|VoxSolaris: The Voice of the Sun|
|The Power Grid Evolution|
Surges on the grid
One beauty of the power grid is that all the energy management is done for us, behind the sceens. When we suddenly draw a large current, the power is almost always forthcoming with little or no detectable voltage drop. The energy managment built into the grid is complex but benefits considerably from large scale statistical smoothing. While the power consumption of an idividual household can vary dramatically at the flick of a switch, the combined power consumption of millions of households, hundreds of thousands of shops and offices and thousands of heavy duty industrial plants, tends to stay within a narrow margin of what is expected for any given time of day. That expected level of consumption still has sharp peaks and troughs however. When the TV adverts start so does the kettle - in millions of homes at once! A typical kettle consumes 3kW so 10 million of those is the full output of thirty 1,000MW power stations.
Generators differ widely in their ability to cope with variable loads with hydro faring far better than either gas or steam turbine. All are constrained by the need to keep a constant speed so as not to vary either the voltage or frequency. This is particularly so in the general case where grids are energized by multiple generators that must be kept exactly synchonized at all times. Generators can only cope with varying load by varying the applied torque although grids can widen the range by switching in generators as required - providing they are already spinning in sync.
Managing a grid is a lot easier if all or a large part of the total generating capacity is hydro. With a head of water behind a large dam the hydro plant is in effect, a huge battery that can meet a surge in demand by opening more nozzles to increase applied torque. Alas, most grids don't have this luxury. There is either insufficient hydro or no hydro at all. They have to make do with gas and steam turbines which don't act as batteries and burn lots of fuel just to keep spinning. And turbines are slow to spin up. A typical grid class gas turbine can take anything from 5 to 30 minutes to spin up. Steam turbines can be spun up in a similar time but only if there is already a head of steam. To crank up that head of steam in a coal or nuclear fired power station can take as long as 24 hours. Grid operators have a shrewd idea of what the consumption pattern will look like minute by minute for any given day and what factors will influence this and to what extent. Their data feeds include detailed real time weather information and forecasts and the TV schedule. This helps them keep the right number of turbines spining so as to meet the baseline demand and expected surges but without wasting too much fuel.
In spite of its narrow range of power output and slow startup times, the turbine dominates because in terms of efficiency, it has always had the edge on the much more responsive and quick starting piston engine. And although little has changed in either technology, material advances allowing higher temperature operation have helped the turbine more. Today a large diesel engine can achieve 50 percent thermal efficiency but a combined cycle gas turbine can achieve 60 percent. Just as importantly, the turbine is more flexible on fuel. The piston can run on gas and oil as can the gas turbine. The steam turbine can run on anything that makes steam so a nuclear reactor or coal or flamable waste or even worn out tires. Of these coal dominates because of its relatively low cost and widespread availibility. The turbine remains the heat engine of choice but there is a drive to add grid-storage class batteries to smoothe out the surges in demand and allow the number of spining turbines to be better matched to baseline demand. A clear inhibitor to grid-storage battiers has been the price.
The Offgrid scenario
Long before solar panels and small scale wind turbines made off grid solutions a competative alternative to being on grid, there were diesel generators for those the grid did not reach. When the diesel was running managing surges in power demand were a relatively simple matter but it was a very different story otherwise. The shortcoming lay in the battery which back in those dark days was expensive and inferior to what is available today. Without a baseline power consumption to justify running the diesel at all times, it fell to the battery to provide all the power requested at least until the diesel started up, an action which itself sucked power. Common strategies for managing these limitations included putting heavy loads on a separate curcuit so that they could not be switched unless the diesel was running.
Now that solar panels and small scale wind turbines are economic and in most off grid solutions are intended to provide the bulk of total power produced, it still lagely falls to the battery to meet surges in demand since there is not the benefit of any statistical smoothing. And although for home scale off grid there is now the Tesla Powerwall which nails the problem very effectively, that is still a little pricey for some, particularly for residents in rural parts of developing countries. And if you are not in the market for a Powerwall you are even today, looking at deep discharge lead acid as the only practical off the solution. At the less exotic end of the battery market, changes have been a lot slower. Moreover, on a total cost of ownership basis the Powerwall is very competative to lead acid meaning that if you can't afford one you are looking at lower battery capacity and will have rely more on demand managment. At least certain things are easier with solar. On a good day you can run the washing machine without killing the battery while on a bad day you might be less inclined to run it anyway. To a certain extent, solar fits our natural demand patterns, particularly if we use air conditioning.
