Efficient Solar Energy Utilization

H

HB13DISH

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In Israel we have the sun and the heat, but till now these sources of energy haven't been used effectively to produce electricity.
Roof tops are being used to install these horrid solar water heaters for individual apartments. For the size and area they occupy on the roof, you would expect something better than just heating water for showers or dish washing.
They cost two to three times the cost of an indoor electric water heating system. They need more maintenance because of leaks and corrosion and they have shorter life.
The difference in price between indoor and roof top installations is balanced after ten years for saving on electricity bill, without taking into account the maintenance cost during this period.
They also waste water, especially in cold weather until hot water reaches the shower head from the roof top.
If there is a new machine that can generate solar electricity and installed on the whole area of the roof top, it would be better to get rid of all the solar water heaters so that the whole building can benefit from the generated power which can be returned to the electricity grid.
There is a new offer by the electricity board promoting the use of either solar or wind energy and they pay x3 the price of their tariff.
Question is, what can we have on a roof top that can generate electricity that would make it worth while to get rid of the solar heaters?
My estimate is that you need at most 1 KWH/day on average for each apartment to heat water for showers and other things.
(An apartment can have single, married couple and married with children. I made an average of two heads per apartment)
My building with 15 apartments is saving only 15 KWH/day by using solar heaters. Big deal !!!!
With a machine utilizing the whole roof top, I am sure that it will generate more than 15 KWH/day.
Taking into account the x3 generous offer by the electricity board, all we need is a 5 KWH/day machine to pay for the electricity.
Then there is the cost of the machine to take into account, which can be paid of in 10-20 years or even less depending on how much power it can generate.
Any suggestions or comments or flows in my suggestions would be appreciated.:)
 
Rick

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As far as heating water goes there should be very little corrosion and maintenance in a solar heating system. The idea is that solar heating works on convection and the same water is circulated through the system and is passed through a heat exchanger which heats water in a storage vessel. As the water in the panels and the water to be used never comes into direct contact Inhibitors can be put into the system to prevent the corrosion of the pipe work etc, much in the same way that central heating systems are treated. Certianly in the UK it is mostly a false economy to install solar heating as we don't get anywhere near enough sun. However in a country such as Israel I would expect solar heating to be much more economic. Solar heating is usually used to boost the temperature of the water so that the boiler has less work to heat the water to its final temperature. i.e it takes less energy to heat water from 20 - 65 degrees than it does to heat the same water from 10 - 65 degrees.

I am not very familiar with the electric side of things but I would guess that a combination of solar cells and wind driven turbines could be used to produce electricity.

Not sure how much help that is :confused
 
PaulR

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It would seem that you have slightly different installations over there which may be a cause of some of the problems.

HB13DISH said:
They need more maintenance because of leaks and corrosion and they have shorter life.
They certainly shouldn't leak. This sounds like bad installations. There also shouldn't be any corrosion as the water flowing through the heating coils should have corrosion inhibitors. What maintenance is needed other than a simple checkover?

HB13DISH said:
They also waste water, especially in cold weather until hot water reaches the shower head from the roof top.
Again this sounds like different practices in Israel. The installations I have seen in the UK and France circulate the water heated on the roof down to a hot water reservoir tank which is then heated up. In the UK installation I have seen this tank is in exactly the same place (in the batroom) as the one it replaced and so there is absolutely no difference in time taken for hot water to reach the shower head.

The French installation did not have a hot water tank as it was previously an on demand heating system. I do know that there was a delay until this hot water then reached the shower. Now they have a hot water reservoir tank downstairs near to the water boiler so the difference should be minimal.

HB13DISH said:
If there is a new machine that can generate solar electricity and installed on the whole area of the roof top, it would be better to get rid of all the solar water heaters so that the whole building can benefit from the generated power which can be returned to the electricity grid.
The problem with solar electricity is that there is a much higher initial cost which then takes longer to recoup. It's also very dependant on the amount of light. Solar water heaters will provide a small amount of warm water even on freezing days which can be stored but elctricity panels very quickly fall off in production. Obvioiusly in Israel you have a lot more sun than the UK so electricity panels are a better bet than in the UK.

