**John:**

Here is how one computes the payoff time for the
system

**Life expectancy of the PV System (less the cost of
changing and maintaining the storage
batteries): **

Mono-Crystalline & Poly-crystalline ~
25 years

Thin Film or Amorphous PV ~ 10 years

**Data Required for Computing Cost benefits:
**

** 1. Insolation data** (amount of sunlight in
kWh/sq. meter) obtained from maps prepared by National Renewable Energy
Laboratory ( www.nrel.org or check with Google
NREL site provides the approximate daily insolation
(amount of sunlight) in kWh/sq.meter that falls on a south-facing surface for an
average day.

**For example, for
Houston, TX this value from NREL maps Insolation - ln. (Hstn) = 5
kWh/sq.meter**

[The value in Alaska ~ 3
kWh/sq.meter. The value for Southern
Arizona ~ 7 kWh/sq. meter] from U.S. Map.

**2. Energy provided by Sun/ sq. meter = E(sun) = 1
kW/sq.m**

**3. The average Efficiency of the
Solar PV Panels, eff (PV) ~ 12% (for our
calclculations)**

** 4.** Yearly consumption of energy from
Utility Bill = E/year in kWh/year

Let us
assume for example: E/month = 450 kWh/month (average);
or E/year = 5400 kWh/year

This
information can be used to compute average energy usage per day
=

**Average Energy Consumption /day= <E/day> =
[E(consumed/yr)/ 365 days/yr] = <E/day> ~ 15
kWh/day**

*Computations:
*

*(a) *Area of PV array
(in sq. meters) needed to provide this much Energy/day
=

**
****[ (<E/day in kWh/day>)
/ [(Insolation in kW/sq.m ) X (eff. of PV)] =
**[15 kWh/day] / [(5 kWh/sq.m/day)
X (eff. 012)] = 25 sq. meter

*(b)* Output (peak)
of selected PV Array:

**
[ E(sun) X (eff.of PV) X (Computed area of PV array)] =** [ (1 kW/sq.m) X (0.12) X (25 sq. m)] = 3.0 kW (Peak)

**(***c)* Number years to payoff
the cost of PV System: N (For our Hypothetical
example)

**
Let us say, Total System cost = C(syst) for
example $18,000**

** Average,
Yearly Utility Bill =
C(util) **** for our example
is #3,000/year **(which by the way will
always be increasing every year)

** ** **N = [C(syst)] / [C(util) = **[
$18,000] / [$3,000] = 6 years

**
i.e. It will take ~ 6 years to pay off the Cost of PV System (not considering the cost of replacing batteries)
**

**Therefore,
one can recover the cost this system in our example
in about 6 years, and the only extra cost will be to replace and
maintain the matteries. For next 19 years the electricity cost will
literally FREE (since there is no fuel cost at all). **

**I checked my utility bill and found that half
the charges were for Fuel - a charge which which will keep on increasing.
**

**I hope the above example clarifies the mystries of PV Systems, and
the Cost savings in the long run over 25 year period - the life expectancy
of Mono/Poly -Crystalline Silicon PV Systems. **

**Bashir A. Syed **

----- Original Message -----

**Sent:** Friday, September 02, 2005 2:40
PM

**Subject:** Re: [hreg] Assistance

`Jane, we can help you but will need more deatails to give
payback. perhaps `

we can do this offline.

send info or call
me

thanks

jmiggins@...

John
Miggins

Harvest Solar & Wind Power

"renewable solutions to everyday
needs"

www.harvest-energy.com

Phone/Fax
918-743-2299

Cell: 918-521-6223

----- Original Message -----

From: "Jane Edgar" <jedgar@...>

To:
<hreg@yahoogroups.com>

Sent: Friday, September 02, 2005 12:30
PM

Subject: [hreg] Assistance

> Can anyone give me factual
calculations on the use of photovoltaics i.e.

> cost benefits and
payback period.

>

> I need to convince my company that we could
actually run our offices on

> solar. We have so many covered walk
ways that we could fit arrays of

> modules to them.

>

> Best
regards Jane

>

>

>

>

>

> Yahoo! Groups
Links

>

>

>

>

>

>