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small scale solar/wind power costs

 Poster: A snowHead
Poster: A snowHead
I am examining the prices for powering small electrical equipment using stand alone solar panel/wind power either from a van or at home as back up to central electricity.

As a general rule of thumb, if the small scale system in total costs less than 2x - 2.5x the max solar panel output, then this seems a fair price. This includes a leisure battery, connections, and charge controller as well as the panel. It does not include the installation. (DIY)

So for a 100 watt solar panel, the total system should cost £200-£250 and be good value. Obviously you can pay more for better solar panels, better charge controller, and better battery. Some may improve efficiency by 10%-30% but if the price increases by 50%-100% this is not sensible.

Wind power is bizarre. I have found a wind generator which can be connected you your van, and will generate up to 100 watts. For £350 ? (https://www.marlec.co.uk/wind-power/caravans-and-leisure/?v=79cba1185463 as the example) The only other wind generators I have seen for small scale are up to 400watts and so are massive and too big for a van. Seems these price themselves out of my considerations, even though they might be useful on occassions as a supplement for solar power (eg. at night)

When you scale up from 100w to large scale, the costs do not appear to reduce. One would assume there was economies of scale. However, these seem to be gobbled up by installation costs, and upgrading equipment to more efficiency.

At £200 a 100 watt system would wash its own face in 10-15 years (with unit electricity costs of 10p-15p in todays money)

I would guess the reason is I am considering using obsolete technology, and made in China equipment.

Is this general rule of thumb consistent with your experiences?

ps. I found this, www.ijmer.com/papers/Vol2_Issue6/EF2645874590.pdf, which shows a curve of system wattage with cost in Indian Rupees for wind and solar power in 2012. 5 years later in UK, the cost in UK is about 5x the cost in India at the lower end of the curve. This is for DIY projects, just including materials. I suspect that there may be a markdown for being an trade buyer.

pps. www.vox.com/2016/8/24/12620920/us-solar-power-costs-falling this article suggests large scale utility solar power installation costs of 2x-3x wattage in US dollars in 2015. This suggests my small scale calculation of 2-2.5x wattage in £'s is very reasonable. Although, my figures are for maximum output whereas their figures were for median output. (likely to be very different, so probably worth doubling my figure, or halving theirs to make them comparable). The article at the end, indicates that the US is one of the highest cost places to install solar power. Germany being one of the cheapest in 2015!


Last edited by Poster: A snowHead on Sun 30-04-17 14:48; edited 1 time in total
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 Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
@Bigtipper, I love the idea of having my own wind turbine producing power, but I doubt the numbers stack up. Will a domestic turbine actually last 10-15 years? Will maintenance costs be prohibitive?

Solar, not entirely convinced by this either. Ugly things and they aren't even entertaining to look at. Do they make much financial sense without the subsidies?
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 Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
I can't see wind power on a small scale stacking up, due to the structure costs. (i.e. you need to attach a pole to the back of your van) The rebates tend to offset the costs of installation and cost increase in excess of efficiency. However, these rebates have been reducing around the world and so they become less relevant when you DIY.

Wind power can be noisy, but solar can be hidden from sight. (if you find the right location)



Putting solar panels on your dashboard reduces efficiency as the extra glass reduces efficiency. I put them there to deter theft. (I was not really interested in efficiency at that time) The angle of the solar panel on your dashboard in winter time, is probably about right. I usually parked facing south, so as to maximise solar power. At the latitude I am currently at the optimal angle in winter is 70 degrees with 30 degrees in summer. So the propped up window angle in winter (as in the picture), and flat on the dashboard (maybe propped up to get 30 degrees) in summer. (although the heat would reduce efficiency in summer and probably melt the plastic).

The solar panels in the picture I have recently taken out of the attic. I have tested them, and both are still working. That is 14 years after I bought them. The plastic on the sides have been nibbled by mice, but that was 5-10 years ago as all the mice are dead and burried and will not return to the attic due to the fibreglass insulation.

