Hello I have at spa/hot tub which holds approx. 1000ltrs water just wondering if you think it viable to incorporate a heater to the system to keep water temperature at a set temperature . the system has a 1.5kw heater witch switches on and off automatically when temperature drops 1 degree . full system running consumes 2.5kw (pumps and lights etc. ). Rather than having a 1.5kw heater switching on and off when needed I thought a smaller heater running continuously from free power might be worth doing even if it only helps a little. Any help or suggestions would be most welcome. Thanks for your time, Steve.
     Stephen Mellenthin, August 2, 2009

Solar power can definately help you here... but I would not recommend solar electricity: you would be better off investigating solar hot water systems.

Photovoltaic panels (which generate electricity from sunlight) tend to be between 6% and 15% efficient whereas solar hot water systems can be up to 70% efficient and tend to be cheaper to buy as well - at least in DIY form, especially if you spend some time shopping around for the best prices.

A solar hot water system incorporating a thermal switch should go a long way towards reducing your energy consumption. Exactly how big your system would need to be would depend on a number of factors - specifically whether your spa is indoors or outdoors; what months of the year you want to use your spa; where abouts in the world you are based.

Meanwhile, you can reduce your current electrical consumption by using energy saving lighting - I recently saw a swimming pool lit by LEDs which looked stunning and are extremely energy efficient.

Dear Mr. Michael Boxwell
Many thanks for the good book, but i have one question, which is in page 15 and 16. You wrote that when connecting in series, we add the voltages of panel together and add the power( in watts)of each panel together you calculate the max. amount of power and voltage the solar will generate, and in page 15 you wrote that 4 panels, each on have 12V and power 20W and when connect in series it will be 48V, 80W array. I think in this case, we have to connect in parallel with another 4 panels with the same V and W to get 48V and 80W.
Best regard
     Rasool Ali, August 4, 2009

Thanks for the comments about the book.

With regards to your question, when you connect solar panels in series, both the voltage and the power increase, whilst the current remains the same. When you connect solar panels in parallel, the power and the current increase, whilst the voltage remains the same.

Let me explain another way, using the example of a 12v 12w solar panel (I'm using 12w because this equals 1 amp at 12v, which makes the maths easier).

If you take one 12v 12w panel, your solar panel provides 1 amp of current at 12 volts. If you take four 12v 12w panels and connect them in series, the power and the voltage is multiplied by four - so you have 48v at 48w, but your current remains the same - 1 amp.

If you then take four 12v 12w panels and connect them in parallel, the power and the current is multiplied by four - so you have 12v at 4 amps, but your voltage remains the same - 12v.

I hope this answers your question.

Is it possible to incorporate PV panels into a south facing conservatory roof?
     Michael Churchman, September 2, 2009

Yes it is possible, but of course that will cut down on the amount of sunlight shining into your conservatory roof.

It also depends on the amount of panels you plan to fit to your roof. A large panel weighs in the region of 18kg and so there may be weight limits if you wish to fit lots of panels.

To secure the panels to the conservatory roof, you would probably be best to bond them to the roof although it may be possible to have special mounts fabricated for the purpose.

Your best bet would be to choose which solar panels you want to work with, get the physical specifications of the panels (height, width, depth and weight) and speak to your conservatory supplier to see what they recommend.

Is there an inexpensive way I can heat my two 16-gallon water tubs for my horses using solar?
     barb henderson, September 5, 2009

Yes there is, but I wouldn't recommend solar electric for heating water.

Instead, I'd recommend a solar hot water system. Depending on what your exact requirements are will depend on the best solution, but if you want to keep to a budget I'd either recommend a simple swimming pool solar heater (typically available on eBay from around £100/$150) or build your own from plans freely available on the web (start at www.instructables.com).

Just wanted to say thanks for your website. I just used your Project Analysis report and it really is excellent. I just wanted a rough guide to see if a potential project was feasible and approximate costs and the report did just that, plus provided some extra tips. If we go ahead with a solar installation, I will definitely buy your book.
One comment, any chance of adding more countries to the Project Analysis? Our planned project will be in Spain, so I had to find the Latitude for our area and then find a place in the USA at the same latitude. Which also meant that the prices given in the report were in US dollars instead of pounds.
thanks again, Rob
ps I found your site through A1 Business Forum.
     Rob, September 22, 2009

Dear Rob

Thanks for your comments. the publishers are adding new countries to the project analysis tool at the moment: by Christmas we should be covering most of Europe as well as India, the Middle East and parts of Africa.

We will also be providing prices in a number of other currencies as well.

Best Regards

Michael

What do you think about feed-in tarrifs?
     John Newman, September 26, 2009

Now there is a big question. How long have you got?

I question what the Government hope to achieve with feed in tarrifs in terms of overall carbon reduction. I also feel that with the proposals as they stand, the 'early adopters' who have already installed solar stand to loose significantly, which is unjust.

However, from the model seen in countries like Germany and Spain, it is clear that a feed in tarrif this scheme will encourage the short term take up of solar for grid-tie applications. Whether that is the best application for solar depends on a number of factors, such as geographic location and how the local electricity is generated on the national grid.

