|
Equipment Sizing and Selection
Before you begin choosing
the equipment for your home power system, look at this basic
system schematic to get an understanding of how the components
fit together.
Equipment Selection
We highly recommend that you purchase good quality
equipment even if it cost slightly more. This will help ensure reliability
and safety. It
will also pay off in the long run since your system will be
more efficient and the equipment will last longer.
System Voltage
The first step in sizing your system and selecting
your equipment is to determine the DC voltage that you want
your system to operate at.
The voltage that you determine (12, 24 or 48) will
affect how many amps are required to meet your power needs.
The relationship between voltage, current (amps), and
power (Watts) is described on out key
terms page.
To determine a good system voltage use the following
table based on your largest continuous power draw (not your
largest surge wattage). These values may not apply if
you are going to be running wires a long distance (greater
that 75'). We would be happy to consult with you if
this is the case or you are not sure what voltage to use.
Check out this wire
sizing link for more detailed information.
Largest Continuous Power Draw
|
Voltage
|
Application
|
| 0
- 600 Watts |
12 |
Small systems (cabins)
|
| 600 - 1200 Watts |
24 |
Small houses |
| 1200 - 1400 Watts |
48 |
Large houses |
System Voltage = ___________________________
Solar Panels
To
determine the number of solar panels that you need
follow these steps:
- Record
the average power* required (Pi) per day
from your load analysis.
- Multiply
power required (Pi) by 1.2 to account for
losses in battery charge and discharge
- Divide
Pi by the solar module efficiency to determine
the total energy that the solar panels need to be
exposed to (PT).
If you have not determined which solar panels
use .12 as the efficiency.
Then redo this calculation when the exact efficiency
is known. The solar module efficiency is given by
the manufacturer.
- Divide
PT by the solar radiation data from your
site analysis.
The site analysis data needs to be in the form
of power per unit area (i.e. KW-Hrs/m2).
This will give you the total area (A) of solar
panels required.
- Divide
the area (A) by the surface of a good quality solar
panel. This will give you the number
of solar panels needed to power your system. Make sure that once you
have determined which panel to purchase that the efficiency
is the same or greater than what you used for your
calculation in step 2.
|
Example Calculation:
- Pi
= 8 KWH/day (from load analysis)
- Pi
x 1.2 = 8 x 1.2 = 9.6 KWH
- Pi2/.12
= 9.6/.12 = 80 KWH = PT
- NREL
data: solar radiation = 5-KWH/ m2: PT/5 =
16 m2
- Solar
panel Area = ~1 m2:
16
Solar Panels Required
|
* Energy is actually
what you need to power your home.
Energy is the power multiplied by the time.
Your load analysis actually determined the energy that
your home needs since it is in watt-hrs, but for these calculations
we will refer to energy as power.
Important:
Do not go and buy this number of solar panels yet. Complete the system final analysis
first!
Wind Generators
The power that is available
from a wind generator varies with each specific make and manufacturer. To determine the best size and kind
of wind generator to purchase know your average annual wind
speed (NREL Data) and then go to our alternative energy links page
to look at wind generators.
The wind generator manufacturer will supply power –
wind graphs for each wind turbine model.
Choose a turbine that has a peak power output at about
1.5 times your average annual wind speed.
Consult with the manufacturer before purchasing.
Example Power – Wind speed
graph:
Micro
Hydro Turbines
Hydro turbine size and selection is basically
the same as choosing a wind generator.
You will need your specific site information before
shopping. Once again, be sure to check you
site analysis information with the manufacturer before purchasing
hydro generator. Our alternative engineering links
page has links to hydro turbine manufacturers
Batteries
You want enough power stored in your battery bank
to run your system for the amount of time that you will not
be generating power.
This means the number of consecutive cloudy days if
you have a solar system, or the number of windless days if
you are mostly wind powered. To determine the size of your battery
banks, follow these basic steps:
1. Record the average power required (Pi)
per day from your load analysis.
2. Multiply Pi by the number of
consecutive days that you will need power (= Pi2).
3. Divide Pi2 by .8 to maintain a
reserve charge in battery bank(= Pi3).
4. Multiply Pi3 by cold weather
multiplier (PT) if you are going to use lead-acid
batteries. Use the average winter time temperature of the
battery to determine the multiplier from the following chart.
Battery Temperature Multiplier
| Temperature |
Multiplier |
| 80oF / 26.7
oC |
1.00 |
| 70 oF / 21.2
oC |
1.04 |
| 60 oF / 15.6
oC |
1.11 |
|
50
oF / 10 oC
|
1.19 |
| 40 oF / 4.4
oC |
1.3 |
| 30 oF / -1.1
oC |
1.4 |
| 20 oF / -6.7
oC |
1.59 |
5. Divide PT by the system voltage
(V) to determine the total amp-hours required for your battery
bank (=IT).
6. Divide the system voltage by the voltage
of the batteries that you wish to purchase. This is the number of batteries
that must be connected in series to meet your system voltage. Each set of batteries in series
is a battery set.
7. Divide (IT) by the amp-hours of
the battery that you wish to purchase.
This is the total number of battery sets that need
to be connected in parallel.
When you purchase batteries, you do not have to
buy the same voltage battery and amperage battery as your
system requires. Batteries work well when connected
in series to achieve the required voltage and connected in
parallel to achieve the required amp-hours.
Alternative energy
links page
|
