Monday, April 9, 2012

Next project: Solar power!

I apologize for the haitus, it’s been quite busy at work, and I’ve also been doing some spring maintenance and grounds work at home.
However, I have my next experimental project lined up – I’m going to be building a PV solar panel from bare cells, building the frame to put them in, and hooking them up to a grid-tied inverter.  I want to see how much fuss is involved in this.  Prices have come down A LOT in the last couple of years, and I think solar is going to be a pretty big deal in the next few years.
If you’re not familiar with the term, a “grid tie inverter” takes power from the solar panel and converts it into AC power and feeds it back into the normal wiring that’s already in your house.(*)  This is a very exciting technology because it means that you can avoid what in the past has been by far the most expensive part of solar – you don’t need a room full of batteries, you don’t need to run a second set of wiring in your house to support low voltage appliances and lighting, you don’t need a whole lot of things.
What happens, then, is that the inverter offsets your usage, and in fact if the inverter is putting out more watts than you’re using, your electrical meter can run backwards.  Most US households use a few thousand watts (I hear that 5000 watts per household is a good working number, but if like me you’ve instituted conservation measures, and especially if you use gas for your various heating needs, it may be significantly less than that.
This is called “net metering” where the meter reads the net amount of power you consume after you’ve fed some power back in.  If you have one of the new, digital power meters, they generally will NOT run backwards, they’re “greedy” and are programmed to not give you credit for power fed back to the grid.  In some states and some power companies, they will actually install a second meter to measure power that you have fed back into the grid.  Of course, in those cases you do not get paid full retail, so they may be charging you 12 cents/kwh for power and only paying you 8 cents/kwh, so if the rules allow, it makes sense to divert some of your solar output into offsetting your own use before feeding any back to the power company.
In its simplest form, you just plug the inverter into a normal wall socket, hook up the solar panels, and you’re done.  I’ve even seen photos of panels just propped up in living room windows.
(*)  These are SPECIAL INVERTERS that are designed for this purpose – don’t think that you can go to the store and buy a camping inverter and plug it in – bad things will happen if you do that (as in bad things that may involve fire trucks and emergency services and not-at-all-amused insurance companies).

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