Personally, I believe the plan is flawed and a better solution would have been to boost the renewable obligation certification scheme (ROC) by improving the funds available and reducing the paperwork and administration for solar home owners to go through.

This would also have been of much greater benefit for off-grid solar systems, which have a much greater potential to reduce carbon emissions over grid-tie systems.

Mr Boxwell,
I'm working on a school project for which I plan to design a solar photovoltaic system to power a small boat (this is one the projects that you talk about on Apendix E of your book). Do you have any additional information on this type of project? Any links, articles, etc would be helpful. I have found some internet sites that have some information on these type of projects but the info is very superficial and does not provide any tecnical details on the design.
Thanks.
Julio Hernandez
     Julio Hernandez, October 2, 2009

My little boat is a small inflatable with an electric outboard motor. The motor is from a company called Minn Kota (other brands are Shakespeare and E-Thrust). I've had it for a number of years and have found it to be a very good little setup for inland waterways (lakes and rivers).

The outboard is a 12v 100w motor. I have an 85 amp 12v leisure battery and charge it using a 20w solar array. This configuration allows me around eight hours of continuous use on a single battery charge, which is far more than I need. The 20w solar array is a bit too small - from a flat battery it would take almost two weeks to fully charge the batteries - but because I don't use the boat that often, this isn't a problem.

Because I only have an inflatable boat, the solar panels aren't actually mounted to the boat itself and I charge the batteries up when the boat is moored rather than all of the time.

All of the other solar boats that I have looked at in detail use a very similar setup to mine - outboard motor, large leisure battery and a small solar panel (plus solar charge controller and battery cut-off switch). You can also add a 12v battery charge gauge if you wish - you can find these easily online or at car accessory outlets.

The total cost of my setup (electric motor, battery, solar charge controller and solar panels) has been comparable to the cost of a petrol-powered outboard motor on its own. For that I have a virtually silent powered boat with no virtually no running costs.

I have no experience of converting a petrol outboard engine to electric power, nor do I have any experience of inboard electric boats. If you are specifically after information like that, I would recommend that you visit the Electric Boat Association web site at http://www.electric-boat-association.org.uk

Mr. Boxwell
Thank you for your prompt response to my previous question. Your answer was very helpful. As a follow up question, I was wondering how the motor speed is controlled? Does the motor you use have its own power electronics to control the speed?
Thanks.
Julio Hernandez
     Julio Hernandez, October 2, 2009

With the electric outboard motor, there is a speed controller built into the outboard motor itself. If you were planning to build your own electric boat from raw components you would need to purchase your own motor controller, along with a potentiometer to work as a throttle and a three way switch to allow you to select forward, reverse or neutral.

The best known make for motor controllers is Curtis Instruments (http://www.CurtisInst.com) and they can supply the motor controllers, the instruments and all the ancillary components you would require. You will require a different type of controller depending on whether you buy a brushed motor ('DC motor') or a brushless motor ('AC motor') - for cost and simplicity, you probably want to stick with a brushed motor design if this is your first electric vehicle.

If cost is an issue, the cheapest way to get the electrical equipment you need would be to buy a second hand electric scooter from eBay - that will give you everything you would need except a solar panel and charge controller: batteries, mains charger, controller, motor and ancillary components.

I am planning a grid tie system/small battery back up system, I have come across some Suntech 200w 18v panels, do you see any problems using 18v panels?
Thanks

     Paul, October 19, 2009

No, there will not be any trouble using 18v solar panels. In order to charge a 12v battery, you need a higher voltage going into the battery in order to charge it up. 18v is fine, so long as you have a charge controller to stop the batteries from being overcharged.

With regards to your charge controller, the most efficient controllers are MPPT (Maximum Power Point Tracker) controllers which will reduce the voltage coming from the panel going into the battery without reducing the wattage. Other controllers will reduce the voltage and truncate the wattage, which in effect means you are likely to loose around 25% efficiency from the panel.

HOw do you calculate the total irradiance foe total solar spectra? i need to know the basic calculations for energy exoposed to object
     Prashant Gharal, October 20, 2009

You can find out all this information on the NASA web site. Start here: http://edmall.gsfc.nasa.gov/inv99Project.Site/Pages/science-briefs/ed-stickler/ed-irradiance.html

What is your advice regarding using a solar panel INSIDE a caravan while on a storage site.
     Mrs Kelly Henderson, October 27, 2009

I do this with my caravan! It depends on what you want to achieve, but if you just want to keep the battery topped up (i.e. not recharging it from being flat) between uses, a solar panel will work reasonably well, so long as it is left in a south facing window and the panel is not completely shaded.

I've got a 10w solar panel for this purpose (its around 30cm square) which cost me £35 on Amazon. It's small enough to prop up inside the window and big enough to provide a reasonable current - even during the winter months - to make it worthwhile having.

I would avoid the very small panels (1.5 - 3 watt panels) for this purpose however as they simply aren't big enough to do anything worthwhile.

