Mixed news on the BBC this week - the rather sad story of the demise of a home wind turbine maker in Glasgow, Windsave, was reported here. As I reported in a previous blog entry, for most people, home wind turbines really don't make sense. Most of us simply don't get enough steady wind to get enough power out of these mini turbines to make a sensible difference. Their website has now been taken down, but apparently there was a statement on it acknowledging the disappointing results from the technology.
I sent an email enquiry to a local wind turbine company asking them if they had a table of wind speed versus power output, but so far I've had no reply. It seems odd to me that you'd try and sell such things if you didn't have good data on their likely performance.
On a slightly more upbeat, but rather longer term note, a Norwegian engineer has developed a floating offshore wind turbine. This uses a slack mooring system - similar to Pelamis I guess? - to moor a turbine in relatively deep water. It's about 100 metres below the surface and about the same above - weighed down with rocks as ballast. The benefit this brings is being able to deploy wind turbines in deeper water than can be managed just now, although at present the cost remains a bit high. The report can be read here. I wonder what Don Quixote would have made of such things?
Saturday 12 September 2009
Wednesday 9 September 2009
Who Killed the Electric Car?
I referred to this documentary in an earlier blog. I was intrigued enough to order the DVD from Amazon and I watched it with my son earlier this evening. I said in the earlier entry that I'm always a bit wary of eco documentaries - they tend to be very selective and it's hard to know how balanced they are. Taking those caveats into account, I was pretty impressed with this film. In fact everyone should watch this and form their own opinions :-). There's a more full account of the film and all it's players on Wikipedia here.
Of course the story is complicated and there's no single culprit - but my earlier comment on lack of sympathy for GM and others today stands. The destruction of vehicles that people wanted to buy was criminal. Toyota also destroyed vehicles - making their current claim to green credentials somewhat suspect.
The documentary looks at the various players and their motives. It also focuses heavily on those who leased the EV-1 - but were refused the possibility of renewing those leases. Another character who appears is Stanford Ovshinsky, the inventor of the Nickel Metal Hydride battery. The initial GM vehicles used lead acid batteries and had problems. GM bought Ovshinky's company but took 2 years to incorporate the NimH batteries into their vehicles. Perhaps that's how long it took - but they subsequently sold their stake.
Among those named as guilty are the car companies, the oil industry, the US government, the California Air Resource Board (CARB) and the consumer.
Another disturbing thing I learned from the film was that Reagan removed the solar cells that had been installed in the White House by Jimmy Carter. Why? What was the point of that? It might have been one thing never to install them, but to remove them was just a political stunt.
The decision by the CARB to pursue hydrogen fuel cells is also questioned - apparently Alan Lloyd the CARB chairman at the time had joined the California Fuel Cell Partnership - an obvious conflict of interests.
I was also struck by the guys responsible for servicing the electric vehicles - the battery issues aside, they didn't need new oil filters, never wore their brakes out and of course didn't need new exhausts. In other words all the dirty bits associated with internal combustion engines don't exist - and more to the point, the huge spares and maintenance industry that goes with today's cars is greatly reduced.
I can't really do this documentary justice - I suggest watching the film or failing that read the Wikipedia entry and form your own conclusions. There are also a few extras on the DVD, including some deleted scenes.
One thing I do intend to do as a result of watching this is to get a hold of Joseph Romm's book, The Hype About Hydrogen.
Of course the story is complicated and there's no single culprit - but my earlier comment on lack of sympathy for GM and others today stands. The destruction of vehicles that people wanted to buy was criminal. Toyota also destroyed vehicles - making their current claim to green credentials somewhat suspect.
The documentary looks at the various players and their motives. It also focuses heavily on those who leased the EV-1 - but were refused the possibility of renewing those leases. Another character who appears is Stanford Ovshinsky, the inventor of the Nickel Metal Hydride battery. The initial GM vehicles used lead acid batteries and had problems. GM bought Ovshinky's company but took 2 years to incorporate the NimH batteries into their vehicles. Perhaps that's how long it took - but they subsequently sold their stake.
