modified on 11 May 2012 at 12:48 ••• 76,201 views

Solar Power HOWTO

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Contents

INTRODUCTION

THIS IS A WORK IN PROGRESS

THIS IS A LONG ARTICLE WITH LARGE IMAGES, PLEASE LET IT LOAD FULLY

The purpose of this Wiki article is to document the process and materials required to build a Hisite (Base Station) that will operate autonomously using RouterBoard Hardware, without any connection to the Grid or Municipal Power Supply.

Some reasons why this may be needed:

  • There is no mains electricity supply where you are building your Hisite. Maybe this is because you are placing it on a mountain or hill in a remote area.
  • The the mains electricity is unreliable where you are putting the hisite and you dont have any automatic generator, or grid connected inverter or UPS
  • You have access to mains power, but find that solar power is often more stable for the RouterBoards, and you can get massive Uptimes and reduce issues.
  • You dont want to pay money to the landlord that is hosting your Hisite, and besides you are an environmentally energy efficient organisation.

DISCLAIMER

First I must point out that I am not an electrician or Solar Power "Expert". The contents of this article is the result of my experiences and lessons learned. I may not have calculated things fully / correctly, and may not have designed things exactly how they should be. THEREFORE you are reminded of this and that the use of this information is made entirely at your own risk. If you damage some equipment or yourself, or you find that this desgin doesnt cover the loads that you have, I can take no responsibility.

REMEMBER working with power and batteries and heights can be dangerous. Observe all industry standard health and safety rules.

CALL TO GURU'S

Can I request that others who have had successes with Solar Power Installations please edit / review this wiki? If you dont have time to make changes you can PM me in the forums and I will make the edits.

AIM

To power the following equipment with the use of Solar Power and NO Mains Power. The system must operate 24x7x365 with no downtime due to power.

Equipment to be powered:

  • 1 x RB433 Routerboard
  • 1 x R52H MiniPCI Radio Card

The system must be installed at the base of the mast and send power (NOT OVER POE) up the mast to the RouterBoard Mounted in an Outdoor Housing at the top of the Mast.

Mast is 30 Meters High.

DESIGNING THE SYSTEM

PLANNING: INFORMATION GATHERING

There are quite a lot of variables when designing a solar power system. You must consider these things:

Sunlight

How many hours of useable sunlight in a day to you receive in your area. This is called Insolation. Obviously this varies during the year with the seasons and so you will have fewer useful hours of sunlight in winter months than in summer months. I recommend that you always use the LOWEST number for your area.

For example in Nairobi, Kenya (where I am) The annual average sunlight is 5.62 Kilowatt Hours per meter squared per day. During the summer months February has the highest levels of sunlight at 6.24 Kilowatt Hours per meter squared per day and July has the lowest at 4.88 Kilowatt Hours per meter squared per day.

Therefore when doing my calculations I must use the lowest number of 4.88 kWhours per day. This ensures that in the winter months my solar system can still charge up the batteries and keep the routerboard running properly during the dark/gloomy hours.

You can get the sunlight data for your area from many places on the net. I got mine from the NASA website

Power Consumption

The Power Consumption of your Hisite. This can be tricky to get right in my experience. Start by reading the user manual for your routerboard, and refer to the power consumption data in the specifications.

The RB433 Manual claims that the RB433 will consume approx. 3 Watts BEFORE you add any radio cards. Radio Cards power consumption varies according to the power output of the radio and other things.

System Voltage

The voltage that your equipment can use. The Routerboard Manual states the following:

"RouterBOARD 433 series boards are equipped with a reliable 25W onboard power supply with overvoltage protection. 12..28 V DC input voltages are accepted, but when powered over long cables, it is suggested to use at least 18V. The system is tested with 24V solar/wind/RV systems with 27.6 charge voltage. Overvoltage protection starts from about 30V (up to 60V), so the board will not be damaged if connected to a 48 or 60 V power line."

And so because Mikrotik say they tested with 24Volt Systems I based my system on 24 Volts.

There are other opinions on this in the Forums, and I have to admit I don't understand the science enough to really figure this out. Do your own checking.

Practicalities

The practicality of the system. Do you want many small panels, or one big one? Do you need many physically small batteries or fewer big ones?

Maybe if you have to carry the batteries up the mountain in your backpack then lots of smaller ones makes more sense.

You also have to balance your workings with what you can get. I am in Africa, and we cant always get the ideal items, and so you may have to adjust your design / calculations to suit what you can get.

PLANNING: THE CALCULATIONS

Size the Battery Bank

STEP 1:

Calculate the amp hours per day:

So: 144 Watt Hours per day / 24 Volts System = 6 Amp Hours per day

STEP 2:

Calculate the battery storage required. We want this system to have three days of storage (or autonomy) in case there is a wicked storm that comes in winter and reduces the charging ability of panel.

So: 6 Amp Hours Per day x 3 Days = 18 Amp Hours of battery storage required.

STEP 3:

Now we need to consider that we cant flatten the batteryƛ completely. Its bad for them, so to choose the right battery size we need to factor this in.

So: 18 Amp hours of storage required / 0.5 (For a 50% maximum discharge of the battery) = 36 Amp Hour Battery Required

STEP 4:

Round up the result attained in STEP 3 to the next battery size that you can get in your area. I chose a 44Amp Hour Battery as there was no option between the 20Amp Hour and the 44 AH. They didnt have a 36 AH battery.

Size the Panel

To calculate the size of the Solar Panel Array we need to work through the calculation in three steps.

STEP 1:

Calculate the watt hours per day.

We know our Routerboard is going to consume ~6 Watts of power, and we know that we are going to run it 24 Hours a day.

