How Solar Power Can Make Heating and Transportation Greener
Clean power sources are gaining a larger share of the global electricity market every year. However, human society would still have significant emissions even with a 100% renewable grid, due to the impact of heating and transportation. To prevent global temperature rise and the consequences of climate change, emissions must be reduced in general, not only in the electricity sector. Distributed solar power can be of great help, especially if combined with energy storage systems.
Emission reductions have been easier to achieve in the electricity sector, compared with heating and transportation. The difficulty is due to the operating conditions found in these applications:
- In terms of operating cost, combustion-based heating is drastically cheaper than electric resistance heating, especially when you consider the high kilowatt-hour prices of Australia. Modern high-efficiency heat pumps can run with electricity while matching the cost of natural gas, although they are still an expensive technology.
- Since vehicles must carry their energy source with them, it must be a source that minimises volume and weight. Before recent developments in lithium-ion batteries, only liquid fuels provided a viable alternative for vehicles.
In theory, heat pumps and electric vehicles (EV) can be used as direct replacements for combustion-based heating appliances and transportation. However, if the local power system is still strongly dependent on fossil fuels, you are only trading direct emissions at the point of use for indirect emissions at power plants. There is a slight reduction in emissions due to the efficiency gain of heat pumps and EVs, but the potential progress is limited unless the grid is decarbonised.
Using Solar Power with High-Efficiency Heat Pumps
Electric heat pumps currently provide the most economic heating solution that does not rely on fossil fuel combustion. Depending on the specific product model and efficiency, they can deliver between 2 and 4 kWh of heat for every kWh of electricity consumed.
However, to eliminate heating emissions completely with heat pumps, you must also use a clean electricity source. There are two significant advantages when heat pumps are combined with solar power systems:
- In Australia, both technologies are eligible for Small-Scale Technology Certificates (STC), which reduce their upfront cost. This improves the business case for both technologies, shortening the payback period and increasing return on investment.
- Electricity sources and heating appliances are operating close together, which eliminates the cost associated with power transmission.
Even with a high-efficiency heat pump, the idea of connecting it to the grid can be intimidating due to the high kWh prices in Australia. However, if you produce electricity locally with a solar power system, you no longer have to worry about increasing your power bill with electric heating.
If a heat pump includes an insulated hot water tank, it can actually operate as an energy storage system. We normally think about batteries when the concept of energy storage is mentioned, but thermal storage is also viable.
- If you export surplus production from your solar array to the local network, you only get a reduced feed-in tariff that is only a fraction of the kWh price.
- A much better option is using surplus electricity to run the heat pump and store hot water. Later in the day when solar generation is no longer available, the stored hot water can be used instead of running the heat pump with electricity from the grid.
Note that thermal energy storage is also possible in cooling applications. The main difference is that you store ice instead of hot water, and the ice can then be melted to deliver space cooling or refrigeration. The most common application of this concept is in chiller plants that serve groups of buildings with large cooling loads, where economies of scale make ice storage very cost-effective.
Solar Power and Electric Vehicles
Electric vehicles have become viable with recent development in lithium-ion battery technology. Conventional lead-acid batteries are not practical for EVs, since they are large and heavy while suffering from low efficiency and a short service life.
A common argument against electric vehicles is that they simply replace direct emissions with power plant emissions, but this only applies for regions that use fossil fuels as their main electricity source. Also keep in mind that an electric vehicles can start using clean electricity from a solar power system at any time, while a conventional vehicle with a combustion engine has no way to use electricity from clean sources.
Although there is already a market for EVs, they must achieve cost reductions to reach a larger market. The lack of charging infrastructure is also an issue, since it places a limit on how far you can drive an EV. However, keep in mind that solar power had similar affordability issues just a decade ago, and it is now among the cheapest electricity sources.
Batteries are among the most expensive components in an EV, but the International Renewable Energy Agency predicts significant cost reductions for batteries throughout the next decade. Cheaper batteries will help reduce the cost of EVs, increasing the size of their potential market.
The concept of a virtual power plant (VPP) uses distributed generation systems and energy storage, coordinating their operation to perform the same functions as a centralised power station. EVs that are parked and connected to the grid can participate in a VPP, using their onboard energy storage system.
Heat pumps and electric vehicles have the potential to achieve drastic reductions of greenhouse gas emissions, especially if combined with distributed solar power systems and energy storage. Although these devices could be simply connected to the grid while deploying a larger share of clean generation, there is a technical issue: a large number of heat pumps and electric vehicles can burden existing transmission and distribution lines, requiring expensive upgrades.
On the other hand, when heat pumps and electric vehicles are combined with distributed solar systems, electricity is generated closer to the point of use and the network load does not increase drastically. The use of hot water storage and batteries adds versatility to distributed energy systems, reducing dependence on the local grid.