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array for any array orientation, using monthly values of
solar radiation on a horizontal surface. The annual
performance of a solar water heating system with a storage
tank is dependent on system characteristics, solar radiation
available, ambient air temperature and on heating load
characteristics. The RETScreen SWH Project Model has
been designed to help the user define the hot water needs,
integrating a Water Heating Load Calculation section in the
SR&HLC worksheet. To help the user characterize a SWH
system before evaluating its cost and energy performance,
some values are suggested for component sizing (e.g.
number of collectors). Suggested or estimated values are
based on input parameters and can be used as a first step in
the analysis and are not necessarily the optimum values.
In the final worksheet "Financial Summary", numerous
financial indicators are provided to help support decisions
(e.g. internal rate of return, simple pay back, net present
value, etc.). The results are then presented in a simple
project cash flows graph for presentation to key decisionmakers.
The Financial Summary worksheet also allows the
user to perform a tax analysis and a Clean Development
Mechanism (CDM) type analysis for the individual project.
The Sensitivity worksheet is provided to help the user
estimate the sensitivity of important financial indicators in
relation to key technical and financial parameters. In
general, the user works from top-down for each of the
worksheets. This process can be repeated several times in
order to help optimize the design of the solar water heating
project from an energy use and cost standpoint.
RETScreen has three families of input parameters: site
conditions, system characteristics, and financial parameters;
while the main outputs are the annual energy balance, project
costs and savings, yearly cash flows and financial feasibility.
The performance of service hot water systems with
storage is estimated with the f-Chart method. The purpose of
the method is to calculate f, the fraction of the hot water
load that is provided by the solar heating system (solar
fraction). Once f is calculated, the amount of renewable
energy that displaces conventional energy for water heating
can be determined. The method enables the calculation of
the monthly amount of energy delivered by hot water
systems with storage, given monthly values of incident solar
radiation, ambient temperature and load.
Comparison of the RETScreen model predictions to
results of hourly simulation programs and to monitored data
shows that the accuracy of the RETScreen Solar Water
Heating Project Model is excellent in regards to the
preparation of pre-feasibility studies, particularly given the
fact that RETScreen only requires 12 points of data
(monthly average daily radiation on horizontal surface)
versus 8,760 points of data for most hourly simulation
models.
B. Location
In this paper, we have selected the sheepfold “Fezlievo
Bacilo” as a location where a large solar water heating
system will be installed. This location was identified in the
RISE Project [4], following the priorities of the specific call
under the FP6 dedicated to the Western Balkan countries:
- A possibility to supply the locations by small low cost
RES
- Economic and social benefits for the local community
- The access to relevant information and availability of
data about the location
“Fezlievo Bachilo” is located near the Albanian border
on altitude of about 1950 m in the National Park
Mavrovo, which is a well preserved entity of a vast
ecological, economical and tourist significance.
It is populated only during the wormer part of the year,
from May till October, when the sheep are brought to the
lower parts to spend the summer. There are about 3000
sheep at the site and 10 employees. This remote location is
with no electricity supply, and it is even without the diesel
generator which was used before the crisis of 2001.
There are two smaller objects there. The first one is used
for the employees (staff room); while in the other one the
cheese production equipment is placed. They have need for
electricity as well as hot water of at least 2000 littres daily
(60˚C) for cheese production and hygienic purposes.
The site has quite good potential for RES exploitation,
being situated in a small valley, exposed to the sun and
protected from winds.
So far no systematic measurements of the solar radiation
have been conducted on the location. However, applying
some well-known interpolation methods (METEONORM
software [5]), the underlying parameters can be calculated,
and conclusions on the solar energy potential can be
derived. The METEONORM software, calculates the hourly
values for the whole year for all solar radiation and
meteorological data. From the METEONORM output, for
each month, the hourly values of the global solar radiation
are calculated as an average over the set of hourly values
from all days from the given month. The same procedure
was applied on the set of hourly data for the air temperature,
relative humidity and wind speed, so that the corresponding
monthly average values have been obtained. These data,
presented in Table I, are the essential input for the
simulating software tools employed when sizing and
determining the performances of the solar system in the
given conditions.
TABLE I.
INPUT DATA FOR THE MODEL OF SWH SYSTEM FOR THE LOCATION
“FEZLIEVO BACHILO”
(M.A.D- MONTHLY AVERAGE DAILY)
M.A.D.rad. on M.A. M.A.relative
Fraction horizontal surface tem. humidity M.A.Wind
Month (0-1) (kWh/m²/d) (°C) (%) (m/s)
Jan. 0.00 1.99 -2.1 79.0 3.8
Feb. 0.00 2.70 -1.3 78.0 3.7
Mar. 0.00 3.54 1.3 74.0 3.9
Apr. 0.00 4.49 5.8 71.0 3.8
May 0.25 5.13 10.5 71.0 3.4
Jun. 1.00 5.22 13.7 71.0 3.3
July 1.00 5.93 16.2 67.0 3.3
Aug. 1.00 5.46 16.2 69.0 3.1
Sep. 0.25 3.93 12.9 73.0 3.3
Oct. 0.00 2.94 8.2 75.0 3.4
Nov. 0.00 1.94 4.0 77.0 3.7
Dec. 0.00 1.45 0.0 80.0 3.7
The calculated value for the annual solar radiation amounts
to 1,368 kWh/m 2 . This value is approximately the same as
the county‘s average leading to the conclusion of
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