If you want to do something a little more ambitious - like recharge the batteries from flat between uses - you would probably be better off fitting a larger solar panel to the roof of the caravan and installing a charge controller to ensure the batteries never get overcharged.

Hi Mike,
I just got your book today I bought last week through Amazon.com. Great piece of work and easy to read. I will probably ask more questions in the future. For now, could you please provide solar irradiance in Nigeria (all states) and Cameroon (all main cities? Why you did not cover many countries in Africa?
Great job,
Alain
     Dr. Alain Nkoyock, November 2, 2009

Thank you for your comments. I am adding new countries all the time - around 10 countries a month. I will update the web site with the solar irradiance figures for Nigeria and Cameroon in the next week. My intention is to cover the whole of Africa, but this will take a little time to achieve!

Hi Michael -
I came across your website after hearing about your book on amazon.com. I intend to order a copy next payday!
I have been to other websites that claim you can construct your own solar panels from materials ready available at local hardware stores. Is this true? If yes, do you address it in the book?
Thanks.
Bob
     Bob Jewell, November 6, 2009

Thanks for your message. I know the web sites you refer to - avoid them. Visit www.diysolar.com and then ask whether the risks associated with home made solar panels are worth taking.

Professionally built solar panels are dropping rapidly in price at the moment. You aren't going to save any money by building your own.

You cannot build a solar panel at home to anywhere near the same quality of a professionally manufactured unit. At best your home made panel won't provide much power and will degrade rapidly. At worst it could end up being a fire hazard.

hi, michael I have a project that I could use your advice on, i have a 20x20 building
it does not have a hot water heater but it does have a small window unit and 2, 8foot for resident lights and it also has two plug-ins on each wall. my deep well pomp is a one horse motor.075kw that I would like to run also.
My question is, what type of inverter should I use? do they make inverter's four 220 outlets. In this building I have had the power company to cut my power off. I would like to run pv and also win power. This building is my office
so I would like enough power to operate this small build. my last KWH USAGE WAS 600
And also thank you for your book it is a good one, as you can tail I am just an amateur at this thank you and God bless.
     larry, November 7, 2009

You can get 220v inverters without a problem - there are lots of different makes and models. I'd recommend a pure sine wave inverter and my personal recommendation for make would be 'Sunny Boy' - they're good quality, reliable units that won't let you down.

You will need to work out your wattage use on a daily basis, as described in my 'Scoping the Project' chapter. This will give you a much better idea of what you will need. At a guess I would suggest that if you used 600kWh of electricity in your last quarter you are going to need to look at reducing this load first.

I am doing an assignmint at college on, reducing the average energy bill of a household. I have chosen solar power and have to go into great detail about what solar power is, how it works, optimum angles, light intensity at my longditude etc. two other solutions were required, i chose wind and solar-wind hybrid. any insight you could give on household solar power would be greatly appreciated. thanks
     Ryan Daly, November 10, 2009

You've got yourself a big subjecct there! The first thing about reducing the average energy of a household is making sure you do the obvious things first - low energy lighting, low energy appliances, making sure everything is switched off if you're not using it, switching off equipment at the wall socket and not leaving them on standby.

Once you've done that, you then need to look at house insulation - making sure your not loosing heat through windows, doors, walls and the roof.

Then you need to look at your heating and hot water. You want the most efficient heating system available in order to keep your heating costs low. A solar hot water can help here, heating the water up that can be used for washing and - in some cases - for household heating as well (especially with underfloor heating systems, where excessively high water temperatures are not required).

Finally, you can look at solar electricity to generate some or all of your electrical energy.

Why do it all in that order? Quite simply, although the insulation and investigating the electrical usage are boring, its where you can make the greatest savings - an average household can save 30% of their bill by doing the simple stuff, and quite often for a very modest amount of money. All those savings can go towards paying for your solar equipment later on.

I'd suggest you use the online calculators on this site, and the solar project analysis tool to help you get some of the core information you are after.

Good luck with your assignment.

I have a photovoltaic system with battery charging and backup that uses TRAC inverters. The system is far too complicated for me to understand or deal with. When I have blown circuits during holiday festivities the battery backup is a failure and requires "resetting" which I, to this day, don't understand. I have no way of knowing how much my system produces and everyone, starting with the installer, says "well, you produced the difference between how much you used last year and this year". My system was inoperable for a 3-6 month period due to fried junction box on the roof that had filled with water. I had no idea it wasn't producing and no measurable way to know. What's the big mystery. Why can't I have a flow meter, just like the one coming IN from the grid, installed coming IN from the solar panels, so that I can see the volume of production. This system is 7 years old and I've spoken with 3 solar installers who all blow me off similarly. I'm a terrible salesman for the solar industry and I'm constantly asked "how's your system working out?" I'd love to be able to tell them. Can you answer this question?
     charles young, November 10, 2009

First of all, congratulations on taking the step seven years ago on installing a solar electric system. I'm sorry to hear you've had problems with it - it does sound like you need somebody to have a look at your configuration. It does not sound right if your battery backup system needs resetting every time you need to rely on it, but without knowing the intracies of your system, it is hard to comment in more detail.

