solar power grid feed-in

[lemur]

It is a popular idea that residential energy users can install solar panels and feed their unused energy back into the grid. But doesn't the voltage have to be at a certain level to effectively traverse the grid? Does the transformer that intermediates power between the lines and residences allow weak voltage charge to flow backward? I wouldn't think the current would be strong enough to add anything to the grid, but if it does, how does that work?

[CaptainPanic]

It needs to be the same voltage and you need to make it AC (instead of DC) too.

But that's not rocketscience. A quick google search taught me that to go from DC to AC, the box you need is called a "Grid tie inverter"... Grid tie inverters may or may not have a transformer, so that may have to be included too to change the voltage.

And you might want to contact your electricity provider for some paperwork too. They may even come to you and install the box for you.

 

It's all a matter of searching Google with the right keywords, getting some result, learning some new vocabulary, searching Google again with the new words, and... result! Until 5 minutes ago, I never knew the name of such a box.

Edited April 1, 2011 by CaptainPanic

[HerpaDerp]

It is a popular idea that residential energy users can install solar panels and feed their unused energy back into the grid. But doesn't the voltage have to be at a certain level to effectively traverse the grid? Does the transformer that intermediates power between the lines and residences allow weak voltage charge to flow backward? I wouldn't think the current would be strong enough to add anything to the grid, but if it does, how does that work?

 

Hi lemur,

I just joined and looks like I was lucky enough to find a question I know quite a bit about. I'm an electrical engineer in power transmission (Very High Voltage Power) , which is technically not the industry that deals with home PV installations but I know enough about the general concepts. As the other poster said, the power on your grid is in AC. This is basically because it's easier and more efficient to transform AC voltages. But to specifically answer your question, the power your house creates won't be going very far anyway. It will most likely just be powering next door's plasma tv. From the point of view of distributers (Lower Voltage Utilities), home PV solar is seen as just reducing the combined load of say your street or neighbourhood. This is actually in a lot of ways the purpose of these home PV initiatives from the government. They reduce peak load at critical times (PVs create more power on hot days when you are using your air con). Since networks are designed for peak loads and not average loads, this allows governments/utilities to delay major improvements to the network. But it is a very expensive quick fix and i digress.

 

In AC, current flows back and forwards equally (50 times a second in my country) so the electrons realistically go nowhere. So you need to picture power "flowing" through the lines rather than current (like you would with a DC circuit). It's true, there are physical limitations but you don't really need much current to allow power to flow through the transformers you wrote about. They are designed to operate under low currents. The only restriction is the magnetising current of the transformer, not really the voltage (even though voltage and current are essentially two sides to the same coin). This is typically very small and I think I'm going into too much detail anyway

 

So, the only thing the inverter needs to do is to create an AC voltage from the DC voltage from your PV cells. This AC voltage need to be at the normal level (my country has 240V) at the same frequency and phase as the network. Once it has done that, the power that your PV setup creates can flow into the network (the current will vary depending on the amount of power) and into your neighbour's tv.

 

I think i answered your question but if you want to know more, feel free to ask questions. I can make the answer as complicated as you want

[lemur]

I think i answered your question but if you want to know more, feel free to ask questions. I can make the answer as complicated as you want

Your level of detail is useful, as far as I'm concerned. I guess my question boils down to whether the power fed into the grid from a household solar panel gets conserved if it goes back through the transformer or whatever it is that intermediates power lines and household supply lines. I see what you mean that excess solar power could be sold to a direct neighbor without the energy having to go back onto the main grid, but I wonder if that's not its only possibility. It is interesting to picture entire grids consisting of solar-generating buildings where the excess power gets sent to a central storage-center, such as a water tower, but I wonder if it's even possible to get solar power from a grid to power a pump to pump water into the tower(s) during daylight hours.

Edited April 14, 2011 by lemur

[boogieman]

Your level of detail is useful, as far as I'm concerned. I guess my question boils down to whether the power fed into the grid from a household solar panel gets conserved if it goes back through the transformer or whatever it is that intermediates power lines and household supply lines. I see what you mean that excess solar power could be sold to a direct neighbor without the energy having to go back onto the main grid, but I wonder if that's not its only possibility. It is interesting to picture entire grids consisting of solar-generating buildings where the excess power gets sent to a central storage-center, such as a water tower, but I wonder if it's even possible to get solar power from a grid to power a pump to pump water into the tower(s) during daylight hours.

 

my pennies worth of criticism :

1. The single biggest misconception that "laymen" , myself included, have is that we tend to think of electricity in the same terms as we see water flowing in a pipe. You need to toss that idea (the water concept).

2. AC power cannot be stored - someone please correct me if I am wrong.

3. The cost and energy wastage to build a water tower and pump water, boggles my mind. You would need TWO reservoirs (one high and one low), electric pumps, hydro-electric turbines, some serious invertors and probably a boat-load of batteries. You would NEVER recover your cost and the maintenance-issues will eat a hole in your peace of mind.

 

my pennies worth input :

1. Solar power (and any other home power for that matter), works on the basic principle of charging up Batteries (in DC), and THEN you draw your power from the batteries, convert it to AC to run the lawnmower, spa-bath etc. .