HB13DISH said:
There is a new offer by the electricity board promoting the use of either solar or wind energy and they pay x3 the price of their tariff.
This is entirely dependant on the government passing legislation. I think that Germany (and Belgium?) have a very advantageous payment scheme as well. This has resulted in a great many schemes being set up but if the economics are done it's very expensive electricity as the subsidies paid by the government could, arguably, have been better spent on larger solar generating projects which would produce elctricity at lower cost.

Reading the beginning of your post it looks as though the water heating coils on the roof directly heat the water. This is probably the cause of a lot of the problems as you will obviously have a long lead time for the water to reach downstairs and opportunity for leaks.
 
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Crisbe

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Here in the South of the Uk I made enquiries about putting solar panel on our roof. It worked out that we could get approximately 2.5kw from the maximum size of panel we could fit (we only have a small house). This 2.5 kw would of course only be getting produced during the hours of daylight.

I did the figures and worked out the total cost of an installation which could feed any surplus back into the grid compared with the amount of money we would save and /or get paid for any surplus. It worked out that it would take over 15.5 years to break even (assuming no maintenance costs during that time).

When I took in to account the amount of interest I would lose, if that money was no longer in my savings, it worked out that the break even point would be more like 18.5 years and more like 20 years allowing for maintenance costs over that period. So reluctantly, I had to consider it an uneconomic proposition.

If our governments are so keen to go green, they should give people, that want to put solar panel on their roofs, a grant to cover the cost, and then say that any surplus power is the property of the state and the money for it should go back into state funds. That way it would create a boom in solar panel installations, it would create thousands of jobs, both making and installing the equipment, and would reduce the global greenhouse effect a huge amount. They would also slowly get the money back from payment for the surplus energy sent in to the grid.

I am sure if this was organised on a national or even global scale the price of the equipment would come right down with the economies of large scale production.
 
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HB13DISH

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Thanks for the replies.:)
All I am saying is, get rid of the existing solar water heating systems so that we can have a larger clear area on the roof top and then install a solar-electric generator that would use the whole area to generate more power.
Alternatively, newly built buildings, should have these machines installed, and forbid the use of solar water heating systems.
The stupid things are sitting on the roof tops doing nothing from sunrise till dawn, except when the tenants take their showers and only then they might start working again to heat the water or wait till next morning if the hot water is already fully consumed.
With a solar-electric machine, it will be generating power and giving electricity to the grid between 8-12 hours a day, depending on the months.
I can see a big flow in my suggestion and that is the tenants would not be easily convinced to chuck out their water heating systems as they would have to install an indoor one instead and participate in the cost of the solar-electric generator and pay more for the electricity.

What I am after is, if there is already a solar-electric generator for apartment buildings and what is their maximum power and of course their cost.
 
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HB13DISH

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Crisbe said:
Here in the South of the Uk I made enquiries about putting solar panel on our roof. It worked out that we could get approximately 2.5kw from the maximum size of panel we could fit (we only have a small house). This 2.5 kw would of course only be getting produced during the hours of daylight.

I did the figures and worked out the total cost of an installation which could feed any surplus back into the grid compared with the amount of money we would save and /or get paid for any surplus. It worked out that it would take over 15.5 years to break even (assuming no maintenance costs during that time).

When I took in to account the amount of interest I would lose, if that money was no longer in my savings, it worked out that the break even point would be more like 18.5 years and more like 20 years allowing for maintenance costs over that period. So reluctantly, I had to consider it an uneconomic proposition.

If our governments are so keen to go green, they should give people, that want to put solar panel on their roofs, a grant to cover the cost, and then say that any surplus power is the property of the state and the money for it should go back into state funds. That way it would create a boom in solar panel installations, it would create thousands of jobs, both making and installing the equipment, and would reduce the global greenhouse effect a huge amount. They would also slowly get the money back from payment for the surplus energy sent in to the grid.

I am sure if this was organised on a national or even global scale the price of the equipment would come right down with the economies of large scale production.
Thanks Crisbe. This is very interesting.
Can you please give me a link to the solar panel system that you considered and what was the maximum panel size?
Our building roof top without the solar water heating system can be large compared to your roof. Maybe 200 sq meters.
Perhaps we can have several solar panels, depending on the best places to fit them.
Apart from solar panels, is there any other solar possibility?
 
