Solar Power Calculator

A reader pointed me to the National Renewable Energy Laboratory PVWATTS 2 calculator, which uses your local weather information to calculate likely power output, including adjusting from nominal DC output to AC (because of inverter losses).  I ran the data for a nominal 1 KW system (four of those Westinghouse panels), using the default inverter efficiency, and our current 7.8 cents/KW-h.  I also assumed a fixed tilt array.  (Changing the angle four times a year helps, but not dramatically.)  I am not assuming that I will get my proprietary improvements working.

"Station Identification"
"City:","Boise"
"State:","Idaho"
"Lat (deg N):", 43.57
"Long (deg W):", 116.22
"Elev (m): ", 874
"PV System Specifications"
"DC Rating:"," 4.0 kW"
"DC to AC Derate Factor:"," 0.770"
"AC Rating:"," 3.1 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 43.6"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 7.8 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 2.88, 276, 21.53
2, 4.16, 359, 28.00
3, 4.93, 463, 36.11
4, 5.77, 507, 39.55
5, 6.12, 542, 42.28
6, 6.47, 541, 42.20
7, 7.05, 582, 45.40
8, 6.93, 587, 45.79
9, 6.40, 536, 41.81
10, 5.30, 481, 37.52
11, 3.48, 313, 24.41
12, 2.80, 272, 21.22
"Year", 5.20, 5459, 425.80

I should point out that the 7.8 cents is for the 0-800 KW-h consumption rate -- Idaho Power actually charges us more than that above 800 KW-h per month.  Sixteen of those panels would cost $9600 plus shipping; I am going to have to pay something to my electrician to put in a 20 amp breaker to connect this to the main bus.  I will also have to spend some money and time build a support system to position these on the hillside that allows me to change angle four times a year.  Still, it is hard to imagine that this plus shipping will exceed $600.  A $10,000 investment thus takes 23 years to pay for itself, ignoring rising electricity prices and leaving out the 30% tax credit from the federal income tax return and the relatively trivial tax deductions on the state income tax return.  It also does not include the inevitable drop in output over the life of the panels.

This is beginning to make less and less sense.

UPDATE: Of course, if the cardiologist calls me back next week and says that I need an angioplasty, all of this will need to be delayed.

UPDATE 2: This isn't California.  Idaho Power's net metering program is somewhat limited:

Is there a limit to the size of generation from the customer? 
Yes. For residential and small commercial customers, generation is limited to 25 kilowatts of nameplate generation or less.

I am guessing that they mean 25 KW-h per month.  Not a problem; I can't imagine investing that much capital in solar panels.

Is there a limit to how many Idaho Power customers can participate in Net Metering? 
Yes. At this time Idaho Power limits the total amount of customer-owned generation to 2.9 MW. The actual number of systems will vary depending on the size of the individual installations. 

I have no idea if they are at limit yet; I've put in a call to their office to find out.  Worst comes to worst, we skip net metering and just settle for wasting the extra energy. Perhaps this would encourage not putting in more panels than I would likely use at any given moment.  Or it might make sense to look at using excess power to charge batteries for use after dark.

UPDATE 3: Details on Idaho's alternative energy tax incentives are here.  You are allowed to deduct 40% of the purchase price of the system in the first year from your income taxes, and 20% in the following three years.  Idahoans who can afford to consider alternative energy are going to be in the 8% marginal state income tax bracket, so a $3000 investment means a $1200 reduction in your taxable income, or about a $96 tax reduction the first year, and $48 tax reduction for the next three years.  The website previously linked isn't very clear on how the $5000 maximum incentive per year, $20,000 maximum incentive total, works; Idaho Code 63-3022C gives the details.  It appears that you are not allowed to take more than $5000 of deduction in any year.  The Idaho Code says nothing about a $20,000 maximum incentive.

If you are a greenie, Idaho law is a sign of what a backward, primitive, stingy state we are.  If you are anyone else, they are a sign that Idaho legislators like the idea of alternative energy, but didn't drink the green Kool-Aid.  The incentives are so tiny that they are essentially a sop thrown to greenies to make them think that Idaho cares about Mother Earth.

Simplifying Solar Power

One of the big problems that I have with solar power is that installation is typically half or more of the cost of a photovoltaic system -- turning what might be a temptation into a "this doesn't make sense" situation.  Worse, if you want to just experiment, by putting in a couple of 200 watt panels to see how much you are getting, those installation costs make it absurdly expensive.

There are several companies that are producing what are intended to be DIY (do-it-yourself, or disaster-is-yours, depending on your competence) solar systems.  Westinghouse, for example, has this panel with an integrated mounting system and inverter, as well as simplified connectors.

What is pretty interesting, however, is how some companies are producing plug-and-play products, like this Goal Zero 1250 watt-hour solar generator over at Lowe's.  It is a combination of two 30 watt solar panels with inverter and deep discharge battery.  This isn't intended as a primary solar power system, but as an alternative to a backup generator.  The two 30 watt panels are supposed to fully charge the battery in 20-22 hours, or you can recharge from the grid in 16-20 hours.  When fully charged, it gives you 1250 watt-hours -- which for short-term emergencies is probably sufficient.  They also claim that you can add more panels to reduce charge time, or add more deep discharge batteries to increase capacity.  And it is all portable.  For $1799, this doesn't seem like a bad product idea.

The Westinghouse Instant Connect 235W panel is available for about $860 on eBay (including tax and shipping).  That's not a particularly impressive price if you are only looking at the dollars per watt, but it does include the inverter, and I guess that you could just plug it into a wall socket.  I believe that our backup generator already has a grid disconnect built-in, so something like this would be a plug-and-play device.  This wouldn't run our power meter backward without net metering equipment installed, but in the heights of summer, when our electric utility bills are high to pay for air conditioning, this would make a lot of sense.

UPDATE: Reading the DIY installer instructions for the Westinghouse give me pause.  They are still written for an electrician.

A reader points out that he suspects air conditioning costs are a big chunk of the average household's electricity use.  I suspect that he is right, at least in summer.

There is an amusing synergy here: air conditioning is a big cost in areas where solar energy is most available and reliable.  When solar energy is not so available, air conditioning costs drop nearly to zero.  In addition, electric utilities charge higher electricity costs above some threshold level, so even in places where solar power as a source for all your electric power might not make economic sense, solar power might make sense for getting your electric consumption down below that threshold.

UPDATE 2: An email from Westinghouse Solar indicates that the pricing will be back on the website shortly, and at about $600 per 250 watt panel.  This isn't really a bad price, considering the panel has its own AC inverter.  This is cheap enough that it should call my electrician and find out what he would charge to do the connection to the breaker panel.

UPDATE 3: I was just paying my electric bill this evening.  My consumption last month was 680 KwH, or about 22 KwH per day.  At the peak of last summer, we were consuming 41 KwH per day; in the depths of winter, about 29 KwH per day (with spring and fall generally less).  A nominal 4 Kw system operating 12 hours a day (pretty typical around here at the height of summer) would produce enough power to satisfy all of our needs.  In winter, we might average 4 hours a day, or a bit less than half of our needs.  Spring and fall would produce about 25-28 KwH per day, a bit more than we need.  Of course, that would mean 16 $600 panels, or $9600.  With the 30% federal tax credit, and the fairly minor state tax deduction, that means a net cost of about $6500.  I would expect to see our annual electricity bill fall from about $700 a year to perhaps $150 a year.  That would mean about an 11 year payoff at current electricity rates -- and a bit less with the likely rise in electricity prices.

Time to call my electrician, and find out what he will charge me to hook this up.  I could start with two panels, and perhaps add two panels a month once the fall semester starts.