Wednesday, May 11, 2011

Goodbye, and good riddance, to the central inverter?

I regularly report on new energy technology here, to help students keep up with this very fast-moving field, and as a way to begin to organize my own thoughts about energy sources so I can see how best to advise users and government agencies.

Most recently I posted on grid-scale battery developments, which are likely to help break down the remaining intermittency issues with renewable energy generation.

A key feature of the new dry cell, grid scale battery technology is modular design; the batteries are "plug and Play" and can be custom-organized in battery banks much as we currently do with computer servers.

I also heard the idea recently (on the Diane Rehm Show) that there would be no need to create buildings for such battery banks but instead power companies and other consumers of grid scale batteries would use trailers -- regular tractor-trailer rig-style trailers would work just fine.

Another new development, which I just found out about today, is the roll-out of modular AC inverters for solar PV. Now, instead of a central inverter coasting several thousands of dollars, a small AC inverter is attached to each panel.

I have a good few central inverter dinosaurs that I use for various demonstration and practical solar and wind projects, and I can report from experience that they are a pain. Typically big grey or white wall boxes that sit near your power distribution panel and are hard-wired, they cost thousands and often don't work. If something breaks with a solar power system, on-grid or off, 90% of the time it will be the inverter. You have to shut off all the power to switch out the inverter, using at minimum a flashlight and screwdriver, and it's a total pain and you can get electrocuted to boot, if you don't follow the proper procedure.

(Batteries are the next most unreliable component, being very sensitive to charging cycles, and have their own maintenance pitfalls and OSHA dangers, largely overcome by the dry cell technology, but that's another story.)

So getting rid of the central inverter is a great idea, especially if the new modular inverters are cheap and can be easily replaced. I haven't been able to locate data on cost, but a good price would be $50 or less, a fraction of the cost of the panel.

A solar panel with a built-in modular AC inverter might also be connected to power distribution just about anywhere. You could essentially just hang it out of a window and connect it to a wall socket, although on ordinary male-prong 110V plug would need to be made fail-safe using electronics in the inverter for this purpose.

You wouldn't want to touch the contacts on a sunny day, otherwise.

A few years ago an award-winning student-run start-up called Veranda Solar (out of Stanford U) tried to begin selling a modular panel with a mini-inverter for young 20-somethings to go green in their college dorms. I'm not sure what happened to V-Solar or their art-deco panels, but the same basic idea seems to have been used here.

This is just another interesting contribution to the renewable energy solution to climate change, and will likely make solar PV yet cheaper by reducing installation costs and training costs for installers.

What I want to know is, when and where can I buy my new panels with modular inverter at the Home Depot or online?

I have long been interested in putting a solar roof on the Womerlippi Farmhouse, but for several years now, like the good energy wonk that I am, I've prioritized reducing heat energy costs though my ongoing super-insulation project.

Essentially, I'm converting a 100 year old Maine farmhouse to a passive solar building at about $1,500 a year. I already have the oil and electric heat bills down to about $300/year, but that doesn't count the three cords of wood I make from our own woodlot. PV is in the plan, for after I get the insulation and sealing done, and after I get solar hot water fitted.

With quite a bit of this low-hanging fruit to pick, I haven't wanted to add solar PV just yet, especially when the minimum cost is several thousand dollars for a central inverter and, say, a kilowatt of panels.

But if I could buy one or two modular panels to begin, at say $500 each, and get one a year for several years, you could convince me to start the PV part of the project sooner rather than later.

And if I'm interested, others would be. I'm an energy economics curmudgeon and I only ever pay attention when the new ideas are cheaper than the old.

The new modules also present a major sales opportunity for household PV, by potentially reducing the barrier to entry that is the central inverter.

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