With regards to the information you can get from your system, the technology has moved on in the past few years and most particularly it has moved on in terms of the information you get from the systems. There are two answers - the expensive one is to replace your inverter with a newer model. This will give you all the information you could ever want, but at a cost of a new inverter.

If it were my money though, I'd go for a much cheaper solution and fit a standard utility electricity meter between your inverter and your load. This will give you a flow reading from your photovoltaic system into your home. Nice and simple to install and it will give you the basic information you want, plus change from $100. Some battery powered meters don't even need you to cut the wire, but clamp around it, which makes it really simple to install.

You will be able to buy a suitable meter from your local electrical hardware store, or you can buy online from companies like http://www.kwhmeters.com.

Are solar panels better than wind turbines
     Anonymous, November 11, 2009

I answer this in my article 'Wind Turbines vs Solar Panels', which you can read at http://www.solarelectricityhandbook.com/Solar-Articles/wind-turbines.html.

Unfortunately, there is no clear answer to the question - wind turbines can work extremely well if you have the perfect site for them - if you have a site with higher than average wind speeds, a clear air flow with no obstructions and no turbulance, wind turbines can be hard to beat.

The problem is, very few people have the ideal site for a wind turbine, and if you don't have a good site for a wind turbine, you are going to be very disappointed with the performance of your wind system.

How much is it to get solar panels?

     autumn, November 11, 2009

Prices are coming down all the time - a 5w solar panel can cost around $30 and capacities and prices go up from there.

There is a Solar Project Analysis tool on the web site that can give you some indicative prices for your project based on how much power you wish to generate. I'd suggest you work out what power you need, then fill in the questionnaire on the project analysis web page. That should give you a reasonable idea of what your system will cost you.

Hi Michael,
I have not got a question as yet but know I will have soon but I just wanted to congratulate you on the best book I have ever read! Your style is so easy to understand so practical and so honest and as a heating engineer with a reasonable knowledge of solar for hot water and a good basic knowledge of electricity you are not patronising. Brilliant well done.
I lied about no questions, can you write a book, like this one, about wind turbines and other forms of power generation please.
Best wishes,
Martin Downes

     Martin Downes, November 12, 2009

Thank you Martin, I really appreciate your message - I've had a tough day today and your comments have really cheered me up!

A book on wind turbines is on the cards... but that is going to be a little while away yet: my next book is on electric cars, and that one is coming out early next year.

how many kilowatt hours per month with 30 200 watt sanyo panels with 3 2500 watts sma inverters in las Vegas with ajustment in tilt thank you
     Roger Cooley, November 14, 2009

That is quite some setup! Assuming you have a site without any shading issues, I would expect an average daily figure of around 17½kWh +/- 20% at this time of year. That will drop to around 15kWh a day in December.

During the height of summer, I'd expect you'd be generating around 37-42kWh +/- 20% a day, although because of the intense heat you get in the summer, you'll find you'll generate more power on cooler days than on the very hottest.

Hello Michael, thanks for writing the book, it's got a lot of useful advice in it and is written in a accessible style - Hooray!
My dilemma is two-fold; I'd like the government grant to help pay for the solar panels, so that rules out installing it myself (for a system just over 1kw, which is all I have room for, the grant is a sizeable percentage of the cost) and secondly I'd like a back up supply in case of a power failure. Page 137-8 (Appendix E) describes a back up system but it doesn't spell out if this works with a grid-tie inverter.
As a follow on to the second question, I have heard that in the US inverters exist that can send power back to the grid but which don't shut down when there is a power cut - I presume they have an isolator switch which stops the flow of electricity out of the house - can an isolator of some sort be fitted to a UK-style grid-tie system at a later date, if the system in Appendix E doesn't work with a grid tie inverter?
     Gary Miller, November 18, 2009

Dear Gary

Thanks for the comments about the book. You are right about the current grant system in the UK - you're going to have to get a professional installation in order to get access to these funds.

With regards to a power backup system, there are grid-tie systems that now include a power backup system as well: in effect, these work like uninterruptable power supplies (UPS's) so that power to the building continues even if there is a mains power failure.

You are also right about the US inverters that do not shut down when there is a power cut. As far as I am aware (and I could be wrong on this count), there is no such inverter yet available in the UK. Of course, a manual isolator could be fitted, but getting approval for this for a grid tie installation could be tricky.

Hello Michael,
I got your book for Christmas and it was the first thing I read.
Examples and calculations are excellent as is the total book & website content. Could not recommend it highly enough.
Just a quick question regarding the feed in tariffs.
We are being offered (relatively) high tariffs but the system compels you to use a Microgeneration Certification Scheme approved installer.
This means that you have to pay 'top dollar' for the installation, parts etc. with no choice of components at all. This outweighs most of the cost benefits of installing solar PV in the first place and really puts back the payback period.
Do you know whether any of the schemes are being expanded to allow inclusion of DIY systems? These are just as valid, especially as the final mains connection has to be done by a qualified electrician.
Thanks a lot.
Best Regards
Mike Norton
     Mike Norton, January 7, 2010

Dear Mike

Thanks for the comments about the book. It is much appreciated.

