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DRAFT
Yes, we can use a battery monitor to see how much power is going into the battery bank. And we can look at the solar charge controller to see how much power it is making.
But how can we tell how much untapped power does our solar have in reserve? Put another way: how much more stuff could we be running off the solar?
about these summaries
Plug it in and see if the solar can support it without affecting the battery bank. Easy peasy.
You can get a feel for overall system efficiency by
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 the cosine of the angle at which it actually strikes the ground, or strikes a flat-mounted panel.
This cosine is 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.
For 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:
panel wattage x system efficiency x cosine
…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).