[amsat-bb] Re: Solar Power (I was wrong)

Bob Bruninga bruninga at usna.edu
Fri Oct 2 06:03:18 PDT 2009

> My simple math says it'll take almost 
> 16 years to be reimbursed on a $30k system.

Its more like 5.5 years.. I'll show you my numbers for Maryland:

> Initial outlay:  $30,000
> US tax credit:  5%

No, Federal Credit is 30%

> US reimbursement:  $1500 (this is not 
> real money, but a reduction in taxable income)

at 30% it is $9,000 and it is a *credit*, not a deduction, so that is cash in your pocket off the tax you pay.

Then most states, give either similar Tax *credits* or grants, in my state it would be about $4,000 check, payable to me when installation is complete.  Then the county makes up the difference to 50% of the cost of the system.

> Total:  $28,500 

No, here, my net outlay is reduced to 50% or only $15,000.

> Savings per year in electricity:  $1800 

That, plus Solar Energy Renewable credits paid to you by the power company or brokers at about $250 per KW capacity for a 4 Kw system = $1000 per year.  They buy this credit from you so that they dont have to build solar systems.  By paying you this credit, they get to subtract the capacity from the amount they are required to build by the year 2020? or whatever.  So add the two and you get a payback of $2800/year.

> $30k / 1.8k = 15.83 years

* My numbers show $15k / 2.8 = 5.3 years (even less if electric rates go up)

> One of the points of the post, I think, 
> was to make ourselves less dependent on 
> foreign oil..

> Personally, I do not think PV cells are 
> that efficient.  To get the 12VDC I need 
> to power my remote... repeaters, I...
> lose more than 30% in generated heat.

Yes!  That was my mistake too. Energy Storage in batteries is very inefficient.  About 30% or more losses.  But GRID-TIE systems are 95% efficient PLUS you are selling the power to the grid at PEAK rates in the middle of the day, and buying it back at discout rates at night.  Net effect is not a loss, but a GAIN.  Of course, this does not help at a repeater, but do not carryover these losses to a Grid Tie system where it does not apply...

> they only last so long.  
> Twenty years, tops maybe?  
> Do they really pay for themselves?

You bet for sure!  Compare that to a $30,000 car, which is junk in 10 years and you have nothing.  The solar system cost $30,000 (actually $15K) and you MAKE $15k in the first 5 years, and for the next 15, you make $45,000, and then your array has decayed to maybe only 80% of its original life... but it is still MAKING money at then CURRENT rates...

The 20 and 30 year life does not mean they die, it is just that their power has dropped by XX%...  Im guessing that the threshold is 80%?

> in California. .. the power company is 
> only required to pay you the WHOLESALE 
> cost of electricity. This amounts to 3 
> to 4 cents per kw-hr.

Ah, but if you pay 15 cents per KWH during the day to run your home, and you have enough solar to balance that, then the payback to you is still 15 cents per KwH.  Its only the excess you generate that pays you the low rates.

The key word is "net metering".  In other states with net-metering, they have to give you the full 15 cents credit for the excess power you generate.  But in most all cases, you cannot beuild up credits beyond a year cycle.  

> ... bird poop to cut the efficiency.
> be prepared to get on the roof every 
> month or so to clean the panels.

AMEN.   PV cells are in series.  One big splat that covers one CELL, reduces the power of the ENTIRE PANEL.  A single Flag Pole shadow across a roof, can reduce the power of the entire roof array tremendously...

>> if you sell back over 50,000 watts 
>> of power you will incur additional taxes, 
>> ... you are considered a "generator" 

I assume that is NET.  To build up that much excess capacity would require an array on my house covering 3 times the roof area I have available.  And it would make no sense to build an array that big, since you aleady know that you get paid peanuts for excess net power (wholesale). 

>>  Lets say you were able to generate 
>> and sell back 100,000 watts to the 
>> utility company.

Yes, that is my annual consumption.  But my array will be sized so that I generate 100,000 in that same year.  SO the NET "sell back" is ZERO.  And I got all my electricity for FREE that year.  You are right, that if I make my array TWICE as big as I need, and spent about $100,000 for it, that then, I would generate twice the electricity I need, and would not get paid but probably HALF the rate for it PLUS the taxes you mentino.  Oh, and that array would coer 8,000 square feet almost an Acre...  So I would not worry about a homeower making the mistake of building too big a system...

>>> > 1) Solar panels (PV) are 1% of what they cost in 1970
>>> 2) PV dropped 40% this year due to 2007 Energy Boom and 2009 economic bust
>>> 4) $5,000 to $20,000 tax and cash back incentives for YOU
>>> 5) Grid-tie systems operate at 95% efficiency compared to 70% of battery systems
>>> 6) Local electric rates DOUBLED in the last 2 years
>>> 7) Laws require utilities to pay you the same peak rates they charge you.
>>> 8) Solar Energy credits can gain an additional $275 per 1Kw system per year
>>> 9) Payback is at least 10% per year or better
>>> 10) The same money in the bank gets 1% interest

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