Category Archives: Renewable Energy

Solar & wind power etc

Solar Panels PV

Renewable Energy – Solar Power (PV)

A to B Solar PanelsWhether you believe the catastrophic predictions being made by some scientists, or prefer the lower key approach of others, there’s no doubt the world is heading for uncertain times, thanks to our misuse of resources, primarily over-consumption of ‘fossil’ fuels. But we can ALL do something about it.


Reducing or eliminating car use

Motor vehicles are a very real problem. More than a quarter of all CO2 put into the atmosphere in the UK comes from transport, and nearly all of that from the road transport sector. A typical two-car household will consume 77 kW of energy per DAY just running the cars. That’s more than the energy consumption of a typical home. Just think about that for a minute – we are using more energy travelling around than we are cooking, bathing, keeping our houses light and warm, watching TV and every other power-consuming activity. There are many ways to reduce your reliance on the car. We use bicycles for short journeys, and the train for long journeys. In between, we use electric bicycles and folding bikes that can be carried by train or bus. By these means, we have more or less eliminated our transport energy consumption.

A folding bicycle enables you to integrate your life with often irregular and poorly integrated public transport. For more information, we suggest starting with the page Why Choose a Folding Bike? More recently, electric-assist bicycles have begun to make a real impact. Many people have now swapped a second car for an electric-assist cycle. For more information, we suggest starting with the page Why Choose an Electric Bike?

Reducing energy use in the home

By a number of measures we reduced the energy consumption of our home (plus the A to B office and all electric bicycle charging) from the national average of about 70 kW to 22.5 kW per day. More information can be found in A to B 53 – see Back Numbers for more information.

Generate your own power

Not as easy as it sounds, but in July 2006 we moved house and our new home had an unshaded south-facing roof, making it ideal for Solar Photovoltaic panels that generate electric power from the sun. Once again, full details in A to B 56, see Back Numbers for more information.

Obviously moving house caused a great deal of disruption (and extra CO2!), but things soon settled down. We fitted cavity wall insulation, loft insulation and double glazing, and in mid-October 2006 our Solar PV roof came on stream. There were still many problems – our wood-burner was not yet fitted and we were cooking electric while the gas supply was sorted out (this would run on for months), but the table below indicates our daily energy usage when the PV was first fitted. Total electricity consumption is something of an estimate, because our digital house to grid meter is unable to run backwards, so we have to estimate how much power is being exporting to other nearby houses. We’ve assumed that about 3kWh of our daytime power generation is actually being used in the house, with the remainder being exported. On this basis (reasonably accurate) we have done quite well, actually crossing the barrier into carbon neutrality in the first week of April 2007. Since then, we have regularly crossed that magic barrier in June, July and August.

Our Average Daily Power Consumption

A to B Solar figures chart


Our Average Daily Power Consumption

Year/ Month Notes Gas
per day
% from
Late2006 Oct We had inherited an inefficient gas central heating system, which accounts for almost all of that 29 kW a day, despite sparing use. The good news is that our wood burner was finally installed on 4th November, and the central heating was finally turned off. October is a bad time for Solar PV, but the last week was very good, and for the three weeks the solar PV was in operation, we generated 30% of our electric power this way. How will the woodburner get on? How much sunshine will we see? Find out next month! 29 7.6 3.0 39.6 8%
2006 Nov Wow! What a difference a month makes! The woodburner has proved up to the task of heating the whole house, and runs well on recycled timber of various kinds. This has more or less eliminated our gas useage (we only turn the boiler on for baths). It’s also been a good month for PV. The result is 16% (plus the wood, of course) from renewable sources. 8 10.1 3.7 21.8 17%
2006 Dec A miserable month. Very little sun and increasing electricity consumption. The only good news is that the gas boiler has barely been used at all. 1.5 10.9 1.6 14 11%
2007 Jan Continuing nasty weather, but it’s a amazing how a few bright mornings can generate a lot of PV power, keeping the percentage up despite growing demand. Over one weekend, we produce more than 10 kW. Our overall electricity consumption is up however – partly space-heating in a child’s bedroom, but also our new dishwasher! Can we bring consumption back down? 2.3 14.1 2.3 18.7 12%
2007 Feb Some scientists think the recent pattern of hot summers and cold, wet, stormy winters will become the norm. If so, our power generation will be very seasonal! Despite some terrible weather, there were a handful of clear, bright days in February, some producing in excess of 10 kW. The mean of 4.3 is a big advance, and with slightly lower demand, helped to push the solar contribution up to 25%. 2.5 9.3 4.3 16.1 27%
2007 Mar Interesting to see solar energy double in February and double again in March. Despite rather high consumption, that’s enough to get us very close to 50% from solar. Incidentally, if the energy useage seems high, it covers our business, home and all electric bike transport, so pretty low considering. We’re working hard to cut household and office consumption. 1.8 2.3 8.6 12.7 68%
2007 Apr Super-fine weather in early April resulted in a week or so when we were net exporters of energy, but across the month as a whole, we narrowly failed to beat that 100% target. All the same, 98% from renewable sources overall is quite good going for the time of year. 1.24 -1 10.6 10.8 98%
2007 May A mixed bag of weather in May drops our home generation total. But towards the end of the month we install three Schott solar water panels to back up the PV and replace our aging gas boiler with a new condensing boiler designed to accept solar pre-heated water . This should reduce our energy consumption further, but will we simply use more of this wonderful new source of hot water? 1.7 -0.5 9.6 10.8 89%
2007 Jun New boiler and new pre-heating panels have meant a bit more luxury, and a near halving of our gas consumption. Disappointingly, two weeks of terrible weather knocked back our solar power from what should have been the best month of the year. 0.99 -0.7 8.7 9 97%
2007 Jul These figures are a little difficult to interpret:
SOLAR ELECTRICITY: It was one of the wettest (and darkest) Julys on record – solar electricity generation was lower than it might have been!
GRID ELECTRICITY: With builders working in the house almost every day, baking for a family party and other odds and ends, we used more grid electricity than we might have expected, but overall consumption is down because part of the load for the dishwasher, washing machine and shower is now provided by gas
GAS: The new pre-heating boiler works well, and has reduced electricity demand, but we’re using more gas! Some fine-tuning might be useful : On hot days, hot water is supposed to flow from the solar tank direct to the taps, leaving the boiler off. It does, but the boiler often cuts in unnecessarily. Something to look into when the last bits of plumbing arrive
SOLAR HOT WATER: Overall energy consumption appears to be up, because we’ve recorded the amount of solar hot water produced, which has little to with the amount used. The process of getting energy from the roof to the bath is rather inefficient, but it’s free energy, and even if we only manage to use a quarter of it, we’re still cutting our fossil fuel consumption. By managing the solar supply better, we should be able to improve on these figures!
1.4 -1.6 9.3 4 est 13.1 102%
2007 Aug Our best ever result, thanks to two weeks of more or less unbroken sun. All the same, the days are getting shorter, so we have to expect lower power figures from now on. 0.8 -1.9 9 3.9 11.8 109%
2007 Sep Oh dear! Not a good month for various reasons. Builders still using a lot of power, which explains our relatively high electricity consumption, but the gas is a bit of a mystery. One possibility is that we’re simply using the solar system to have more hot baths! 2.9 1.8 7.9 3.4 est 16 71%
2007 Oct This is more the sort of thing we were hoping to achieve. Producing 50% of your energy from renewable sources in October really is not bad in the UK. Gas consumption is still higher than we hoped, but it’s good to see the solar water still coming on stream almost every day, pre-heating the cold feed water. 3.4 3.5 4.8 2.1 13.8 50% 62.6%
2007 Nov The lack of pre-heat to the water tank (zero on many damp, dark days) shows in the higher gas consumption. And it’s been a bad month for solar electricity too. All things considered, we’re lucky to have produced 25% of our energy. 5.1 7.4 2.9 1.3 16.7 25% 63.3%
2007 Dec Several changes – a new more efficient washing machine, and a new gas/electric cooker, instead of the electric only model. And a pretty miserable month. 6.3 8.2 1.6 0.7 16.7 14% 63.5%
2008 Jan A new baby has added a lot of extra energy consumption in the short-term. For two or three nights, we kept the central heating on, and of course, there’s a lot more washing! The other change, just noticeable in the figures, is a new gas/electric hybrid cooking stove. As we were previously all-electric, this has increased gas consumption a little and reduced electricity use by about the same amount. 7 7.8 2.8 1.2 18.8 21% 64.3%
2008 Feb Not a warm and pleasant month, but plenty of sharp, cold frosty mornings. These are good for us, because the solar water and pv panels work extremely well, even with temperatures near or below freezing. 4.8 5.0 5.2 2.2 17.2 43% 65.6%
2008 Mar Disappointingly high gas and electricity consumption this month. Hard to explain, but a baby means a lot of washing, and we used the central heating on two days – it’s a bit scary how fast the gas consumption can rise with just a few hours of central heating 6.2 4.4 6.8 2.9 20.3 63% 65.2%
2008 Apr That’s a bit more like it, but we will have to get used to the idea of our consumption being higher now there are four of us. 3.5 -1.1 9.4 4.0 est 15.8 85% 64%
2008 May Slightly down due to grotty weather. 3.4 -0.9 9.0 3.8 15.3 84% 63.7%
2008 Jun Excellent weather and our best solar month yet. 2.4 -4.3 11.8 5.0 14.9 113% 65%
2008 Jul Weather going downhill again. Gas consumption is stubbornly high – bit of a mystery, because the new cooker uses gas only for the rings, and the boiler should be pretty efficient. Electricity use is low, despite all the washing and cooking. 2.5 -1.0 9.4 4.0 est 14.9 90% 65%
2008 Aug An appalling month – cloudiest August for 40 years, hence the very poor results. Add on considerable extra energy consumption for various reasons and it’s by far the worst result we’ve ever seen in August, and broadly similar to March. 4.5 3.1 7.4 3.2 18.2 58% 64%
2008 Sep Better weather, but too late in the summer to make much of it. Our consumption remains stubbornly high, but that’s the impact of having a baby in the house, and a bigger busier office. 3.0 2.4 7.0 3.0 est 15.4 65% 65%
2008 Oct Better weather, but too late in the summer to make much of it. Our consumption remains stubbornly high, but that’s the impact of having a baby in the house, and a bigger busier office. 4.6 4.7 4.6 2.0 15.9 42% 59%
2008 Nov A miserable month. 5.9 8.9 2.3 1.0 18.1 18% 59%
2008 Dec A relatively good month for solar power production, especially the PV panels which like the very cold weather we’ve been having, but the cold weather has meant several boosts from the gas-powered central heating, and entertaining at Christmas has added extra dishwasher use, and extra electricity consumption from other sources too. All things considered, we’ve done well to produce 14% of our power. 7.3 9.9 2.0 0.9 20.1 14% 58%
2009 Jan, Feb, Mar Everything thrown at us, from snow to a big freeze, but some lovely sunny days too, so quite a good result. 5.3 5.0 5.0 2.3 17.6 41% 58%
Solar Panels PV

Home solar PV schemes – Letter

Solar PVA to B 80, October 2010

My mum has recently seen details of a company called ‘Homesun’ who offer to install solar power on your roof for free, you get any electricity you use for free, but they get the feed-in tariff. My mother is both very environmental, and not very well off, so this seems like a potentially good deal for her. On the other hand it is a 25-year contract, and although you can buy yourself out, it is straight-line depreciation, that is to say you have to pay half of the cost after 121/2 years and so on. Realistically my mother may not be alive in 25 years!

Do you know anything about this company, or this sort of scheme in general? She would have to pay £100 for a survey, which is refunded if you go ahead, but is not refunded if they say your roof is not big enough, or that there are issues of shading etc that mean they’re not very keen on your roof. So it could be a scam to get £100 out of lots of vulnerable pensioners, or it could be a perfectly bona fides scheme. Equally, if the feed-in tariffs are super, super generous, then it might be more sensible for me to pay £15,000 to have such a system installed on my mum’s roof, and to collect the feed-in tariff myself! I think her roof is about 26 square metres, and is close to south facing (slightly east, but not by more than 20°). Homesun would fit 18 square metres of solar panels.

John Wilson

Inevitably, with the arrival of the generous new ‘feed-in’ tariffs for small solar power generators, commercial companies have seen an opening, and these schemes have caused a flurry of interest, HomeSun and others being overwhelmed with enquiries. Basically, the company puts a solar PV system that would normally cost £15,000 on your roof at no cost to you, but keeps the feed-in payment, currently worth 41.3p for each Kwh generated, plus 3p for each Kwh exported to the grid. Commercially, the company is in a win-win situation. It will have to borrow a lot of money initially, but not as much as you, because it’s fitting the systems at cost price, yet taking advantage of a grant system designed to encourage individuals paying a full market price for the solar panels and other equipment. As the income from the government is guaranteed for the 25-year life of the contract, HomeSun is more or less guaranteed to make an excellent return. It doesn’t even need to gamble on the suitability of the site, because you’re paying them to do the survey. In John’s case, the site is close to ideal, as there is some evidence that a morning sun is more reliable, so panels slightly east of south make a better return.

You may be wondering what is left for the home-owner? As widely advertised, your mum will get to use any electricity the panels produce for nothing.This will cost HomeSun 3p for each Kwh she consumes, and save her about 13p per Kwh, which will be deducted from her normal electricity bill.

It all sounds very tempting, but for most people there are some serious disadvantages. The main problem is that you’re not always able to make use of your free solar power. Think how often you turn on the oven, washing machine, dishwasher, lights and other equipment when the sun is shining? If the sun’s out, the chances are most people will be at work, or out enjoying the fine weather. Under these circumstances, your free electricity will be exported, an extra 3p per Kwh will go to HomeSun and your neighbours will pay a market rate for ‘your’ electricity. The only way to make good use of the free energy would be to programme your washing machine, dishwasher and other equipment to come on by rotation during the day, but for the meagre savings, it’s unlikely anyone would be willing to go to that much trouble.

Clearly the HomeSun scheme is an interesting option for pensioners, the unemployed, or perhaps those registered sick, who are more likely to be at home, and less likely to have the capital to fit the panels themselves. They will be in a position to make good use of the free energy, with the option to buy the panels at a later date should they find the capital to do so. Thereafter – like all those who have bought their own solar PV panels – they will receive the generous feed-in payment whether they use the power or not, but obviously it would still make sense to use power-hungry equipment when the sun is out if possible.

For anyone else, these schemes would be a big mistake.With interest rates so low, solar panels are now one of the best investments you can make, so if you have money available, you really should invest yourself by loaning the purchase cost to your mum, or anyone else who wants solar panels and free electricity, but can’t afford to make the installation. Suddenly, you’re in the HomeSun business!

So much for new solar PV generators. Long-term readers may recall that A to B fitted solar panels a few years ago, when the generating tariff was very small. When the last Labour government announced the new feed-in tariffs, the small band of early-adopters were left in the lurch, although the Tory party faithfully promised to correct this anomaly once they were in power. In the event, the Tories found themselves in a coalition, and in the rather odd position of blaming the normally ‘green’, anti-nuclear LibDems for shutting the door on the people who blazed a trail for green power.

To quote Tory MP Oliver Letwin: ‘Chris Huhne [LibDem] very carefully considered the possibility of adopting the Conservative policy as a Coalition policy, but I am afraid that his investigations led to the conclusion that this would not represent value for money – and, indeed, his Department made clear that they would require an explicit Ministerial direction to do something that did not represent value for money if you were to pursue this policy.’

Some, but not all, of these early adopters received grants for the original installation, but it seems unfair that those who invested in solar power for philanthropic reasons are now receiving a lot less than those who have signed up with a prospect of a sound financial return. A politician’s promise is a delicate and fragile thing!

A to B 80 – Oct 2010

Solar PV Panels

Solar Powered Bicycle – The Results

Professor PivotSolar Power Results

Readers may recall the launch of my solar vehicle experiments in the last issue. At the time – having made a number of purely theoretical calculations – I concluded that a 20 watt solar panel might just be viable on an electric bicycle. In the event, for reasons of panel size and cost, it was necessary to settle on a pair of five watt panels, reducing the potential gains, but keeping the apparatus down to a manageable size.Why two panels? It’s simply that most small solar panels provide a 12 volt output, but the Lafree (the subject of my experiment) is, like many other electric bicycles, 24 volt, requiring two smaller panels connected in series.

Fitting solar panels to the bicycle brings a number of advantages: greater range, a less traumatic life for the battery (thanks to the constant trickle charge, reduced peak loading, and ‘shallower’ charge cycle), plus greater efficiency, because of the direct motor supply. Batteries are around 90% efficient when charging and much the same when discharging. That’s pretty good as these things go, but a direct supply will still give a bonus.

The disadvantages are the weight and cumbersome nature of even the smallest panels, and the potential screening effect of roadside buildings and trees, the rider, and of course vehicle orientation. In other words, if the panels are not angled towards direct sunlight for most of the journey, there is little point in carrying them around.

Static panels are remote from the vehicle, so range is unimproved. On the positive side, the panels can be positioned to capture most of the available solar radiation from dawn to dusk and they’ll charge all day, every day, and even in the rain, when the bicycle might be under cover. A spare battery is not obligatory with this system, but it does mean charging can be undertaken continuously – more effective if the bicycle is away for most of the day.

The Roof Option

After a few measurements, and long hours weighing up the options, it became clear that even the smallest solar panels would be unsuitable for use on a conventional bicycle that has to be wheeled through narrow gaps, leant against shop windows, dumped on the ground, and so forth. A recumbent trike would be a different proposition, of course, and I hope to investigate this option in a later issue.

The A to B long-term test Lafree spends most of its life towing a trailer.The roof of a child trailer would make a good location for solar panels, but one would need to plug and unplug the panels whenever the trailer was connected, and charging would not be possible while riding solo.Trailer mounting could make sense for a long hilly touring holiday, or for a commercial bike/trailer outfit left connected all day, but not for typical ‘school-run’ or commuter applications.

…a roof of this size receives a steady eight kilowatts of power from the sun…

Taking all these factors into account, it became clear that static ‘base station’ panels were the best option, and such was the persuasiveness of this argument that no attempt was made to rig the panels to the bike or trailer, even on a temporary basis.

In this case, we were fortunate to have a building aligned east-west, giving eight square metres of south-facing roof at 20 degrees to the horizontal.That’s a good compromise in British latitudes, although a steeper angle would be more productive in winter, and a flatter roof slightly more efficient in summer.

A roof of this size receives a steady eight kilowatts of power from the sun on a bright day, which could generate around 800 watts, working on our 10% efficiency formula from the last issue. But would our tiny five watt panels provide enough power?

solar-powered-bicycle-1The answer depends on the time of year, the amount the bicycle is used, and the cloud cover.The solid line on the graph indicates solar charging on a typical June day. Recorded just a week before the summer solstice, daylight hours are obviously very long, although one should not assume that solar radiation is necessarily stronger in June than at other times in the summer.

Note that the panels begin to provide a small charge well before sunrise, and continue to work after sunset, albeit at a low rate of charge.The real current flow begins when the sun first strikes the panels at 9am, climbing rapidly to peak at 2pm, before falling equally rapidly until 6pm. Note the pronounced troughs in production during the afternoon, when the sun is obscured by passing clouds. Readers will hardly need reminding that this is a fairly typical pattern in the United Kingdom, as clouds bubble up in the heat of the day.

Solar PV PanelsIn ideal conditions, we can expect our two 5 watt panels to produce about 70 Watt/hours (Wh) of electricity, and in practice, our representative English early summer day produces just under 60 Watt-hours. One could expect to do a little better, or much, much worse, according to conditions. Angling the panels to follow the sun would produce a little more power, but certainly not enough to justify the complication involved.

Sixty Wh is not much, but it’s enough to propel the efficient Lafree for about seven miles with gentle pedal-assistance. In other words, if your daily range does not exceed that amount (or, for example, 14 miles every second day), a ten watt power station should keep you moving in fine summer weather without the need to plug into the mains supply.

Our test bike travels further than this – about ten miles four days a week towing a child trailer (an effective solo mileage of 13.3 miles per day), plus smaller variable distances on the other three days, so a conventional supplement is required.

And the weather is not always fine! The figures below cover a typical 16-day period in late June. Early summer 2003 will be remembered as a very dry period, but cloud cover was about average, so the figures can be regarded as typical:

Average Daily Mileage Daily Conventional Charge Daily Solar Charge Solar Charge %
9 miles* 28Wh 36.6Wh 57%

* The actual mileage of 6.8 miles per day has been multiplied by 1.33 to make allowance for the trailer. Nine miles would be a more realistic solo mileage.

In the summer, and with modest mileage, this basic system works well. By doubling the number of panels, we could either produce 100% of our power requirements, or double our daily mileage. Conventional rigid roof-panels are somewhat cheaper than the flexible panels we have used in this experiment, so for example, £300 should buy two 12 volt, 15 watt panels, providing a surplus of power under most conditions.

Rather than directly charging an expensive spare electric bike power pack, another option is to charge a cheap-and-cheerful 12 volt car battery direct from a single 12 volt panel, topping up the bike power pack through an inverter, which converts the 12 volts from the panel to 240 volts to run the conventional charger, which converts it back to the voltage used by the bicycle. One large panel is cheaper than two small ones; a second bike battery is unnecessary; and the car battery provides capacity of 500 watt/hours or more to carry the system through gloomy days. However, the efficiency of this multi-stage operation can prove alarmingly low, and there’s the extra cost to consider.

A 30 watt solar power station will cost around £300 for the solar panel and regulator, plus £100 for a basic car battery and inverter. In fine weather, such a system would easily generate enough power to give a daily solar range of 20 miles or more.This would also be the best solution for charging a 36 volt machine such as the Powabyke, for which three 12 volt solar panels would be too expensive and cumbersome. Note, though, that the Powabyke is a less efficient machine, so mileage would be rather less.

The Bottom Line

Sceptical readers may have noticed the accent on weather conditions throughout this article.The problem is that a ten watt panel will indeed provide a peak output of ten watts and a mean figure of five watts or so on a sunny day in June. But on an overcast day, these figures can be halved, and in really grim weather – even in high summer – output can fall to 20% of the rated figure, or even less. Note our average daily figure of 36.6Wh, which equates to about 3.6 watts over ten hours. And don’t expect to save any money: our ten watt system might produce eight kilowatt/hours per year, but at a cost of over £2 per Kwh (compared to £0.06 from the mains), assuming a ten-year panel life.

But if you have a hankering to run a solar vehicle, the means is clearly available.The Lafree/solar panel combination is relatively cheap, simple to use, and should provide 1,000 solar miles a year, even in temperate Britain, although we have yet to verify the winter figures… Despite all the talk of sustainability, no other vehicle or power system can match this sort of result for such a modest outlay.

Solar panels, inverters and other equipment are available from a number of specialist suppliers, principally yacht chandlers, such as Compass Watersports: A guide to watts, amps and volts can be found on our web site:


Solar Powered Transport

Professor Pivot“I’ve always been interested in the idea of solar-powered transport, but no-one seems to have built anything practical yet. Is a solar vehicle a practical proposition in the UK?”

Jonathon Crouch
King’s Lynn

Professor Pivot replies:

Clean inexhaustible solar power has been a transport dream since photovoltaic cells first began converting light directly into electricity, but the reality seems as far away as ever. Solar cells have many applications these days, from lighting remote telephone boxes to powering satellites, but for transport, the problems are two-fold: cost and energy efficiency. At £5 to £20 per watt (bigger panels are much cheaper), the cost has changed little for some years: It’s the classic Catch 22 of high technology produced in low volumes, but increased demand for other high technology products has seen prices tumble, so the same is bound to happen to photovoltaics eventually.

Energy efficiency is a more taxing problem. Photovoltaics are improving rapidly, but most convert only 10 to 15% of the light energy hitting their surface into electrical power. Specialist cells of 25% efficiency are becoming available, and 35% or more is possible in the laboratory, but to avoid disappointment, we should work on a performance of a little over 10%.

Solar Cars?

Cover the horizontal panels of a typical car in photovoltaics, and you might cram in six square metres, trapping around 3 kilowatts of energy, but giving a peak output of only 0.4 kilowatts of electricity.To reproduce internal combustion performance, you’d need 30 kilowatts or so.Thus, with today’s technology, under ideal summer conditions, we could expect to generate around 1% of the peak power required. In practice, cars spend far more time sitting in the sun than moving, but even with the best panels charging a battery all day long, range would be very limited, and practically nil in winter.

Solar cars have achieved some amazing feats, of course, but the successful machines utilise a large surface area of priceless aerospace-grade panels to optimise power input, with sophisticated motors and lightweight construction to optimise performance. And it’s no coincidence that the annual solar challenge takes place in the Australian desert… But as we all know, cars are notoriously energy-hungry machines, and we can do a great deal better with other modes. Motorcycles and planes are even worse in the power requirement/surface area stakes, but low-speed motor boats are feasible, and a few have been produced. Best of all, though, is the humble bicycle – true, it offers a modest surface area, but it has an even more modest power demand.

…bicycles, like cars, spend a lot of time sitting in the sun, going nowhere…

The power requirement of electric bicycles varies a great deal, but we know from experience that the Panasonic-equipped Giant Lafree is the most efficient currently available, with a mean consumption of less than 100 watts under typical conditions.We could generate 100 watts from a panel measuring about 1.5 square metres, which would certainly be feasible on a faired recumbent. However, with a battery on board, there’s no need to generate all the power, particularly as bicycles, like cars, spend a lot of time sitting idly in the sun, going nowhere. In practice, a much smaller panel generating 20 watts would more or less recharge the Lafree battery during a long sunny day, giving a daily solar range of nearly 20 miles. If one were to start the day with a full battery, the solar boost might extend the non-stop range from 20 to 24 miles, or anything up to 40 miles spread over the course of a day, provided the bike was left in the sun between rides. A solar charger of this kind might also enhance the battery life, thanks to reduced current drain on hills and a steady trickle charge, rather than a daily boost. Suddenly the technology looks more practical.

In Practice…

uni-solar-usf-5-solar-pvThe bad news is that solar panels are generally unsuited to use on bicycles. Although the panels themselves are light, they’re fragile too, so they’re usually housed in a heavy rigid frame.A few lighter, flexible panels are produced for boats and mobile homes, and although these are not particularly space-efficient, we must concentrate our search in this area.

Taking weight, space constraints and price into account, a pair of Uni- Solar flexible USF5 panels look like a good compromise.The two panels weigh 1.1kg, measure 44cm x 54cm and cost around £180 in the UK. Rated output is 300mA at 33 volts, or 10 watts – only half the power required to refill the battery during the day, but enough to provide some reliable data. By comparison, a spare battery for the Lafree would give twice as much mileage (in all weathers, of course), but cost a little more and weigh three times as much.

I’ll be fitting the panels to A to B’s long-term Giant Lafree in the next few weeks, and reporting back in subsequent issues. In terms of practicality, this is cutting edge stuff:We The Uni-Solar USF5. The border is unproductive, but gives aim to find whether panels are the panel some protection from inevitable knocks practical in our gloomy climes, or whether the weight and bulk cannot be justified for everyday use.

Perhaps carefully angled panels on a south-facing roof would be more effective? Or a combination of the two systems? More in the next issue.