Among those named as guilty are the car companies, the oil industry, the US government, the California Air Resource Board (CARB) and the consumer.
Another disturbing thing I learned from the film was that Reagan removed the solar cells that had been installed in the White House by Jimmy Carter. Why? What was the point of that? It might have been one thing never to install them, but to remove them was just a political stunt.
The decision by the CARB to pursue hydrogen fuel cells is also questioned - apparently Alan Lloyd the CARB chairman at the time had joined the California Fuel Cell Partnership - an obvious conflict of interests.
I was also struck by the guys responsible for servicing the electric vehicles - the battery issues aside, they didn't need new oil filters, never wore their brakes out and of course didn't need new exhausts. In other words all the dirty bits associated with internal combustion engines don't exist - and more to the point, the huge spares and maintenance industry that goes with today's cars is greatly reduced.
I can't really do this documentary justice - I suggest watching the film or failing that read the Wikipedia entry and form your own conclusions. There are also a few extras on the DVD, including some deleted scenes.
One thing I do intend to do as a result of watching this is to get a hold of Joseph Romm's book, The Hype About Hydrogen.
Tuesday 8 September 2009
Storing energy for rainy days
One of the problems with renewable energy is that for wind, wave and solar power the supply is not constant or predictable on a day to day basis. Statistically we can figure out what we're likely to get from any one site based on observation over a period of time and extrapolating that into the future, but we can't predict accurately a long time in advance (i.e. more than a few days based on weather forecasts) how many kW will be available.
Unless we want to build huge amounts of extra capacity, then we need to consider the problem of storing energy for when we need it - in the case of solar power, literally putting something away for a rainy day.
This takes me back to my school days when we were learning about converting energy from one form to another. For example converting electrical to chemical energy in batteries and converting between kinetic (movement) energy and potential energy by raising things up hills and letting them run down again.
What are the options? More to the point, what are practical solutions?
Batteries are plainly useful - but to store the amounts of power we would need to cover for cloudy days with no wind will take a lot of them. One of the solutions being touted is what is known as V2G - vehicle to grid. The theory is that we hook all our electric cars up to the grid to charge - but in such a way that the grid can take electricity from all the plugged in cars when demand is high or supply is low. That will require the kind of smart grid I talked about in a previous blog entry. There are a few practical problems to overcome with this as well. Batteries that are designed for powering cars may not be the best kind of battery for retrieving electricity from rapidly. Then there's the problem of being able to rely on one's vehicle. If you plug it in at night you expect it to be ready to drive in the morning - but if the grid has emptied the battery of all its charge then you won't be going anywhere quickly.
Another option is hydro electricity. Hydro power stations already use off peak electricity that would otherwise be wasted to pump water back up the hill so's it can be used again. There is obviously a net energy loss due to inefficiency, but it's still a pretty good solution. In that sense our hydro power stations are already primarily storage units. It is however very questionable as to whether we can have enough hydro power on tap to meet all our storage needs.
Given that we will likely be challenged to construct enough storage facility to cope with all the lulls and increases in demand in cold weather or when Scotland are about to win the world cup and everyone has their tv's on we need to look at alternatives. For example, it is unlikely that the whole world will be becalmed at any one moment - so trading arrangements supported by HVDC lines for moving electricity between and around countries would seem to be a sensible way to go. The only down side perhaps is that we would be at the mercy of another country in maintaining our electricity supply - but if you consider that we are already pretty much in that state for oil and gas then we'd be no worse off - and perhaps if we have enough renewables, in times of plenty the boot would be on the other foot.
Unless we want to build huge amounts of extra capacity, then we need to consider the problem of storing energy for when we need it - in the case of solar power, literally putting something away for a rainy day.
This takes me back to my school days when we were learning about converting energy from one form to another. For example converting electrical to chemical energy in batteries and converting between kinetic (movement) energy and potential energy by raising things up hills and letting them run down again.
What are the options? More to the point, what are practical solutions?
