Cities around the world, including 22 cities in the United States and a growing number in Canada have pledged to go 100% renewable. It’s a noble, collaborative effort to be the cleanest, most environmentally sustainable cities on the planet, with an ultimate and cumulative end goal of each city doing its part to reduce worldwide carbon emissions.
Many cities that have made the pledge don’t yet have a route to an all-renewables, carbon-free destination. Some don’t have ownership of their electricity providers and thus have little or no influence over power fuel sources. Others depend today on energy sources that are based almost entirely on fossil fuel, making the renewables transition particularly difficult. Still others are dealing with high permitting costs for popular renewable options like rooftop solar, as well with other regulatory obstacles. Technologically, anyone switching to a renewables-based grid must, by default, deal with the intermittency and reliability issues imposed by wind and solar. Even hydro electric energy is generally limited by the amount of water flowing in rivers, a quantity that can vary significantly over time.
A broader question, however, is why a fully renewable grid is more desirable than any other combination of zero-carbon energy sources. And what the overall effort and cost would be to decarbonize via that pathway alone.
In other words, if our goal is to cut carbon emissions, there might be other – and better – ways to do it. One needs to ask the question – are there alternatives that would achieve the same carbon reduction objective? And are their ways to do this that won’t involve significant increases in energy costs, which could have devastating results on our communities? We think the answer is yes. Some of the significant potential issues, opportunities and examples are discussed below.
Solar, Wind, CHP, EV…. What’s the Answer?
Solar is seen by many as the answer, yet many attempts to rely on solar have had questionable results. Germany, as an example, has implemented large amounts of solar capacity since 2010. There have been contradictory results: much higher costs, no coal plants shut down and more than 10 new coal fired generating stations under construction.
Wind was installed in large quantities in Ontario, but it appears that the night wind capacity is displacing nuclear capacity, a source that is carbon free, and cannot dispatch down to accommodate surplus wind. Costs for many consumers have increased significantly because the nuclear capacity is already paid for, regardless of use.
An ideal replacement power generating source would have very low or zero emissions, be capable of being fully dispatched at any time for power control, and could be distributed to provide power very near the load site. Such technology may already exist in a commercialized form, allowing it to be used immediately,with some certainty on costs.
But before digging into the detail, it is worth a few moments to understand the physics behind all systems.
Coal generation is among the largest source of electricity in the United States. It is NOT a clean burning fuel, emitting about 100 kG/GJ of energy. Most coal plants use steam turbines to power the generators, a process that is typically about 33% efficient. Delivery of 1 GJ of electricity (278 kWh) of electricity would one potentially emit about 300 kG of emissions.
The same comparison can be used with natural gas, with a few changes. Natural gas emits about 55kG of carbon for each GJ of energy burned, producing a little over half of the emissions from a similar amount of energy from coal. The technology to burn gas, however, has advanced.
Adding CHP to the Equation
Combined cycle gas plants can operate at efficiencies of over 60%, and the use of a combined heat and power (CHP) plant has the capacity to utilize almost 90% of the energy from the primary gas, meaning that the emissions would potentially be very small.
CHP systems have been well-utilized in medium-to-large buildings to provide electricity, heating and air conditioning, Overall efficiency is generally very high (>80% - but certainly not 100%). What CHP systems do very well is to produce energy where and when it is needed. This eliminates electrical delivery losses, which can be more than 10%, and they can deliver more energy without the need for large new central facilities that require transmission systems for delivery. They can provide ancillary services back to the electric grid, and they have ability to provide a back-up source of either heat, cooling or electricity in the event of an emergency. They can firm and support renewable capacity.
They can also add locally-generated energy to charge EVs at night. A typical motor car is less than 20% efficient, but EV efficiencies typically exceed 60%. An EV can utilize electricity generated at a conventional gas powered plant, and still result in significant emission savings. Charging an EV from a CHP could reduce emissions by 85-95%.
All Renewables or a Well-Planned Mix?
Our communities may be very wise to have a second look at their current plans for reducing carbon emissions. The elimination of all fossil fuel could well cause serious issues including high costs, high demand for electricity and major additions to the electric grid to meet this demand.
There is no doubt that the future will be largely based on distributed energy sources, and solar and small wind capacity will have a key role in this supply. But to integrate the intermittent sources, manage voltages and keep costs at acceptable levels, there will need to be a lot more.
The future is more likely to be drive by a mix of renewables, dispatchable process loads, high efficiency gas and conservation. A future where all these pieces work together makes more sense; if any of them is pushed too far, it becomes more costly and difficult to manage than the optimal system.
This has a far higher probability of success in creating the greenest cities in the world – where people can afford to live. No scientist has said that we must switch to renewables; we simply must cut emissions – by a lot, and soon.