1. ALTERNATIVE SOURCES OF
ENERGY

2. INTRODUCTION:
With this assignment we’d like to show you
how a Portuguese family (a couple with two
children) can save in water and electricity if
they use alternative sources of energy

3. ON WATER:
 A family spends on average 25 Euros monthly
 Renewable energy produced by water is
cheaper by 9,2%
 The family pays:
€ %
25 100
X 9,2
X = (9,2x25) : 100
X=2,3
25€-2,3€= 22,7 €

4. Monthly the difference can be very low but the
total cost/sum in a year makes up for
Let’s have a look:
Yearly a Portuguese family saves 27,60 Euros if
using energy produced by water
25€x12= 300€
2,3€x12=27,6€

5. ON ELECTRICITY:
 They spend monthly an average of 76 Euros
 If they use solar energy 9% cab be saved
 The family pays:
€ %
76 100
X 9
X = (9x76):100
 X= 6,84
76€ - 6,84 € = 69,16 €
76€ x 12 months = 912€/year
6, 84€ x 12 months = 82,08€
Meaning that a family saves up to
82,08 Euros if they use solar energy

6. For a family to use this kind of energy, they need
solar panels.
This system is enough for the use of the following
equipment:
 Five light bulbs 10W (3 hours a day)
 A TV set 50W (four hours a day)
 A fridge (class A) (daily consuming 500W)
Approximate cost: 3900 Euros

7. If the family buys a solar panel, they will be
paying the solar energy equipment for 56 months
meaning that if the family didn’t use
alternative sources of energy they would spend
more 4286,4€ - 3900 € = 386,4€ for more or less
56,4 months
3900€ : 69,16€ = 56,4 months
56,4 months x 76 € = 4286,4€

8. We have come to the conclusion that a family:
Without alternative sources of energy
25€+76€=101€
With alternative sources of energy
22,7€+69,16€=91,86€
Savings 101-91,86€=9,14€
So, a family saves 9,14 Euros if they use
alternative sources of energy.

9.  Elizabette Brito and Claudio Moura
 Agrupamento de Escolas Rafael Bordalo Pinheiro