RV daisy chain power grid
After every RV trip (I'm back from Burning Man) I think of more I want RVs to do. This year, as we have for many years, we built a power distribution system with a master generator rather than having each RV run its own noisy, smelly and inefficient generator. However, this is expensive and a lot of work for a small group, it is cheap and a lot of work for a larger group.
There's been a revolution in small generator design of late thanks to the declining cost of inverters and other power conversion. A modern quality generator feeds the output of its windings to circuits to step up and step down the voltage to produce the required power. The output power is cleaner and more stable, and the generator is spun at different RPMs based on the power load, making it quieter and more efficient. With many models, you can also combine the internal output of two generators to produce a higher power generator.
RVs have come with expensive old-style generators that are quieter than cheap ones, and which produce better power, but today they are moving to inverter generators. With an inverter generator, it's also possible to draw on the RV batteries for power surges (such as starting an AC or microwave) beyond what the generator can do.
I'm interested in the potential for smarter power, so what I would like to see is a way for a group of RVs with new generation power systems to plug together. In this way, they could all make use of the power in the other vehicles, and in most cases only a fraction of the generators would need to be running to provide power to all. (For example, at night, only one generator could power a whole cluster. In the day, with ACs running, several would need to run, but it would be very unlikely to have to run all, or even 75% of them.)
In such a system, the RV's shore power cord (3 conductor, 10AWG able to do 30 amps) would become a smart power connector, able to send data and power in various forms. Of course, an adapter would exist to plug the shore cord into standard RV receptacles (TT-30) at 120v and 30a. However, on the other end of each RV would exist a smart jack into which another RV's smart plug could be placed.
Once a network or daisy chain starts up, the power systems would communicate. They would probably switch to sending DC or synced AC at the highest safe voltage (perhaps 480v) over the connection, allowing over 14kw to flow over the wires if need be. RVs could contribute power to the system, take power or pass it through. Higher voltage means less current, and less voltage drop over long distances, however high DC voltage has risk of arcing so special cables and connectors are a must. (Power would not flow unless solid connection was established, and would be shut down in the event of arcing or ground fault.)
The systems would negotiate who would provide power. They would meter watt-hours going in and out to track their contribution and the contribution of others. By and large, generator usage would be balanced, so everybody provides as many kwh as they take unless otherwise agreed to. If the users input how long they expect the grid to last, this can be done with long periods, otherwise which generators are running might change every few hours. Other factors might change the balance:
- It is better to use generators in the middle, so power is not sent over the full length of the chain
- Some people may have more efficient generators or bigger ones which should be used
- Some people may be lower on fuel and only able to contribute so much power
- Some people may have noisier or smellier generators whose use is discouraged or even forbidden at night.
In this case the system could keep an account, and for those so inclined, automatic electronic payment could be made between users of such a temporary grid.
Because of the presence of large batteries, initial loads would be served from the battery bank. After a short time, it might be decided a generator is needed. A short microwaving might never require any generator. An AC would probably involve starting one right away if one is not running. Ideally devices (especially AC controllers and thermostats) would be made aware of the system. Thus the AC might announce, "I am going to need a 3kw spike and then 800 watts continuous ASAP" and the system could assure the power is available before telling the AC to engage.
Most RVs come with a 3-4kw generator, but in fact their AC usually only draws about 1kw, and their microwave may draw something just below that. The 3-4kw is needed to handle the start-up spikes, plus other highly unlikely events like plugging in a vacuum cleaner or some other power tool or appliance at the same time. In reality, a single generator with battery assist could run 3 ACs in many cases. In addition, ACs don't operate on 100% duty cycle so the more you have, the more the power evens out. The poor power factor of motors on startup is also evened out when you are running several.
A basic daisy chain could also support one "dumb" RV which receives 120v AC via an adapter from the last RV in the chain. In some cases it could also contribute with a smart adapter plugged into its generator or output. (Some RVs have the generator be sort of stand-alone -- you plug your shore power plug into your generator when on generator, and physically move it to the post when in an RV park. You could have a special plug and socket that goes between them.)
Such a system could also be used with an external generator, with one or more RVs plugging into it directly and having others daisy chain from those.
Finally, one could imagine fancier concentrators that go beyond daisy chaining. A master distribution box could allow 2 or more RVs to plug into it, providing or taking power, avoiding long wire runs. However, if you can get to 480v long wire runs are not as big a problem. In addition, if an RV has to smart receptacles it can become a T in the network, and that's handy enough that many might pay to add one or it might be possible to rent a module to add one from RV stores and rental houses.
RVs with any significant solar power would also want to join networks because in most cases solar panel output is wasted once batteries are not under significant discharge. Connecting to a net would make it easier to use all the power of the panels.
Mutli-RV group dry camping is actually a fairly popular thing, making such a system worthwhile for much more than Burning Man. Indeed, with a proper accounting system (with offline payment tokens exchanged and payment done when returning to the online world) people could just set up ad-hoc systems when camped in rows at national parks. Indeed, the parks, while not offering power to the RVs, could bury the wire between campsites to let the RVs share. Low-power campsites could also offer minimal power (ie. enough to run lights and other small appliances and slowly charge batteries) to the RVs and the RV clusters could fire up one of their generators when more power is needed. (It is often vastly easier to offer say a single 120v 15a circuit to a group of 10 RVs than to offer 30a to each of them!) Indeed, with the ability to recharge batteries slowly from a 150w-per-RV circuit, almost everything except the ACs could be run without a generator. A microwave might draw 1000w for 10 minutes but an hour later the batteries would be restored. Sharing with all the other rig's batteries also puts less discharge strain on all of them.
It's also even easier if the low-power park could provide power at a higher voltage to smart-power systems, since then it's possible to power large groups of campsites with a single lower-current circuit. I am not saying national parks must provide power to campsites, but if they can easily do so and it stops the running of generators, it makes a lot of sense.