Batteries are plainly useful - but to store the amounts of power we would need to cover for cloudy days with no wind will take a lot of them. One of the solutions being touted is what is known as V2G - vehicle to grid. The theory is that we hook all our electric cars up to the grid to charge - but in such a way that the grid can take electricity from all the plugged in cars when demand is high or supply is low. That will require the kind of smart grid I talked about in a previous blog entry. There are a few practical problems to overcome with this as well. Batteries that are designed for powering cars may not be the best kind of battery for retrieving electricity from rapidly. Then there's the problem of being able to rely on one's vehicle. If you plug it in at night you expect it to be ready to drive in the morning - but if the grid has emptied the battery of all its charge then you won't be going anywhere quickly.
Another option is hydro electricity. Hydro power stations already use off peak electricity that would otherwise be wasted to pump water back up the hill so's it can be used again. There is obviously a net energy loss due to inefficiency, but it's still a pretty good solution. In that sense our hydro power stations are already primarily storage units. It is however very questionable as to whether we can have enough hydro power on tap to meet all our storage needs.
Given that we will likely be challenged to construct enough storage facility to cope with all the lulls and increases in demand in cold weather or when Scotland are about to win the world cup and everyone has their tv's on we need to look at alternatives. For example, it is unlikely that the whole world will be becalmed at any one moment - so trading arrangements supported by HVDC lines for moving electricity between and around countries would seem to be a sensible way to go. The only down side perhaps is that we would be at the mercy of another country in maintaining our electricity supply - but if you consider that we are already pretty much in that state for oil and gas then we'd be no worse off - and perhaps if we have enough renewables, in times of plenty the boot would be on the other foot.
Monday 7 September 2009
No Fossils in MY house...part 3 - Solar Photo-Voltaic cells
Solar power can either be used to heat something up, or in the case of Photo-Voltaic or PV cells, generate electricity directly. These are devices, usually made of silicon, that respond to sunlight by producing electricity. They are rated in kWp, which is kilowatts peak - the amount of electrical power they produce in direct sunlight.
Putting PV cells on the roof to generate electricity sounds like quite a neat idea. We could easily angle them to face south. In Edinburgh the average incident solar energy that falls is about 100 watts per square metre. PV cell efficiency is a bit of a challenge however. There is a theoretical limit to the efficiency of solar cells due to something called the band-gap problem of about 50%, however the best today are about 20% and typical ones are about 10% efficient.
The other slight problem is that last time I looked, the sun doesn't shine at night, so that suggests that one needs to charge batteries for overnight power. The other slight problem is that in the winter when the daylight hours are shortest is when demand for electricity tends to be highest. The battery problem can be overcome in a sense if one is "grid connected". The theory is that one generates excess electricity during the day and sells it to the grid - effectively using it as a storage system - and then buys it back during the night or during periods of insufficient generation. Of course, this assumes that someone somewhere has spare capacity when you need it during the night - not an unreasonable assumption.
As well as the PV cells, one needs an inverter to convert the DC from the cells/storage battery in to AC.
On the plus side, solar cells should be relatively cheap at the moment due to overcapacity in manufacturing. This article describes the problem. That might explain why Maplin had a sale on a while ago for solar products.
As well as the cells and a set of batteries to charge, you also need an inverter to turn the electricity from DC to AC. I haven't investigated this completely - but I am assuming that devices are available that will allow one to become grid connected - basically as well as generating AC, it needs to match the phase and frequency of your generator to your local supply. The Distribution Network Operators have different policies when it comes to connecting one's generation system to the grid. Again I haven't investigated the details of this yet either.
A quick survey suggests that a 120W cell will work out at about 600 pounds, plus batteries, charge controller and inverter. I'm guessing we would need 3 or 4 such devices to allow for not having full sunlight all the time to achieve 120 watts - let's say 4 for luck. I would need to do some more figuring to determine how many watts we should aim to generate and store - but let's assume we want to generate our full 7500 kWh per year.