PaulR

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HB13DISH said:
Thanks for the replies.:)
All I am saying is, get rid of the existing solar water heating systems so that we can have a larger clear area on the roof top and then install a solar-electric generator that would use the whole area to generate more power.
That might work in Israel but in the UK there isn't enough sunshine to make it viable in under a 15 year return of investment. It costs a lot to heat water and you get a quicker return for your money by going down the waterheating route.

HB13DISH said:
I can see a big flow in my suggestion and that is the tenants would not be easily convinced to chuck out their water heating systems as they would have to install an indoor one instead and participate in the cost of the solar-electric generator and pay more for the electricity.
I certainly would object if I had to pay for hot water to heated by electricity if I used to get it for virtually nothing! And then to add insult to injury I would be paying for electricity when I am selling it back to the electricity company!

The obvious amswer is have both of course. Providing the roof is big enough.
 
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HB13DISH

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Sorry PaulR, but perhaps I should have mentioned that my suggestions were directed in general to sunny countries like in the Middle East and specifically to Israel.
But as we have more members from the UK trying always to help, the suggestions obviously would not be applicable to the UK.
I think that solar water heating systems in the UK are superb and neat and I wish we have adapted such systems here, but this is the common way they are manufactured and installed in Israel.
I did my calculations twenty years ago whether to have a solar water heating system or indoor one, and I am glad that I decided on the indoor one. I may have wasted electricity, but saved money and water in the long run.
And now I want people here to understand that it would be better to have a solar electricity generator than saving few Shekels a month using their solar water heating system.
We could save on the building monthly electricity bill for light and elevator use and even get money back from the electricity board. But I know that it would be hard to convince them.
Only a massive promotional offers by the government might get people to understand the benefits.
 
Turok

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here,its via vesa alot of solar cells,on the roofs,that coasts around 7000€,for one household,but not so much sun!
the goverment here support the cells,with around 30% of the price!
but you can pay a power bill for nearly 15 years,what the cells whould coast!

they say it is clean engergy from the sun and nature,but the dont tell us,how many recurces and power needs a solar cell in his production state,same then on a engery saving lamp!
 
Channel Hopper

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In any sunny country the most efficient use of solar radiation is for direct heating, which includes cooking.

Anything to do with warming / heating water through pipes is a half-way solution to the age old problem of intermittent electricity (or other) supply, nothing more.

As this is posted on a satellite forum, you can search for the other ways a parabolic reflector (polished) can be used around the house. Solar cookers in Israel should be popular, as should be self-contained pasteurisers/sterilisers, but I am surprised they don't appear in more households.
 
Rick

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It sounds like your solar water heaters in Israel are very inefficient. Might it be worth looking into the cost of converting your system to work on the principals we use in the UK ? Certianly the type of system typically installed in the UK would work very well in a country with alot of sun. And as you already have the solar heaters the conversion costs should be limited. I would guess that the savings v cost would be better than installing new equipment.
 
Huevos

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Solar water heating is more efficient than photo-voltaic without question. Let's just have a quick look at the facts. Energy from the sun is arriving at about 1.3 kW per square metre. When you take into account day/night, angles of attack, atmospheric losses, etc you are down to an average of about 200 watts per meter if it is a cloud free day. Taking into account that a panel is about 10% efficient you will end up harvesting about 0.5kW/h per metre per sunny day. My personal use is about 16kW/h per day so going by this I would need 32 square metres of panels, more in winter when the days are shorter and the angle of attack is lower. This is about right too because a neighbour of mine who is not on the grid has 40m2 of panels and has to be very careful in winter. If they use the 42" tele they run at a defecit and have to use the 25" instead. BTW we have about 2000 hours of sunshine annually.

As for saving the planet the most cost effective thing you can do is put some insulation in. Have a read of this (Solar panels take 100 years to pay back installation costs but have a maximum lifetime of 30 years): _http://www.independent.co.uk/environment/climate-change/solar-panels-take-100-years-to-pay-back-installation-costs-917202.html
 
Channel Hopper

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Huevos said:
As for saving the planet the most cost effective thing you can do is put some insulation in.
Which is a poor fourth to,
1)using only the energy in what you actually require,
2)recycling anything you may have unwantonly used without considering the environment, and
3) ensuring your neighbours don't get away with screwing the environment and passing on the charges to everybody else.
 
