What does this mean?
US solar capacity is expected to grow from 129 GW today to 336 GW by 2027, according to the Solar Energy Industries Association and Wood Mackenzie.
Source: US poised to hit 336 GW of solar by 2027 – pv magazine International
It’s an idealized number that tells us little:
If you add the capacity of all the solar panels in a photovoltaic system, the result is the installed capacity in megawatts-peak (MWp):
- Assume an industrial facility uses 20,000 panels, each with a rated power of 350 watts.
- In this case the total power is 7,000,000 watts-peak, or 7 MWp.
This would be the power output if the entire solar array operated under Standard Test Conditions (STC) used by solar panel manufacturers. These conditions assume a photovoltaic cell temperature of 25°C, a solar irradiance of 1,000 watts per square metre, and the incidence angle of sunlight for a latitude of 35° north during summer. These are idealized conditions, but they allow standardized testing for all solar panels.
The number is useful for comparing solar power installations but not useful for comparing cumulative power output to that of conventional power plants.
On my solar PV system, the panels are rated at about 4.3 KWH at noon.
We lose about 300 watts due to cabling and heat related resistance losses, giving us about 4.0 KWH at peak energy production.
We average about 6.5 MWH of electrical production over the course of 12 months. However, if we multiplied the 4.3 KWH peak production times the hours in a year, we’d have 38 MW. Thus, our actual power production is 17% of the theoretical maximum production output over the course of the year. If I am doing that calculation correctly. And if so, does that mean that the 336 GW figure above works out to about 57 GW over the year? Note – my solar PV has some early morning shading, and during the winter, some late in the day shading – thus, its not ideal throughout the day. The 17% figure might be 20+% for better situation panels.
The daily output varies from zero (night, and when covered in snow) to around 10 KWH on a sunny, short winter day up to almost 35 KWH at peak day in June. This year, we had a long, wet and cool spring and ran our pellet stove the last time on June 20th! We lost much potential solar production during what would usually be our peak production on the longest days of the year – but this year the days were mostly cloudy.
The upshot of this is that the headline of “336 GW of solar” by 2027 does not mean anything and cannot be compared to say, a 1 GW natural gas power plant that runs 24×7.