Assuming an average10 hours daylight per day - which is probably a bit optimistic, and 4 cells generating 120W (let's call it 100 for the sake of round numbers) for 10 hours would generate 1 kWh per day. That means we'd need 20 such arrays (hmmm...my roof will be a bit full with that lot on it,) - or maybe 80 cells at the cost of about 600 pounds each. That's not far off fifty thousand quid! The cost of the other bits disappears into the noise! Payback time? Given that one of the cells is about the same as our annual electricity bill, it's going to be about 80 years.
This doesn't look like a very good plan either. Maybe solar cells will get a lot cheaper and maybe my estimates of the number needed are a bit awry - but the payback period still looks to be pretty long.
Putting PV cells on the roof to generate electricity sounds like quite a neat idea. We could easily angle them to face south. In Edinburgh the average incident solar energy that falls is about 100 watts per square metre. PV cell efficiency is a bit of a challenge however. There is a theoretical limit to the efficiency of solar cells due to something called the band-gap problem of about 50%, however the best today are about 20% and typical ones are about 10% efficient.
The other slight problem is that last time I looked, the sun doesn't shine at night, so that suggests that one needs to charge batteries for overnight power. The other slight problem is that in the winter when the daylight hours are shortest is when demand for electricity tends to be highest. The battery problem can be overcome in a sense if one is "grid connected". The theory is that one generates excess electricity during the day and sells it to the grid - effectively using it as a storage system - and then buys it back during the night or during periods of insufficient generation. Of course, this assumes that someone somewhere has spare capacity when you need it during the night - not an unreasonable assumption.
As well as the PV cells, one needs an inverter to convert the DC from the cells/storage battery in to AC.
On the plus side, solar cells should be relatively cheap at the moment due to overcapacity in manufacturing. This article describes the problem. That might explain why Maplin had a sale on a while ago for solar products.
As well as the cells and a set of batteries to charge, you also need an inverter to turn the electricity from DC to AC. I haven't investigated this completely - but I am assuming that devices are available that will allow one to become grid connected - basically as well as generating AC, it needs to match the phase and frequency of your generator to your local supply. The Distribution Network Operators have different policies when it comes to connecting one's generation system to the grid. Again I haven't investigated the details of this yet either.
A quick survey suggests that a 120W cell will work out at about 600 pounds, plus batteries, charge controller and inverter. I'm guessing we would need 3 or 4 such devices to allow for not having full sunlight all the time to achieve 120 watts - let's say 4 for luck. I would need to do some more figuring to determine how many watts we should aim to generate and store - but let's assume we want to generate our full 7500 kWh per year.
Assuming an average10 hours daylight per day - which is probably a bit optimistic, and 4 cells generating 120W (let's call it 100 for the sake of round numbers) for 10 hours would generate 1 kWh per day. That means we'd need 20 such arrays (hmmm...my roof will be a bit full with that lot on it,) - or maybe 80 cells at the cost of about 600 pounds each. That's not far off fifty thousand quid! The cost of the other bits disappears into the noise! Payback time? Given that one of the cells is about the same as our annual electricity bill, it's going to be about 80 years.
This doesn't look like a very good plan either. Maybe solar cells will get a lot cheaper and maybe my estimates of the number needed are a bit awry - but the payback period still looks to be pretty long.
Sunday 6 September 2009
No Fossils in MY house...part 2 - wind power
As part of the ongoing research into how we might lessen our dependency on the grid I looked at windpower as a possible option. There might even be a possibility of selling any excess electricity back to the grid and becoming part of the micro-renewables community.
There are a few companies that will sell you turbines - A company called Renewable Energy Devices offers Swift Turbines for example. On the face of it these look like nice devices, with an option for battery storage which is probably essential if you're going to get the best out of them. The brochure claims about being quiet and bird and bat safe are impressive.
They estimate that a turbine that is capable of generating 1.5 kW of power will cost about 7000 pounds to buy and install. That can be reduced to the end user if grants are available as they typically are in the UK. It's not clear if that costs includes planning permission. They further suggest that that could generate about 2000 kWh of electricity per year. That's less than a sixth of the theoretical maximum (24 * 1.5 * 365 = 13140 kWh) so may be realistic for a typical UK residential site with minimal obstructions such as up on a roof.
