Solar Basics

December 2018

The basic technology and economics of solar PV panels has been worked out and other than a brief overview, I would point you to the Internet for as much detail as you would like.  First, solar comes in two flavors, one of which is the PV collector system we got.  The other is a solar water heater, which uses the sun to concentrate heat on tubes that produces hot water for home use.  Within the solar PV universe, there are again two choices: on the grid or off the grid. Most people probably think of the off-grid option when the words “solar panels” are spoken.  Off-grid means that the solar panel system is self-contained and the home would not be connected to any external electrical service.  No solar system will generate electricity at night (remember the joke about the solar powered flashlight?). For an off-grid system to work, it must be paired with a battery backup and be robust enough to generate enough electricity during the maximum months of usage (for us in the summer).  Off-grid systems make sense in remote areas with sketchy electrical service.  But we are in suburbia and with a generally reliable system (thank you, PP&L).  We have perhaps 1-2 outages a year, which rarely last longer than 4 hours. For us, an integrated on-grid system makes more sense.

Solar Panels stacked and ready to go, worth their weight in brisket.

Solar generation is the same on- or off-grid, the sun hitting PV collector panels and making DC electricity. From there, each panel has a power optimizer attached to it that independently maximize the power produced and coordinates with the other panels to keep voltage constant and maximize power production.  The electricity is merged into a single line that goes into an inverter.  The inverter changes the DC electricity to AC.  If you have rechargeable batteries in any form – think power tools or cellphone –  you have inverters.  This inverter does a bit more, since it also gathers and transmits data regarding the real-time operation of the system and can link to a computer.  From the inverter, the AC electricity feeds into an independent meter that tracks generation and then into the service box.  The service box is still connected to the meter outside the house. When we use less electricity than we are generating, we are energy producers and the outside meter runs backwards. When we use more electricity than we are generating we are energy consumers and the meter runs forward. Once a year, there is an accounting of the net usage.  So some months we are going to be to the good, and some months we will be drawing on that surplus

Inverter and meter, installed in basement.

As a matter of estimation, we calculated enough panels to produce 95% of the electricity we use each year.  In Pennsylvania, PP&L will buy our excess if we were to use less than we produce, but the rate is not ideal as it does not include distribution costs.  Generally, the perfect situation is produce 1 watt/hour less per year than we would use.  We have 18 panels in a 6×3 array, that is anticipated to produce 7,500 kWh per year, close to our annual consumption.

Other Considerations

As noted above, if your energy needs are greater than ours, solar may make even more sense.  We don’t heat with electric, but some do.  We do not have an electric water heater, but some do.  

Even with the constraints of being at this latitude in Pennsylvania, there are clearly better and worse spots.  Ours is nearly ideal with a south-facing and unobstructed roof that is far enough away from large trees and large enough to hold an adequate array.  The pitch of the roof also makes a difference.  Ideally, a fixed, roof-mounted solar energy system should be at an angle that is equal to the latitude of the location where it is installed. Our latitude here in New Cumberland is 40 degrees.  Our roof pitch is much less – 23 degrees.  The recommended range of pitch is 30-45 degrees.  We are probably giving back some watts, but that is the pitch we have to work with.  If your pitch is closer to 40 degrees, you have closer to the ideal pitch for this area.

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