2. You are ALREADY storing surplus "power", why take it out your piggy-bank, send it up to your "water tower" and store it again, when all you need (at low cost) is to get extra batteries and release it directly into the net.

3. Your concept is good. So good in fact, that I seem to recall seeing something to the effect that there are municipalities out there that are in fact doing this very thing.

4. The biggest problem we have here in my country is convincing people to convert to home power. The cost to remove your old geyser and install solar is about 2 months of FULL salary. Of which the government rebates about half, but ONLY afterward. HOWEVER, if you build a NEW house, the cost difference only adds-on about 0.5% to your total cost, which will repay itself in less than one year, with the rebate - it would cost ZERO!!! ONE simple change to legislation to FORCE this onto new home builders will solve all my countries power problems.

[lemur]

1. The single biggest misconception that "laymen" , myself included, have is that we tend to think of electricity in the same terms as we see water flowing in a pipe. You need to toss that idea (the water concept).

How did I suggest that electricity is like water flowing through a pipe? I just thought that pumping water into a tower would be a way to store energy as gravitational potential, that could drive turbines as it flowed back down at night.

 

2. AC power cannot be stored - someone please correct me if I am wrong.

All power can be stored by converting it into potential energy. This can be chemical potential as in batteries or mechanical potential in the form of compressed springs or gravitational potential in the form of mass elevated to some altitude.

 

3. The cost and energy wastage to build a water tower and pump water, boggles my mind. You would need TWO reservoirs (one high and one low), electric pumps, hydro-electric turbines, some serious invertors and probably a boat-load of batteries. You would NEVER recover your cost and the maintenance-issues will eat a hole in your peace of mind.

Here I will concede that I have no idea how much energy would be lost in the conversion using a pump, water tower, and turbines on the down-pipe.

 

1. Solar power (and any other home power for that matter), works on the basic principle of charging up Batteries (in DC), and THEN you draw your power from the batteries, convert it to AC to run the lawnmower, spa-bath etc.

I would like to know more about the efficiency of using chemical battery storage at the levels needed to save solar power everyday for nighttime use. The water tower idea seemed good to me because you could use the same water tower for many years whereas batteries seem to lose their ability to hold charge, which means they need replacing, which means they require factories, energy, and shipping to replace/recycle old batteries.

 

3. Your concept is good. So good in fact, that I seem to recall seeing something to the effect that there are municipalities out there that are in fact doing this very thing.

I've read about it, too. I hope I didn't give the impression that it was my brainchild. I was just wondering if anyone knew how feasible it would be, how much power could be stored, the (in)efficiency of power loss in the process of pumping and driving a turbine as it flows back down, etc.

 

4. The biggest problem we have here in my country is convincing people to convert to home power. The cost to remove your old geyser and install solar is about 2 months of FULL salary. Of which the government rebates about half, but ONLY afterward. HOWEVER, if you build a NEW house, the cost difference only adds-on about 0.5% to your total cost, which will repay itself in less than one year, with the rebate - it would cost ZERO!!! ONE simple change to legislation to FORCE this onto new home builders will solve all my countries power problems.

By "geyser," I assume you mean a gas water heater. If so, why remove these at all? Why not just teach people how to build their own solar water pre-heaters by connecting a bunch of CPVC water pipes and painting them black to use as a pre-heater? If their existing water-heater has a thermostat, it will automatically use less energy because the water was already hot when it entered the system. I think there may be some other problems with pressure build up in the CPVC pipes, but if you have clever people innovating, they should be able to work out the bugs and share the info with consumers.

 

 

[boogieman]

How did I suggest that electricity is like water flowing through a pipe? I just thought that pumping water into a tower would be a way to store energy as gravitational potential, that could drive turbines as it flowed back down at night.

 

Sorry, wasn't referring to you directly, was referring to a popular misconception, originally held by myself included.

 

 

All power can be stored by converting it into potential energy. This can be chemical potential as in batteries or mechanical potential in the form of compressed springs or gravitational potential in the form of mass elevated to some altitude.

 

I was specifically referring to storing AC in THAT form. Once again in layman terms, if I grab onto the terminals of a battery, I am going to land on my arlie and wonder what hit me. I wouldn't philosophize about "chemical potentials etc", I would consider myself as being shocked by electricity . In THIS context, AC cannot be stored.

 

Here I will concede that I have no idea how much energy would be lost in the conversion using a pump, water tower, and turbines on the down-pipe.

 

Neither would I - lol As a Civil Engineer, I could put a fair cost value to a couple of reservoirs, and divide it by the number of households in a typical residential area and come out with a reasonable accurate pay-back period of about 200 years.

 

I would like to know more about the efficiency of using chemical battery storage at the levels needed to save solar power everyday for nighttime use. The water tower idea seemed good to me because you could use the same water tower for many years whereas batteries seem to lose their ability to hold charge, which means they need replacing, which means they require factories, energy, and shipping to replace/recycle old batteries.

