Solar Questions

Michael Boxwell I've been asked solar questions by so many people over the past six years since the first edition of my book was published. In fact, one of the most fun aspects of having written my book has been meeting and talking to the countless enthusiasts who have bought the book and have implemented their own solar energy systems.

If you have any questions about solar, you can get in touch with me through my ask me a Question web page. Below you can see some of the questions I have been asked before about solar power, and my answers.

Solar Questions and Answers Archive:

I am looking for wire sizes.
6 panels 280 watts Canadian solar.Wire size to the combiner box?,Wire size to vfx3648.
16-12avr170et batteries in a 48 volt series.Wire size for jumpers? Can I run the 4 positives and four negative off the batteries to a 4 20 watt breaker panel?. Then run two wires to the vfx 3648.
1 - outback flex vfx3648
I need the wires sizes to connect everything ..
Thank you
     Sean Kirk, September 11, 2013

    Whenever electricity runs through a cable, there will be a resistance, resulting in a voltage drop. The amount of resistance depends on the cable you are using, the voltage and the length of the cables. You've told me what you want to connect, but the vital bit that is missing is the cable lengths!

    No matter, there are a couple of on-line calculators that will tell you everything you need to know. There is a good one here: http://www.southwire.com/support/voltage-drop-calculator.htm. They do an iPhone and Android app as well if you want to calculate it on your phone.

    Work out the voltage, current and cable length for each part of your circuit separately. Then enter the information into the on-line calculator and you will have all the figures you need.


i have built a couple of small panels using 20...3x6 cells they keep my single 60amp car battery topped up, im hoping to add to the system as money/time permits, i use it in my shed for led lighting and small 12v appliances,im very interested in solar power my question is this what is the purpose of the small solar cells ie 6x1 3x1 2x1 they all produce 0.5v but the wattage and amps are minimal so why would anyone use these?
your comments would be appreciated,thanks graham
     graham lawrence, September 13, 2013

    Its always good to hear about people who are doing small, simple projects with solar and using it as a learning experience. Keep up the good work. You are right, these solar cells are pretty useless on their own for the general public, but the reason they exist is that from a manufacturing perspective, it is cheaper and easier to produce small cells rather than large ones. These cells can then be linked together to create a much bigger solar panel.

    These individual solar cells have another use as well: they're used by manufacturers to embed solar into all sorts of products - garden lights, radios, mobile phones, AA battery chargers, torches, toys and gadgets of all shapes and sizes. They all use tiny amounts of power, and solar is a great way of providing it. By building small cells, manufacturers can use the cell as a building block for producing lots of different products to sell.


the cost of a Solar powered 1.5 hp pumpset in India is about $2500 if it is to run on 12V dc. If a 1.5hp machine wereto be manufactured to run on 220v DC the cost would be $5oo/.In your handbook, there is a statement that..it is more efficient to use DC over AC supply. I plan to have about 10,000 W solar panels installed on my farmhouse roof top to power my farm operations.An electric motor manufacturer has agreed to make for me a pumpset to run on 220v DC at my risk. the distance from my roof top to the pump set site is 100meters. If I take the risk,what all should I forsee to work my pumpset and other farm machinery on 220vDC. Will the plan be safe and economically viable? I plan to use the DC power produced only during sun light hours.[7am to6pm]. hence i will not need batteries. Awaiting your reply, Abraham Tharakan.

     PG Abraham Tharakan, September 13, 2013

    Wow! That is a huge difference in cost from $2500 down to $500. I suspect the $2500 pump would be more efficient, but that efficiency is more than outweighed by the cost saving.

    Is solar power supplementing a link to the grid, or is this an entirely solar powered operation with no other source of power?

    The issue if it is entirely stand alone is that you will get big fluctuations of power output from your solar throughout the day. Your pump set will be consuming somewhere in the region of 1.2kWh of energy, which is well within the capabilities of your proposed solar array, but if you are using other farm tools as well, you may have periods of cut-out if you are consuming more power than you are actually producing at any time.