Typical for the UK, the Microgeneratoin Certification Scheme insists that you use registered installers. Like the solar hot water systems this then means that instead of having a solar hot water system installed for under £1000, it costs you three to four times as much.

The old scheme that they have phased out allowed for DIY installation, and worked extremely well. The new scheme that is now coming in penalises people who have already put in solar power and dramatically increases the cost for installing solar in the UK: I suspect the scheme will actually mean less solar power is installed in the UK rather than more.

Solar electricity is a very simple form of power generation that is easy to install, so long as you follow some basic rules. Unfortunately, the bureaucrats have got it badly wrong, and as ever, the rest of us have to suffer.

However, there is an answer. I think we'll see a lot more 'small scale' solar in housing from ingenious DIYers - powering the lighting system in a home, for instance, is a straightforward thing to do and can be done entirely independently of the main power in your home. It depends what you want to achieve - and how much you want to spend - but my advice would probably be to start with a small stand-alone system and then build that up over a period of a few years.

In my small off-grid system, I would like to provide the ability to charge the battery bank from the grid during prolonged cloudy periods. Is there a way to automatically do this without damage to the Morningstar MPPT controller?
     Emery Mitchamore, January 7, 2010

There are controllers around that will allow you to do this automatically - but they aren't cheap.

I don't know the Morningstar MPPT controller so I am not entirely sure what would be the best and most cost effective way of achieving this. I'd recommend talking to MorningStar to see what they suggest.

Two options come to mind - both of which would require further investigation. The first is to install a small transformer to bring mains voltage down to an appropriate voltage and feed the power into the system as if it were a solar array. Check with MorningStar before you go this way.

You would still need to manually switch the transformer on and off - you could partially automate it using a timer switch - but making a fully automatic system could be very complex - unless you are handy with electronics.

The second alternative would be to charge the batteries directly when they run low. Again, check with MorningStar to see whether you would need to disconnect the controller if you went this route.

Creating a manual transfer switch would be very straight forward, but an automatic transfer switch would be much more difficult: you would need to have another controller that is measuring the charge from the batteries, measuring the amount of power coming from the solar array and then switching across to the mains supply if the solar power and the batteries are both low, and then switching back again afterwards. If you're handy with electronics, it could easily be done, but otherwise I think you would struggle.

So sorry - I can't give you a full and complete answer, but I hope that will give you something to go on.

Thanks for the great book (2010 edition). I need to build some grid fallback systems for a construction site. I was thinking about using an inverter/charger. As you probably know, these act like UPS systems where AC is the priority source. I was thinking about using an automatic switch so turn off and on the AC supply to the inverter. If the batteries deplete the Inverter/Charger turns on, charges the batteries and supplies grid power. If the sun comes out then the panels can aid the charge. Once the batteries have reached their full charge voltage (or some set voltage you have selected) the switch disconnects the grid source. I want to know if there is such a switch? And where do I find one? I think they are like a generator auto start switch but I need one used for grid source instead. Appreciate any insite or ideas you may have.
     Dean Sala, January 11, 2010

There are solar controllers available that will do exactly what you want. Alternatively, all you are actually after is a relay between the mains supply and the battery charger, which switches on and off depending on whether your solar inverter is running or not.

There is an excellent introduction to relays here: http://www.reuk.co.uk/Relays-and-Renewable-Energy.htm

Depending on how your system works and how much electricity you need, your other alternative may be to fit a timer to the charge controller so that it only charges at night. This could be done either in conjunction with a relay or separately.

The benefit of this is that you can then use cheap rate electricity (if you have a night tariff) and the carbon footprint of the National Grid at night is much lower than it is during the daytime. If you are based in the UK, you can actually monitor the carbon footprint of the National Grid in real time: http://www.owningelectriccar.com/national-grid-electric.html

Hi Michael,
Can I ask - have you investigated the use of parabolic mirrors to focus light sources onto solar panels?
If so, can you comment as to whether this increases their power generation?
Thanks!
     Nathaniel Trevivian, January 12, 2010

Yes I have, and yes it works... but proceed with caution.

I have only experimented with parabolic mirrors for fun and never in a live installation. The issue is that although it increases the intensity of the light and thereby increases the power generation, it can also burn the solar panels and destroy them if you end up with too much intensity.

I have experimented with parabolic mirrors in the winter months, and I have also experimented with them at night (to see how much power I could get from the moon!) and they can be quite fun, but I would not recommend them for a serious application.

Dear Michael,
Many thanks for the great book.
I have a quick question about inverter sizing for a grid-tied system. How close to the maximum power rating of an inverter is it advisable to go ? For example an SMA Sunny Boy 3000 has a max DC power-rating of 3,200W (http://www.sma.de/en/products/solar-inverters/sunny-boy/sunny-boy-1100-1200-1700-2500-3000.html), could I install panels with a nominal power rating of 3.2kWp (or even higher given that actual power generation is never likely to hit this particularly in the UK), or is it advisable to leave a 'safety margin' for the inverter to ensure maximum relaibility/lifespan - e.g only install a maximum of 3kWp of panels with a 3200W rated inverter ?
Many thanks
Bill
     Bill, January 13, 2010

Dear Bill,

Thanks for the compliment.

