Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,059
- It's a 26 foot boat. I can put (2) 100 watt panels on it. Not 3, not 4. There is no usable/clear location! I suspect a van would have similar constraints.
Hope you're using the highest efficiency panels to pack the most watts you can into that space. My older ones are 12% to 14%, newer are 20% so by replacing I get 50% more in the same space.
Also, does/would an MPPT charge controller harvest the most power for you? With PWM, panel voltage is pulled down from Vmp = 17V or so to 13.5V or whatever battery is, and the delta voltage is lost power. If the panels are oriented identically so they can be wired in series to get the voltage headroom needed for MPPT, it will extract the most power over a wide range of conditions.
My whole motivation for this thread was reading that: Inverters are most efficient near their rated output. That a large inverter running at low output would be far more wasteful than a low-wattage inverter. That's all that prompted this thread. I was hoping that someone here could definitely validate whether this was marketing hype or marketing BS.
Is that what the data shows for inverters you're looking at? The ones I know of peak around 25% load
(Which would make 80W from the 300W inverter you're looking at ideal, except for the 85% actual efficiency you determined.)
The 65% figure was for Snoobler's 5kW inverter delivering 71W. (Not bad, that's almost 4x as big as your 1500W.)
Your interpretation of marketing "up to" numbers calculated out to 108W/84W consumed for large/small inverters.
Since your measured figure for small inverter differed considerably, would be interesting to see how large inverter measures.
What I've seen for multiple models/brands is that power wasted is power consumed at zero output plus a term which is proportional to the square of output power. Resistive losses in the output transistors and copper windings goes as the square of current.
For my large battery inverters, here's the efficiency curve.
At 100% (6000W), efficiency is 91% to 92% depending on battery voltage.
At 25% (1250W), it is 95% to 96%
At 10% (600W), it is 93%