I have also done some calculations on petrol invertor generators. Even on a marginal cost basis (i.e. the cost of petrol alone without the upfront costs of buying one), the electricity generated costs about 5x -10x per unit cost compared to grid delivered electricity at 10p-15p per unit. These figures do not stack up either, and so I would stick with cheap solar power.
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I have lived off the grid on a sailboat for many years so know my way around both wind and solar.

Unless you are on an exposed coastal site in winter solar is the way to go.

Semi flexible panels tend to have a short life 6 months is not uncommon most fail by 3 years. My rigid Kyocera marine grade panels are 10 years old and still at 95+% of their original capacity.

A good MPPT controller will squeeze an extra 2 - 5 % from your solar. NB most cheap Chinese controllers advertised as being MPPT are not.

If you can tilt the panels to follow the sun then you get more amp hours. The set up shown with the panels on windscreen of the red van is both good and bad. Good because the panels are tilted towards the sun. Bad because wipers are casting shadows over the panels, shadows like this reduce the panel output by 80 - 90 %. Bad because the panels are easily stolen by breaking the side window. Mount them on the roof using security bolts that need a special screwdriver.

If tempted by wind generators be aware that most manufacturers exaggerate the output, exaggerate the reliability [ most need annual rebuilds ] and ignore the noise the damn things produce. An Airmarine X in 25 knots sounds like an old 707 on takeoff power.
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Anyway, snowHeads is much more fun if you do.
I have been testing my old panels (they have been sitting in the dark in the attic for several years now). Yesterday, when there was clear skies and sunshine all day I started testing at 7.30 am two hours after sunrise. I put the panels at 30 degrees facing south (adjusted slightly by 2 degrees for magnetic declination). The open circuit wattage (volts x amps) started close to 0% of the panel wattage (15 watts + 5 watts in parallel) and rose to 102% at 2pm. It then fell to about 95%, and collapsed at 4pm to 10% when the sun went behind a tree. After going around the tree it rose to 56%, but fell again down to the last reading I did at 7pm two hours before sunset when it read about 8% of the panel wattage.

If you calculated the area under the graph of points, you get about 615% of the panel wattage over the whole day. In other words about 125 watts could have been captured and transferred to a battery from a 20 watt solar panel.

From what I understand about MPPT solar controllers is that they can increase efficiency if the voltage delivered is significantly higher than the battery voltage. The voltage in my readings, when the wattage was highest went up to 17.5 volts. At the end of the evening, when the wattage was falling and below 50% of panel wattage, the voltage went up further to almost 20 volts.

If I was to transfer this to a 12 volt battery, an MPPT solar controller would not improve the efficiency much over a standard charge controller (which had little resistence). So it would be a waste of money, unless I was to upgrade, add panels in series (and so increase the voltage), or add some very high voltage panels (250 watts for example tend to go up to 36 volts at times)

Small shadows on my solar panels reduced the efficiency by about 5% of the stated output, or about 20% of actual wattage. (a TV arial cast such a shadow at 10.30 am in the morning and there was a dip in the linearly rising curve)

I had to take the 5 watt solar panel apart, as it initially read zero voltage. On doing this I noticed the soldering had come apart (probably due to me pulling at the wire). I re-soldered the panel before taking all the readings yesterday.

If I was to get a 100 watt solar panel, and it was just as efficient or more efficient than my 15 year old panels, I would have generated 615 watts over the full day. Just a little bit more than half a unit of grid electricity, which would cost 6p-8p. roughly.

It does not seem like much, but that would be enough to watch TV, play on a laptop computer, and have some high efficiency lighting. If the electricity was outaged due to low capacity, I would still have basic power.

I do not think I will need a MPPT charge controller, although a cheap PWM chinese one which says it is MPPT would probably work just as well for my needs.
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Ditch the laptop and get a tablet.

Get some LED lighting.

Get a LCD screen TV OR watch TV on the tablet.

