Electrical Panel Upgrades for Solar: A Technical Case Study

John Smith is a homeowner in California looking to reduce his electric bill by going solar and he decided to call an installation company that he found on the internet.

The next day, a rep from XYZ Solar came out to his house and, after looking at his electric bill, told John that he would need an 8.5kW PV system to offset 100% of his past 12-month usage.

The economics made sense and shortly thereafter the rep walked around to the side of the house and snapped a couple of photos of the main service panel.

We covered Main Panel Upgrades in Pick My Solar LIVE! Patrick and Kyle share a full look into how to determine if a breaker upgrade is necessary for your solar project.

Two days later, John received a call from the same rep and was told that, unfortunately, the main panel upgrade would be required, adding an additional $2,000 to the cost of the project.

When the rep tried to explain why an upgrade would be necessary, the explanation made much less sense. In fact, it made no sense at all when the rep told John, “Normally, an upgrade would not be necessary, but your main service panel is center-fed, which is why an upgrade – in your case – is required”.

In many cases, a homeowner could be spared the $2K expense if the installation company were to perform a simple load calculation to determine whether or not de-rating the main breaker is possible, safe, and passable by city inspectors.

For John’s project, a 7600W string inverter is being proposed by the installation company – a good choice, and the spec sheet shows 40 amps of back-feed protection is required by the main service panel in order for this inverter to be connected. Now, John looks at the sticker on the inside door of his main service panel box, which says 200A. The main breaker switch also says 200A.

But how can John figure out the amount of back-feed protection available on his main service panel?

A simple formula is as follows: 200A buss bar (as shown on the sticker) X 120% = 240. Then, take 240 minus 200 (main breaker) = 40A. Since we need 40A of back-feed protection, we are good to go.

Check out this video to understand the amps of your panel box

Project aspects like this might sound slightly complicated, which was why Solar was founded – to ensure the consumer is protected when technical aspects of projects are laid out.

We play the role of homeowner’s advocate to make sure there’s always an unbiased solar expert to bounce questions off of.