After a lot of experimentation and costs, my 100% PV-DC residential power system (aka self-hosted PV2L DC Micro Grid) has passed its first tests and is in active use. The system is unique, supplying 24×7 Off-Grid residential DC (direct current) utility power right to the wall outlet and appliances, with the battery being offline – and used only when it’s needed. In this design, the battery is only used to “prop up” the micro grid voltage during cloudy weather and/or for nighttime use.
PV2L Hybrid: The Battery Becomes Secondary
The battery is no longer a core part of the off-grid system. Instead, direct DC Solar photovoltaics take the front row seat, supplying power to household loads. When solar array power production is too low causing the DC micro grid voltage to sag, or the sun goes down, the battery is automatically connected to the circuit, helping to lift the micro grid voltage up into the correct operating range.
PV2L Hybrid Model – Micro Grid
PV-To-Load or PV2L for short, refers to an unregulated Photovoltaic DC bus powering appliances and useful loads directly, bypassing the traditional paradigm of solar panels to charge controller to battery to inverter to loads. Power straight from the solar panels to the appliance: it doesn’t get any cleaner or better than that!
By combining properly matched PV solar panels, matched loads and custom DC appliances plus a matched 51.2v LiFePO4 battery, I created a residential DC micro grid using common NEMA wall outlets. Due to the fact that solar power literally comes out of the wall outlet, I also describe it as PV-to-Wall (PV2W). The wall outlets being installed in my home look familiar – but no AC comes out. Just pure clean DC straight from the photovoltaic bus to power loads.
The entire system operates at 55 Volts DC nominal from end to end: no DC conversion is required at any stage. For several years I have been developing household appliances that run on 55Vdc natively. The solar power flows directly from the panels and onto the DC micro grid for direct consumption by the appliances, with generally nothing else in between.
No Charge Controller – Zero DC Conversion
PV2L-MG is a hybrid solution – so batteries still matter. If a battery is in the circuit, and there is excess solar power available, it will charge through what I refer to as an electromechanical ideal diode. This means even though a diode is in the circuit, it is generally bypassed so even the ~0.2-0.5v a blocking diode might introduce is also eliminated. Meanwhile, appliances and loads continue to run on the micro grid with no interruption.
Since the battery operates in the solar vMPP region for most or all of it’s voltage profile, a charge controller becomes obsolete. It is no longer necessary! Only a simple OVP (over voltage protection) circuit is used to protect the battery. Once the battery is full, it gets disconnected and goes into standby for cloud cover situations or nighttime use.
Lowering Entry Barriers to Solar Power
The efficiency, simplicity and cost-effectiveness of such a system is incredible. There are fewer components, lower costs, fewer points of failure. Efficiency is high because no DC conversion is needed.
Bypassing the purchase of major components like charge controllers and inverters completely changes the game. Off Grid solar power becomes more affordable with lower initial costs, and more people can take advantage of off grid solar power for their household, while spending only a fraction vs. typical systems available today.
Prototype Live Testing – Current Status
I have been developing and testing the PV2L DC Micro Grid concept for several years. But I never had a chance to physically hard wire it into my home. As of this writing, I have the prototype installed and running in my home for further testing. Although the system is still in its early stages of installation, I created a video introducing the concept and showing some of the appliances operating.
My plan is to use it to power my home on pure DC while continuing to refine it in real time. Cabling, fuse panels, outlets and other equipment are slowly being installed as finances and time permit. At the same time, I am developing and testing cooktops, space heaters, ovens, various machines and even an electric clothes dryer that can operate on DC. This is true real-world testing and research.
Hopefully there will be more video footage and details about this system, including a long form video. Things have been very rushed and haphazard around here, so the work takes longer than it should.
If you are interested in projects like this, feel free to subscribe to this blog and my YouTube channel. Thanks for reading and have a great day! -Dave, SPE
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