Just for comparison, the biggest industrial wind turbines are now capable of generating 5 Mega Watts - and 2.5 Mega Watts is typical.
Given that we pay just over 10 pence per kWh (and we use about 7500 kWh per year,) it would seem we could reduce our grid electricity usage by about 25% and save 200 pounds a year. That would suggest a payback period of 35 years! Perhaps that could be reduced to 20 years with maximum grants. Their brochure somewhat misleadingly claims that on a good site payback could be as little as 5 years. This can only be achieved if maximum output can be maintained unbroken for that 5 years. (13140 * 5 = 65700 kWh @ 10p per kWh = approximately 6500 pounds.)
One has to dig through the brochure small print to discover that 1.5 kW is from a rated wind speed of 12 metres/second. Unfortunately there is no table available on the site showing the performance under different wind speed conditions. They do claim that it will work in extreme wind conditions - although they don't explain what that means. I happen to have a remote weather station on my roof. I haven't been monitoring it very closely recently, but between October and December 2008 the average wind speed, from snapshots taken every 15 minutes, was 3 metres/second. Even today, which is fairly windy, the average is under 4 metres/second. That seems to fall a long way short of the number needed for efficient generation from this turbine.
Update - 8th September - a very windy day and the average is still only around 8 m/s. Strongest gust was just over 15 metres/second. (1 metre/second = 2.237 mph).
I am therefore lead to conclude that investing in personal wind power at this stage doesn't seem like a good option for our household. A payback time of 5 to 7 years would not seem unreasonable but 35 years strains my sense of credulity.
There are a few companies that will sell you turbines - A company called Renewable Energy Devices offers Swift Turbines for example. On the face of it these look like nice devices, with an option for battery storage which is probably essential if you're going to get the best out of them. The brochure claims about being quiet and bird and bat safe are impressive.
They estimate that a turbine that is capable of generating 1.5 kW of power will cost about 7000 pounds to buy and install. That can be reduced to the end user if grants are available as they typically are in the UK. It's not clear if that costs includes planning permission. They further suggest that that could generate about 2000 kWh of electricity per year. That's less than a sixth of the theoretical maximum (24 * 1.5 * 365 = 13140 kWh) so may be realistic for a typical UK residential site with minimal obstructions such as up on a roof.
Just for comparison, the biggest industrial wind turbines are now capable of generating 5 Mega Watts - and 2.5 Mega Watts is typical.
Given that we pay just over 10 pence per kWh (and we use about 7500 kWh per year,) it would seem we could reduce our grid electricity usage by about 25% and save 200 pounds a year. That would suggest a payback period of 35 years! Perhaps that could be reduced to 20 years with maximum grants. Their brochure somewhat misleadingly claims that on a good site payback could be as little as 5 years. This can only be achieved if maximum output can be maintained unbroken for that 5 years. (13140 * 5 = 65700 kWh @ 10p per kWh = approximately 6500 pounds.)
One has to dig through the brochure small print to discover that 1.5 kW is from a rated wind speed of 12 metres/second. Unfortunately there is no table available on the site showing the performance under different wind speed conditions. They do claim that it will work in extreme wind conditions - although they don't explain what that means. I happen to have a remote weather station on my roof. I haven't been monitoring it very closely recently, but between October and December 2008 the average wind speed, from snapshots taken every 15 minutes, was 3 metres/second. Even today, which is fairly windy, the average is under 4 metres/second. That seems to fall a long way short of the number needed for efficient generation from this turbine.
Update - 8th September - a very windy day and the average is still only around 8 m/s. Strongest gust was just over 15 metres/second. (1 metre/second = 2.237 mph).
I am therefore lead to conclude that investing in personal wind power at this stage doesn't seem like a good option for our household. A payback time of 5 to 7 years would not seem unreasonable but 35 years strains my sense of credulity.
Subscribe to:
Posts (Atom)
Posts
