Sharing solar energy

Question

Solar installers have said that our flat-ish roof isn't going to work for panel installation. Our neighbor is building a new house that will have ample electricity generated by his panels. They are open to us joining forces and sharing the electricity. Anyone know anyone who has done this or resources we could consult?

Thanks much

Answer 1

Here's something you need to know: solar panels will not keep your house electricity on in a power outage. When the grid power is out, your solar panels are useless in most cases.

Normally, this makes no sense whatsoever

The vast majority of solar panel installations are "grid tied", meaning only work when the grid is up. They do not feed your appliances directly or in any special way.

That means they are nothing but a financial transaction. You are making electricity and selling it to your local utility. It doesn't matter whether your solar panels are on your roof, your driveway, another parcel of land across town, or the Mojave Desert in California (much more sun, and near a market hungry for clean power).

You have solar panels and a place to put them that gets sun. The utility has energy needs. It's a sales contract.

Some people kick a fuss about how much solar panels you need and whether you have "extra". They are comparing the amount of solar they generate to the amount the house uses, as if that's a magic number.

• From a "green" perspective, this number is largely poppycock. Because electricity must be used instantly and is really hard to store for later. The times your solar is generating power is not the same as the times you are using power, like evening A/C use on the typical thermostat settings (unless you get smart like this guy). So that means you're using power when the sun don't shine, so methane or coal is being burned to make that power.
• From a money perspective, who cares? The more the better. The only special thing about "the amount of electricity you use" is that some electric companies are still offering "net metering", where they buy your power at list price but only as much as you use. But power companies are moving away from that.

A transaction here boils down to leasing roof space

And that is exactly how you should treat it in contract law. They have extra roof space, and you are leasing it.

Roofs are not null space. A roof has One Job. Keeping rain out. That is not insignificant just because it is boring as heck. As such, I think a roof is the stupidest place possible for solar, because the surface is already really busy doing another job. Punching a bunch of holes to mount panels hurts its ability to do that job, and will complicate the heck out of roof replacement years down the road.

I have longed for "solar shingles", where the solar panel takes responsibility for the roof's job, instead of getting in its way. But it's never really taken off.

If you are using a "net metering" rate plan, you will need to physically transport the solar-generated electricity over to your house, so it can be fed into your electric meter. That is going to be tricky, because it needs to work with their Rapid Shutdown system: The button on the side of their house which firemen can push to de-energize all the solar panels on that roof. Sometimes this happens by pulling their main breaker, which will shut down all microinverter type panels.

In fact, your scheme would work best with microinverter panels, because a) it is the easiest way to implement Rapid Shutdown (have a contactor powered by their service that disconnects your panels from AC power when their power is cut). And b) you are handling transport to your house as AC power, which every electrician and inspector understands. Electricians and inspectors won't want to work with you on a high voltage DC interconnect.

Power out / off-grid performance

I think microinverter panels are the way to go for all the reasons I said above. However, if your system is off-grid or if you want to have a battery system so your house can keep power during grid-down events, you will need to use fairly exotic and expensive grid-forming inverters.

These are more sophisticated than a simple off-grid inverter. They do a bunch of extra jazz to make the power they're generating behave like the power grid does. When the microinverter panels see this, they will go "ok, grid/utility power is connected" and will start to generate power. The grid-forming inverter absorbs this extra energy and stores it in your battery bank. As a result the microinverter panels think they are on the grid, and keep generating.

However, this creates a complication, since the contactor to assure Rapid Shutdown will not be energized unless they have a grid-down battery system too. "whoops"

So, having the system work "grid-down" when it's on somebody else's roof may not be practical.