What’s actually inside a data center? A San Diego explainer

Updated Oct. 29, 2026: The San Diego City Council voted unanimously on Oct. 27 to put a temporary pause on new data centers in the city. We added a section below on what the moratorium does, what it doesn’t cover, and what happens next.

Data centers have entered the San Diego conversation. This month, Voice of San Diego reported that Manchester Financial Group, the developer the Navy selected to redevelop its 70-acre NAVWAR campus in the Midway District, has explored a 400-megawatt data center as part of the project. The company says a data center is one of several options under consideration, along with possibilities such as a hotel, medical center and university campus, that the final project will include housing, and that no final project has been approved.

The news raises a question many of us have never had to think about: what is a data center? Here’s a plain-English look at what’s inside one, what it needs to run, and the questions that come up when one is proposed.

So what is a data center?

When you visit a website, save files to the cloud or use an AI tool, the work happens on computers in a data center. San Diego County describes these computer systems as servers, data storage devices and network equipment, physically connected to larger electrical and telecommunications networks. That core technology is the same in every data center, whatever its size.

Most of the San Diego region’s existing data centers are small. According to the County, they typically use under one megawatt, hold fewer than 1,000 servers, and serve institutions or small and midsize businesses such as healthcare providers and banks. Growing use of cloud services, internet-connected devices and AI is driving demand for much larger facilities, which can hold thousands of servers in buildings ranging from tens of thousands to over a million square feet.

Take a look inside

Spin the illustration below and tap each number. The parts follow the electricity from the grid to the servers.

What a big one needs

Power

Electricity runs the servers, storage devices, network equipment and cooling systems. The County describes large data centers as facilities with an electricity demand of over 100 megawatts. Most rely on grid power, with onsite generators as backup so they can stay online. Nationally, Lawrence Berkeley National Laboratory estimates data centers could account for about 11.8% of all U.S. electricity use by 2030.

Cooling

Servers give off heat, and cooling equipment runs continuously to manage it. Approaches include evaporative cooling, closed-loop systems, hybrid air-water systems, and liquid or immersion cooling. U.S. Department of Energy researchers note that cooling can account for as much as half of a data center’s energy use.

Land, water and fiber

According to the County, the availability and cost of land, power, water and fiber are the most important factors in choosing a site. Being close to businesses and other users also reduces how long data takes to travel. Data centers have historically been built near population and technology hubs.

How big is 400 megawatts?

The County estimates the region’s roughly 20 existing data centers use about 25 megawatts combined. A single 400-megawatt campus would be about 16 times that. For another yardstick, SDG&E reported its service area reached a peak demand of 5,032 megawatts during a September 2024 heat wave. 400 megawatts is about 8% of that figure.

A single 400-megawatt campus would be about 16 times the electricity demand of every data center in the San Diego region combined.

Questions people ask

Would it raise my electric bill? How much water would it use? What about noise and air quality? Does it bring jobs? These are some of the questions that may come up when a data center is proposed. Here’s a general idea of what to expect. On bills, new California laws taking effect Jan. 1, 2027, direct state regulators to make data centers pay for the grid upgrades and added power they need, so other customers aren’t left with the cost. Water use depends on a site’s size and cooling design. Some of the largest data centers can use up to 5 million gallons a day, though the San Diego County Water Authority told the County it expects data centers are unlikely to affect the region’s water supply. Cooling equipment makes a steady, low hum, and backup generators, usually diesel, run during outages and tests under air district permits that limit their hours and emissions. As for jobs, most come during construction, with a limited number of permanent jobs once a data center is running.

San Diego just hit pause on new data centers. Here’s what that means

A week after a developer floated a 400-megawatt data center for the Navy’s NAVWAR campus in the Midway District, the city moved to get ahead of the whole category. Mayor Todd Gloria signed an executive order on Oct. 22 asking for a temporary moratorium on new data center development, and the City Council ratified it unanimously on Oct. 27.

The city’s reasoning is the same set of questions this explainer walks through: water, electricity demand and costs, housing, infrastructure and what a big facility does to the neighborhood around it. In the mayor’s words, the city “cannot allow a rapidly expanding industry to get ahead of the rules needed to protect our residents.”

What the pause does

• Stops the clock on new projects. It pauses new data center development within city limits while the city writes permanent rules on where and how they can be built, run and expanded.
• Uses a state “interim ordinance” tool. The mayor’s order calls for an interim ordinance under California Government Code section 65858. Under that law, this kind of moratorium lasts 45 days at first. The council can extend it twice after a public hearing (for 10 months and 15 days, then for one year), so about two years total at most. Each step needs a four-fifths council vote.
• Uses the state’s definition of a data center: “a facility, or part of a facility, that houses computing infrastructure” used to process, store or distribute electronic data.

What it doesn’t do

• It doesn’t decide NAVWAR. The NAVWAR site is federal property, and the city doesn’t control land use there. The mayor’s order instead directs his government affairs team to push for state and federal legislation covering data centers on state or federal land.
• It isn’t a permanent ban. It’s a pause while the city writes the rules, and the city says it welcomes tech investment and jobs.
• It doesn’t change your SDG&E bill today. The bill questions in this explainer still apply. California laws taking effect Jan. 1, 2027, aim to make data centers cover their own grid upgrades.

What happens next

• The mayor will appoint a Data Center Stakeholder Working Group of up to 15 people, drawn from groups like labor, community advocates, utility and water experts, housing, environmental and higher education.
• Within 180 days, the City Planning Department, Development Services and the working group bring preliminary recommendations to the mayor and City Council.
• Within another 180 days after that, the city starts the public process for permanent rules: public notice, a Planning Commission recommendation and a City Council vote. That’s where residents get to weigh in.

If you want to follow along, the mayor’s newsroom and City Council agendas are the places to watch. We’ll update this story when the working group is named or an extension vote is scheduled.

Related: SDG&E wants to raise rates in 2027. Here’s how to speak up

The bottom line

A data center is a building full of computers that process, store and send data, along with the power and cooling systems that keep them running. Whether one is ever built at NAVWAR is still an open question.