Renewable and resilient energy systems to power residents' everyday needs
The EcoBlock will be supplied by a solar-powered microgrid that can stay online even during a PG&E power outage. An electric microgrid is a miniature electrical utility system that includes:
- a micro power plant (in this case solar electric PV panels on rooftops of houses),
- a means of storing this electrical energy (e.g. battery or flywheel storage),
- electrical cables and a control system to distribute and monitor the energy, and
- appliances that consume this energy, such as residential space heating and cooling, water heating, clothes washers/dryers and dishwashers.
If the regular utility power is disrupted or there is a power outage, the microgrid can supply power to the homes that are connected.
Microgrid Design & Strategy for the Oakland EcoBlock
Microgrids have become popular in recent years, and there are many different types. One thing all microgrids have in common is that they can operate independently of the local utility grid as a power island. What’s difficult about this is being able to match the energy supply and demand of the block at any moment.
Traditionally, most microgrids have used diesel generators, which can easily adjust their power output second-by-second. But of course, diesel generators create air pollution and even new fire hazards. Besides, when there are already solar panels on rooftops, it only makes sense that we should be able to use them in an emergency! Many people don’t realize that unless they also have a battery and special switch to turn their house into a power island, the solar panels on their roof can’t do anything useful when the grid is down. But that kind of battery setup is more expensive than most people can afford for their individual homes.
The plan for the EcoBlock is to demonstrate a new, cooperative solution. Instead of everyone having to buy a large battery system that supports their entire house, we can get much more value out of the investment if we join together and share the resource! It’s no longer necessary to spend extra money on oversizing the power and energy capacity of the battery, especially when we add in some smart controls.
With some visibility and control over our electricity, we can do two things:
- First, prioritize the most important energy uses over those that might be less urgent during an emergency.
- Second, make sure that not all appliances are using maximum power at the same moment.
For example, if we know that there will be a scheduled Public Safety Power Shutoff (PSPS) for two days, we still want to stay comfortable and have all our lights and refrigerators working— but some of us might be happy to let a load of laundry wait a while to help the whole block’s battery last longer! And in case we do need to get that laundry done, the microgrid controls will make sure that our clothes dryer doesn’t start up at the exact same time as our fridge and make the lights dim.
Normally, the block microgrid will stay connected to PG&E, allowing it to either take in extra power if needed or provide solar power to the larger electricity distribution network. Only when the block is operating as an island–during a PSPS or any other type of grid outage–will there be a need to pay attention. Of course, the EcoBlock may save money by being smart about the timing of its total power use—or the strategy for charging and discharging the battery at different times—on any normal day. Our goal is to build a user-friendly control system that lets you choose your priorities without having to push little buttons all the time.
The original EcoBlock design proposed building an entirely new, direct current (DC) microgrid for the block. Unlike alternating current (AC) power, which comes from traditional, rotating electric generators, DC power goes with solar photovoltaic (PV) panels and batteries. Alternating current changes direction 60 times each second, the same speed at which generators spin. Standard electric appliances are designed to work with AC, although an increasing number can use either AC or DC. Direct current flows in just one direction, like from the positive to the negative terminal on a battery. A DC microgrid would have some interesting advantages and drawbacks. On one hand, DC technology is more cutting-edge and efficient because the electricity goes through fewer conversion steps (aka inverters) between PV panels, battery, and appliances. On the other hand, this model would require a new DC service panel at everyone’s house, along with new wiring both inside the home and along the street or underground, which costs money.
In the past, building a new, separate infrastructure would have been the only way to create a microgrid for the block. Allowing solar panels to form an island on PG&E’s regular distribution system would have been strictly against the rules. However, PG&E is currently working with our project team to design an innovative and affordable microgrid solution that uses the existing AC distribution wires. Together, we are looking into the equipment that would be needed to make this work safely and whether installing this on the pilot block is realistic. If successful, multi-customer solar microgrids could become a new standard for how PG&E provides resilient power without using diesel generators, especially in places like the Sierra Foothills where the wildfire danger is so extreme.
Our team is carefully weighing the pros and cons of the DC and the AC options, but the AC approach is looking more likely. In any case, our bottom line is this: Residents should have electricity for all their essential needs, even if PG&E’s grid is out for an indefinite period of time. And when all is said and done, their utility bill should be less than it is now.
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