4 ms·

Because of their simplicity solar-cell based systems have become lower-cost and easier to install and maintain for water heating as panel + electric water heate

by dv_dt 11mo ago

Because of their simplicity solar-cell based systems have become lower-cost and easier to install and maintain for water heating as panel + electric water heater, vs a piped direct solar thermal heating system. Higher "efficiency" for the direct thermal system, but overall system costs are lower for panel + heat. I still love seeing the interplay with different combinations of physical systems and clever things humans figure out. Including with solar panels + other system items.

taneq 11mo ago
Is this a good point to mention that simple solar heating circuits work better if you use diodes in series (for a fairly constant voltage drop across the solar cells) than if you just use a resistive element? :)
- dv_dt 11mo ago
  You hint at something that is interesting to think about - that question might be: is there a different charge controller, heating element controller pairing that is possible with much less complexity and cost than using an inverter to ac and back to driving a resistive element. would it be worth a system cost of dedicating some panels to just that kind of control
- kragen 11mo ago
  Diode heating does a better job of "MPPT tracking" than a resistive wire, but diodes are orders of magnitude more expensive, and they only work at low temperature (typically up to 175°, though SiC diodes can go a little higher). Resistive wires can easily work up to 500° or 1000°, which is potentially much better for sensible-heat thermal energy storage like this sand system. It might be better to run your resistive wire with a 3¢ microcontroller running an MPPT algorithm and controlling a 60¢ power MOSFET, something like a PSMN4R0 (https://www.digikey.com/en/products/detail/nexperia-usa-inc/PSMN4R0-30YLDX/4368826 https://www.digikey.com/en/products/detail/nexperia-usa-inc/...), which is rated to control almost 3000 watts (30 volts at 95 amps).

by dv_dt 11mo ago

taneq 11mo ago

Is this a good point to mention that simple solar heating circuits work better if you use diodes in series (for a fairly constant voltage drop across the solar cells) than if you just use a resistive element? :)

dv_dt 11mo ago
You hint at something that is interesting to think about - that question might be: is there a different charge controller, heating element controller pairing that is possible with much less complexity and cost than using an inverter to ac and back to driving a resistive element. would it be worth a system cost of dedicating some panels to just that kind of control
kragen 11mo ago
Diode heating does a better job of "MPPT tracking" than a resistive wire, but diodes are orders of magnitude more expensive, and they only work at low temperature (typically up to 175°, though SiC diodes can go a little higher). Resistive wires can easily work up to 500° or 1000°, which is potentially much better for sensible-heat thermal energy storage like this sand system. It might be better to run your resistive wire with a 3¢ microcontroller running an MPPT algorithm and controlling a 60¢ power MOSFET, something like a PSMN4R0 (https://www.digikey.com/en/products/detail/nexperia-usa-inc/PSMN4R0-30YLDX/4368826 https://www.digikey.com/en/products/detail/nexperia-usa-inc/...), which is rated to control almost 3000 watts (30 volts at 95 amps).