Site Analysis & Solar Resource Flashcards
As an initial estimate, a 2.5 kW array of crystalline silicon PV requires approximately ___________ square feet of available space.
250
2.5 kW array = 2,500 watts
2,500 watts ÷ 10 watts per square foot = 250 square feet
Based on an average grid-direct system price ranging from $2 to $5 per watt, and not accounting for any rebates or credits, the installed cost of a 4 kW grid-direct PV system could range from:
$8,000 to $20,000
The average installed price range for grid-direct PV systems is wide, usually ranging from $2-$5 per watt, or $2,000 to $5,000 per kilowatt, although it could be higher or lower due to system complexity or competition.
True or False: Remote site analysis can provide electrical details as reliably as an in-person site visit
False
While remote site analysis can be very reliable for roof dimensions and shading analysis, it is impossible to verify details like service disconnect size, location and voltage remotely.
In addition to hand sketches, measurements, and written notes, what is the best way to reliably and accurately capture the required information on a site visit?
take LOTS of clear photos
One year of hourly data that is most representative of median weather conditions over a multiyear period is called a __________.
typical meteorological year
A typical meteorological year (TMY) consists of one year of hourly data that best represents typical weather conditions over a multiyear period, which includes all original solar radiation and meteorological data condensed into one year’s worth of the most usual conditions
A typical meteorological year is used to estimate __________.
PV system production
Calculating a TMY includes evaluation of solar resource data, wind speed, and ambient temperature, and is more complex than just a simple calculation of median values. TMY data are used to estimate PV system production.
True or False: in the Northern Hemisphere, the sun is at its highest point in the sky at solar noon on December 21.
False
In the Northern Hemisphere, the sun is at its highest point in the sky at solar noon on June 21, the Summer Solstice.
The vertical angle above the horizon, measured in degrees from the horizon to the sun’s position in the sky is called the __________.
altitude angle
The altitude angle of the sun essentially refers to how high in the sky the sun is.
The sun’s position in degrees east or west of true south or true north is called the __________.
azimuth angle
The azimuth angle essentially refers to where the sun is (east or west of) in relation to the north/south axis. It can be helpful to visualize azimuth angle as looking straight down on a point on the earth and measuring the angle between the location of the sun and true south or true north.
A measure of power derived from the sun and expressed as W/m² is __________.
irradiance
Irradiance is an instantaneous power value that can be measured, and varies throughout the day depending on the position of the sun and weather conditions. In other words, irradiance represents the power per unit area. This value is related to the power (real time value) that a PV array can produce at a given instant. Irradiance is measured in W/m² and is the data provided by instruments such as the pyranometer.
Another name for the number of hours per day that the amount of irradiance reaching Earth’s surface is equal to 1000 W/m² is __________.
peak sun hours
A “peak sun hour” is defined as one hour when the intensity of the sunlight is an average of 1000 watts/meter². A daily “peak sun hours” value is calculated by taking the cumulative solar irradiation available over the course of a whole day and dividing by 1,000 W/m². It’s important to note that peak sun hours are not the same as hours of daylight.
Power from the sun is expressed as __________.
watts per square meter
The amount of solar radiation, when expressed as power, is measured in watts/m². This power that strikes any location on earth varies from sunrise to sunset and throughout the year due to clouds or rain blocking the sunshine, the sun’s changing position in the sky, and what’s in the atmosphere (reflecting light). The maximum solar radiation occurs at solar noon when the sun is highest in the sky (unless, of course, it is cloudy!).
Energy from the sun is expressed in __________.
watts-hours per square meter
Energy from the sun is the cumulative value of irradiance (or instantaneous power) over a period of time, e.g., hours during a day. This is why solar energy or radiation is measured in Wh/m²/day. For example: power (W/m2) accumulates over the hours of the day (h) to obtain a value of energy (Wh/m2), expressed for the period of a day (Wh/m2/day).
One factor that will reduce the amount of power a PV array will produce is __________.
non-optimal azimuth angle
In the northern hemisphere, PV systems generally face south; an installation in the southern hemisphere will face north. Regardless of location, ideally a PV array should be oriented towards the equator
What reduces the amount of irradiance that reaches a PV array? (3 things)
snow, soiling, and shading
Due to losses in a PV system caused by dirt, shade, snow, or non-ideal tilt or orientation, the amount of peak sun hours (PSH) a site receives is not the same as the PSH the PV array receives. This difference always equates to some loss in energy production.
