🧮 Calculating Solar Production
4 min
Now that we know the factors that affect a project’s viability how do we accurately estimate how much solar power will be generated? If we want to calculate how much you can save we need to answer the following three questions:
- What is the cost of the system?
On average, residential solar panels cost between $2.50 and $3.50 per watt. Learn more about costs here.
- What is the value of energy produced by the system?
The value of energy produced by the system depends on local energy rates and consumption patterns, but it generally provides long-term cost savings on electricity bills and potential revenue through net metering or feed-in tariffs.
- How much solar energy (kWh) can be generated per panel (or kW)?
The amount of solar energy generated per panel or kilowatt (kW) depends on factors such as geographical location, panel efficiency, and weather conditions.
This next section will help you understand how we calculate solar production.
Determine the climate data
Above we’ve discussed the various items which can impact the local climate. But how does all this tie into solar?
We take the historical climate patterns at a particular location and average them out to create a “synthetic” year. This represents the expected climate at that location over the long run. Various days of different weather conditions are included per month based on the historical data. This climate data is prepared and maintained by government entities and our data sources include:
- National Renewable Energy Laboratory - TMY3, PSM V3 (USA)
- Canadian Engineering Climate Services Unit – CWEC (Canada)
- ASHRAE - International Weather for Energy Calculations, v 2.0 (Global)
The actual weather experienced in a particular year can differ from the average by up to 10%, but is typically much less.
Model the Site
We use high quality overhead imagery to create 3D models of the house and nearby obstructions. We also use LIDAR data to aid and support in our design work.
LIDAR, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth. These light pulses—combined with other data recorded by the airborne system — generate precise, three-dimensional information about the shape of the Earth and its surface characteristics.
This LIDAR data allows us to accurately determine several key characteristics:
- The height and tilt of the roof
- The height of nearby houses
- The height and shape of any nearby trees
- The height and shape of any rooftop obstructions
Sample LIDAR Image:
We then run a model to see how much sunlight each part of the house will get by simulating each hour over an entire year. This simulation factors in sun position, our climate data, roof orientation, roof tilt, and modeled obstructions. The result is an irradiance map outlining how efficient each roof section is.
Place panels
Now, we can lay out solar panels on the available roof space and simulate how much electricity they will produce. We factor in the same sun position, orientation, tilt, and obstruction data (shading) as before, but we also include the following additional factors:
Light-Induced Degradation (typical 1.5%): Solar modules experience a loss in output power when they are initially exposed to sunlight. This is dependent on the particular module.
Snow (typical varies by location): In some areas snow cover can affect energy production of solar installations. This information is determined using our climate data.
Soiling (default 2%): Soiling accounts for dirt and dust accumulation on the solar panels. Depending on the location of the project this can vary.
Connections (typical 0.5%): Represents resistive losses in connectors in the system
Wiring (typical 2%): This accounts for resistive losses in the wiring of the system (both on the DC and AC side).
Age (typical 0.25-0.5% per year): We factor in an expected degradation in performance over the life of the system based on the equipment chosen.
System Availability (typical 1-3%): System availability accounts for downtime of the system due to maintenance and grid outages.
Once complete we have a profile which will tell us how much each panel in the system is expected to produce each year.
Fortunately, you don't have to do any of these calculations yourself as they're all handled by our System. The point is, we put a lot of effort into properly evaluating a solar site to make sure our systems produce what we say they will!