Solar PV
Solar Panels in Lethbridge
Solar Panels (photovoltaic, PV) create direct-current (DC) electricity when exposed to the sun. The DC electricity is converted into AC and conditioned so that it may be used in the home or sent to the grid.
The grid describes the electricity generation and transmission lines used to distribute electricity to the user, like your home. The grid does not store electricity, so any electricity being generated for the grid must be used. If too much is being generated, some must be sold to other grids (like other provinces or to the United States) if they can use it, or it is wasted. If too little electricity is being generated at any one time, the grid could brown- or black-out. It is the job of the AESO in Alberta to balance the grid by adjusting electricity generation up and down, or on and off. There are backup reserves of generation that allow the electricity operator to manage the grid so that we always have electricity when we demand it.
Electricity is not an energy source, it is an energy carrier. This means that other energy sources are used to create electricity, which is then distributed through the grid. Energy sources used to make electricity in Alberta include coal, natural gas, wind power and some hydroelectric and photovoltaic (solar) power. The mix of energy sources at any one time will determine the greenhouse gas emissions produced for each kilowatt-hour of electricity used in the home. The following chart from the IPCC shows the life-cycle emissions for each energy source. Alberta’s current energy mix for electricity generation (predominantly natural gas and wind power) results in 540 g CO2/kWh.
There is another important difference in how emissions are distributed over the life-cycle for any generation technology. Technologies using coal and natural gas as an energy source are typically large, centralized generation plants with an initial investment of emissions embodied in the facilities and ongoing emissions from the burning of fossil fuels. Technologies like wind and solar power have most of their emissions embodied up front within the technology and small amounts of emissions over the life-cycle. The chart below illustrates the ongoing emissions of electricity generated with fossil fuels compared to the ‘dilution’ of emissions for a renewable technology like solar PV from the initial investment of energy over its life-cycle production.
Compared to electricity generated from fossil fuels, the solar PV will be producing lower-emission electricity after two years of optimum production. Over its life-cycle of 25 years, the average emissions from electricity for solar PV will be about 41 gCO2/kWh compared to 540 gCO2/kWh for the current electricity generation mix in Alberta.
Solar PV in Lethbridge
Solar PV work best when light from the sun impinges the panel at 90 degrees (a right angle). But the position of the sun is always changing through the day, and from season to season. Some solar farms are able to move the panels along one or two axes so that they are always tracking the sun, but this type of system is too complicated for a home. The panels on a home are fixed in one direction and one angle, depending on the roof they are mounted to. A rough rule-of-thumb for optimum electricity generation is to have the panels facing south and at an angle equal to the latitude of the home. In Lethbridge this is roughly 49 degrees from horizonal. Unfortunately, most homes have roof slopes lower than this, from 12:12 (or 45 degrees) to 4:12 (or roughly 20 degrees). Higher angles of installation will also help reduce snow accumulation on the panels (even though electricity production in the winter is already diminished by the low sun).
Other important considerations when installing solar PV is to avoid shading (from trees or other homes), as this will reduce the output of the solar PV array. Even a small amount of shade can reduce the conversion of solar radiation into electricity. The ambient temperature can also impact performance – warmer weather reduces the amount of electricity produced. Dark roofing materials may increase the operating temperatures of the array, with losses of 5 to 8% possible on hot, windless days (though there is not much one can do about this).
In Lethbridge, the electricity generated by a square-meter of panel (assuming 20% conversion) will vary by month and the angle of the array. A low angle (10 degrees from horizontal) will produce more electricity in the summer but less in the winter, while a higher angle (50 degrees from horizonal) will have a flatter curve, as shown below.
Adding up the electricity generated over a year, the solar PV will produce about 1380 kWh/kWp of electricity at 10 degrees; 1555 kWh/kWp at 30 degrees; and 1590 kWh/kWp at 50 degrees. The latter array is optimum for a fixed panel at our latitude. As you can see, there is about a 15% reduction of electricity generated for an array at 10 degrees – but you don’t really have control over the slope of your roof.
Another factor that you may not have much control over is which way the roof slopes are facing. The optimum direction is south, but your major roof area may face another direction. The chart below shows the electricity generated for an east- (or west-) facing roof and at different angles. This chart may be compared to the one above for a south-facing roof.
The chart shows that there is not much difference in electricity output for different roof angles. In fact, there is a slight advantage for lower angles, with an annual electricity production of 1250 kWh/kWp of electricity at 10 degrees; 1215 kWh/kWp at 30 degrees; and 1140 kWh/kWp at 50 degrees. The loss for facing east or west compared to south, however is substantial – roughly 25%.
An Example for Lethbridge:
In general, you are able to install a solar PV array that will meet your electricity needs based on your consumption history. There is some movement being made to accommodate the transition from fossil fuels to a ‘green’ electricity grid, like electric vehicles and heat pumps to heat your home (using electricity).
For our example, we will use an average electricity consumption of 7200 kWh per year in a home. It should be said that this number represents a home that has made very little effort in reducing electricity consumption. It is always better to reduce your electricity consumption before you spend money on a solar PV array to generate what you need.
At a nominal conversion of 20% of the radiation from the sun to electricity, each kWp of solar PV will cover about 5 m2. Panel sizes will vary between manufacturers; we will use a panel that is 1.760 m x 1.096 m (an area of roughly 2 m2).
Other common panel sizes are shown below:
Using an optimum south-facing array at 50 degrees from horizontal, the annual output will be 1590 kWh/kWp. For a home using 7200 kWh/year,
Annual consumption / estimated annual solar PV electricity production =
7200 kWh/year / 1590 kWh/kWp/y = 4.5 kWp
4.5 kW x 5 m2/kWp = 22.5 m2 of area
22.5 m2 area / 2 m2 per panel = 12 panels
Another consideration is that the solar PV system degrades over time – roughly 0.5% per year, for a life-cycle of 25 years.
The life-cycle production of electricity from 12 solar PV panels is:
12 panels x 2 m2/panel / 5 m2/kWp x 1590 kWh/kWp x (100% - 25 years x 0.5%/y / 2) x 25 years
= 178,900 kWh over the life-cycle of the array.
GHG Emission Reduction:
(540 gCO2/kWh – 41 gCO2/kWh) x 178,900 kWh = 89,300 kgCO2 over the life-cycle.
Economics:
Cost for a solar panel = $2500 / kWp installed
Total cost = $2500 /kWp x (12 panels x 2 m2/panel / 5 m2/kWp) = $12,000
Assuming the cost of electricity increases at the rate of inflation,
Cost of electricity = $12,000 / 178,900 kWh = $0.067 / kWh
The current price of electricity is roughly $0.124 / kWh, so there would be a cost savings installing an array of solar PV (about $400 / year facing south)
Cost payback = $12000 / (12 panels x 2 m2/panel / 5 m2/kWp x 1590 kWh/kWp x $0.124/kWh) = 12.7 years
Cost of Emissions:
In a sense, since one is saving money by installing a solar PV array, there is no cost for emission reduction.
But, as a worst case, if one were to look only at the initial capital investment (assuming no real cost savings for operation over the 25 year life-cycle),
$12,000 / 89.3 tonnes CO2 = $135 / tonne CO2eq
Summary:
Installing a solar PV array in Lethbridge to produce 7200 kWh of electricity each year:
The current cost of electricity on a 5-year plan will vary widely depending on your location and provider. I am paying $0.124/kWh. Currently, all array orientations and angles will produce electricity at a lower price for the life-cycle of the array (25 years). Though this is conjecture, with increasing electricity demand as we transition to a net-zero economy by 2050, it is unlikely that electricity prices will drop significantly over this period.