Accurately sizing the components of your solar electric or PV system helps ensure that your system will meet your desired energy requirements without failure especially important for stand-alone systems which are not connected to the electricity grid. However, you can always have more additional panels should your energy requirements exceed the installed system
1. Fill out a power needs table
To establish your daily, weekly or monthly power needs fill in the table below;
Add 25% for total system inefficiencies
Multiply the Total power per week which you got at the bottom right of the table above by 1.25.
Example: 16363.25 x 1.25 = 20454 Wh/w
Convert to watt hours needed per day
Divide the amount from step 2 by 7, since there are 7 days in a week.
Example: 20454 / 7 days per week = 2922 Wh/day
The most important step in designing for your system, is understanding your energy needs. The following steps guides you through the process of designing for your solar power system;
1. Fill out a power needs table
To establish your daily, weekly or monthly power needs fill in the table below;
 |
| Example Of Power Needs Table |
Add 25% for total system inefficiencies
Multiply the Total power per week which you got at the bottom right of the table above by 1.25.
Example: 16363.25 x 1.25 = 20454 Wh/w
Convert to watt hours needed per day
Divide the amount from step 2 by 7, since there are 7 days in a week.
Example: 20454 / 7 days per week = 2922 Wh/day
Based on the table of needs above this is the total daily power consumption in this household. From this we should be to size our battery bank size, which we will discuss in our next article but first..
2. Inverter sizing
The first thing you have to know about your inverter is what will be the maximum surge, and for how long. Surge: All inverters have a continuous rating and a surge rating. The surge rating is usually specified at so many watts for so many seconds. This means that the inverter will handle an overload of that many watts for a short period of time. This surge capacity will vary considerably between inverters, and different types of inverters, and even within the same brand. It may range from as little as 20% to as much s 300%. Generally, a 3 to 15 second surge rating is enough to cover 99% of all appliances.
Typical is what the inverter has to supply on a steady basis. This is the continuous rating. This is usually much lower than the surge. From our table above our typical rating should be at 420W or above depending on avalable inverter sizes. The surge rating is 20% more at 120%*420 = 504W.
3. Battery Bank sizing
Our total consumption is 2922 Wh/day). Ideally, a battery bank should be able to supply you with power, even if there is a problem with the solar panels or charge controller. You should now decide how many days' of backup power you would like and multiply the power consumption figure from step one by the number of backup days. e.g. 2-days' backup : 2 x 2922Wh/Day = 5844 Wh
Regardless of battery type and cost, the longest service life will be achieved by discharging them as little as possible. Decide on a calculated 'maximum depth of discharge' (DoD) whereby the lower the better and divide the result from Step 2 by this (decimalised).e.g. 50% DoD: 5844 / 0.5 = 11,688 Wh
All batteries are less efficient at lower temperatures and we can compensate for this in our calculation. Choose the factor that corresponds to the lowest average temperature your batteries will have to work in. Multiply result from Step 3 by this number.
e.g. 21deg = 1.04 x 11,688 = 12, 155Wh
Depending on the voltage of your electrical system, you may need to connect batteries together to create a bank at 12, 24 or 48V. Using a higher voltage is also a useful way of reducing voltage loss over longer distances or reducing the size of charge controller you need. In order to work out the minimum capacity of your battery or battery bank, divide the result from Step 4 by the desired voltage. e.g.12,155 / 24 = 506.48Ah
Finally, identify how many batteries you need. Ideally, we try to stay within 5% of the calculated size required, so based on the bank voltage and the target Ah capacity.
e.g. 100Ah (12V) batteries for a 500Ah 12V battery bank:
12V = 500 / 100 = 5 batteries
Keep in mind that it’s best to keep the number of parallel strings of batteries to three or fewer. If you parallel more than three strings of batteries, you risk shortening battery life due to uneven charging.
4. Solar Panel sizing
This is the easiest part is coming up with the number of panels needed for the system. We have our total daily power requirement at 2922 Wh/day. We have chosen the panels rated at 250W. In Kenya, the sun is out for most part of the day throughout the year. Divide the total daily power requirement with the solar panel ratings i.e 2922Wh/day dvide by 250, this equals 11.688No. panels. Our system requires about 12 solar panels rated at 250W to meet our daily load requirement.
Contact us for a analysis of your home power usage and subsequent design of a solar power system that will meet your power requirement without dependent on Kenya Power supply.
Our total consumption is 2922 Wh/day). Ideally, a battery bank should be able to supply you with power, even if there is a problem with the solar panels or charge controller. You should now decide how many days' of backup power you would like and multiply the power consumption figure from step one by the number of backup days. e.g. 2-days' backup : 2 x 2922Wh/Day = 5844 Wh
Regardless of battery type and cost, the longest service life will be achieved by discharging them as little as possible. Decide on a calculated 'maximum depth of discharge' (DoD) whereby the lower the better and divide the result from Step 2 by this (decimalised).e.g. 50% DoD: 5844 / 0.5 = 11,688 Wh
Temp. °F
|
Temp. °C
|
Factor
|
|---|---|---|
80
|
26.7
|
1.00
|
70
|
21.1
|
1.04
|
60
|
15.6
|
1.11
|
50
|
10.0
|
1.19
|
40
|
4.4
|
1.30
|
30
|
-1.1
|
1.40
|
20
|
-6.7
|
1.59
|
Depending on the voltage of your electrical system, you may need to connect batteries together to create a bank at 12, 24 or 48V. Using a higher voltage is also a useful way of reducing voltage loss over longer distances or reducing the size of charge controller you need. In order to work out the minimum capacity of your battery or battery bank, divide the result from Step 4 by the desired voltage. e.g.12,155 / 24 = 506.48Ah
Finally, identify how many batteries you need. Ideally, we try to stay within 5% of the calculated size required, so based on the bank voltage and the target Ah capacity.
e.g. 100Ah (12V) batteries for a 500Ah 12V battery bank:
12V = 500 / 100 = 5 batteries
Keep in mind that it’s best to keep the number of parallel strings of batteries to three or fewer. If you parallel more than three strings of batteries, you risk shortening battery life due to uneven charging.
4. Solar Panel sizing
This is the easiest part is coming up with the number of panels needed for the system. We have our total daily power requirement at 2922 Wh/day. We have chosen the panels rated at 250W. In Kenya, the sun is out for most part of the day throughout the year. Divide the total daily power requirement with the solar panel ratings i.e 2922Wh/day dvide by 250, this equals 11.688No. panels. Our system requires about 12 solar panels rated at 250W to meet our daily load requirement.
Contact us for a analysis of your home power usage and subsequent design of a solar power system that will meet your power requirement without dependent on Kenya Power supply.
