How do solar panels work in Alaska?
As solar grows across Alaska, there are two different types of panels you may be seeing: solar photovoltaic (or PV), which generate electricity, and solar thermal, which generate heat. While they both turn sunlight into energy for your home, they have very different applications. To help determine which one is best for you, you need to consider your site conditions as well as your heating, plumbing, and electric systems.
What’s the difference?
Solar thermal, or solar hot water, collectors absorb heat from the sun and transfer it to water or glycol to provide space heating or hot water for your home. The most common types are flat-plate collectors and evacuated tubes, with flat-plate collectors being dominant. They generally consist of a 4×8-foot glass-encased panel that contains a thin metal sheet with a dark coating to absorb energy. Beneath the sheet are coils filled with heat-transfer fluid. As fluid circulates through the tubing, it absorbs heat and transfers it to a storage tank. A typical residential system used to supplement domestic water heating includes two panels.
An evacuated tube collector contains several rows of glass tubes connected to a header pipe. Each tube is a vacuum, which acts like a sealed thermos and eliminates heat loss through convection and radiation. Because of this, evacuated tube collectors lose less heat to the environment than flat-plate collectors. The glass tube contains a small copper pipe filled with glycol, water, or some other antifreeze fluid. The fluid heats up, vaporizes, rises into the header pipe, and transfers heat (through a heat exchanger) to another fluid-filled pipe, which ultimately carries heat to the water tank. From there, water can be used for hydronic heating and domestic hot water or converted for other uses.
Solar power
Solar PV panels convert sunlight into electricity using a silicon sheet made up of semiconductors. When light strikes the sheet, part of the energy is transferred to the semiconductors, which knocks electrons loose and allows them to flow freely through connected wires. This flow of electrons is called direct current (or DC). The current then flows into an inverter, which changes it into AC (alternating current), the power used by your appliances. If there is no immediate demand in your home, this power can be stored in a battery or returned to the electric grid.
Cold Climate Specifics
Alaska is a unique place for solar energy because of the excessive summer sun and the virtual darkness in winter months, which means a few months a year where solar doesn’t contribute much. For example, the 12-kilowatt photovoltaic array at the Cold Climate Housing Research Center in Fairbanks produces more than 10,000 kWh from March-September (about 30 percent of the building’s electric demand) but only 1,833 kWh during the other half of the year.
Most residential solar thermal systems are used to offset primary heating sources. If you want to use solar thermal as a main heating source, you need some type of seasonal thermal storage system to bridge winter months. PV systems, in most cases, simply offsets electricity purchased from the grid.
With PV, you can produce more power from your panels year-round if you keep them free of snow and change the tilt angle twice a year. The most productive months for CCHRC’s panels are April and May, when they enjoy long daylight hours and also capture reflected sunlight off the snow cover.
Different types of solar thermal panels perform better at different times of the year. For instance, evacuated tube collectors produce more BTUs during the spring and fall shoulder seasons, while flat plate collectors produce more heat during the summer.
Which ones are better to install?
To figure out which is a better investment, you need to consider what your installation costs would be and compare them to your current heating and electricity prices. Let’s look at an example.
In Interior Alaska, a 1,000-watt PV array will produce about 1,000 kWh a year. Assuming electricity prices of 20 cents a kilowatt-hour, that would save you $210 a year. A two-panel solar thermal system could produce roughly 7 million BTUs a year, offsetting either 54 gallons of oil (saving ~$150 at $2.50 a gallon) or 2,050 kWh of electricity (saving $410). In other words, homeowners with electric water heaters stand to save more from solar thermal than those heating with other fuel types.
The actual cost of solar thermal in Interior Alaska (roughly $2.50 per watt over the lifetime of the system) is lower than solar photovoltaic (less than $4 per watt as of June 2019). Yet PV panels are still more common in Fairbanks largely because they are easier to install, don’t require plumbing, don’t have to be integrated into existing mechanical systems, and have no moving parts (whereas solar thermal systems have fluid and pumps that must be replaced). Solar thermal systems will also shut off once your hot water tank is hot, whereas solar electric will power the electric hot water heater up to 8 months of the year, and will continue to produce energy to offset other electrical loads even when the hot water tank is hot, thus always providing peak efficiency.
The actual output and cost of your system will depend on many factors, including the solar exposure of your particular site, the type of heating or hot water system, and how many heat exchangers are required. With the cost of solar constantly dropping and fossil fuels always in flux, solar is becoming an increasingly attractive long-term investment for anyone with a good site.