    That said, what you are proposing sounds very feasible. It certainly can be built to be safe and the cost savings from using a 220v pump make it a worthwhile solution.


if your grid tied solar system has microinverters built into them do you still
need another inverter at the electric panel?
     michael marciano, September 13, 2013

    No. The micro-inverters do it all.

how to design solar irradiation system
     dhananjay bhosle, September 14, 2013

    The glib answer is to buy the book! If you are just looking for some basic information, fill in the solar calculator questionnaire on this website (http://www.solarelectricityhandbook.com/solarcalculator.aspx) and it will email you a report that describes what you need to put together a basic system.

Good day sir, please I used your online calculator and I got the analyses you gave on my required load per day...Please you said the power my solar panels need is 300w for about 8hrs on insolation of sunlight in my location.And this power can charge my 300AH battery(s) of two days of independence ..My question now is, when the 300watts panel(s)is charging my battery, can I use my rated appliances without the fear of my battery(s) at the end of the 8hrs not FULLY charge my battery all because I was using the solar system during the day instead of leaving it to charge the battery(s)?..... Thanks
     Samuel Pearl, October 4, 2014

    You will certainly have times when the batteries will not be fully charged. The aim is for the solar system to keep the batteries topped up, but as you are also using the energy, you will usually find that the batteries are normally only between 85-95% charged. Sometimes the charge will drop below this, sometimes they will be much closer to 99%. It is very rare that they are totally charged up.

    That is not a problem in reality. If a battery was always 100% charged, it would begin to lose capacity. A battery must be used regularly in order to remain effective.


it is possible agriculture equipments run with solar power whole day & battery also charge for night using

     g t raju, October 5, 2014

    Absolutely. You need to make sure your battery is big enough to maintain the power supply for when the sun is not shining, but so long as your solar array is large enough, it can then recharge the batteries during the day.

Hi, first thanks for making a great book, really helped me to start of in the solar world!!
So i'm down in Kenya and have a DC solar pump system and I want to know that I don't blow the MPPT controller (now use 120W panels instead of 100W) so I need to calculate the maximum voltage for this specific solar irradiance and temperatures. The problem I have is that I can't find maximum W/m^2 (Only Wh/m^2) for this site. I know that high temperature takes away some of the power but with high irradiance can't the panel go over (for a short time) the Voc that is in the product sheet? Feels like that should be possible with the irradiance here
Best regards
Hack
     Solarhack, October 6, 2014

    Hello Hack, thank you for your comments.

    Yes, a solar panel can indeed provide more power than the panel is officially rated at, particularly in areas close to the equator. At this point, the voltage will be higher, but usually not by more than 4-5 volts. You'll probably find that this occurs more in the winter months than the summer, simply because of the drop in temperature.

    When you have a disconnected solar panel and connect a voltmeter to it, the voltages can go extremely high. I've seen a 12v solar panel showing a voltage of 60v in very strong sunlight! As soon as you connect your solar panels together however, and start using the power, the voltage drops very quickly and that same 12v solar panel then shows a much more realistic voltage of around 15-16 volts.

    Don't confuse watts with voltages. They are different things! There is no table for voltages simply because they are panel specific and what is correct for one brand and model will be different for another.

    If you work on the rated specification for the panels and MTTP controller, and are happy that based on the official specification that you are not overloading the controller from the solar panels you are using, you will be okay.


can i connect the 250 watts 37.95 V to 250 watts 36 V in parallel connection? and attach to PWM Solar Charge Controller Spec: 48 V 60A and my Battery Bank is 4 pcs 12V 150A connected in series connection system? Thanks for your consideration.
     Roy del valle, October 6, 2014

    36 volt solar panels are rare. Are you measuring the open voltage of the solar panels with a voltmeter (i.e. the voltage the solar panels show when not connected to a circuit) or are these the specifications of the panel themselves?

    When a solar panel is not connected to a circuit, the voltages that you can read from a 12v solar panel can go extremely high. I've seen a 12v solar panel show a voltage of 56 volts on a sunny day! As soon as you connect an electrical load to the solar panel, however, the voltage drops dramatically and you get a much more sensible reading - typically somewhere between 14 and 17 volts.

    If you have got 36v solar panels, you will not be able to use them with a 48v charge controller. The charge controller cannot increase the voltage of the solar panels, only reduce them.

    I suspect you have probably got either 12v or 24v panels, in which case you will need to connect them in series to build a 48v solar array. This can then be connected to your PWM Charge Controller.


