A faithful reader has commented on the DIY (do-it-yourself) potential of solar panel construction, and cited a source promising solar panel construction for extremely affordable sums. Here we are, not to debunk the claims of the "You Can Do It With My Special Video" entrepreneurs, but to give a framework of data to help you in your research.
A single solar cell consists of two wafers of highly engineered silicon, joined carefully by a conductive bond, fastened to a supporting backer, with electrical leads. That cell can typically generate .7 volts of direct current power. Connected in a cluster behind a clear glazing, the assembly, or "panel," can be configured to deliver a maximum of 12, 24 or 48 volts direct current while sitting in the sun on your roof.
The catch, and there are a few, begins with efficiency. Silicon responds only to narrow frequencies of light, operates poorly at high temperatures, and seldom delivers, in many lower cost panels, more than 5% to 15% of the potential power of the sunlight falling on it. Here's a NASA link that explains some of the challenges and how they're met. Optical reflectors, wafer stacking, and various cooling techniques can improve panel efficiency up to 20%. In my previous post, titled "3 kwh per square meter per day..." we did some math about the potential of any rooftop to deliver solar electricity, and this efficiency factor has to be part of that math. Even a well-constructed solar panel will only absorb and convert one watt in five in full sunlight.
Once the solar panel is on the roof and receiving sunlight, it needs to talk to a device that converts direct current to alternating current, which is the form of power distributed by utilities and used in your house. The Inverter, as it is called, massages that direct current of some lower voltage into alternating sine wave current at 120 or 240 volts for American homes to use. Voltage may vary by global region. The inverter operates at about 90% efficiency, depending upon a lot of factors, so use that in your calculations.
If your system will be tied to the grid, your panels and inverter will be specified and dictated by the utility. No home-brew systems that I'm aware of can be grid-tied with CL&P's approval. The engineering of the specified inverters carefully matches grid voltage, among other things, and instantly shuts down the system if the grid loses power. This prevents the deaths of linepersons working during outages. It also prevents you from using your system, even if you manually disconnect it from the grid, during an outage.
As of this writing, photovoltaic panels can't be bought at WalMart, except for specialty applications like charging lawnmower and car batteries, and powering tiny landscape lights. Solar panels are available through Home Depot in modest wattages, and they also subcontract installations in some regions. You cannot yet just fill up two shopping carts and be on the grid by sundown, at least not in Connecticut. In some ways the equipment is less complicated than the permits and inspections required by most utilities.
But we're getting there. So, hats off to you DIY enthusiasts, I hope your time comes soon for affordability and regulatory friendliness. Meantime, you can do smaller projects at home, limited only by your purse and daring. Our time is coming, and your questions are always welcome.
A single solar cell consists of two wafers of highly engineered silicon, joined carefully by a conductive bond, fastened to a supporting backer, with electrical leads. That cell can typically generate .7 volts of direct current power. Connected in a cluster behind a clear glazing, the assembly, or "panel," can be configured to deliver a maximum of 12, 24 or 48 volts direct current while sitting in the sun on your roof.
The catch, and there are a few, begins with efficiency. Silicon responds only to narrow frequencies of light, operates poorly at high temperatures, and seldom delivers, in many lower cost panels, more than 5% to 15% of the potential power of the sunlight falling on it. Here's a NASA link that explains some of the challenges and how they're met. Optical reflectors, wafer stacking, and various cooling techniques can improve panel efficiency up to 20%. In my previous post, titled "3 kwh per square meter per day..." we did some math about the potential of any rooftop to deliver solar electricity, and this efficiency factor has to be part of that math. Even a well-constructed solar panel will only absorb and convert one watt in five in full sunlight.
Once the solar panel is on the roof and receiving sunlight, it needs to talk to a device that converts direct current to alternating current, which is the form of power distributed by utilities and used in your house. The Inverter, as it is called, massages that direct current of some lower voltage into alternating sine wave current at 120 or 240 volts for American homes to use. Voltage may vary by global region. The inverter operates at about 90% efficiency, depending upon a lot of factors, so use that in your calculations.
If your system will be tied to the grid, your panels and inverter will be specified and dictated by the utility. No home-brew systems that I'm aware of can be grid-tied with CL&P's approval. The engineering of the specified inverters carefully matches grid voltage, among other things, and instantly shuts down the system if the grid loses power. This prevents the deaths of linepersons working during outages. It also prevents you from using your system, even if you manually disconnect it from the grid, during an outage.
As of this writing, photovoltaic panels can't be bought at WalMart, except for specialty applications like charging lawnmower and car batteries, and powering tiny landscape lights. Solar panels are available through Home Depot in modest wattages, and they also subcontract installations in some regions. You cannot yet just fill up two shopping carts and be on the grid by sundown, at least not in Connecticut. In some ways the equipment is less complicated than the permits and inspections required by most utilities.
But we're getting there. So, hats off to you DIY enthusiasts, I hope your time comes soon for affordability and regulatory friendliness. Meantime, you can do smaller projects at home, limited only by your purse and daring. Our time is coming, and your questions are always welcome.
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