Will solar energy and battery storage force homes to switch to DC wiring? {dkim-fail}

[Rob Lewis]

The Power over Ethernet spec uses 48VDC and can deliver up to 25W over Cat 5. Not too shabby, and a lot of sites already have Cat 5 in place. 

It’s true that switching supplies have reduced the need for iron, but the DC-AC-DC conversion still carries a substantial penalty. 


On May 30, 2015, at 12:27 PM, Ned Freed <ned.freed at mrochek.com> wrote:

>> I’ve wondered for years why we couldn’t have low-voltage DC wiring in our
>> homes to power all the little devices that we keep getting more of. Think of
>> all the copper and transformer iron (and weight) that could be saved without
>> the need to have an AC power supply in every last clock radio and phone
>> charger.
> 
> That weight saving would be offset by the need to have much heavier wiring to
> carry the increased current. Remember, the lower the voltage, the higher the
> current, and the heavier the wire. Heavier wire also carries with it increased
> installation costs. And speaking as someone who has installed a large amount of
> high gauge stuff, you're dreaming if you think this is an insignificant
> concern.
> 
> This argument may have made sense back in the days of simple
> transformer-diode-capacitor power supplies. Not only are the transformers
> heavy, the conversion efficiency is lousy - 30-40% at best.
> 
> But with the advent of inexpensive switching power supplies capable of
> operating at 95% efficiency and requiring a much smaller transformer, I doubt
> very very much that the ecomonics work out even if the will to do it was there,
> which AFAICT it isn't.
> 
> Surely you've noticed that modern "wall warts" are a fraction of the size and
> weight of the old ones? Indeed, it's a good idea to replace the old
> non-switching ones whenever it's practical to do so.
> 
>> This article says that the advent of solar power with battery storage will
>> force a change:
> 
>> http://www.cepro.com/article/will_tesla_batteries_force_home_wiring_to_go_low_voltage/
> 
> It's also rather amusing that he compares home wiring to that of a boat.
> Apparently he's unaware that marine wiring is often done at 48VDC, not 12VDC,
> in order to save on wire and installation costs.
> 
> That said, the prospect of switching to 48VDC or perhaps 96VDC, while hardly
> low voltage, has a lot more appeal. But this doesn't get rid of wall warts, it
> just changes them from switch power supplies to buck or boost regulators.
> 
> I'll also note that a lot of grid tie solar power systems put panels in series
> and operate at 48VDC or more as a result.
> 
>> It points out that going from solar panels and batteries (DC) to house wiring
>> (AC) back to electronics power (DC) can waste 20–40% of the energy.
> 
> He claims that it's 20% loss on both sides, which overstates the losses
> substantially, and then adds those values to get 40%, which is bad math. (The
> correct number is 36%.)
> 
> Indeed, whatever else you think of the Tesla Powerwall, according to its
> specs it manages to acheive 92% round-trip efficiency.
> 
>> Sounds kind of like a no-brainer.
> 
> No, actually, far from it.
> 
> 				Ned