Please,i want to ask on the state of charge.If i double my battery following the rule of Thumb,can i still read my state of charge in voltage for the doubled battey like the way i would for just a single battery. For example, if i am to read a fully charged 12v 100AH battery which is 12.6v full charge,when i double this following rule of Thumb,connected in parallel,in other to take note of 50% Depth Of Discharge,will i still read 12.6v full charge with a multimeter or will it be 12.6v + 12.6v = 25.2V ??? #Thanks so much in anticipation.
     Samuel, October 7, 2014

    Hello Samuel. Thanks for your question.

    It depends on how your batteries are connected up. They can be connected up in two ways: in series, where the negative pole on one battery is connected to the positive pole on the next, or in parallel where the batteries are wired up positive to positive and negative to negative.

    If you are connecting your batteries in series, your voltage doubles but your current remains the same. Your circuit is now running at 24v. Therefore, based on your batteries, your 50% depth of discharge will be 25.2v.

    If you are connecting your batteries in parallel, your voltage remains the same but your current doubles. Your circuit is running at 12v. Therefore, based on your batteries, your 50% depth of discharge will be 12.6v.


Please sir,can i use a higher voltage solar panels combine with a lower voltage panel and will it be effective? For example : using a 36v 300w solar panel together with a 12v 130w solar panel or where can this be applied in solar installation.
Also do you have a pdf e-book that can guide me on how to build a solar tracker or is it not neccessary?
     Samuel, October 7, 2014

    You cannot use two different specification of solar panels together. Ideally, all solar panels in the array should be identical. If they are not identical, then the specification of the panels should be the same as the efficiency of the entire array is based on specification of the weakest panel.

    If you have two totally different solar panels, the answer is to create two separate solar arrays, each with their own controller. I've seen that work very effectively for smaller installations where people are assembling simple solar chargers using whatever components they have lying around.

    Solar trackers are quite specialised pieces of machinery and because of their price, it is often much cheaper to use additional solar panels rather than have the expense and complexity of a solar tracker. There are a number of people who have built home-made solar trackers, which may be of interest for a hobby project, but several that I have seen are not particularly suitable for professional installations: solar panels are heavy, bulky and require strong mounting. Most of the DIY solutions that I have seen are not mechanically robust enough to withstand years of use.

    Consequently, I cannot recommend any of the DIY guides that I have seen on building your own solar tracker. If you want to experiment, however, I would suggest visiting the instructables web site (www.instructables.com) and see what you can find there.


Hi Michael,
Do you have stats on how much money you save creating a solar panel yourself vs. buying it already made and assembled? My husband and I want to know before we dive in and start reading books, etc., on the subject. We live in the desert where the sun shines most of the time and air conditioning costs a fortune!
Thanks!
Larry & Karen
     Karen, October 7, 2014

    Do not build your own! Solar panels are built in clean room environments to very specific specifications. Reproducing this at home is virtually impossible. Most of the 'build your own solar panel' guides are misleading, many of them are plain wrong.

    Many of them are built on a wood frame, which is not suitable for the extreme temperatures that solar panels build up, particularly in very hot environments like deserts. Poor connections between cells also creates huge heat build up. Either one of these is enough to start a fire.

    If you want to build a solar panel for fun, and you don't use it unsupervised or connected to a building, then that is fine. If you actually want to use the solar panel to generate electricity that you will use, don't risk building your own. Buy one ready assembled.


Hi - I want to install an electric gate motor, but will have to run at least 30m of cabling to power it. I already have the unit and it has a backup battery in case of power failures. I am knowledgeable with electrics, but don't understand much about solar power. The battery is obviously recharged by the A/C supply and then powers the motor if the A/C supply is interrupted. My question is: can this standard battery be charged by a solar panel on a permanent basis, thus avoiding the costly exercise of having to wire it into my household supply?
     Michael, October 10, 2014

    Absolutely. Powering this by solar should be easy enough, so long as you can generate enough power to keep the battery topped up all through the year.

    Connect up the gate motor and measure the current drain on the battery when you open and close the gate. Multiply this by the number of times you plan to open and close the gate each day and add a 20% contingency. This will tell you how much energy your solar array needs to collect for you.