Power grids have brought power to the people but that was an effect rather than the prime mover. Regardless of any political issues surrounding grids today, the fundamental driver has always been the economies of scale. However grids don't have to be large to offer tangible economies of scale. A community grid linking say 100 homes in a small villiage, offers a surprising degree of statistical smoothing. Instead of each house having say a 10kWhr battery, the whole villiage might have a single 500kWhr battery. Instead of each house having a small wind turbine the villiage as a whole can have one or more large turbines. And they can bulk buy solar panels. Since electricity is inherently more valuable at the wall than it is on a state-wide grid there is more to be gained by the villiagers selling power firtly amongst themselves before selling it to the main grid, if indeed there is one.
Such grids are springing up mainly where grid electricity had failed to establish itself, in rural areas of developing countries, where people are already installing and extending home based solar and wind solutions. A decade ago people in these areas were aquiring systems that comprised little more than a single solar panel, a car battery and a lightbulb. Other than see at night for two or three hours you could plug in the radio and if you earned well, charge your mobile phone. Thanks mainly to much cheaper solar panels things have changed. Today more and more have TVs and fridges, microwaves and electric hobs. Another decade and how many people in these areas won't also have an electric car?
The Future for Large Scale Grids
Electricity use is changing. Historically and still today, usage is higher during the day than at night but it is very likely that a new peak demand period in the early evenings of weekdays will emerge. This will be due to commuters pluging in their electric cars after a hard day in the office. Our assesment is that widespread adoption of electric cars, with or without IC engine range extenders, can be assumed. Aside from batery chemistries showing greater promise, lithium ion is already viable and there are no technological barriers to further price drops. While cheaper and thus ever more prolific solar is steadily reducing the extent to which we all rely on the grid, the advent of the electric car is probably the one thing that will stop housholds as a whole, be they part of a community grid or not, with or without storage, from becoming net exporters of energy.
But the big changes to the grid won't come from changing consumptions patterns as much as they will from changing production patterns. Cheap solar is giving rise to solar farms which are significant exporters. And as the install bases rises, they are begining to wreak havoc upon the the large scale grids. It is easy with the data they have to know the baseline consumption. It is not so easy to know much of that will be met by solar, less still by wind. Accurate weather forecasting will give a good pointer as to which solar farms and wind farms will be producing what level of output and when, but that won't suffice. The reports have to be reliably accurate and to date, that just hasn't happened. Without reliability and accuracy we will continue to see turbines spinning needlessly and wasting fuel just in case the sun goes in unexpectedly. Unless of course we aquire more grid storage capacity.
While community grids proliferate in areas previously not served by a grid few housholds in areas of long established grids will be part of a community. And these housholds will likely lag in battery capacity. We expect to see a significant increase in solar installations with most houses having them. One problem that will have to be addresses is that the grid was not actually designed to receive small inputs from millions of generators and although it is increasingly being made to work that way, it is not being done efficiently and if anything, as the install base rises, it is becoming less efficient.
As the grid is all about economies of scale, state wide or large scale grids will become more akin to 'central bankers' of energy. One thing is very clear, overall grid storage capacity will have to rise significantly. We think the best way of achieving this is the Sodium Sulphur Flow Batteryas this could become particularly cheap for large scale operators. To mitigate what would still be onerous grid storage requirements, we forsee a new class of service agreement emerging - intermittent supply. This would be used for industrial processes such as electrolysis which are inherently tolerant of an intermittent supply. To meet these changes we foresee widespread adoption of HVDC (High voltage DC). This technology has been greatly helped by the advent of the supercapacitor and is now relatively cheap. It removes the need for AC synchronization between different parts of the grid allowing the large scale grids to become a patchwork of small grids.