Photovoltaics (solar cells, or simply PV) have been intermittently popular since the 1970's, and although they've become much cheaper they are still not even close to competitive with grid generated electric, especially in the Northwest where electric is much cheaper than in most of the country.  While we don't have an actual estimate, the rule of thumb we were told is that PV costs about $7/watt installed for a grid connected system, or about $7000 for a 1kw system.  This compares fairly well with the numbers we have seen in Home Power magazine, which is dedicated to people who generate their own power (including wind).  In our case there is really no need for battery backup, since our power is extremely reliable, on average it goes out less than once a year, and even then its usually for only a few hours maximum.

In order to meet our "approaching zero energy" goals, we would need to install at least a 1kw system, which would generate somewhere between 1 & 1.5kwh in the dead of winter up to about 6kwh in the summer.  As with the active solar system, at this point we don't think our budget had room for PV, which is really a shame.

A quick "back of the envelope" economic analysis is interesting. Assuming we could install a 1kw system for $7000, and assuming that it would generate on average 3kwh a day, we we get 1095kwh a year out of the system.  At ten cents a Kwh (quite a bit more than Seattle City light charges), that amounts to $109.50 a year-or about a 64 year payback.  Even if we could get 4kwh a day (which seems highly unlikely) and electric was worth twenty cents a Kwh (which would be the most expensive electric in the US), that still only amounts to $292/yr or about a 24 year payback-still a very long time horizon -although at least the system ought to last that long.

This simple analysis ignores the effects of more expensive electric in the future, which only becomes interesting if the price of electric goes up faster than inflation (or rather faster than we otherwise could get a return by investing that $7000).  While this would seem like a likely scenario, political pressure will probably prevent electric prices from rising too fast, and we have no way of knowing whether inflation (and hence the return on investment you can get) will rise just as fast or not.  It is much more likely that the installed price of PV power will go down by a lot when we as a country finally decide to get serious about it.

The correct analysis involves calculating the present value of the cost of all the electric used over the likely lifetime of the PV system, because you are essentially buying electric in the future with today's dollars.  First you have to get the currents years value. Then you have to calculate the cost future cost of electric in today's dollars, by using an assumption of the average per year rise in the cost of electric and the average corresponding rise in inflation.  Then you sum these costs over the lifetime of the system (this could easily be done in a spreadsheet program). 

Even if the price of PV could come down, the utility grid apparently has a lot of work to do to prepare for completely distributed generation.  Their current compromise is that they limit how much power you can generate and require you buy a "non-islanding" inverter- meaning that is power goes out of the grid, your excess power doesn't go out there to replace it.  This is to protect power company worker who are expecting a downed line to have no power in it.  While we have no data, we expect that if everyone put grid tied PV on their roofs the power gird would not handle it gracefully, or maybe not at all (if anyone has any good information on this, please email us).  Although PV is a really good idea, and distributed generation is potentially more reliable than centralized generation, this doesn't mean that small systems on people homes is the way to go.  One alternative is larger systems (say 20-50kw) installed on commercial building and actually operated by the power company (saving the homeowner the maintenance tasks).  The current reliance on homeowner installed PV is all due to the fact that we have the gumption to do it and utilities don't.  Presumably they look at the simple economic analysis and don't look very far into the future. 

Our conclusion is that utilities are a really good deal: not only is electric cheaper than out can generate it yourself, but you don't have to maintain it yourself.

Of course it can still make sense to install PV, and certainly we don't pay for the true cost of electric (or any other energy for that matter) in our monthly bill.   Concerned citizens have been installing PV for years, and even some commercial buildings are beginning to use them.  We hope to install at least a 1kw system as soon as we can afford it.  In the meantime we're hoping for a breakthrough that will lower the price of PV by big chunk.