    Now put this information into the Off Grid Solar Analysis questionnaire from this website (http://www.solarelectricityhandbook.com/solarcalculator.aspx) and you'll get a report telling you what you need sent to your e-mail address.

    Don't worry, your e-mail address and details are not kept on the system once you've filled in this report. I hate junk mail: once you've received the report, all the data you have entered is cleared.


I purchased you 2014 book and have been reading it, it's wonderful but could you show me the formula for determining how long it will take to charge a set of batteries using "x" watt solar power @ 12V. I would really appreciat any formulas you can provide on this and anything els.
Thanks Dan Rumfelt
     Dan Rumfelt, October 10, 2014

    Thank you for your comments. Multiply the solar insolation for your area (using the Solar Irradiance tables found here http://www.solarelectricityhandbook.com/solar-irradiance.html) by the peak wattage of your solar panel. This will tell you how many watt-hours of energy your solar array will generate on an average day, broken down for each month of the year.

    Then check your battery and find its Amp-Hour (Ah) rating. Multiply the amp-hour rating by the voltage to find its watt-hour rating. Then add around 10% for efficiency levels.

    Then divide the second figure by the first. This will tell you how many days it will take to recharge your battery from your solar panel.

    Example: Assume you have a 100Wp solar panel and the solar insolation for your area in October is 3. Multiply 100 x 3 = 300. This is the generation capacity of your solar panel for October on any given day (+/- 20% for weather).

    Then assume you have a 50Ah 12v battery. 50 x 12 = 600 watt-hours. This is the capacity of your battery.

    600 divided by 300 = 2 days.

    This means that during October, our solar panel will take two days to fully charge the battery from flat to full.

    I hope this helps.


I filled the Grid-Tie Solar Calculator Questionnaire and when I click to receive my report I receive an error: Server Error in '/' Application
     Alfonso, October 10, 2014

    Sorry. We occasionally have these problems and have not been able to get to the bottom of it. Usually if you click on the BACK button on your browser and resubmit, it works.

I want to set up a solar electricity system for 2 ceiling fan and 4 energy saving light (15 watt each) in my home.
1. What is the equipment required ?
2. How much cost involve?
3.What is the stability of solar system
4. Any schedule repair Maintenance required?
5.where the equipment is available?

     Mohammad Abdul Hamid, October 12, 2014

    Thank you for your message. I presume from your message that this system has to be completely stand alone, not connected to mains electricity?

    You can buy 12v ceiling fans - here is an example of what is available - http://sunrisecor.en.alibaba.com/product/686093974-213260495/DC_12V_Ceiling_Fan_w_Emergency_Light_36_42_48_56_60_64_.html. As you can see from the specification, depending on the size of the fan, they use between 12w and 30w of power when in operation.

    To get a clearer idea of exactly what you are going to need and to get an idea of price, fill out the Off-Grid Solar Calculator questionnaire on this web site (http://www.solarelectricityhandbook.com/solarcalculator.aspx) listing the four lights and two ceiling fans. You will then get a report sent to you with details of what you will need.

    I hope this helps.


Dear Michael
Thank you for your excellent book which is the best Iíve read on solar pv. I have been working with a number of Ghanaians to replace kerosene lamps with solar lights for a raft of reasons which Iím sure you are well aware. We have been moderately successive using small lanterns but we would like to provide systems to villages for lighting, communication and storing medical products. Clearly the challenges you faced in Ethiopia, Kenya, Uganda and the Sudan were very similar. I would be most interested to know the kind of system configurations you used. I noted that other correspondents that they had expressed concerned about the quality of unbranded Chinese solar panels, controllers, inverters and batteries. Is it your opinion that the quality of unbranded Chinese products has continued to improve over the last few years? At the moment I am looking at a suitable supplier for sealed lead acid batteries from 7Ah up to 200Ah. I noted that Leoch batteries do not seem to get very good reliability reviews. Do you have any experience of Leoch batteries? Can you recommend any Chinese suppliers for batteries, panels and controllers? Would you recommend using monocrystalline or polycrystalline panels in Ghana? Any advice you may be able to provide would be most appreciated. Kind regards, Paul.

