Wattage limiter?

I am planning an installation of a four-panel array (ground mount). I have four (Candian Solar 72 cell) 300 watt PV panels already procured. I am using these to power a hybrid air conditioner/heat pump. The system requires only 3 panels and maximum 840 watts.

But to deal with shading I want an extra panel. This will ensure that during daylight I will get the longest possible duration of usable solar power to run the device. The load I want to power will handle a maximum of 840 watts. Most of the time it will be a struggle to provide that even from four panels. But since there are four panels the possibility exists I could surge up to 1200 watts for brief periods.

The hybrid unit I am powering is interconnected with A/C power. So I do not have batteries or a charge controller. What kind of device can I use to limit the wattage to protect the equipment? I don't want anything to cut the circuit like a fuse, just want it to limit the maximum wattage coming off the array. I don't expect to be wasting power very often, just for protection in case it occurs for ten minutes or so.

Thanks,
DIY installer

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,055 admin
    Re: Wattage limiter?

    Welcome to the forum "Iron".

    Can you gives us a link to your heat pump system/hardware? I am not clear how it interconnects to solar panels+AC power.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ironiron Registered Users Posts: 3
    Re: Wattage limiter?

    Sure: here it is http://www.hotspotenergy.com/HotSpot-ACDC12.pdf
  • ironiron Registered Users Posts: 3
    Re: Wattage limiter?

    I think I may just be worrying overly much. The only thing that would hurt an electrical device would be a big surge in current (amperage). In that case you want a fuse to blow. If there is an excess 8 amps or so of current should not affect the device, now that I think about it.
  • BB.BB. Super Moderators, Administrators Posts: 31,055 admin
    Re: Wattage limiter?

    Not enough information to make any informed decision.

    However, my guess is that there is a good chance it will work fine--You need to call the Mfg. and ask them.

    There is one error that I can see in their accessory documentation. When you have 3 or more panels (strings) in parallel, you need a fused/breaker equipped "combiner box"... This puts a fuse/breaker (~15 amp typically) in series with each panel (string) to prevent problems if there is a broken panel or short circuit in the array (the other panels feed the short in the bad panel/wiring and could start a fire). Not a big deal--Combiner boxes are common and easy to get/wire up.

    Depending on their design--It could require one "extra" ~30 amp or so circuit breaker/fuse prior to the input of the heat pump power controller--To prevent too many panel from feeding a short circuit in the units wiring/electronics (just common safety requirements--Not any comment about their specific design).

    It is possible to get a DC to DC converter with output voltage/current limit--But I would talk with the Mfg. first--Much easier and less parts to play around with. Adding converters will add costs and complexity--And could cause confusion in the Heat Pump's power electronics/system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Solar Expert Posts: 1,384 ✭✭✭✭
    Re: Wattage limiter?

    It looks like the unit can take up to 39V and your panels can produce ~44V. You need to limit the voltage, not the watts.

    I am available for custom hardware/firmware development

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Wattage limiter?

    The seer rating of 35 is a bit misleading... The high 35 seer rating is based on how much 240 volt AC it uses (very little) when the sun is shining on the panels. When the sun goes down, it only uses 240 volt AC for power and its seer rating is then 19.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Wattage limiter?

    Panels only produce what the load demands. They can not force more power into a load just because they are capable of producing more power.

    But jonr's note about the Voltage should be examined closely. PV has both Voc and Vmp ratings, and the unit must be able to safely connect to the Voc rating even if it runs at the Vmp rating. If 39 Volts is for PV Voc there is a problem. I suspect it is meant to run from grid-tie panels which normally have a Vmp aroun 30 and Voc around 36.
Sign In or Register to comment.