How to automatically prioritize loads based on pv power avalible?

Needfullthings

Hello all and thank you for this opportunity to pick your brains.

summary   I am designing a solar array to heat water.  I am wanting to use water as a large battery.
I have a 120 evacuated tube solar hot water system currently installed and working
I use that to heat  a garage  and a 15000 gal pool and a 900 gal hot tub. Granted this is not working well  
I am looking at adding 2 10kw solar pv arrays on the roof.  25 345w pannels
The first array will be grid tie  and will be used to carry the 6 pumps one domestic hot water heater,frig, freezer, and house loads. 

The second array will only be used for heating elements wanting to use straight dc voltage no rectification.
 I have 6 elements   was wanting to know if there was a DC controller that would regulate loads based off a priority (provide max current till limit hit then dump remaining power to next priority
Priority 1   hot tub  2 3500w 250v elements  temp 102
Priority 2   solar hot water storage tanks 2  50 gal water heaters   2  4500w 250v   temp 160      (Radiant floor loop,Existing Pool loop)
Priority 3   pool heat  3 4500w 250v inline water heaters   heat dump  15000 gal in-ground pool  insulated walls and insulated top

located in zone 4 area 4.5 hours peak sun 

Marc Kurth

The lowest cost would be a small PLC (programmable logic controller) with sensors. It would do all of that with ease, if you can learn some simple programming steps. If you are not comfortable with that, hire a local controls contractor who can put together a system with a graphic user interface. This approach will provide you with an easy path to monitor, data log and tweak settings for changes and/or fine tuning.

Dave Angelini

The highest cost and commercially available is something like this from Schneider Electric. Have one at our little mountain town hospital.
https://www.ascopower.com/us/en/products/transfer-switches.jsp

NANOcontrol

There are many ways to do that. Most average people can't do. There is a method of matching heating elements in direct connect based on panel voltage. For $13 you can get voltage timer relays and add a SSR for another $10.  That drops out one heater at about 70% power point voltage and reconnects it at power point voltage. This increases the heating  by double when current are 50% of max. For this extra $25 It vastly improves performance over direct connect to the ideal resistance.

That is one load. I suppose you could increase the numbers slightly for each progressive load as voltage will increase as each load drops out.  Direct connect is pretty much crap and wastes a lot of potential power.  I designed a microprocessor system for a guy that did pretty much this with six heating elements and 4K of panels.  It would only PWM one heating element at a time and progressively add heating elements fully on one at a time. If one or more heating elements shut off, it would just push the power to the next one in line.  This always kept the panels at the power point voltage for maximum efficiency.  

Dave Angelini

And all of these methods are on there way out for residential. Once all the loads are directly wifi compatible and more each day are.

 No more solenoids, raspberries/plc's, and wiring that many insurance companies would void your policy on.

NANOcontrol

This is all theoretical. None of these methods are easy for the majority in solar. WIFI, that's easy. Took me four hours to connect my drone to my phone.  High voltage DC heater element in a hot tub, your looking at codes far away in the rear view mirror.

mwk1000

I realize this is an old thread but I was searching for something similar and found this:
https://www.fronius.com/en/solar-energy/installers-partners/technical-data/all-products/solutions/fronius-solution-for-heat-generation/fronius-ohmpilot/fronius-ohmpilot

it's 230v euro so it will not be plug and play here, same with askowall components ( heating elements )