*DC* from PV panels

Not just different current, but different voltages. Both vary with the level of light if you are shooting for maximum power. The voltage also varies with temperature significantly.

Converting back and forth between DC and AC is not terribly inefficient. EVs do it all the time. I think you would have a hard time trying to match a variable source like solar panels to a DC load. The load wants to set the current. What do you plan to do with the excess? Are you going to design your own controllers? What is your thinking here?

• Not a matter of "want"; IR drop in the panel is the concern. PV panels develop DC, not your implied AC/??

• PV panels cannot generate AC! AFAIK one PV cell produces about 1.2V, output of a "panel" can be whatever you need; connect enough in series for 200VDC.

• Yup!

A shunt regulator? With a big heatsink for killing unwanted power?

I suspect that your losses (~2%) with the fattest Schottky diode you can find to wire or them together will be somewhat lower than the losses in a typical active DC to DC converter. This is especially true when compared to panels in series with for example one partially shaded.

Wired OR you get the current from all the ones in full light but in series your maximum current is limited by the weakest link in the chain. Also when not in direct sunlight the diodes drop will be less.

I guess it depends a lot on whether your load can tolerate the variation in supply voltage that will come from the solar panels directly.

Wouldn't an MPPT do the job? Typically they can handle up to 150-volt input a give a regulated 48V nominal output (settable up to 60-volt) Example:

Domestic PV rooftop panel assemblies intended for grid tie inverter usage have open circuit voltage typically 60-80V with strong negative temp coefficient. They are approximately current sources, if ultimate efficiency isn't needed just parallel them and load them down enough to get the target 48V.

piglet

Yes, that is what you need. And probably with a battery as well to cover the drops (and maybe the night).

These are effectively DC-DC converters but they have an input characteritic that tries to obtain maximum power from the solar array by choosing the optimal voltage/current combination. When you don't care about that (or have no battery where the temporary surplus will be stored) a plain DC-DC converter can be used as well. Or a 115VAC to 48V DC SMPS with the AC rectifier removed.

So just waste it as heat? I think the OP said something about not wanting to convert DC > AC > DC because of the efficiency issues. Why would he want to design in such losses?

I think the reality is he has not given this much thought or at least not described his thinking here very well. The first point to clarify is whether there will be a battery in the circuit to provide power when the sun is clouded. But maybe he's running a water pump and doesn't care if it drops out for a bit. I don't know.

Hi Don, so what exactly do you need the 900W of electricity for?

If I suppose the goal is to store every bit of ENERGY collected per day, then we need a lossless storage medium, and a medium whose energy that can be efficiently drawn from at an arbitrary rate.

So Rick's idea of heating water is not so crazy, if the energy capacity is high enough. Might be a cheaper start-up & more reliable than a large bank of storage batteries. And safer than splitting water into H2 and O2.

Or, of course, some hybrid approach, using both thermal & chemical... If you're really ambitious :-)

But simpler is probably selling excess energy to your E company and get some $. regards, RS

LFP batteries go pretty close to that ideal. Not as cheap as water, but anything thermal is going to have much bigger losses.

CH

What is the load?

I was being a bit cheeky, but yes, you gave a sane answer. Indeed, for off the shelf products, the home energy storage marketplace is using Lithium chemistries (LFP, LNMC, LTO). I found this article to be very informative:

I dunno. Some of these converters claim really high efficiencies -- 95-97%. There's just a shitload of competitive pressure on the industry to deliver the most power per incident solar watt.

Unfortunately (for me), that's in line with generating AC for domestic use.

In my case, the "naive" approach -- a "typical residential solar installation" with a 48V 40A power supply "bolted onto its back" -- starts out at a lower efficiency over the solar solution as the power supply won't be 100% efficient.

Just tying the panels together leaves you with the same old PV problem; getting the most *power* out of the panels.

My thinking is that a controller on each panel driving into a 48V output setpoint with the outputs of these tied together is likely the best compromise. If a panel is shaded/degraded, the controller will still try to maintain that 48V -- albeit at a reduced current. So, the panel is still contributing to the output capacity.

And, if a converter fails, you just lose the output from that panel (it's as if the panel is permanently shaded). Contrast that with the single inverter (or "power supply") failing in a "naive implementation" (AC inverter feeding DC power supply) and rendering the entire facility useless.

Likewise, if you ADD a panel, you don't have to upgrade the inverter (or, buy it with excess capacity to start with) or the power supply.

And, you can harvest (digital) information from each controller as to its instantaneous performance so you know if the system's output is falling, how much "untapped surplus" is available, etc.

Finally, converters can sit on the panels, outdoors, so I don't have to move that waste heat out of the household interior. (OTOH, they will have to operate in 120F+ ambients)

The question is whether the same sorts of overall efficiencies are available when tackling it in smaller pieces.

They have solutions that allow underperforming panels to pass the full current of the rest of the chain. The voltage is lowered to the point where the required current can be supplied (or, shunted)

I want 48V +-10% (5% would be nicer but not worth much in recurring costs).

And, ideally, if the source can't supply the required *power*, the voltage is maintained but available current drops. E.g., shed load or supplement supply.

I started looking into a converter design (as I already have something similar for a different design) but have had to discipline myself NOT to pursue it until I get these short term deadlines met (I committed to releasing six designs by year end -- but, then went and "played" for a while, travelling and, in general, "having fun". So, now I'm under the gun to get those off my list as promised... thankfully, release engineering is relatively uneventful, just time consuming. Five more to go!)

It's a "sufficiently interesting" problem that I've managed to interest my power supply guru friend to "come out of retirement" to review my design. I'm sure he'll spot efficiencies (and potential fault modes) that I'd have overlooked!