I know this sounds insane. But this is an insane world.

We at DNV GL are dedicated to supporting a resilient and sustainable energy future. We spend our time thinking about practical energy solutions in a range of potential future scenarios. This includes provision of independent energy supply to small off-grid communities, such as those who may be sheltering from the insatiable hunger of hordes of reanimated dead.

We accept that, whilst preparing for the possible mass resurrection of flesh-eating corpses may be a priority for some, most of our clients have other, more current, considerations. Planning for resilience in the face of potential disruption of infrastructure and services is, however, a real and serious matter. Extreme weather events resulting from climate change may cause mass breakdowns in energy supplies. In unstable regions of the world, disruption in utilities is a common effect of acts of war and civil disturbance. In such circumstances, the ability to continue to operate as an isolated independent system can help to maintain wellbeing, health and order in affected areas.

Nevertheless, the zombie apocalypse is a popular cultural metaphor for the fears associated with the breakdown of the social and physical fabric which holds together our wellbeing and standard of life. In this spirit we consider the challenges of maintaining a resilient islanded off-grid energy system within the framework scenario with which some clients may be vicariously, if not personally, familiar.

This is what life looks like now

Unfortunately there is little real-life data available on this subject. As a result, our research has mainly centred on the popular but fictional AMC TV show The Walking Dead. Dedicated fans will know that by series 6, Rick Grimes and his band of survivors had taken shelter in a gated community in Alexandria, a town in the US state of Virginia 20 minutes south of Washington DC. Details on Alexandria safe zone (as it is known) are sketchy, but a few things are apparent. It seems to have about 15-20 residences. As far as we can tell, the community has a population of 50-60, although this fluctuates somewhat with new residents joining and others dying in extraordinarily gruesome ways.

We know that the safe zone was designed to be a high-end sustainable community with its own solar farm, micro-grid and sewage processing system. However, the show’s writers strangely omitted to explore the finer details of the configuration of the energy system. However, based on various clues, we have deduced certain aspects of its technical specifications. There appear to be 5 solar arrays, each fitted with what seem to be 20 standard 250 W 1 x 1.6m solar panels. This suggests a total nominal peak output of 25 kW. Based on typical solar radiation levels for that part of the USA, this would provide the zombie dodgers with a total of approximately 33,000 kWh per year.

We assume that the community is fully electric. In principle it would be possible to produce gas using biodegestors, possibly making use of the abundant availability of free-ranging, decomposing organic material. However, as has been found in real crisis-hit areas of the world, the gathering of biomass for energy use is a potentially dangerous activity, greatly compounded when that fuel is trying to eat its harvester.

Alexandria will face a challenge familiar to real-life offgrid systems, namely the uneven distribution of energy supply and load across the year. The community will have available to it more than twice as much electricity in June (approximately 121 kWh per day) compared to December (53 kWh per day). By way of comparison, a community of 20 average US households would currently consume approximately 600 kWh per day. This means that, assuming the solar array is the only source of distributed electricity generation, the community was presumably not originally intended to be completely independent of the grid. As such the microgrid will have been designed to synchronise with the local network, whilst retaining the option to disconnect and automatically balance loads with distributed generation and storage.

We can assume that there would at least be sufficient energy storage to ensure that no electricity produced on-site is injected back into the electricity network, thus ensuring minimum possible import from the grid. We estimate that a total of approximately 50 kWh of installed electricity storage capacity would need to have been installed for this purpose.

Stuff and things

Some of the energy produced will be needed for communal purposes, although it is probably wiser for the community to dispense with street lighting. This is not advisable in a real-life setting due to the negative impacts in terms of security and health and safety. However in the scenario case under consideration this will be more offset by the fact that it will help to keep the area hidden from ravenous cannibalistic ghouls as well as marauding gangs of feral survivors.

The homes are also presumably well insulated and fitted with the most efficient appliances and low energy LED light bulbs. Even assuming the most energy efficient equipment available, the residents will need to ration energy consumption carefully. Some energy will be needed to power the sewage treatment and water pumping facilities; we assume this would take a total of about 10 kWh per day. With 20 homes, this means that each house will have 5.5 kWh per day in summer for domestic use.

In summer, assuming careful energy management, residents could manage to maintain a reasonable level of civilisation and comfort. Each home could typically expend the following energy daily for the following basic requirements:

2 kWh for cooking;

0.5 kWh for lighting;

1.5 kWh for a medium-sized modern refrigerator;

1 kWh producing approximately 15 litres of hot water every day; this is less than 10% of typical US household consumption of hot water and would need to be used sparingly.

This compares to a current average US daily household consumption of about 30 kWh. As a result any real-life microgrid would normally retain the ability to synchronise with a wider grid. Alternately the community would need to consider a much higher investment in renewable generation facilities and electricity storage, back-up fossil fuel generators and/or greatly reduced levels of consumption compared to the average.

You keep the windows intact, you keep society intact

The most challenging aspect would be the climate control. Alexandria lies in a humid sub-tropical region with average high summer temperatures of approximately 32 C. Climate control is likely to take the most efficient form, namely ground source heat pumps. However, running the heat pump to provide air-conditioning for just 30 minutes would easily burn through the remaining 0.5 kWh. This same amount of energy could be used to operate two small high-efficiency desk fans continuously for half a day.

It may even be possible to expend about 0.5 kWh every few days on running a washing machine for about 1 hour on an economy setting, although a longer wash cycle may be required based on the level of soiling suffered during the day’s activities. It could also be wise to maintain a cordless electric chainsaw on charge, as this could prove useful in a range of possible applications.

Residents may, every so often, also choose to take their mind off their grim situation by expending 0.5 kWh on 2 hours on a large screen LCD TV and DVD player, thus allowing, for example, one George A. Romero movie.

The situation in winter would be considerably less comfortable. In December each home will have about 2.2 kWh per day available, due to much lower levels of solar radiation. This will be coupled with a greater demand for lighting and space and water heating with average winter lows which will typically dip below 0 C. In this period, residents will need to make hard choices about their priorities for energy use. Even after cutting back on lighting, hot water usage and cooking, there is likely to be very little energy remaining to have any noticeable heating space heating effect. There will need to be a marked pooling of resources, possibly with communal spaces heated using a ground source heat pump, allowing for some homes to be left unheated.

One of the most important activities of the Alexandrians, other than fending off incursions from the ghastly ravenous revenants of their decreased neighbours, will be maintaining high levels of energy efficiency. This means ensuring that homes are kept in a good state of repair, which particular attention to repairing windows and doors and maintaining an effective seal at joints between fittings.

As in any isolated microgrid system, the balancing of load with electricity supply would be a challenge. Energy consumption would need to be tightly controlled and certain activities, such as for example water heating, should be conducted during daylight hours to make optimal use of battery capacity. There needs to be a system for monitoring consumption with provision for controlling demand so as meet supply. This is important so as to ensure an equitable and efficient allocation of energy, but also to ensure that the microgrid remains within technical limits.

Someday this pain will be useful to you

Energy resilience is essentially about planning for risk. The danger that the dead will rise from their graves and feast upon the living is, despite the fevered imaginations of science fiction aficionados, a high impact but very low probability scenario. However severe climate and civil disorder events are real concerns which should be planned for. In certain circumstances, the ability to operate an independent electricity system for a protracted period can provide security, stability and continuity.

DNV GL Energy is the largest provider of renewable energy and sustainability services in the world. We are working together with government, non-government and private organisations to bring about a sustainable energy future which will remain resilient in all circumstances.