy-conserver philosophy, no dishwasher or clothes dryer, a small television and stereo, high-efficiency clothes washer, and 120 Volt refrigerator: wire system for 24 Volt batteries and provide an inverter with 2,500 Watts peak power and up to 3,000 Watt-hours per day energy. The system will require solar module panels of between 800 and 1,000 Watts peak output with a backup generator for “dark months.” Depending on the location, more PV may offset the need for a generator provided winter sun hours are able to provide 100% of the daily load.
- Full time residence with all the electrical (high-efficiency) goodies, possibly including a home theatre system, dishwasher, gas clothes dryer, central vacuum, washing machine, and electric refrigeration: System may be wired for either a 24 or 48 Volt battery. Use 24 Volts for total daily energy consumption below 7,000 Watt-hours per day and 48 Volts for larger systems. Provide an inverter of between 2,500 Watts minimum and 4,000 watts peak output or larger, depending on final peak loading. Will require a PV array of 2,000 Watts peaks or higher depending on load. For off-grid systems a backup generator will be required.
References: The Renewable Energy Handbook, by William H. Kemp.
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