     Paul Merritt, October 13, 2014

    Thank you for your message Paul, and for the kind words about the book.

    Your project is very exciting. For the project I did in Eithiopia back in 2010, I was able to use Kyocera polycrystaline solar panels. They certainly weren't the cheapest, but if the budget to buy the Kyocera's had not been available, I would have been quite happy to use Chinese solar panels.

    The quality of the Chinese solar panels has been getting better. What I would recommend for your application is if you are using budget panels, over specify by 10%. Also, make absolutely sure you use good quality interconnection cables - don't skimp on those - and make sure there is no shading issues and a reasonable air-flow behind the panel so that it doesn't cook. Then, make sure the solar controller is mounted away from the panels away from direct sunlight and has plenty of ventilation around it. If you do all of that, you won't go far wrong.

    I haven't used Leoch batteries, so I cannot comment on them. My personal preference has been US Batt and Trojan batteries. Trojans are readily available as the company produces them in China as well as the US. You pay a little more to buy them, but they will last more than twice as long as many of the unbranded Chinese batteries.


Hi Michael,
Thank you for your great work.
I would like to know where the solar irradiation data that is displayed in your comes from (Which data source?)and how it was measured.
Thank you in advance for your help.
Regards,
Mario
     Mario, October 15, 2014

    Thank you for your comments. The irradiation data was supplied by NASA.

    You can find out more about how the data was collected and measured at the NASA web site on https://eosweb.larc.nasa.gov/cgi-bin/sse/sse.cgi?rets@nrcan.gc.ca


How many amp charger controler do i need for 37kw solar panel set up
     Noel santillan, October 17, 2014

    That depends on the voltage that you are running your system at. A 37kW solar array is a pretty huge array, to be honest. It depends on the precise application, but my instinct would be to consider running it as a number of smaller arrays, each with its own charge controller. This would probably be a more cost effective solution as well as when you get over 4kW, solar charge controllers tend to get very much more expensive.


How many amp charger controler do i need for 37kw solar panel set up
     Noel santillan, October 17, 2014

    A 37kWp solar array is pretty huge, and solar charge controllers that can manage that load are very expensive.

    It depends on your application, of course, but I would be tempted to split the array into multiple 4kWp arrays, each with its own solar charge controller. This has the advantage that you have greater redundancy and you are using lower cost components, which could save you a considerable amount of money.


On a 24v system what is the lowest I should let my batteries get to before the generator turns on?
     Joe, October 18, 2014

    It does depend on the batteries you have. Look at the technical documentation for your batteries (if you don't have it, you can usually find it online) and find out what the voltage of the batteries are at different states of charge.

    Although this a generalisation, you would usually not want the batteries to drop much below a 50% state of charge before the generator kicks in. At the absolute lowest, you need your generator to kick in before the batteries drop to 20% state of charge.


Dear sir
my question is I want to use 2fan 1tv and 5cfl how much watt of this and what watt penal & invater & battery we use
and how much money of this in india ?
     Basudev, October 19, 2014

    You will need to check the watt rating on each appliance you wish to use. It usually tells you what it is on the product itself. Once you have this information, fill in the 'off grid solar analysis' questionnaire (http://www.solarelectricityhandbook.com/solar-calculator.html) and the system will tell you what you need and give you a reasonably accurate indication of price.

please i want a calculator to estimate the solar irradiance within units of (w/m2) not to be function on day and hours (kwh/m2/day) ,please reply me if you know?
thank you
     Sasa Mohamed, October 19, 2014

    You are looking at power (watts) rather than energy (watt-hours), which will vary enormously throughout the day. That is why we calculate the total energy rather than power snapshots which do not give you any realistic information.

    If you want to work from the raw data, you can go to the NASA website (http://www.esrl.noaa.gov/gmd/grad/solcalc/) and calculate the information you are requesting from their raw data.


What is the optimal operating temperature range for a solar pv panel?
     Andy, October 21, 2014

    It varies a little from one manufacturer to another, but in general, the cooler the panels, the better they perform. Generally, when ambient temperatures go up much over 25 degrees celsius (77 degrees fahrenheit), the efficiency of the panels start to drop.

