hallo people. of late kenya power has beome too unreliable that am now thinking of a solar solution. could someone advice me on the kind of a solar panel and battery that can power 1 computer and 1 bulb for atleast 10 hours. I will appreciate if you could give me the price and all the technicalities.

Though I do not have the prices, I can provide you with information that will help you make decisions.

You have two main options, one is to go off grid, meaning to be fully independent and not depend on KPLC at all. Since you have mentioned that you need a solar panel, this could be an indicator that you want to go off grid.

The other alternative is to have both KPLC and a backup power system, which will not require a solar panel. With this setup, when there is power, the battery gets charged, if the battery is full, it stops charging, but the moment that there is a power outage, the battery powered backup kicks in, just like a UPS.

1000 watts = 1 Kilowatt (KW)

Watts = Volts x Amps

A 12v battery can have 20 amps, this means that the battery can store and supply up to 240 watts of power. Different batteries have different ratings.

If you have a light bulb that is rated at 60 watts, this means that the light bulb will be able to be powered for 4 hours before the 240 watts battery bank is depleted. 240 / 60.

To figure out that which needs to be purchased, you will first need to figure out the total amount of power that your equipment will be consuming, once you have done that, you will then be able to determine what to purchase.

You mentioned that you will need to power a computer and a light bulb for 10 hours. You did not mention the total power ratings on the machine + monitor (unless it's a laptop), nor did you mention the bulb's, so, we will hypothetically rate the computer at 300 watts and the light bulb at 80 watts.

We will then add up the totals in watts (300 + 80), bringing it to 380 watts. This means that in order to power the computer and the light bulb for 1 hour, you will need at least 380 watts of power from the battery bank.

Since you need 10 hours, you then multiply 380 with 10 bringing it to 3800 watts or 3.8 Kilowatts.

This means that your power storage needs to have a capacity of at least 3800 watts, in order for you to power your machine and bulb for 10 hours.

Having determined your daily power needs, you will need to get either:

A solar panel, a solar battery charger and an inverter

or get

An inverter charger

If you want to be wholly independent from KPLC, you will need to choose the first option, but if you want to use both KPLC and your power backup, you will need to choose the second option.

If you choose to be fully independent, then you will need to determine the solar battery(s), solar panel(s), the solar charger and the inverter.

Power storage

If you find a 12 volt, 80 Amps battery, which is equivalent to 960 watts, this will mean that you will need at least 4 of these batteries in order for you to be able to meet your goal of having at least 3800 watts for 10 hours. (3800 / 960).

In the Lead-Acid arena, you have the common battery that is used to startup vehicles, these batteries are not the most ideal for a home power system, for they are not optimized for that type of application. These batteries are for providing large amounts of power for short periods of time, they require a lot of maintenance, it leaks and gives of toxic gasses. On the other hand, there are batteries that are optimized for applications such as what you need. These batteries can have high amperage, some exceeding 200 amps, they can be maintenance free - no need of adding acid etc..., they are sealed and do not give off any gasses - allowing you to keep the battery indoors, where the temperatures are more stable, which ensures that they operate as effective as possible, because drastic temperatures either low or high hamper the batteries effectiveness, in ways such as, but not limited to: increased discharge rates, minimized battery age and limited battery capacity

In your your case, you will need to have a battery farm, since one battery is not enough, if you can get a 12V with 210 amps, you will be able to get 2520 watts from that 1 battery. Since you need 3800 watts, you will be 1280 watts short, meaning that you will need another battery. It is advisable to have identical batteries, with no difference in ratings.

Solar panels

To know the number of solar panels that you will need, you will need to take the total needed power per day, it this case, it is 3800 then divide it by (a single solar panel output power x number of sun hours per day)

The number of sun hours are needed because it is during those hours that the solar panels will be able to produce power.

Let us suppose that the solar panel is rated at 200 watt, meaning that when there is light, it can output 200 watts. The equation will be 3800 / (200 x 7) = 2.7 which translates to 3 solar panels.

Solar Charger

A solar charger protects the battery from overcharging as well as keeping the battery from discharging, while there is power to charge.

There are two popular technologies employed by solar regulators, these are Pulse Width Modulation (PWM) and Maximum Power Point Tracking (MPPT)

The main advantage of PWM over MPPT is that PWM is cheap. PWM being cheaper, it comes with a disadvantage of which MPPT is the solution, making MPPT a better option, despite the extra cost.

For this example we have:
- A battery that operates at 12 volts
- A solar panel that can produce 100 watts because it has a rating of 20V and 5 amps, if there is full light.
- We have full light, hence we should expect the solar panel to produce 20 volts and 5 amps giving us 100 watts.
- Understand the fact that while charging, the voltage going to the battery from the charger must match the voltage which the battery is operating in. In this case, it is a 12v battery, hence 12v needs to come out of the charger.