Inverters are funny things. They're not so fussed about the power coming into them as they are the power going out of them.

So you'll wear out an inverter quicker by using all 3.2kW of electricity than you will 'over feeding' the inverter in the first place.

You really want to match your inverter to your solar array as well as you possibly can. The reason for going for a bigger inverter than your array can handle is really down to whether you can forsee wanting to expand your array in the future.

As a rough rule of thumb, you should be aiming to use no more than 50-70% of your inverter capacity as 'constant' power - so your 3.2kW should be a peak rather than a constant load. Do that, and your inverter should last you a very long time.

Q.1 I would like to install a solar panel on my RV unit(recreational vehicle); Do you have some detailed instructions how that could be done specifically on an RV.
Q.2 I have read somewhere that the "Peel and Stick" solar panels are more efficient than glass panels, shatterproof, flexible and easy to apply.? What are your thoughts on these flexible panels? And especially how these would work on the roof of an RV?
Thank you,
Alex. Sztogryn
     Alex., January 15, 2010

I have fitted solar panels to my caravan and it is very easy: use an exterior grade bond such as mastic to fix the panel onto the roof of the RV making sure you seal all the way around the panel.

If you drill a hole in the roof to feed the cables through, make sure you also seal this with the same method.

As an aside, make sure the panel you choose uses toughened glass. The vast majority of them do, but there are a few of the cheaper panels that don't.

The peel and stick panels are shatterproof, flexible and easy to apply, but they are not as efficient as the glass panels. The panels I have come across have all been amorphous panels providing around 5% efficiency. They are great at what they do - they are widely used by river boats because you can even walk on them - but they are not cheap. For an RV, I'd recommend a glass covered panel every time.

Dear Michael,
I just read you book (2010 edition). I found it really good.
I am in Buenos Aires, Argentina.
I started a solar company three months ago and I need to find information about solar insolation in my region (Argentina, Uruguay, Bolivia, Peru, etc). I couldn't find any information of those countries in your website.
Could you help me with this ?
Best Regards,
Maxi
     Maxi Postigo, January 19, 2010

Of course I can. I shall update the solar insolation tables and solar angle calculators with information for Argentina, Uruguay, Bolivia, Peru and Costa Rica this afternoon.

If you check the web site in two hours time, you should have all the information you need.

All the best,

Michael

Dear Michael,
I am just reading your book and i wanted to simulate with your online calculator. I am from italy and there is not italy between the countries for irradiance and tilt calculations.
Is it possible to add?
thanks
     giulia suriano, January 22, 2010

My apologies - I cannot think how Italy has been missed. I have got the data for Italy and will update the web site in the next half hour.

We are thinking about installing rooftop solar wall panels in order to prewarm outside air for a set of commercial air handlers. The installation requires multiple rows of solar heat panels and ducting. The panels in each row are approximately 3 ft high. We do not want the panels to steal sunshine from each other. Would you please tell me the mean sun angle for Seattle Washington so I can properly space the rows for optimal performance?
Thank you for your time and I look forward to your reply.
Regards,
John Payne
     John Payne, January 24, 2010

Thanks for your e-mail. 'Optimal performance' will vary at different points throughout the year. Are you looking to provide optimal performance during the winter months, the summer months or an average that will work throughout the year?

If you want to achieve optimal winter performance, I would suggest an angle of 26 degrees from vertical. For optimal summer performance I would suggest an angle of 58 degrees and for all year round performance I would suggest an angle of 42 degrees.

Can you tell me what to spend for annual maintenance? Should I budget 5% of the system cost? What is likely to break? Other than break/fix, are there additional maintenance tasks that need to be done?
     John Parlapiano, January 28, 2010

Annual maintenance is very cheap unless something actually fails. Excluding failures, budget $10 a year and an hour of your time every three months or so for regular maintenance. That maintenance consists of checking electrical connections, checking the batteries and topping up with water (if using 'wet' batteries) and making sure the solar panels themselves are clean and in good condition.

The most likely thing to fail is the battery pack, although it is not unknown for controllers or inverters to break down.

If you have a battery based system, you will need to replace the batteries at some point during the lifetime of the system: how long the batteries last will depend on your system setup - see the section on Batteries in the chapter on Component Selection and Costing for more details. As a rough rule of thumb, I'd suggest you need to budget for a complete change of batteries every four years if you're using cheap batteries or every seven years if you're using good quality batteries.

how much energy does an average home 1500 sqft require? in kwh
my bill says 856kwh in this period. do i average that by 30 then know the actual daily demand and from there determine the equipment sizes
     geo, January 30, 2010

Yes - that is absolutely right. Devide the number of units of power used by the number of days.

In the UK, the average home uses 0.8kWh of electricity each hour. In the US, the average home uses 1.2kWh of electricity each hour. Of course, these figures will depend on how you heat (and/or cool) your home, how many people live in your home and so on.