    Thanks to the low temperatures and all-day-long sun, I am told that solar panels at McMurdo Station close to the South Pole perform brilliantly during the summer!


What is panel generation factor and how is it determined. On the LEONICS website to provide guidance but fail to explain in detail where the panel generation factor for thailand of 3.43 comes from and how it is determined.
     Nigel Pontac, October 22, 2014

    I am not sure what Leonics means by 'panel generation factor', but I would imagine that it is based on the average solar insolation figures for your area. If I am right, it would mean that you multiply the watt-peak rating of the solar panel by the 'panel generation factor' to give you an indication of how much energy you could generate in one day.

    You will get a much more accurate figure using the solar calculators on this web site. Look at http://www.solarelectricityhandbook.com/solar-irradiance.html, enter your information and you will get the same information, broken down by your location and solar panel angle, for every month of the year.


I ahve a 7kw solar array and a Delta 6.6 TL inverter, I'm not sure if this has been brought up before because a lot of solar panel owner usually care about the power they harvest or generates. My question is about my inverter, according to my owners manual, my unit during ght mode it should only use approx 1 watt, but when I hook up my amp meter on the disconnect between the inverter and my utility panel my meter reads 1.5 amps, this is the reading between a Fluke and an Extech amp meter, both are a very reliable and accurate meter as far as I know. When I talked to delta people, first he told me that this is not normal, after a week he said this is normal, looks like I have a load of 300 watts on my inverter, now I'am confused because this is bothering me too much, can you please help me if the unit should draw 1.5 amps during night mode or I need to argue with my installaer, any help is greatly appreciated.
     Rusty Santos, October 22, 2014

    You will have a drain on your inverter. If the inverter is idle, I would expect a drain of 1-20 watts.

    If your inverter is in use, then there will be a greater level of inefficiency. 300 watts represents around 5% of the power output of the inverter, which is around the right sort of ballpark.


hi i have purchased ur book. thank you. i am building a off grid 80m (4m wide by 20m long) square house soon. I plan to have a diesal generaator as back up. I need help to plan the system. Im thinking 24 volt may be best with an invertor and run 240volt appliance and lighting. I will use gas for cooking and hot water. Appliiances i neeed are fridge, freezer maybe, kithcen appliance, tv dvd stereo, charge abd use laptop, washing machine. The generator may charge battery and even run things like washing machine i guess? Can you help tell me what sort of system to run. I am in NZ. cheers Stuart
     stuart murray, October 23, 2014

    Thanks for buying the book. I don't know your exact power drain, but my gut instinct would be to set everything up to run at 48 volts rather than 24v. Some of your appliances are fairly high drain and a 48 volt system will cope with that far better than a 24v.

    If you haven't already done so, do the 'Off Grid Solar Analysis' questionnaire from this website (http://www.solarelectricityhandbook.com/solar-irradiance.html), which will give you more idea of what is involved.


Hi. I have a house in Spain thats off grid. I plan to install solar panels but as a temporary measure is it feasible to use a generator to charge the battery pack until I manage to install the panels themselves. In other words I will have the batteries and inverter in place before I install the panels. The idea would be to connect a heavy duty 12v battery charger to my generator and use the output to charge the batteries.
Bought your book, 1st class. The calculator is very useful. As you say, the first go came out very expensive, but with some tweeking it is now viable. Many thanks, Steve
     Steve Dix, October 24, 2014

    Thank you for your comments about the book, Steve. Yes, it is feasible to use a generator to charge up the battery pack. You can get charge controllers that start up the generator automatically once the voltage from the battery pack has dropped.

Hi,
How can i get solar radiation data manual for flat-plate collectors? I am looking for new data which contain 2010 till 2014 yrs information.
Matt
     Matthew, October 25, 2014

    Go to the NASA solar website and look at their latest solar calculators. http://www.esrl.noaa.gov/gmd/grad/solcalc/

I am looking to build a solar system for my RV
require 1 kw WOULD 4*250 WATT PANELS BE BETTER THAN 3* 320 WATT PANELS
Thanks
     roydredge, October 26, 2014

    You would obviously get a slightly higher output from four 250Wp solar panels compared to three 320Wp panels, but to be honest, with an RV, the main thing is to make sure they all fit nicely on the roof! You will need all the panels to be angled the same way. So long as you can do that, there is no real benefit or disadvantage from different sizes of panel.