In this case, if we are using a PWM solar charger, we will be charging at 60% efficiency, while if we were using MPPT solar charger, we would be charging at 100% efficiency.

This is because a PWM charger will draw 12 volts, 5 amps from the solar panel, then output 12 volts, 5 amps to the battery, leaving behind 8V, while a MPPT charger will draw the whole 20 volts, 5 amps from the solar panel, then output 12 volts, 8.3+ amps to the battery. What a MPPT charger does, is that it converts the excess or the remaining voltage to amperage.

Since the solar panel is outputting 100 watts, a PWM charger will operate at 60% efficiency because the PWM charger will output 60 watts to the battery (12v x 5 amps), while a MPPT charger will operate at 100% efficiency because it will output 100 watts to the battery (12v x 8.3+ amps), this is because it is smart enough to use up all the voltage produced by the solar panel, by sending the required 12v to the battery, and then convert the remaining voltage to amperage, resulting in the full utilization of the solar panels output power.

A PWM charger can only be effective if the solar panel's voltage rating matches the voltage that the battery needs, or else if the voltage from the panels are higher, there will be lost power.

If you can afford it, choose a MPPT charger and make the most out of your solar panels.

Inverter

The inverter will convert DC to AC, so that you can use that power on typical electrical appliances. Most common appliances use AC. Only DC appliances can be connected directly to the battery without the need of an inverter, such as a 12v TV.

There are two main types of inverters, there is the Modified Sine Wave Inverter and a Pure Sine Wave inverter. Pure Sine Wave power is smooth, not distorted, it is high quality power, usually better than the power from the grid.

While many common electrical equipment can operate on modified sine waves, a small minority of certain electrical equipment will not, such as variable speed electric motors, certain microwaves, certain display devices and others, unless they are supplied with a pure sine wave.

Modified sine wave inverters are cheap while pure sine wave inverters are more costly. In your application, a modified sine wave inverter is sufficient, although if you can afford a pure sine wave inverter, then go for it. You just never know when you may get an electrical device that may need it.

If you want to use both grid power alongside with your own power bank, you will need to purchase an inverter charger.

An inverter charger will charge your battery bank while there is electricity, then automatically provide you with AC or DC power from the battery bank the moment that power goes off, just like a UPS.

When purchasing an inverter, you will notice that different inverters have different power ratings, you can find inverters who's power rating range from below 500 watts to over 5000 watts. The one that you will choose will depend on the amount of watts that your electrical equipment will need. We hypothetically gave your computer 300 watts and the bulb was 80, totaling at 380 watts, meaning that a 400 watt inverter is the one that you will purchase, hopefully it will be a pure sine wave inverter.

If budget is tight, you may begin by having a hybrid setup, KPLC + your backup power storage system. This will save you mainly on the solar panels, then, you can later on go fully independent, then sell or keep the inverter charger depending on how you foresee it's use.

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Notes

Cabling is very important, incorrect cabling can lead to great inefficiencies in the power system, such as losing power during transfer from one component to another.
You can operate your battery bank at different voltages, 12, 24, 36 ...
The higher the voltage the thinner will the cables need to be, while the lower the voltage, the thicker the cables need to be. If 100 watts is being transported, it can be either (12v x 8.3+ amps) = 100 watts or it could be (48v x 2.08+ amps) = 100 watts hence the higher the voltage, the lower the current and thus the thinner the cable, saving cabling costs.

Monitor - with this, you will be able to see in real-time figures of the power from the solar panels, battery bank levels and other important information. Some inverters, some chargers and some inverter chargers have built-in monitors, in the case where there is none, you can purchase an external monitor.

Prolonging battery bank - To prolong the battery bank, it is advisable to keep the batteries in the most ideal environment, sheltering the battery from extreme temperatures, whether it be high or low. The battery manufacture should be able to state the ideal operating temperature. Lead Acid batteries will last the longest if the discharge level is not allowed to drop below 50%. This threshold can vary from battery to battery. Currently, your 10 hours is attainable if the batteries discharge 100%, since this is the case, it means that the battery bank capacity will need to be doubled, since you intended to get 10 hours of use, while not not allowing the discharge to go below 50%. Consider this factor while determining the components for the system.

Backup for multiple days - If your want backup for more that 1 day, then multiply your capacity for one day with the number of days that you may need backup power, then work out the equipment that you will need.

Inefficiencies - There can be in efficiencies such as dark cloud cover, or with the cabling or with the batteries and in other places, to make up for these inefficiencies, you will need to increase your battery power bank capacity by about 25%. This will protect you from unexpected outages. Consider this factor while determining the components for the system.

All the best.

You can use Portable power generator or UPS devices for backup power for your computer. The price should be high starting from $500.

@D32 nice piece, well written!!!

Wow,

Now that is one person who actually went to school. If only everyone who went to school offered advice in his/her area of specialisation, then we would have gone far as a country/society. The aim of education is to solve societal problems.