Electrifying the Transportation Grid and Sharing DC Power
By: Vern Scott
Tags: Heat Pumps, Hydrogenfuelcell, Global Warming, Renewable Energy, Vehicle Electrification

Electrifying the transportation grid is a daunting but doable task, using methods such as HVDC, battery storage, hydrogen fuel cells, more electrified buses and rail. Electrified space heating will require much more electricity than is already produced (where will it come from?)

Alternative technology experts in search of changes in our infrastructure to increase energy efficiencies mention three things: electrifying the transportation grid, the sharing of excess renewables via large DC power grids, and the electrification of space heating. Large scale transportation electrification might include (but not be limited to) massive rail electrification, extensive usage of electric autos, electric auto trains (roads that power cars as they move in groups as they charge off that road). Building electrification may include a massive conversion from fossil fuel burning to electric heat pumps. The electricity might come from large desert photovoltaic arrays, hilltop and shallow ocean wind chargers, wave-energy arrays and hydroelectric systems with perhaps some short-term dependence on redesigned nuclear or scrubbed natural gas plants, all shuttling time of use energy between markets according to need via large DC transmission lines.

The state of renewables is currently manageable because it is not more than 25% of the energy produced in any market, and can contribute during the day (when it is most likely available) while gas (or sometimes coal) generated plants augment at night, during bad weather, or when renewables are otherwise not available (ie much of the time). Elon Musk’s Tesla battery storage systems notwithstanding, energy storage is prohibitively expensive (currently about 30 times the cost of the energy produced, per kwh), so naturally the question becomes “what will we do when renewables become 50% or more of energy produced and coal plants are offline?” which is more or less the upcoming scenario in California and Germany (very soon) and many other places by the year 2030. At the same time, there is pressure to limit the use of oil for powering cars, buses and trains, and limit natural gas for heating (some California cities have already banned natural gas for use in heating new buildings). Naturally, energy “moderates” such as myself, while lauding these energy goals, see a kind of “train wreck” coming, unless energy storage becomes very cheap very fast. More likely, natural gas cleansed through Carbon Capture and Storage (CCS) or better Carbon Capture and Utilization (CCU) and Bill Gates modified Nuclear plants will need to be a “bridge”, while we wait for energy storage costs to come down and renewables to take over completely.

A great means of avoiding the energy storage problem is the use of high voltage direct current (HVDC) transmission lines, already built between many states (and countries) by utility companies to balance energy demands. There are currently several such lines in Europe (between Scandinavian countries and Germany, and between England and France, for instance), the “Pacific Intertie” between Oregon and Southern California (laid in coastal waters in the 80s), and several in India, China, Russia, and the rest of the world. These HVDC networks can and may decrease the need for storage in our Country, as they create the possibility that the “renewable-rich” west and southwest could sell renewable energy to the relatively “renewable poor” East and Southeast. There are HVDC projects proposed that will shuttle windfarm energy from Oklahoma to the Southeast, and perhaps someday, other Great Plains states to the East Coast. The change in time zones would mean that energy produced at 4 pm Central Time in the Winter, might be readily available at a primetime 5 pm Eastern time demand, plus it would be energy delivered to a much bigger market, all of which might preclude the need for massive energy storage.

Without getting into the historical “Tesla AC vs Edison DC” debate, AC was originally the choice to carry high voltages over long distances with low line-loss, as high voltage DC technology was unknown until the coming of the semiconductor age, about 40 years ago. HVDC grid ties are advantageous as they are not phase dependent like AC transmission lines, and they have less transmission loss compared to HVAC. Overall, the transmission of electricity has traditionally suffered from nearly 50% loss (35% converting fuel to electricity in the generating plant, 15% in transmission). Though about half the 15% transmission loss is unavoidable because of stepping up and stepping down voltages through various devices, HVDC can lower line loss over long distances (more than the “break even” point of about 250 km). At 1000 km, HVDC line losses are about 20% lower than HVAC, which really adds up when you’re moving large amounts of power. Challenges to the implementation of HVDC are of course cost, and sometimes right of way (although they can generally occupy the same right of way as existing HVAC lines, or even road or rail right of ways), and sometimes safety (as HVDC is an emerging technology and doesn’t yet have the track record of HVAC). Another complication is not really knowing where the future renewable generation will take place…will it be primarily near the ocean (most likely the West Coast), the desert (most likely the southwest) or the Great Plains? Naturally, an HVDC line between West and East Coast would be ideal, but no one has ever built an HVDC line that extensive (the longest is the 2375 km Rio Madiera line in Brazil), and such a line would have to be close to 5000 km long and go over the Sierras and Rockies (difficult).

Another potentially large offset of the renewable energy storage problem is the introduction of electric vehicles on a massive scale, since each has a battery pack and could theoretically store about three days worth of energy. If EVs were charged during the day (when renewables were operational) this may also be a storage problem offset. Note here that although EV batteries are relatively expensive, they are worth the expense as they offset standby losses (ie wasted energy at stoplights), plus there is really no other current means of powering an EV, unless you consider the advent of hydrogen fuel cell cars (fuel cells are essentially another type of “battery”) or a roadway electrified car (via an electrified rail or maglev type system)

In Sweden, there was a recent pilot project in which an electric rail was placed within a roadway, for the purpose of charging electric cars. The concept is simple and similar to that which powers many electric trains. This concept might be part of a combined DC distribution and EV charging system (both creating expanded uses for renewables). Maglev highways may be the ultimate technology for car electrification, as they may eliminate the need for contacts between car and electrified rail (the vehicle rides on a magnetic cushion, which also eliminates friction). However, there are currently few trains in the world running on Maglev systems (due to first cost and some technical problems), so Maglev auto trains may not be in our near future.

Meantime, the full electrification of the transportation system has similar challenges. Although Maglev trains are quite energy efficient (reducing drag and eliminating electrical contacts), they are costly to build and inflexible (when first-cost for a fixed-rail system is great, you need to hope that ridership is high). The more traditional electrified third rail or overhead electrification systems currently used for most light and heavy rail in the world are cheaper to build and safer, though less efficient.

On the space heating side, electric heat pumps are being proposed as another way to use renewables in real time (without storage) while increasing efficiencies and weaning ourselves off fossil fuel. This is a noble idea, but not without criticism. For one thing, the current demand for space heating is enormous, and would overwhelm the relative trickle that renewables currently produce. Next, there is the irony that much of the current electricity comes from fossil fuels. However, electric heat pumps (which can provide both heating and cooling) are a great bet for the future, when renewables are more plentiful.

Finally, there is the proposal that renewables be used to make hydrogen, to be used with hydrogen fuel cells, which though currently pricey, could solve the storage problem. In addition, this would eliminate the need for remote renewable installations to have transmission lines (instead they might have a hydrogen tank, which was periodically replaced).

The issue of renewables, energy storage, HVDC, and electrified transportation and space heating is enormous and dynamic. It will be dealt with in future articles.

Like this article? Read more in Vern Scott’s new book “Civil (Engineering) Disobedience”, available on Amazon.com