I had a 1.85kWp solar system installed 4 years ago and it is averaging 1760kWh per year compared with the quoted expectation of 1623kWh. Last June I had a 2.04kWp system installed on the same roof. To date the new system has generated 708.5kWh whereas the old system in the same period generated 822.7kWh. Both systems use the same Suntech panels. Would you suspect that there is something wrong with the 2.04 kWp installation? If so what is the likely cause?
Many thanks for your advice.
Derek Morgan
     Derek Morgan, October 26, 2014

    That does sound like there is a problem somewhere. Unfortunately, trouble shooting it is not going to be easy. It could be a faulty cable somewhere in the system or a rogue solar panel that is pulling down the production of the array. You will need to check the resistance of each panel and each cable to see if you can find any anomalies.

i have connected 2 x 50 watts solar panels to a 24v system, with 2 x 12v batteries.
but i need to know what size (Amps) of a regulator do i need.
     Bennette, October 27, 2014

    You will need a 3 amp regulator ( 50 watts divided by 24 volts = 2.08 amps. Round up to the next whole number = 3 amp regulator).

How does a solar panel know what voltage it is? For example, a panel is 12 volts dc--how is that voltage established?
     Annie, October 29, 2014

    Solar cells within a panel, are typically around 3 volts each. They are wired up in series within the panel to create a higher voltage. So, for example, a 12v solar panel will be made up a of string of 4 cells, whilst 24v solar panels will be made up of strings of eight cells.

We are planning a grid tied solar power system but our load consist of motors that are turned on and off quickly, like elevators or compressing machines. Would it be advisable to use solar to lower our electricity bill? You know, since one minute we are using solar, then selling excess next. Or is solar better off used for constant load application like lights or machines that uses inverter technology?
     Robert, October 30, 2014

    Most inverters struggle with sudden changes of loads, and this might cause a problem for you. Inverters tend to prefer constant loads or occasional sudden changes.

1.Why do you think solar cells are not used as our main source of electricity in South Africa?
2.What should we do to make people more waare os solar cells and their advantages above other electricity sources?
     kholeka, October 31, 2014

    Prices for solar have been dropping dramatically for the past six to eight years. It is only now that solar is becoming affordable enough to be worthwhile.

    Solar is a terrific way of providing electricity to remote villages that currently have no electricity, or who do have electricity but have an unreliable supply. I've been involved in a project in Ethiopia, creating a solar power station that can provide power to an entire village. This has been very successful in the main, the biggest problem has been security and theft: people steal the batteries.

    What will make people more aware of solar is the availability of cheap, solar power units that can provide a useful amount of electricity at a price people or villages can afford to pay. Once the right unit is available commercially, you will start seeing solar being taken up in a much larger way. I personally think that we'll see the commercials for this start to work in the next year to eighteen months.


can i produce a solar panel from local stones and some plant extracts? and how? or how can i make a solar panel apart from using some solder?
     muhwezi derrick, November 2, 2014

    No, you cannot make a solar panel from stones and plant extracts. I would strongly recommend you do not make your own solar panel: they are very difficult to build properly and safely and the cost savings are virtually non-existent. You can buy professionally built panels for about the same price as buying the components. The individual solar cells that you can sometimes buy tend to be the factory rejects.

My problem is I have two battery together
The battery have power 12 volit but no
Power comming out .thanks
     kent, November 6, 2014

    Have you checked each battery with a voltmeter? A fully charged battery should read around 13 volts, whilst a flat battery will read around 10.5 volts. Anything less than 10.5 volts probably means your battery is dead.

hello, my question is that how you calculated the vertical/tilt angles for different regions? whats the formula for that? thanks
     amina rehman, November 7, 2014

    The tilt angle is based on the angle of the sun. If you know your latitude, you can calculate an average sun angle by using the following calculation:

    90-your latitude = optimum fixed year round angle

    This angle is the optimum tilt for fixed solar panels for all-year-round power generation.

    The angle of the sun changes throughout the year at different seasons. Each month of the year, the angle of the sun changes by 7.8 degrees - higher in the summer and lower in the winter.


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