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this post was submitted on 26 May 2024
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Futurology
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These micro inverters are a cool near-term portable solution for those looking to dip their toes into home energy storage. Ultimately, I hope we see residential DC electrical become more commonplace soon. That will make the grid integration that this tackles a non-issue for most (i.e. those who aren’t selling their excess solar capacity) but will ultimately be simpler and more efficient for the grid as a whole.
The average home has only a few devices left that still use AC internally (mostly large or old appliances) and home storage systems lose energy to power conversion overhead in both directions at multiple stages. Since each conversion represents a loss of up to 20%, the AC standard introduces an increasing amount of unnecessary friction close to the point of delivery.
Illustration: if your home charges from the grid, that’s one conversion AC —> DC. If you then use that power to charge an electric vehicle, that’s two additional conversions AC —> DC —> AC —> DC (currently few EVs support DC charging unfortunately). If you then charge your laptop in the car using the official charger, that’s two more conversions AC —> DC —> AC —> DC —> AC —> DC. Altogether this requires about 3x as much power than necessary with residential DC electrical, since then the power can go from solar to storage to car to laptop without the need for power inverters.
What voltage of DC would you propose for the common household? Keep in mind that one good reason for alternating current is for safety. Higher voltage AC will allow your muscles to release if contacted. Higher voltage DC does not. Additionally, using higher voltage with either type reduces actual wiring cost in the walls to deliver similar wattage. I don't have the math on me for sure, but delivering 12vdc to every outlet would require much larger in wall cables... And that doesn't even touch the subject of voltage drop (with the exception that larger cables can mitigate this somewhat).
Well it’s not standardized yet to my knowledge, but for example if we used something like the USB-PD protocol it could be a baseline 5 volts, with device negotiated step up to 9, 12, 15, 24, 28, 36, and 48. Higher voltage isn’t out of the question; EV systems safely run closer to 400 and a number of home batteries range up to 600, but I’d be iffy on the idea of the average contractor putting that voltage in the walls of the average home.
It’s true the copper for longer, higher current, or lower voltage DC runs could get very expensive, but even without HV for distance, thoughtful distribution of storage to expected points of delivery would limit the number of heavy lines needed for current spikes.
Long short, I’m not talking about switching entirely from AC, or pumping DC power through existing residential circuits. I’m talking about adding a secondary system that’s a more integrated version of the ubiquitous portable power station / “solar generator” batteries. It would be a home modernization upgrade, similar to running Ethernet to PoE enabled jacks in each room, installing a fancy intercom system, or what have you.
I dig that solution for sure. I know I've seen others in the past only suggest the low voltage DC piece and not have the solution to run 100 foot or more in the wall - but essentially you could load up highly efficient power transformation as well as built in batteries for each device to request the power it needs.
Only real problem next would be the added cost. Not only for the edge devices (which may save money) but for the home transformation itself. 110vac outlets are around a buck or so; pretty hard to beat. My guess is that this would be something better served with early adopters and then attrition.
I would prefer 48 V, because it is as high as possible while still being safe and leaving some margin (note that 60 V DC is considered maximum safe voltage).
Note that 48 V is 80% of 60 V. So the margin is 20%.
I am against negotiating the voltage dynamically, because I fear that it makes every device drastically more complex, and therefore drastically more expensive. (and drastically more prone to errors)
DC voltage is considered safe (cannot penetrate human skin) up to 60 V.
So I would propose 80% of that, to leave some safety margin. That would be 48 V, which btw is also a multiple of 12 V, which is commonly used today.
I agree, all of this AC power was introduced to facilitate conventional power grid, but does not longer make sense in the context of solar power. An update would improve efficiency, and probably some other advantages, such as: