The system will work.
How much rubbish you can compact how many times depends on
- How much sun the panel gets.
- How big the panels are (Watts peak power in full sun)
- What technology they use (crystalline silicon, amorphous silicon, CdTe, ...) - And energy required for trash compaction (bin volume, rubbish type, rubbish volume)
Added long after:
Big Belly technical specification in my dropbox and on their site
In some places below I've added [Actual: xxx] figures next to my prior assumptions.
Based on calculations below it appears that
At a bad inner city location location (sun wise) in Chicago
in midwinter on an average December or January day
using a 20 W mono-crystalline silicon PV panel [Actual: 30 Watt]
and lead acid battery,
You'd probably get 10-15 compactions/day.
For all except 2.5 months of the year you'd get 2+ x that.
That sounds useful.
See below for the derivation of that result and the "assumptions" that it is based on.
As explained at the end, "assumptions" are initial conditions established based on best known information and past experience. They are stated clearly at the start so that the limitations of the system can be understood and so that they can be easily changed if other conditions apply.
The table below is from the wonderful www.gaisma.com site - provides solar and insolation & wind & more information from a vast range of sites worldwide.
The first line = insolation = equivalent hours of full sun daily on average, month by month.
Peak is 6.04 "sunshine hours" per day average in VII = July and lowest is 1.50 sunshine hours per day in December.
A "sunshine hour" will deliver 1000 Watts per square meter.
So an eg 50 Watt panel subject to 1.5 sunshine hours will deliver 50 x 1.5 = 75 Watt hours of energy if the sun is either full on or full off.
For reduced sunshine levels (cloud, shadow, rain, dawn/dusk, fog, ...) the light level will (of course) be lower.
As light levels reduce the best a cell can do is produce proportionately less power, but some cells are better at providing output at low levels than others.
The output of Silicon Monocrystalline cells reduces about in proportion to light level and they have the best output per sunshine hour of any technology commonly used.
Efficiencies vary with what you want to spend but the best cells have over 20% efficiencies and whole panel efficiencies of 17% but a target of 15% - 15% all up is reasonable. At 15% 1 m^2 = 150 Watts and 1 foot^2 = about 14 Watts. Lets assume a 20 W panel for now.
Gaisma Chicago
A 20 W panel in December gives an average of 30 W.h /day and in June - July it gives 120 Wh/day. By the time that gets stored and then used to power the compactor you'll get maybe 50%.
In winter 30 W.h x 50% = 15 W.h.
Assume the compactor uses a 1/4 HP or ~= 200 Watt motor [Actual: 1/6 HP, 130 Watt]
and that a compaction cycle takes 10 seconds (both of which I'd think should be very very adequate for a single garbage bin.).
200W x 10s x 1/3600 s/hr = 0.555 Wh/compaction - say 0.5 Wh.
So with 15 Wh available you get 15/.5 = 30 compactions/day.
BUT that's with a fully illuminated panel that gets what Chicago Winter sun it can when its available. At reduced light levels you get less.
I'll put compactions/day in [[square brackets]] in the following assuming 30 on a good winters day with panel pointed at sun.
A bright clouded sky when you can't see the sun location but it almost hurts your eyes to look at can approach 0.5 suns (50,000 lux)[[15]]. A good bright clouded sky, sun not obvious and not dazzling bright can be 20% of a sun = 20,000 lux[[6]]. Dimly overcast and in deep shaded skyscraper valleys etc can go from 10% / 10,000 lux on down [[<= 3]].
I think the 200 Watts/10 seconds per compaction is probably rather higher than needed. 200 W = 20kg.metre/second. At say 50% electrical to mechanical that's say 10 kg force over 10 metres or 100kg over 1 metre with 10 seconds of operation. You'd have to have some rather stroppy rubbish and a big bin to need this - so you may be able to get say 3 to 5 x as many compactions/day as above.
ie 10 - 15 compactions on an average winter day in a rather unfavourable location.
The above was based on a 20 Watt panel. Resize as required.
I said 50% panel to output via storage.
Battery has current storage efficiency - say 85% for lead acid, and
and voltage conversion efficiency = Vbattery out / Vpanel_rated.
- Using a lead acid battery (most usual) a panel rated at 18V (usually) delivers output from the battery at ~~ 12V so that's 2/3 efficient to start and current charge efficiency of LA is good but not 100% so say 2/3 x 85% =~ 57%. Add some wiring and connection losses and you have ~=50% panel to output.
[Actual battery: 12 Volt. Type unspecified but wording used suggests lead acid.]
A lead acid battery is assumed only for getting a feel for charge/discharge efficiencies. There are many other factors in battery choice but the most significant one is liable to be operating temperature range. In subzero conditions none of the "traditional" batteries do really well.
Overall, if lowest lifetime cost is wanted plus operation in a wide range of temperatures, efficient use of the PV panel then the battery technology of choice is Lithium Ferro Phosphate (LiFePO4). About the only factor which may cause it not to be chosen is initial cost. The mass and volumetric energy densities are lower than for LiIon and for top NimH batteries, but this is unimportant in this role.
Gaisma Chicago
Related material:
"Assumptions"
A user question shows a misunderstanding of the engineering concept and implication of "assumptions".
A student of the art said ...
You make unnecessary assumptions about the system ...
This is extremely important.
An "assumption" is not a restriction per se but the assignment of an initial value to an equation set.
To "make an assumption" is NOT to set a value in stone but just the opposite - it is to say "this is the value we are using but you may wish to vary it depending on what parameters are considered important" etc. The initial values assigned to "assumptions" should not be random but would be expected to be the best available engineering guesstimates based on known data and conditions.
If you can assign a value to something AND if varying that value will affect the result then it is not "unnecessary". If you leave out something which can affect a result to "make things simpler" you risk making them, as Einstein warned "simpler than they can be". It may be that a variable has potential effect but that the solution is insensitive enough that it can be left as a constant or implied in other calculations. Here the volume of the bin may be decided to be unimportant NOT because it does not affect the end result but because all concerned have a general feel for the range of sizes that a rubbish bin is liable to take. My power & energy estimates carries an implicit "assumption" that eg we were not dealing with a 14 cubic metre dumpster.
By identifying factors that affect the result and assigning explicit values you make your answer usefully flexible and allow its limitations to be determined. By leaving possible factors unstated you deem them unimportant. If you find that you have included factors that the result is insensitive to they are simply assigned as constants.
Lets examine the "assumptions in my answer and see which ones are "unnecessary".
Depends on how much sun it gets,
how big the panels are and
what technology they use and
energy required for trash compaction.
4 points. All are key. Substantially vary any one and the result varies accordingly. Next ...
For a 20 W monocrystalline silicon PV panel and
lead acid battery
you'd probably get 10-15 compactions/day at a bad location (sun wise) in Chicago in midwinter on an average December or January day. For all except 2.5 months of the year you'd get 2+ x that.
That sounds useful.
All the above is a statement - its based on the following calculations. A 20 Watt panel is the sort of size seen on road signs and similar in typical city use. Lead acid is the battery technology of choice for industrial use. It's not the best by most measures, but it has low capital cost and some other advantages and it's liable to be what they use in the bins now.
The table below is from the wonderful www.gaisma.com site - provides solar and insolation & wind & more information from a vast range of sites worldwide.
The "assumption" here is that hard data on available solar energy will be "useful".
The meaning of the data table is explained. Degree of and language is targeted at typical site users.
...
Lets assume a 20 W panel for now
That's based on a paragraph of explanation .
A 20 W panel in December gives an average of 30 W.h /day and in June - July it gives 120 Wh/day. By the time that gets stored and then used to power the compactor you'll get maybe 50%.
Based on known real world performance.
In winter 30 W.h x 50% = 15 W.h. Assume the compactor uses a 1/4 HP or ~= 200 Watt motor and that a compaction cycle takes 10 seconds (both of which I'd think should be very very adequate for a single garbage bin.).
More assumptions. Stated so users can change them. Based on (my) real world experience, but clearly stated so that anyone change them.
200W x 10s x 1/3600 s/hr = 0.555 Wh/compaction - say 0.5 Wh.
So with 15 Wh available you get 15/.5 = 30 compactions/day.
Actual calculations so users can see how assumptions are used.
BUT that's with a fully illuminated panel that gets what Chicago Winter sun it can when its available. At reduced light levels you get less.
I'll put compactions/day in [[square brackets]] in the following assuming 30 on a good winters day with panel pointed at sun.
That's all fact based.
A bright clouded sky when you can't see the sun location but it almost hurts your eyes to look at can approach 0.5 suns (50,000 lux)[[15]]. A good bright clouded sky, sun not obvious and not dazzling bright can be 20% of a sun = 20,000 lux[[6]]. Dimly overcast and in deep shaded skyscraper valleys etc can go from 10% / 10,000 lux on down [[<= 3]].
Facts from experience.
I think the 200 Watts/10 seconds per compaction is probably rather higher than needed. 200 W = 20kg.metre/second. At say 50% electrical to mechanical that's say 10 kg force over 10 metres or 100kg over 1 metre with 10 seconds of operation. You'd have to have some rather stroppy rubbish and a big bin to need this -
Assumption modification. Clearly stated. Clearly reasoned.
so you may be able to get say 3 to 5 x as many compactions/day as above.
ie 10 - 15 compactions on an average winter day in a rather unfavourable location.
Reassess based on the above.
The above was based on a 20 Watt panel. Resize as required.
...
I said 50% panel to output via storage.
Battery has current storage efficiency - say 85% for lead acid, and
and voltage conversion efficiency = Vbattery out / Vpanel_rated.
* Using a lead acid battery (most usual) a panel rated at 18V (usually) delivers output from the battery at ~~ 12V so that's 2/3 efficient to start and current charge efficiency of LA is good but not 00% so say 2/3 x 85% =~ 57%. Add some wiring and connection losses and you have ~=50% panel to output.
Figures based on experience.
Hmmm.
We seem to be at the end.
I don't see anything you'd want to risk leaving out.
I don't see any fudging, miracles, etc.
Uncertainties? Sure. But stated.
How many watts?
How long a compaction cycle ?
How many cycles a day? ...
If you can offer constructive way to improve on that I'd be pleased to see them.
Best Answer
More later maybe. Quick thoughts:
Various electrical inputs via MPPT (maximum power point tracking) converter to LiFePO4 (Lithium Ferro Phosphate) battery is usually likely to be the most efficient and cost effective way of storing electrical energy. See end for MPPT comment.
Brushless DC motor drive is a top contender for drive efficiency with regeneration of "braking energy" back into the battery where approriate.
Stirling engines are great but are unlikely to be practical from cost or mass density or volume density points of view in real world solutions.
Energy conversion from low grade heat sources such as temperature differentials is extremely inefficient due to Carnot efficiency limit of (delta temperature)/(Maximum temperature) with actual efficincies being a fractin of that. Very low % :-(. Such may be OK for static applications where getting free energy is much more important than weight or cost or size.)
Fuel cells have their place but Hydrogen is hard to deal with well and the technology to use it compactly is still evolving. It's very low mass density and high diffusion rates and other factors make it an unlikely solution in compact portable storage and powering applications. Methanol cells can have higher energy densities but are not yet good as storage solutions.
LiFePO4 batteries can store energy at > 90% efficiency have very good but not superb density compared to th very best battery technologies and have good life-cycle costs (but higher initial costs than eg lead acid.) Lead acid can be extremely good on conversion efficiency with care and has lower initial costs but higher long term than LiFePO4. Various other LiIon storage systems are not as good as LiFePO4 energy wise but have higher energy storage densities.
"Just paddling" has its place but can be over-rated :-).
@Rocketmagnet's suggestion of a sail is even better than he suggests. A practical sail for a Kayak can be of modest size and can be highly practical and provide a very good motive source on lakes and in the sea. You may need Exalted-Grand-Master status to use it above a class 2 rapid - but that may apply to trolling motors as well ;-).
Rocketmagnet's suggestion of using flowing water as an energy source when stopped is also a good one (and is related to my braking energy and regeneration comment). Total potential energy in falling water is mgh = mass x gravity constant x head ~= 10 Watts per kilogram.meter/second or about 12 Watts per gallon.foot/second. Extractable energy is probably around 10% of this in a portable propellor situation.
Of more likely interest is energy due to velocity = 0.5 x m x V^2.
Below -
density = kg/m^3
V = metres/second. 1 m/s ~= 2.2 mph,
Area = prop area in metre^2
Mass/second = Area of prop x velocity x density so
Power at 100% conversion =~ 500 x V^3 x A Watts. V in metres/second. 60% of this max unducted.
Near 100% of this in superb design ducted.
Say 20% or so in real world. So
Power ~= 100 x A x V^3 Watts.
Interest only: The above formula also works for wind turbines with a factor of about 1000 x less power per area for air due to the density difference.
Carrying a small wind turbine with fold out blades for use when stopped can make sense. Use when in motion in a kayak again needs Grand Master status.
MPPT
Wikipedia on MPPT
They say:
MPPT 2 page introduction useful.
Similar + product info similar
Similar
MPPT is useful with many energy sources.
An excellent way of thinking of it is as being an electronic gearbox that takes current and voltage at inout and outputs a different voltage and corresponding current such that
where K is the efficincy of concersion.
For a given set of operating conditions MPPT adjusts the effective load resistance and thus the voltage and current such that maximum power is being obtained and adjusts output voltage or current to suit the target output device.
An example would be an industry standard nominally 12V crystalline silicon PV panel (= photovoltaic = solar panel) charging a 12V lead acid battery. A stanradd panel has 36 cells and an output voltage in full sun of 18V or more. At peak power point (the MPP that MPPT tracks) the voltage will be ABOUT 15V but this varies wit cell efficincy, insolation (sunshine level), age of PV panel, cleanliness of glass, atmospheric conditions and more. The bttery may be optimally charged at a voltage of anything from about 10V (rather dad battery) through 14V+ (certain specialist modes). The MPPT controller matches these different voltage and current levels. If the battery was best charged at 12V and the PV panel MPP was at 15V then if the two ar just joined together the efficiency of PV energy use is 12V/15V = 80%. The 20% extra is lost. This does not mean that the battery necessarily uses the optimum energy as well as it should but the problem then changes from a PV panel loading one to a battery chemistry one.
LiFePO4:
Long cycle life, good temperature range, superb current charging efficiency, very good to excellent energy charging efficiency, relatively robust. relatively flat voltage range, excellent high temperature performance acceptable to good low temperature performance, lowest whole of life cycle-cost of any battery.
This applies t