To get the best out of solar power, you need to see how you can reduce your demand for power: it is more cost effective to halve your power usage than it is to buy a more expensive solar system.

Hi
Firstly, thanks for the book
I need some advice, and would be grateful if you could help.
I am beginning to design a PV system for a beach hut, which will power fridge, lights etc.
I envisage using a MPPT controller, and a 24v system, which I believe will be more efficient, however the recommendation seems to be to take the DC load from the MPPT. Whilst I would take the 24v fridge load from the MPPT, i would need to take the 12v light load direct from one of the two 12v batteries, would this be OK?
Thanks for your help.
Andrew Britten

     Andrew Britten, January 31, 2010

You would be better off connecting two 12v lights in series rather than powering the lights from one of the batteries. Otherwise you will end up with an unbalanced battery pack which will reduce the lifespan of the batteries.

If you would prefer not to run two lights in series, you can get a voltage converter to drop the voltage from 24v to 12v. These aren't expensive and can be purchased from any electronics shop or truck-stop (most trucks run on 24v and an adaptor to run 12v car accessories in the cab is a popular piece of kit).

Hello Michael i have a quick question for you..i bought your book off of amazon and its a great read so far..i have a photovoltaic installation class coming up monday and your book has helped me prepair...anyways i have the 2010 edition and it says its internet linked..could you send me the URL for the website? or explain how i can use the internet and my book together. thanks mike ttyl
     Hans Van Houten, February 4, 2010

Dear Hans

Thanks for your message. You've found the web site - www.SolarElectricityHandbook.com. The web site has lots of resources which will be useful if you are looking to put together a photovoltaic system:

The 'additional resources' section includes lists of web sites, many of which change too rapidly to be worth putting in the book directly.

There is a news section, which reports on interesting news in the solar sphere and new articles that I write on a regular basis.

The most important part is the Online Calculators. These calculators allow you to look up solar insolation and angles for installations across the world - if I put them in book form there would be over 350 additional pages of information! Finally, the solar project analysis tool allows you to enter your power requirements and have a custom produced 11 page report detailing the configuration and likely cost of a photovoltaic system.

Good luck with your installation class!

Hello there, bought your book and am doing some research on your website. I live in Melbourne Australia and was trying to use your calculator to get an idea of my system requirements. I got unstuck at the insolation figures - Can you change the website so that I can enter my latitude and insolation values if I know them (I do..). At the moment picking the "pre-canned" values for the UK, USA, Canada, India/Sri Lanka, etc doesn't help me at all. Thanks kindly. Matt
     Matt, February 6, 2010

Dear Matt

Thanks for your e-mail. I shall have a word with the web designers and ensure that Australia is added to all our calculators. I'll do my best to get this sorted as quickly as possible after the weekend.

Mike

I have a remote cabin that gets maybe 2 weeks of use during a year - one month max - in the summer. Usually there is 2+ weeks between <7 day uses giving plenty of time to recharge batteries via solar panels. We currently have propane lights, refridgeration and stove, so running out of power is not the end of the world. I would like to have better lighting and the option of not having to run a gas generator to vacuum, use power tools, etc. It gets extremely cold there during the winter (-30F or more). I did not see in your book how I would calculate the size of a solar array required for a 2 week recharge of battery power that would give me ~7 days of power. Any word of wisdom on things that I need to consider?
     John Simons, February 11, 2010

That is an interesting project you have there. In essence, what you need to do is work out your power requirement on a daily basis when you are on site. You then need to calculate the size of the battery so that you have seven days of reserve in your batteries.

The good news is that you'll need a solar panel approximately one third of the size of the panel you would need if you were using your cabin all the time, which really brings your costs down.

Hi,
I'm looking at installing a solar pv system around 2KW to take advantage of the government feed in tariff and grant, before it disappears. My research leaves me wanting a system I can add to using distributed inverters, like the SolarEdge Inverters. Is there any equivalent system in the UK?
Anthony
     Anthony Sumner, February 13, 2010

I like what I see of the SolarEdge inverter system, although I have to confess I haven't seen one in real life. For larger solar PV installations looks like a great solution. The concern I would have is the cost - the extra efficiencies of the system are countered by the cost of the additional hardware and I'm not currently convinced that the system has an improved payback as a result.

I'd like to be proved wrong though! There has been some clever thinking going into this system and any way of optimising power generation from solar should be encouraged.

Unfortunately the SolarEdge system is not available in the UK and I am not aware of any other system that is available in the UK that does the same thing.

How many solar pv panels would be needed to provide 2.8 killowatts of electricty thank you
     Ian Antonio, February 15, 2010

I need a bit more information before I can answer that! The size of solar array you need will depend on where you live and what months of the year you want to use your system.

If you can tell me where you are based and what months of the year you want power, I'll let you know what size system you will require.