Yes a MPPT controller does not make sense at your level. PWN will do.

I STRONGLY recommend having a second domestic battery and running off that at night. If running off the engine start battery make sure you have jump leads because you will run it flat one night.
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I'm not ready to buy batteries, be that AGM leisure batteries, gel batteries, or sealed or flooded leisure deep cycle batteries yet. I know that gel batteries work better in negative centigrade temperatures, and that AGM batteries are way cheaper and more efficient than my last deep cycle battery. My cheapo system will probably go for AGM leisure battery or two, as gel batteries are about twice the price (without such improvement in efficiency)

Today I tested what many people with campervans do. I laid the panels flat on the ground, and compared the wattage of the panel facing the sun compared to it flat on the ground. I recorded a 22%-24% fall in power from sunfacing to flat on the ground. This is in summer, in winter when the sun is lower, this would be worse!

My conclusion here is that it makes sense to spend at least 20% of the total system on something which allows me to have angled south facing panels. I have seen many options, which seem to cost about 20% or more in order to obtain this securely in high winds. My conclusion is that I have to work out how to DIY cheaper than 20% material costs.

I would get a LCD DC TV which is small screen, and you can buy these for about £100 on ebay. The inefficiency of converting DC power from the battery to AC, using an inverter, creates heat and loses power. Better to take 12V from a 12V battery direct.

I think I am getting close to selecting my ideal 100 watt solar panel. Certainly on price, I am getting close. The size of it seems right, and the voltage level is consistent or lower than my current panels (so should avoid the need for a MPPT controller).

What type of battery do you use @TQA? (don't say lithium as I will not believe you, as solar chargers are not set up for charging lithium batteries from bicycles unless you use an invertor and then the lithium battery charger)
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 After all it is free Go on u know u want to!
After all it is free Go on u know u want to!
Bigtipper wrote:
If you calculated the area under the graph of points, you get about 615% of the panel wattage over the whole day. In other words about 125 watts could have been captured and transferred to a battery from a 20 watt solar panel.
....
If I was to get a 100 watt solar panel, and it was just as efficient or more efficient than my 15 year old panels, I would have generated 615 watts over the full day. Just a little bit more than half a unit of grid electricity, which would cost 6p-8p. roughly.


On a pedantic note concerning the units you have used, you should be referring to 125 watt-hours and 615 watt-hours as the amount of energy generated. Watts are units of power; watt-hours are units of energy. Madeye-Smiley
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Laughing @Alastair Pink, I saw it but resisted saying anything - thank you, it was difficult holding back.
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@admin, +1
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Ok, I know what I meant and it seems you did too! It takes time to pick up on all these acronyms and jargon. Note there would have been more than 125 watts if there was not a tree in the way for 1 hour at between 90%-60% efficiency between 4pm - 5pm. In other words I am re-locating the panels, to where there the tree shade occurs when efficiency is below 50%.

It is very sunny at the moment. But days like this only occur 25% of the year!
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And love to help out and answer questions and of course, read each other's snow reports.
Bigtipper wrote:


What type of battery do you use @TQA? (don't say lithium as I will not believe you, as solar chargers are not set up for charging lithium batteries from bicycles unless you use an invertor and then the lithium battery charger)


There is no particular magic required to set up a MPPT controller to charge a lithium pack directly these guys https://genasun.com/products-store/mppt-solar-charge-controllers/mppt-for-lithium-batteries/?gclid=CKSK97XQ2dMCFYVahgodZ78ENA have been selling them for years and there are a few liveaboards with lithium set ups. However they are expensive.

I live on a sailboat in the Caribbean. I have 400 watts [ 3 x 135 ] of solar mounted on a rear arch. The panels can be tilted to follow the sun. I use a Blue Sky 2000E MPPT controller feeding 6 Trojan T 105 6 volt golf cart batteries in series parallel configuration. In full direct sunlight I see 25.6 amps charge.

