Both sides previous revision
Previous revision
Next revision
|
Previous revision
|
opinion:frater_secessus:how_much_excess_solar_power [2022/12/14 13:43] frater_secessus [theoretical power available] |
opinion:frater_secessus:how_much_excess_solar_power [2023/04/21 11:50] (current) frater_secessus [Pareto summary] |
DRAFT | DRAFT |
| |
| |
| FIXME |
| |
====== How much extra solar power do I have? ====== | ====== How much extra solar power do I have? ====== |
| |
| |
===== Pareto summary ===== | ===== TLDR ===== |
| |
| |
| |
| |
===== empirical testing ===== | ===== direct testing ===== |
| |
| |
===== observation and prediction ===== | |
| |
| Plug it in and see if the solar can support it [[electrical:solar:offthepanel|without affecting the battery bank]]. Easy peasy. |
| |
| The downside is this is a YES/NO answer; it tells you a specific load will run but does not tell you about how much power is actually available. If you want to see the Bigger Picture then read on... |
| |
| ===== prediction ===== |
| |
==== overall system efficiency ==== | ==== looking up daily insolation (FSE) ===== |
| |
You can get a feel for overall system efficiency by | Hours of Full Sun Equivalent (FSE) is a convenient way to think of the amount of sunlight reaching the ground over the entire day. 4.5 hours of FSE means 4.5kWh of power reaching the ground per square meter. |
| |
- watching your system over time, as described above | To predict daily harvest we will use |
- comparing real-time harvest to theoretical harvest | |
| |
| * FSE |
| * your panel wattage |
| * and your system's overall efficiency |
| |
| |
===== average power harvest for a given time/place ===== | |
| |
==== theoretical power available ==== | |
| |
=== predicted daily harvest === | |
| |
| |
| ==== calculating power available (W) ==== |
| |
=== predicted harvest at a specific time === | |
| |
Real-time harvest is a bit easier since there is no time component. We are working in Watts (W) rather than Watt-hours (Wh). What we are doing is comparing the strength of sunlight reaching the ground (perpendicular) vs [[electrical:solar:output#zenith_angle|the cosine of the angle at which it actually strikes the ground]], or strikes a flat-mounted panel. | Real-time harvest is a bit easier since there is no time component. We are working in Watts (W) rather than Watt-hours (Wh). What we are doing is comparing the strength of sunlight reaching the ground (perpendicular) vs [[electrical:solar:output#zenith_angle|the cosine of the angle at which it actually strikes the ground]], or strikes a flat-mounted panel. |
This cosine is [[https://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html|calculable for a given time and place]]. | This cosine is [[https://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html|calculable for a given time and place]]. |
| |
**Example**: if you have 200w of panels and calculated cosine is .70 then **140w of light is landing on your panels**. | **Example**: if you have 200w of panels and calculated cosine is .70 then **140w of direct light is landing on your panels** in clear skies. |
| |
==== system efficiency ==== | ==== finding and using system efficiency ==== |
| |
| For [[electrical:solar:output|various reasons]] your solar setup will not be able to harvest all the power landing on the panels. For systems with PWM controllers the percent harvested will be something like 70%. For MPPT it might be 83%. These constants will be placeholders you can use until you figure out your specific system's overall efficiency. |
| |
| You can see our system's overall efficiency at a given time: //actual harvest / theoretical harvest//. The numbers will jump around but over time you will start to see a pattern. Maybe yours makes 80% or 86% over time. Use that number to **predict how your system will behave** in another time/place: |
| |
If observed 94w at that place/time the overall system efficiency would be 94w/116.2w = **80.9%**. After you make many comparisons like this you will start to see a patter in your system's ability to harvest power. If it's 81% over time we can start to multiply the solar zenith angle calculations above times 0.81 to predict how much power our particular system could make on average. | panel wattage x system efficiency x cosine |
| |
Continuing from the example above: | |
| |
>> , your mppt controller typically yields 83% after derating, and the calculated cosine is .70 then you might expect ~116w in clear conditions at that time in that location. (200 x .83 x .7 = 116.2). | >> ...if your mppt controller typically yields 83% after derating, and the calculated cosine is .70 then you might expect ~116w in clear conditions at that time in that location. (200 x .83 x .7 = 116.2). |