We now calculate the watt hours per day by multiplying the wats consumed by the number of hours of operation:

6 Watts x 24 Hours Operation = 144 Watt Hours

Then we must calculate the daily Amp Hours requirement for the system. We know in advance that we are choosing a 24Volt System.

So: 144 Watt Hours / 24 Volts = 6 Amp Hours Per Day

STEP 2:

Calculate the required current output from the solar panel in bright sunlight conditions in Amps

Things we know:

  • It is generally accepted that batteries dont store 100% of the energy they are given, so we use a factor of 0.8 to account for inefficiencies.
  • We know that we are calculating on the basis of 4.88 Sun hours per day
  • We know that we need to provide for 6 Amp Hours Per Day

So: 6 Amp hours per day / 0.8 battery efficiency factor / 4.88 Sun hours per day = 1.54 Amps

This means we want a solar panel that gives about 1.54 Amps or more in bright sunny conditions.

STEP 3:

To Size the panel, we can now multiply the Amps needed by the volts of the system:

So: 1.54 Amps needed x 24 volts system = 36.96 Watts

So the Minimum wattage solar panel that you need is say a 40 Watt panel. Or you can take two 20 Watt panels and connect them in parrallel to increase the wattage to 40 Watts.


Results of the Calculations

So having worked through the calculations we know the following:

  • We need a 40 Watt or larger Solar Panel
  • We need a 36 Amp Hour or largery Solar Battery
Spreadsheet to make the calculations

PrvtPilot On the Forums made a Spreadsheet calculator to help with these calculations.

This is a Excel spreadsheet that will make all the calculations mentioned in the article. Just fill in the grey boxes with your numbers and the results will be displayed in the green boxes. Simple.

File:Solar Calculator.xls

I tried to upload the file here, but .xls is banned by mediawiki. So you can find the file here:

Solar Calculator Spreadsheet Post in Forum

THE FINISHED DESIGN

The following drawing shows how the components are connected:

Solar Power Design

BUILDING

KIT LIST

The List of equipment that I have used (Please note that costs are in US Dollars and apply to Kenya):

  • 2 x 40 Watt 12 Volt Solar Panel @ 193 USD Each
  • 1 x 24Volt 15Amp Charge / Load Controller @ 60 USD
  • 2 x 12 Volt 44amp hour deep cycle, sealed lowe maintenance lead acid solar batteris @ 95 USD Each
  • 30 Metres of 2.5mm Twin Core Flex Copper Cable @ 0.8 USD per Meter
  • 10 Metres each of Red and Black 4mm Single Core Copper Cable (20m total) @ 1 USD Per MEter
  • 1 x DC Power Plug (to go into the routerboard)
  • 1 x ABB IP 55 Rated Outdoor steel housing to contain the batteries and controller @ 35 USD
  • A DIY Steel Frame to mount the panel @ 20 USD
  • Many Cable Ties
  • Various cable lugs and terminators

SEQUENCE OF CONNECTION

Please observe these rules when connecting up your solar system to ensure that you dont damage any components.

Always make sure you connect the NEGATIVE cable FIRST when working with DC systems.

Always connect the battery first, then the Solar Panels and FINALLY the Load.

Follow the numbered sequencing as shown in the image below:

Connection-seq.png

PHOTOS OF MY SYSTEM

THE TEST RIG

The photo below shows the system on test. Making sure that my calculations do actually work. As with all these things, BEFORE you put anything in to your production network make sure you TEST, TEST, TEST.

Also be sure to buy a good quality DIGITAL multimeter. You will use this tool to measure voltages, make sure you have things wired properly and to monitor your system as you test.

Solar Power Test Rig

THE FINISHED SYSTEM

The Housing

You need a good strong housing that can hold the weight of the batteries safely, and that will provide weather resistance and yet still provide good ventilation for the batteries.

I had one made by a friend. Its a powder coated steel affair with good side vents.

Housing: Housing.jpg

Vents: Vent.png

The Back Plate

My housing came with a removable back plate that can be drilled and modified to allow you to mount any sort of equipment in the housing. I used mine to mount the Charge Controller, and the fusing system. You can mount anyhting else you like here. Maybe even a routerboard.

Here is my back plate showing the inline fuse on the flex cable to the battery, and the fuse panel for connecting loads (routerboards) to the system. Using the bus bar for the negative, and the fuse panel for the positive load connections means that it is easy to connect or disconnect loads. YOu can just remove a fuse to de-power something without having to get your screwdriver out and remove connections.

All connections are soldered.

Backplate.png

Installed Backplate: Backplate1.jpg

The finished system ready for commissioning

Here it is in all its glory. Batteries installed in parrallel.

Now all we have to do is install the housing on the mast, connect the panels and loads and go for a beer!

Finished-System.jpg

UPDATE: 400 Days Uptime

Well, the proof is in the pudding as they say! Quite pleased with this project.

The screenshot below shows 400 Days uptime on the RB433 with 1 radio for AP (R52H) and 1 Radio for backhaul (R52)

Uptime.png

Further Reading

There is a massive amount of info on the internet about solar. Google is your friend with this.

However here are some of the resources that I have found especially useful:

  • Dr. Arne Jacobsen is a Solar Guru. A lot of great stuff at his site here: [1]
  • One of many online solar calculators: [2]
  • A Mikrotik forum article that spawned the writing of this article can be hound [3]here, and there are other articles in the forums. Do a Search
  • Another Mikrotik forum discussing over and under voltage issues is here: [4]
  • An article about monitoring the solar system with an Atmega8535 board behind a RB433 wireless router is here : [5]