Generally when you have easy access to the US 6 volt golf cart batteries give you the best bang for your buck. I don't know what the cost comparison will be in the UK but golf cart batteries are built with thicker plates than engine start batteries. They cope well with repeated deep discharges. 4 years life is usual with many doing double that if not subject to a daily deep discharge.

As for lithium batteries I have used them in model aircraft but learned quickly to remove them for charging and place them on a firebrick inside a metal box. There is no way I would have them on a boat or in a house. I was in Antigua when the race yacht Titan caught fire due to a lithium Cobalt battery failure. They virtually sank the boat before the fire was extinguished. Once a lithium battery catches fire it is very difficult to put that fire out.

Read more here http://forums.sailinganarchy.com/index.php?/topic/121324-fire-aboard-titan-at-the-docks-in-antigua/
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I read a really good paper last night

https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf

I think that whilst a PWM controller might be cost effective short term, longer term I can see the benefits of MPPT now. The summary at the end

"MPPT charge controller is therefore the solution of choice:

a) If cell temperature will frequently be low (below 45°C) or very high (more than 75°C).
b)If cabling cost can be reduced substantially by increasing array voltage.
c) If system output at low irradiance is important.
d) If partial shading is a concern."

a) Most of the time in Scotland, and in ski resorts, cell temperature will be below 45 C
b) System output at low irradiance is important in Scotland, due to the 25% sunny day statistic
c) Partial shading is not really a concern, as it is location specific

The paper suggests a 10%-20% improvement would be achieved in my conditions using a 100 watt solar panel (this is what they tested in their graphs). So a £20-£40 additional cost for an MPPT controller is reasonable over a PWM controller for 100 watt panel.

More significantly though, if I wanted to add another panel, the MPPT controller with suitable ampage would allow the increase with way better efficiency.

Ultimately, the voltage of your battery system being closest to your panel voltage will be most efficient. So three 6 volt batteries in series might be better than one 12v battery to be charged from an 18v panel. The controller would need to be intelligent to recognise this though, and that is where additional cost is added.

Its a minefield of detail. Not a simple puzzle to solve quickly!

Also when running loads, most will be at 12V DC or 240v AC, and so 12V DC battery will probably be most efficient as you do not need to change voltage.
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You know it makes sense.
When testing my panels at the peak of the day, I noticed that the voltage sometimes went up very high, while the ampage went to zero. I thought that there was an error in my voltmeter, and so I bought a new one to cross reference readings. At the peak of the day both voltmeters read 19.8 volts and zero amps.

I would guess this is part of the VA curve, and is caused by the solar cells getting too hot at the peak of the day. So presumably a MPPT controller would solve this inefficiency too. I am not sure how often this occurs, but I did notice that as the day heated up and the solar panels got more sun, the voltage keeps going up (and presumably sometimes goes too high when I do not take a reading).

I have two voltmeters now, one which often starts with a negative reading, but you can adjust the actual reading for the initial reading and get the same result as the new voltmeter. (which has usually read zero before connecting it to anything)

I do not know how much of a problem this would be in Scotland, but I can imagine it can be a problem in the Caribbean!
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 Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
Some of the things you are saying are making me a little scared for you and your electrical systems. Please use fuses and have a fire extinguisher to hand.

1 you must not connect 3 x 6 volt batteries in series and then connect them to any part of a vehicle electrical system.

2 the reason you got 19.8 volts is that is the panel was in a 'open circuit voltage' situation ie not connected to anything. 19.8 or more is normal. It can never get 'too high'.

3 as I said in an earlier post if you buy a cheap Chinese controller it may claim to be MPPT but is fact is likely to be PWN which is much cheaper and simpler to make. I paid about $ 360 US for my controller. The 25 $ PWN will prevent overcharging but will not convert the extra volts to amps as a MPPT does.

4 HEAT With my panels I get peak output at 24c and it drops off as they get hotter. See https://www.civicsolar.com/support/installer/articles/how-heat-affects-solar-panel-efficiency for more on this.