Hi there.
I'd just like to say that your book has been great in setting a few ideas firmly in my mind for my next project. I'm part of an expedition team set for Borneo, and we're planning on using solar power to enable us to use laptops and LED lighting, as well as charging camera equipment.
The section on irradiance simplified things for me and I now think I've got the numbers and the plan right in my head:
4x40w solar panels, should give us 640Wh of energy per day.
6 hours of 50w laptop use, and 6 hours of 20W worth of LED lights should take us to 420Wh of use per day, plus the camera equipment should be less than 50Wh roughly. We'll also have a small generator in case of emergencies or lack of sun.
I'm thinking adding another 40w panel would be enough to account for 10% loss using an AC invertor, plus another 20%(ish) from a charge regulator - and we can always be flexible with our laptop use too if we're using a bit too much.
So if there are any problems with this plan, it'd be great to hear from you! I just want to double and triple check everything. Any help would be appreciated and we'd love to credit you on our website. The blog is ready at www.fxpedition2010.com and soon we'll have another website up that we'll use to give free resources to schools.
Thanks for the great book.
Kind Regards
Dan
     Dan Sargison, February 15, 2010

Wow! What a wonderful project. I've enjoyed looking at your web site.

My concern with the solar side of things is that you are going to spend a lot of your time in the shade out of direct sunlight, which would severely reduce the amount of power you can generate.

In order to give you the best advice, I'd like to find out more about your project - I'll send you an e-mail with my phone number on it in a few minutes so we can discuss your needs in more detail.

Hello,
Thank you for posting the solar irradiance on the website. The solar irradiance fluctuates all year round and therefore solar module efficiency is directly proportional to solar irradiance. However, could you tell us which period these solar irradiance covers?
Thank you very much
Glenn
     Glenn Miniscloux, February 18, 2010

The information on solar irradiance comes from NASA and is based on satellite monitoring. Solar irradiance measurements are taken every three hours, every single day. The figures shown on my web site are based on the average readings over an entire month, in turn averaged over 22 years of readings.

On any one day there will be fluctuations in the amount of irradiance - often as high as 20%. Within an average day, irradiance figures change throughout the day, with the best figures at solar noon.

If you know your latitude and longitude, you can see the underlying data for yourself here: http://eosweb.larc.nasa.gov/cgi-bin/sse/grid.cgi

on the flat roof, can i install collector flat?
     Arun Bapat, February 23, 2010

Yes you can. You will find, however, that you will have significantly less power from your system - most noticeably in winter, spring and fall. In the middle of winter, the difference can be as much as 50%.

To set up solar panels (probably foldable flex panels) to recharge an e-bike battery at 36Volts 10 Ah, what type of controller do I use? Do I need anything else? Is it easy to set up?
     Ellen, February 26, 2010

An ebike solar charger is a great application for a small solar system. There are a couple of ways of carrying this out.

If you are looking for a fixed system - mounted to the roof of a shed, for instance - your best bet would be to have two sets of batteries, so that one battery pack can always be charging whilst the other set is in use.

If you are looking for a system to take with you, you'll find that the solar panels themselves are going to be too bulky - either that, or you'll end up with a very small amount of power generation that will give negligable benefit.

The biggest issue is going to be finding a suitable charge controller that runs at 36v. The majority of controllers run at 12v, 24v or 48v and whilst some 36v controllers do exist, you may have to do some hunting to get one at a good price. MorningStar do an excellent MPPT controller that can handle 36v. However, these are really aimed at bigger systems and may not be cost effective. The Al-Samawa ASG6001SC controller is another option, which is much cheaper but can be difficult to get hold of.

The actual wiring up is simple - you'll need to modify your battery box so you can plug the solar array into it, you'll need to connect three solar panels together in series to give you the voltage you need, and then you run everything through a solar controller so the batteries don't overcharge. With the right equipment to hand, that bit should only take you an hour or so.

A few years ago, a friend of mine who doesn't own a car and uses his 24v bicycle to go everywhere, modified a bicycle trailer to build in a solar charging system into the lid of the cargo box on the trailer. From memory, he had around 80w of solar panels, charging a second set of batteries in the trailer. The combined battery pack gave him a range of about 50 miles and in the height of summer the system could completely recharge the entire pack every day.

Good luck with your project. It sounds fun.

Hi I have just bought your book, very informative.
My question is:- How do you measure a gable roof from the ground to work out how many sq meters are available for mounting PV solar panels using just one side of the gable roof.
John

     John Bate, February 27, 2010

Trigonometry was never my strong point! I cheat and use an online trigonometry calculator - I can hear my old maths teacher tutting at me even now!

There's a good one here: http://www.carbidedepot.com/formulas-trigright.asp

How come the solar angle calculator shows a greater angle from vertical in June than January. Surely the angle from vertical should be less in June as the sun is higher in the sky then ( i.e nearer vertical )? Doesn't seem right to me. Based on United Kingdom, Birmingham.
Cheers, - Nick

     Nick, March 5, 2010

Hello Nick, thanks for your message.

Are you mixing up your horizontals and verticals? In June, the panel needs to be closer to horizontal than vertical, so based on this there is a larger angle from vertical.

The confusion may well be because many solar experts quote the angles based on a horizontal plane rather than vertical.

All the best