Science has told us that we must reduce carbon emissions if climate change is to be kept below acceptable limits. The transition has led us in many new directions. Most politicians outside the US believe that our energy supply must be based entirely on renewable energy. This alone creates a large issue, in that the electric grid supplies less than 20% of total energy needs. The proposal to replace all fossil fuel with renewable capacity would require a potentially large increase in grid capacity. Ironically, many politicians typically include nuclear generation among the sources to be eliminated. The one bit of good news is that the efficiency of electrical devices is often better than fossil fuel, and the existing grid operation using a generation following load approach results in a system that can deliver more energy.
The results to date have been frustrating, both in costs and performance, and there are many serious problems that may make a complete conversion very difficult. These challenges include a lack of grid and generation capacity to handle the added electrical load, as well as the operation of the existing grid with extensive distributed devices.
We have grown to expect a continuous supply of low-cost energy, but this expectation isn’t always being met. For example, recent changes in pricing in Ontario resulted in many rural customers facing a difficult choice during cold winter months -- purchase energy OR food, but not both. On a wider scale, this would create havoc.
Challenges to Carbon Neutrality
Germany, seen as a leader in the transition to a carbon-neutral world, has experienced energy cost increases of more than 50% over the last 12 years. The EU has published documents that show that the highest average cost of electricity in the EU occurs in Germany and Denmark, where prices are more than twice the EU Average, a huge change from the past. New coal-fired generation is being commissioned to replace the nuclear capacity that is being retired. As a result, over the last decade, the reduction of emissions has stalled, and Germany recently acknowledged that meeting 2020 and 2030 targets for emissions will now be impossible.
In California, the government and PUC have promoted home-based solar energy installations, and investment has been heavy. As a result, there is so much solar power being generated that other states are sometimes paid to use it. The system operator has resorted to exporting energy during sunny afternoons to avoid overloading power lines, paying utilities in Arizona to take, and then sometimes purchasing it back at higher prices a few hours later, after dark.
Ontario experienced similar difficulties after the installation of wind. The province reduced capacity on nuclear generation, without changing the reactor operations. The excess steam was being discharged, through condensers, into Lake Huron. This waste was a direct response to new undispatched wind capacity and the result of keeping generation available that could replace the renewable energy if the wind declined quickly.
Why are we having these issues with a form of energy that seemed ready to deliver such great results?
The existing loads in most utilities are broken into three sectors, each using about 1/3 of the energy delivered. Industrial loads tend to be relatively constant because their rate structures make this the most cost-effective option. Many of these industries run 24/7, meaning that they are a near constant load for the utility. Commercial users operate from morning till night, and while they do have a daily peak, it is not large, and consumption falls at night to a low level. Residential users, with no demand charges (for the most part), have a morning spike, low consumption for much of the day, followed by a large peak, after dark, for the dinner period. At night, the load falls to a low level.
The net result is a load has been relatively easy to predict. It reaches a daily peak at about 6 p.m., is very low at night and is variable during the daytime. Utilities that must generate to match the load on a continuous basis have designed their systems to have base load capability and to deliver the 24/7 power that is essentially non-variable. At the same time, other capacity is available to meet the peak and to provide flexibility. The utility has constraints on most generators, making the selection and design important. Nuclear generators, as an example, do not easily change capacity and cannot be remotely managed by the AGC system. These are ideal for delivering base load capacity. At the other end of the spectrum are simple gas turbine generators. These are ideal for meeting short peaks, and for ramping quickly, but the efficiency is low, and operating costs may be significant. They tend to be used for short periods.
Utility planners have well-established plans, and the system design accommodates the variable loads encountered. Operating staffs have demonstrated strong skills in managing costs, and one can be almost certain that decisions to sell at negative prices or to spill water at hydro generating plants is done to achieve and maintain overall minimal costs.
A Few Cases in Point
A simple example of the planning process occurred in the 1970-1980 period. Nuclear capacity was added to the grid, but at the same time, pumped storage plants were built. The nuclear plants could generate at constant levels, and the pumped storage could store energy at night and provide flexibility and peaking capacity during the daytime. The pumped storage units worked with the nuclear plants to provide the power that was needed at all times.
Today’s political environment has required utilities to accept unknown quantities of renewable energy generated by homeowners, and the overall results are not as good as they could be. Several examples of issues are:
- High ramp rates at sunrise and sunset caused by large amounts of solar energy coming on and going off with the sun. To maintain balance, the utility must have capacity that can provide opposite response to these rapid changes. One utility that we spoke with in the southern US claimed that the only capacity available to meet the requirements for demand and balance were natural gas-powered reciprocal engines that powered generators.
- Reverse power in the distribution system. Although this is an issue that can be eliminated, the net cost could be large and widespread.
- Load shedding intended to reduce capacity rapidly during emergency situations to avoid under-frequency that would cause steam turbine generation to trip offline. In some locations, such as Hawaii, where the use of home solar has become popular, the load shedding may trip a line off, expecting to reduce demand, when in fact, the demand increases – with the distribution feeder generating more power than it was using. Load shedding makes the problem worse.
- Zero energy home design. The customer pays the standard monthly charge for the electrical connection and nothing for the energy consumed. The home owner exports small amounts of energy during daytime through the summer months. Exports at this time are generally not needed or wanted. The customer takes the energy back at or near the winter peak when it is expensive for the utility. Essentially, the process is expecting the utility to provide free seasonal storage at a time when it is most expensive.
The real issue with renewable sources arises when they cannot be dispatched or even monitored, and the utility is expected to accommodate the intermittency of these sources.
Making Things Work
Fortunately, there are solutions to these challenges. To make the whole new paradigm of today’s energy reality work – and work well – renewable supplies like wind and solar need to be carefully coordinated and balanced, perhaps with storage or managed loads. And to leverage all the available distributed resources that exist in today’s energy arsenal, distributed intelligence and control are needed, along with always-on, always-operating grid optimization software that both keeps the grid optimally balanced and harnesses the full value of the connected energy resources.
There is no question that renewables create a new degree of freedom, but the intermittent and non-dispatched characteristics they bring with them need to be controlled. The future utility system will incorporate complex DERMS and VPP control systems to deliver the amounts of energy needed – and to make our distribution systems operate as smoothly and efficiently as possible.