[This post is part of a series about our net-zero residential solar project – to see a list of links to the full Solar Project series, click here or to bring up a list of all green-themed posts, click here.]
I have been getting enough questions from the blog readers and neighbors that it is time to do a frequently asked questions list. I have divided the common questions into four groups: practical questions, financial questions, technology questions, project questions and philosophical questions. These are the Technology Questions.
Technology Questions
Q: What is net-metering?
Net Metering is a regulatory requirement imposed on electric companies in some areas which allows you to earn credit for the electricity you generate with your solar system and send backwards through your utility meter. Exact provisions vary with each state, but the effect is to allow you to generate excess power during the day which is credited against your bill and offsets the electricity you use at night. With a net-zero system, you will generate more power than you use during the course of a year and actually get a credit from your power company. See The Solar Project – Equipment Economics. (return to list of questions)
Q: Are these systems safe?
Yes. Solar cells are mostly silicon, the primary component of sand. Solar electric systems produce no exhaust and no toxic materials. The electricity coming through the inverter is just like the electricity coming from household wall sockets. It is still electricity, so you probably should’t jam a screwdriver into the electronics of your system, but they are wired according to the electrical code and are just as safe as any other electrical system. All the components must be approved for utility interconnection and must be installed according to the best construction practices. (return to list of questions)
Q: Do you get heat or hot water from these?
Not exactly. These photovoltaic systems provide electricity. If your hot water heater is electric, you get hot water indirectly from it. Likewise if your home heating is all or partially electric you get heating from them. You do get cooling though, which is one of the greatest synergies available with these systems – they put out maximum power during times when you want maximum air conditioning. (return to list of questions)
Q: What is a kilowatt-hour (kWh)? How many does my house use?
A kilowatt-hour is a measure of electricity. It is the amount of power (kilowatts) used over a period of time (hours). A 60-watt light bulb that is illuminated for one hour uses 60 watt-hours of electricity, or .060 kilowatt-hours. If it is illuminated for a half-hour, the bulb will consume .030 kWh of electricity. The average house consumes about 20 kilowatt-hours of electricity per day, or 600 kWh per month or 7,200 kWh per year. Our house uses a bit more than average at 10,000 kWh per year (despite our best efforts to conserve!), so our system is designed (and guaranteed) to produce between 11,642-12,868 kWh of solar energy per year. (return to list of questions)
Q: Are these really good for the environment?
The energy created through a photovoltaic solar system produces no pollutants. By offsetting peak electricity demand, solar systems reduce the need for coal-fired power plants. Our system is guaranteed to produce between 11,642-12,868 kWh of solar energy per year. If you translate that into gasoline terms, that is equivalent to 278,045 lbs. of CO2 saved. How much CO2 is that? It is the equivalent of driving an average car 333,645 miles. That same number of miles driven would also produce 312 lbs of NOx emissions. If you wanted to absorb that much CO2 it would require 3,233 mature trees. And if you think of it in terms of solid waste, it is the equivalent of recycling 92,682 lbs of solid waste or avoiding 41,887 lbs of greenouse gas from land-filled garbage. (Source: SunPower Corp. figures). Over a thirty-year period, a 7.6 kWp system typically offsets the same amount of greenhouse gases as 100 acres of trees (Source: EPA EGRID2000 database). See The Solar Project – Financing. (return to list of questions)
Q: You are all set if you have a blackout and the power goes out, right?
No. While it is possible to purchase a backup storage system, this is quite a bit more expensive and complex than a grid-tied system. What you give up in avoiding that cost and complexity is the ability to provide your own power during a black out. The reason for this is that every solar system needs somewhere to put its excess power. Grid-tied systems put that power into the grid – the utility essentially acts as your storage system – and your power company pays you market rates for that power (in the form of a credit against your bill). But for safety reasons, your solar power system will automatically shut off if the power goes out. This is to protect utility workers who might be working on power lines in an outage from being exposed to live electricity. The system will restart automatically when power is restored. (return to list of questions)
If you want the ability to produce and consumer power when the grid is down, you need to remove yourself from the grid completely and provide your own storage system for the excess power. That storage system consists of racks of batteries, and those batteries cost money. This is something I look forward to doing someday when battery technology has improved, but for the time being I am content to suffer the occasional short power outage, and smile at the irony of having 11,000 kWhs on the roof and no power in the house. (return to list of questions)
Q: Does it work at night?
Sunlight must be present for a photovoltaic solar system to generate electricity. At night, your house draws electricity from the local utility, off-setting some (but hopefully not all) of the credits you have built up during the day. (return to list of questions)
Q: Are these panels based on experimental new technology?
No. Photovoltaic cells were invented in the early 1950s and were first used to power satellites. In the 1970s, they began to be used to power telecommunications equipment in remote areas and to power navigational aids. In the 1980s, they began to be used for roadside emergency telephones and traffic signs. Now the technology has reached a level of value and efficiency that makes them viable for widespread residential use. (return to list of questions)
[This post is part of a series about our net-zero residential solar project – to see a list of links to the full Solar Project series, click here or to bring up a list of all green-themed posts, click here.]
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