We live in a 1991 townhouse in Davis. My goal and dream has always been to move away from our current natural gas system and fully use electricity from the sun. But how is that actually achieved?

Many smaller and older homes begin life with a 100 ampere main service electrical panel (abbreviated in this article as 100A, which can be pronounced as “100 amps”). Accommodating all-electric appliances throughout a home and/or adding electric vehicle (EV) charging sometimes requires a subpanel or an upgrade to 200A utility service and a 200A electrical panel.

While many newer homes are built with 200 amps — which makes the switch to all-electric equipment and appliances easier and cheaper — this townhouse only has 100 amps.

Definitions for ampere and amperage

The ampere (or amp for short) is a unit of measurement for the amount of electricity flowing per unit time ― that is, electric current. Electric current powers electrical end uses in your home. Appliances and equipment are typically rated for watts – a unit for the power they consume at a given moment — but also amperage – how much current flows to them.

A 60-watt equivalent LED light bulb draws only a fraction of an amp at a time, the condenser unit alone in an electric heat pump uses between 9A and 13A (the full system draws more), and a lightning bolt can carry 100,000A or more.

Wiring and cables are rated to handle a certain maximum amperage. Many appliances, like heat pumps require equipment (wiring and circuit breakers) that are rated above the normal operating current because the current at start-up can be much higher than normal operation at full load.

Upgrading can be hard to do

So back to my all-electric townhome that was built with 100A service and panel. Upgrading the electrical panel to 200A is not the biggest challenge. What about upgrading the incoming utility service to 200A?

Sounds easy, doesn’t it? Not so fast; my electrical line is buried underground and is fairly long, which for upgrading is a huge disadvantage. I would need a bigger and thicker cable coming up into my house. When I went out to get some estimates, PG&E (our local utility) was wanting to charge me a small fortune (their projection was up to $30,000) to upgrade a buried line, plus the street transformer is basically maxed out, not allowing for increases in power even if we could upgrade.

I could do some load calculations and hope not to overload the line, but this is also probably not the best solution with the loads I am imagining. Below are my electric load calculations.

My 240V house loads would consist of:

  • 30A space heating heat pump
  • 30A heat pump water heater
  • 50A electric stove
  • 30A electric dryer
  • 40A for the solar hookup and possible battery backup
  • 40A for future Level 2 EV charging capabilities

(Note: all the amperages listed are outlet / fuse ratings so not close to actual load)

These 240V loads are in addition to the 120V loads that are currently served by the main panel, including lighting, plugs, and kitchen appliances.

As you can see, 100A electric service doesn’t go very far. To do your own calculations, use the following website calculator to see if you can get away with your existing electrical service and panel: www.redwoodenergy.net/watt-diet-calculator/.

Another possibility: I could try to find equipment and appliances with the lowest possible amperage and get some savings there. So, for example, replacing a standard 30A dryer with a 20A dryer, or installing a heat pump water heater with only a 15A capacity. The problem here is there are limited choices and savings are unfortunately not that big.

My discovery

At the 2022 InterSolar event in January in Long Beach I came across an intriguing solution. Install a smart electrical panel. A company named Span had a booth there and they shared great information on their product (www.span.io).

Looking at it, it seems that a smart electrical panel might be my only real choice, as it would provide active management so I would never exceed the 100A rating of my panel or service. How can that be if the items and appliances I outlined above use almost double the amount of available current?

The thing is, these appliances are almost never used at the same time and a smart panel will watch over that through constant circuit-level monitoring and control. That means that you will be able to switch over completely to electricity/renewable energy without ever overloading the system. Span also offers a panel that adjusts EV charging amps depending on other loads on the house.


New companies, new products

Realistically, the cost of such a panel is not cheap (around $3,500), which is more than a traditional panel, and an electrician would be required and cost almost the same amount to install it. However, when you compare it to the PG&E quote to upgrade the service line, it is a much cheaper option.

Another company with a separate electrical box is Lumin (www.luminsmart.com); in my opinion not quite as elegant. While there are not a lot of smart electrical panel options designed for existing homes for purchase at the moment, this is the direction all manufacturers will have to go and Span is taking the lead.

The last word

It’s my personal opinion that all new houses and major upgrades in Davis should only be approved if natural gas is cut out of the game. Smart electrical panels are one solution for homes with buried electrical lines or other load issues.

NIST Definition of an Ampere


Eugen Dunlap is a member of the Davis Electric Vehicle Association and has been driving electric vehicles since 1999 including the GM EV1. Eugen lives with his wife at the Muir Commons community in Davis, which is one of the first in California and possibly the US to adopt multi-family EV charging for every unit. Eugen has been charging an electric vehicle at the community since 2001.

Thank you to Bill Dakin of Frontier Energy for his expert review of this article