 

Because of various "mistakes of the past", our under-privileged communities developed in the absence of electricity, resulting in a massive market for battery-powered TV's. This in turn resulted in the development of a "Deep Cycle" car-sized battery. It holds charge better, can be drained to zero and be rapid charged without damage, and generally out-lives the conventional battery significantly. Regarding energy-efficiency, I can only imagine that it is more superior when compared to the energy losses anticipated when moving water to-and-fro, and the electrical/mechanical machinery involved.

 

 

I've read about it, too. I hope I didn't give the impression that it was my brainchild. I was just wondering if anyone knew how feasible it would be, how much power could be stored, the (in)efficiency of power loss in the process of pumping and driving a turbine as it flows back down, etc.

 

Sorry, it wasn't my intention to sound facetious. I slipped that in for the benefit of our other readers that may not be aware that the technology exists and is in fact already in use.

 

By "geyser," I assume you mean a gas water heater. If so, why remove these at all? Why not just teach people how to build their own solar water pre-heaters by connecting a bunch of CPVC water pipes and painting them black to use as a pre-heater? If their existing water-heater has a thermostat, it will automatically use less energy because the water was already hot when it entered the system. I think there may be some other problems with pressure build up in the CPVC pipes, but if you have clever people innovating, they should be able to work out the bugs and share the info with consumers.

 

South Africa is WAY not ready for gas. Our infrastructure never developed that way. In fact the only City that I am aware of ever trying it decommissioned their pipes about 20 years ago. I was referring to electric water heaters. Regarding CPVC, locally we have a thin-walled black pipe called LPDe. Your idea is already in use here, especially with regards to swimming pool heating. As I said previously, over here we have a lackadaisical attitude towards energy usage that will only get changed if/when Legislation forces it upon us.

 

 

My original response was not intended to criticize your OP, but rather to add additional comment on the topic for other readers to consider.

 

kind regards

[lemur]

I was specifically referring to storing AC in THAT form. Once again in layman terms, if I grab onto the terminals of a battery, I am going to land on my arlie and wonder what hit me. I wouldn't philosophize about "chemical potentials etc", I would consider myself as being shocked by electricity . In THIS context, AC cannot be stored.

What does that context have to do with whether energy can be stored or not? AC power is converted into DC power in my battery-charger, I believe. Does that mean the energy being stored in the batteries is DC and not AC? I don't think so. As you said, electricity isn't a liquid running through a pipe.

 

Neither would I - lol As a Civil Engineer, I could put a fair cost value to a couple of reservoirs, and divide it by the number of households in a typical residential area and come out with a reasonable accurate pay-back period of about 200 years.

I was thinking more in terms of the amount of power used to fill up the water tower minus the amount generated by letting the tower run empty through the generator turbines. Then I would want know the total costs of building and maintaining the water tower and peripheral equipment over the lifespan of the tower. Then I would want to divide that by cost per household-served per month according to a certain level of nighttime power usage. Intuitively, it does seem inefficient compared with chemical batteries. I think it would actually make more sense for each device to have its own battery designed to give it a certain amount of nighttime functionality. A refrigerator or water-heater would just have to maintain its temperature overnight, but the battery systems could adjust to different temperature conditions.

 

South Africa is WAY not ready for gas. Our infrastructure never developed that way. In fact the only City that I am aware of ever trying it decommissioned their pipes about 20 years ago. I was referring to electric water heaters. Regarding CPVC, locally we have a thin-walled black pipe called LPDe. Your idea is already in use here, especially with regards to swimming pool heating. As I said previously, over here we have a lackadaisical attitude towards energy usage that will only get changed if/when Legislation forces it upon us.

Or economics does. The problem in regions with large income gaps is that something that could be very profitable for those with low income can be blocked by the fact that businesses don't want to provide high levels of access at prices that those with low income can afford. I'm tempted to say that this is less of a problem in regions where there is less economic disparity, but in reality I think they're all part of the same global economy that makes it difficult for the poor to get access to the means to improve their material conditions.

 

 

[danie]

The intenlegent grid wil be part of our lives in the future. People will be able to generate electricity on roofs and use what they need. The extra power can then be fed into the national grid.

 

This consept of "grid storage" will eleminate the use of batterys.

A single household wont generate much electricity but if you multiply it by a million you can replace one (nuclear) power station.

 

The techonology is availeble in most countries.

[random]

We had solar panels at our old place, The best way to set it up is to actually take your power from the grid and feed ALL your solar power into the grid. R.E we pay 4.5 cents per kwh consumed the power company pays us 42 cents per kwh generated and fed into the grid. I have since heard they have increased this rate to 63 cents (or was it more?) and they agree to pay this rate to you for 20 years.

 

This is how they are trying to get us Canadians interested in micro solar energy farms.

 

Solar beats wind hands down in a day to day analysis of kwh generated (we had both)

however it is exciting to watch the energy peaks generated by a wind mill during a wind storm.

 

If you buy the panels wholesale it is actually possible to turn a profit fairly quickly.

 

Interesting note : we also installed a water source heat pump absolutely wonderful and comfortable system that will easily keep your home at 74 all winter, and you get a central air system for summer too!