Turok

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Very Good for winning engergy,install on the surface of a bigdish,solarpanels,with the egis solartracker,the dish,moves always in the direction of the sun,and wins engergy,all the time,until its dark!:)


_http://natur-licht.org/trac2_de.html


other question,how much a real evektive and good solarpanel should maximum coasts?
there are so many diffrent systems on the market,that its not posilbe to say,its the price now to high or to low for it!
the bigest solararea,in the world i see on a report on discovery,located in sunshine state california,looks amazing,but i forgot,the name how this area was called!

and after 20 years,the solarcells are out of power,and have to be replaced,so in non sunshine countrys like most of europe,with a solarsystem,you never save money!
 
Huevos

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Channel Hopper said:
Which is a poor fourth to,
1)using only the energy in what you actually require,
2)recycling anything you may have unwantonly used without considering the environment, and
3) ensuring your neighbours don't get away with screwing the environment and passing on the charges to everybody else.
I was talking about what can be done in the home to save energy. It kind of goes hand-in-hand with your number one.

Here I'll do anything to save energy but to be honest it is really related to money. If it doesn't save money I won't do it. For example to cook and heat water (on demand boiler) I use butane. I get through eight or nine 12.5kg cylinders a year. At 10.50€ that's about 90€ a year. To stop using that gas I could build my own solar cooker and water heating system, but even a DIY system would cost 1000€+ so I'd be looking at 10 years to break even.

BTW people are talking about convection to circulate and a water tank etc. Some of they DIY ones I've seen here are a lot simpler. A bank of radiators in sealed insulated boxes all connected in series. The water in the radiators is mains water. The capacity is only about 25 litres and then the cold starts to flow but that's plenty to have a shower and the new load heats up in minutes. But we do get plenty of sun here. Even with no preheating (tap open condition) with 10m2 of radiator you are probably getting 3kW of energy into the water.
 
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HB13DISH

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Just an idea for heating water in a sunny country.
Supposing you have a container of a size which is normally used for solar water heating systems ~120 liters, sitting on the roof top.
The container is totally transparent and for the sake of argument let us say it is made of glass (change it later for a less breakable material).
How long would it take for the water inside to get to a reasonable shower temperature of 40-50 degrees C?
After it gets to this temperature, cover it with an insulating material so that the temperature remains high for as longer time as possible.
I could try this with an empty plastic mineral water, which is reasonably transparent.
A bank of 60 empty bottles of 2.0 liters would get you 120 liters and would cost you nothing. At least save on the environment as you will be using them instead of throwing them.
A normal shower per person can be a lot less than this, but let us say this is for a couple with one child.
 
Huevos

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HB13DISH said:
Just an idea for heating water in a sunny country.
Supposing you have a container of a size which is normally used for solar water heating systems ~120 liters, sitting on the roof top.
Here that container is called un bidón. It's plastic, 1 cubic metre, 1000 litres. If you filled it and left it out all summer the water inside wouldn't ever get to much more than 35 degrees. Swimming pools here get to about 29 degrees (same as the med). For heating interfaces you need high surface area and low volume but without conductive losses.
 
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HB13DISH

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Huevos said:
Here that container is called un bidón. It's plastic, 1 cubic metre, 1000 litres. If you filled it and left it out all summer the water inside wouldn't ever get to much more than 35 degrees. Swimming pools here get to about 29 degrees (same as the med). For heating interfaces you need high surface area and low volume but without conductive losses.
Obviously 1000 liters is not going to get that hot, but a bank of smaller containers should.
I remember when we used to go on holiday in the south (Beer Shiva area), the black plastic water containers we had of 15 liters each would get so hot that we could take a shower with it. Put it in high position, stick a plastic tube and insert one end into the top opening and suck the air until the water starts to flow from the other end.
 
Turok

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Hello!
does israel,also have any vulcan activity?
i was in greece,on some island,the water in the ocean was so hot,that you can cook eggs in it:)

how much good solarcells in israel coasts?
 
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HB13DISH

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Turok said:
Hello!
does israel,also have any vulcan activity?
i was in greece,on some island,the water in the ocean was so hot,that you can cook eggs in it:)

how much good solarcells in israel coasts?
The last time someone asked me this question, we had an earth quake the same day.:-rofl2
No idea how much solar cells cost here, but they should be within the normal cost globally, otherwise nobody would buy them, except the filthy rich, but they can afford to pay their electricity bill and I doubt if saving few KWH can make any difference to them.
 
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