Power Sharing - Topping up Solar power generation for realtime use.

Thread Starter

pmd34

Joined Feb 22, 2014
518
Hi guys, I was looking for a few ideas for how to efficiently "power share" - the scenario is:

I will have some DC grow lights, about 36V (but this can be changed) 100w+ . I would like to get as much as possible of the power for these from one or more solar panels, and then top up the additional "missing" power with a mains - DC power supply. (For when it becomes cloudy or in order to extend the "daylight" hours.

The easiest option would be to have a battery system that is charged by both mains and DC, but I want to avoid this as all in all with the set up cost and lifetime of the battery it would simply be cheaper running the whole thing from the mains directly!

Im thinking the solution might be along the lines of a 2-phase switching type regulator. Storage capacitors are fist charged with 1 cycle from the solar panels, and then one "top-up" cycle from the DC supply.

But any ideas? I guess something like this exists already?!
 

Bernard

Joined Aug 7, 2008
5,682
Some ramblings. Solar panel- OCV = 37V, SC A = 4.4, W = 115, best power = 29V. AC power supply
output 20V @ 5A. OR the two sources into a boost-buck regulator with output set at 36V.
If less than 24 hour operation add a timer or solar switch. Any time that SP OC V is greater than 20 V, the SP will add some power to input, remainder is covered by AC . SP loaded output = or greater than 20 V then no AC required.
 

Thread Starter

pmd34

Joined Feb 22, 2014
518
Some ramblings. Solar panel- OCV = 37V, SC A = 4.4, W = 115, best power = 29V. AC power supply
output 20V @ 5A. OR the two sources into a boost-buck regulator with output set at 36V.
If less than 24 hour operation add a timer or solar switch. Any time that SP OC V is greater than 20 V, the SP will add some power to input, remainder is covered by AC . SP loaded output = or greater than 20 V then no AC required.
Hi @Bernard thanks for the reply. It's along the lines of what I was thinking. BUT how do you "OR" the 2 power sources. As the solar panel will not always be at full power so it will need some "mppt" wizardry to optimise it, and then require additional topping up with the DC power source, and how do you do the topping up part?
 

Bernard

Joined Aug 7, 2008
5,682
OR gate made from 2 shottky 50V, 7A diodes, cathodes tied together. SP to one anode, AC power to other. As input to regulator is almost always lower than output, just a boost regulator is needed. I would skip "mppt". MPPT is only useful if the load can accept any power that SP can deliver. 7 AM, AC P on, SP V climbing ; 9 AM SP @ 20V and contributing 1 A; 11 AM SP @ 20V @ 3
A, AC still supplying about 30 W; 1 PM SP = 29V @ 3.9 A, AC = 0 P. Losses not counted, all guesswork. For 100 W load, SP = 150W +- .
 
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