5 do your panels have integral diodes? This is critical otherwise they will drain you batteries at night. Cheap panels often don't.
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 Poster: A snowHead
Poster: A snowHead
1. Unless the vehicle requires 18V (I do not know of any vehicles which do, but it is possible)
3. I have two charge controllers, both of which were bought before they invented the acronym PWM. One was made by the same company as the solar panels, the other was made in Germany and bought on ebay. Paying more than 20% of the cost of the solar panel is inefficient in order to increase inefficiency by 20%. It would be more efficient to buy another solar panel, and accept the inefficiency.
4. I need to keep the panels cool, so laying them flat on a metal roof (be that lead, or steel), is likely to cause overheating when the metal heats up in the sun.
5. Both panels have bypass diodes, and the 5W panel can be connected directly to a 12V battery as a trickle charger. It is unlikely to overcharge anything. I have verified this by taking the 5W panel apart, seeing the diode, and soldering the ends as they had come loose. I also connected them in parallel, which would have been a problem if one of them had no diode.

I have not decided what to buy yet, it is clear I need more research before it makes sense. Maybe solar panels will reduce in price by the time I have done the research. If past trends continue, this seems likely!
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 Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
@TQA, It has been raining all summer, and so I am glad I have not gone ahead with any rash purchase as the electricity genererated would have been very limited this year and the panels will only get cheaper next year.

Have you relocated your boat somewhere out of the path of Hurricane Irma? Puzzled
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 Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
@Bigtipper, I'm not sure where you live but for the UK and England 2017 has been significantly sunnier than average. (Wetter in some parts and at some times, but sunnier)

http://www.metoffice.gov.uk/climate/uk/summaries/anomalygraphs

I don't mean you specifically, but I'm always amazed by how short our weather memories are (me included). The Spring and Summer (up until about 20th July) was incredibly dry here in S. Central England. 20 July through until about 20th August was unusually wet, but it's been pretty good since then.

This tool offers slightly more detail. Interesting stuff. http://www.metoffice.gov.uk/climate/uk/summaries/anomacts
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The rainfall in Scotland in June, July and August and across UK was higher than the average over 1961-1990 according to your first link. ("It has been raining all summer .....")

Sunshine levels in UK were 92% in June, 103% in July and 101% in August compared to the average over 1961-1990. This is hardly significantly sunnier than average!

In Scotland levels were 74%,122%, and 95% of averages in June, July and August. So I would say that was lower than average.

The second link suggests sunshine in UK has been best in South East of England and worst in North West of Scotland (where I am).

However, there have been no hurricanes here which would have ripped the solar panels off the roof anyway. I cannot imagine what it must be like living on a boat in the Caribbean currently. I would probably have headed up the coastline a long time ago!

Having said that there was much more sunshine in Scotland in the first half of 2017 than recent averages, but June was dire.

2010 was the best January I remember in Scotland for snow and cold. This agrees with mean average temperatures for January in 2010 which was the coldest since 2001. Since 2010 there has be no January to compare to 2001 or 2010, so this suggests that we are due a cold January in 2018/2019/2020. I am not sure we will see the likes of 2010 again for a while. The snow stayed on the low levels here for weeks on end, and you could go cross country skiing on the cycle pathways. Possibly even dog sledding....
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I stay South in the Eastern Caribbean in peak hurricane times. Currently I am in Grenada with my solar package pumping out it's regular 25 amps while I chase up reports from cruisers I know who play hurricane roulette and stay North. All are OK but some have lost their boats. The carnage in St marten and the BVI is really bad. Miami is next on Irma's agenda I fear. My panels are mounted on a rear arch and swivel. The angle is controlled by 5 mm ropes on cleats. They have survived short periods at 60 to 70 mph.

Setting up solar panels to work on cloudy days. You need to buy high voltage panels and a good MPPT controller. This can give you up to 25 % more charge than simple panels of equal wattage.
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