Idea for offsetting solar/wind with grid power... 1

[spdracer22]

I'm an auto/mech engineer, and have only had a couple circuits classes, so please forgive me if I'm talking out of my you-know-what. But, easily-integrated 'green' power generation interests me, so here I am, trying to learn...

When a solar panel or wind turbine is added to a home, it's either:

A) Connected to the main supply, allowing all loads to feed off of it, and feeding any excess to the grid. It may have a battery bank between the generator and main.

B) Somewhat like a UPS. Charge a battery bank that feeds a few devices directly, then switches to main when bank dries up.


The idea:

Somewhat like B, only without the batteries. There would be a box that the load device(s) and generator would be plugged into, then the box would be plugged into a standard 110V wall outlet. 100% of the generated power would be used all the time, which would be supplemented by the wall outlet. So, for a 100W load, 10W may come from the solar panel and 90W from the wall, etc, etc.

So, my questions are:

1. Does anyone know of a company that builds such a device?

2. How would one go about building such a device? Is it as simple as just putting the supplies in parallel?

3. Or, is a better/simpler way just to invert the generated DC into AC and plug into a wall outlet? (I've heard this is a bad idea, but thought I'd throw it out there anyway)

 

[waross]

Use an alternate energy system to charge the batteries of a Uninteruptible Power Supply. Set the charging voltage of the alternate energy source higher than the charging voltage from the grid powered charger.
If the UPS and its load are large in relation to the alternate energy source most of the energy from the alternate source will be utilized.
Automotive type lead-acid batteries have some flexibility in the charging voltage. The two charging voltage levels will only allow grid charging when the alternate energy source is insufficient to carry the load.
This scheme should allow almost full utilization of the available alternate energy and avoid the safety issues inherent with feeding alternate energy directly into the grid mains.
You can probably go with an off the shelf UPS. Change out the batteries for larger lead acid batteries and adjust the maximum charging voltage. Disable the bypass mode or use logic to inhibit bypass when the alternate energy supply is above a set minimum level.
respectfully

 

[IRstuff]

The whole purpose of net metering is to account for the fact that most houses don't use much electricity during the periods when solar generates the bulk of its electricity. That's why you sell it back to the utility and buy it back later.

If you tried to store all the generated power, you'd need a truckload of batteries, which is hardly economical nor exactly low maintenance.

TTFN

FAQ731-376

 

[LionelHutz]

That's the problem I have with this IR. You want to use all of the available green energy you can. So, you either grid tie and net meter or you store it and balance the energy production and storage with the usage. Storage requires batteries and the negatives that go with them.

 

[2dye4]

Thats why I want to approach it from the other end. Simple installation, no discernable difference to user, very minimal loss of power from the grid and when available the alt source is used if needed.
It does make very poor use of the potential of the alt source but in our current situation it seems like pain free (other than cost) systems don't exist.
If the loads were selected based on daytime usage maybe it could someday pay off. ( televisions, computers, refridgeration...)

Just think if one day some wise guy really makes solar panels cheaply then this would become much more attractive.



One possible usage is pre-heating the incoming water in a seperate tank before it reaches the main water heater. This would allow some energy storage and usefullness as hot water is a major draw of electrical energy.

 

[IRstuff]

Unless you're running a laundry from your home, that basically means that you're wasting all the solar. And, you'd only need about 2 m^2 to heat 50 gal of water, so the economy of scale isn't even there.

What's wrong with net metering? You get to sell your electricity at premium rates and buy it back at a lower rate.

TTFN

FAQ731-376

 

[itsmoked]

Part of the net metering problem is the whole torrent of bureaucracy one subjects themselves to. The POCO often charges some exorbitant "meter charge". Permits... Inspectors crawling around, etc, etc. Basically violating the premise of allowing the average Joe to make some little contribution to The Problem and to his wallet.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[2dye4]

Net metering meets with much resistance from the utilities. This example from kansas as much as states openly that the utility cannot afford the competition for power production.

http://www.kepco.org/news/netmetering.html

This should not be an allowable argument. How would they adress a person who gets most of his power from alt energy and then occcasionally buys some from the grid. They clearly cannot oppose this on some moral/legal ground. They can make a claim that they have fixed costs from providing the availability of power and they would be right to charge enough to keep suppply available.

If this argument is allowed to prevail it means there will be no independent power production because everyone has to buy their share in order to keep the infrastructure operating. In other words their monopoly is a neccessity.
Doesen't sound like the free market to me.
Oh I forgot that only applies when you loose your job or pay high prices at the pump.

 

[spdracer22]

2dye4 - An OS project would be ideal. My vision would be to have the plans available online, then work out a deal with a supplier to provide DIY packages of all the parts needed to build it yourself. This would allow people to just print the plans and source the parts themselves, or buy a ready-to-build kit, or even sell assembled kits.


To address another thing...

I use solar merely as an example. Obviously, it doen't work at night when most people are actually at home. But, during the heat of the day, it can offset the power needs of a refrigerator, window A/C, fans, pumps, etc. etc. Basically, all of the stuff that needs to run even when no one is home.

However, my thinking doesn't stop there. Since any dc supply can be easly plugged in, it will allow people to develop new, novel ways of generating electricity. For instance, I saw on Instructables.com that, as a school project, someone made a wind generator out of a Pringles can. It doesn't produce a lot of power, but they're really cheap to make, and a small farm of them on an outdoor balcony could be a decent contribution.

But there's also a lot of other things you could build... What about power generating exercise equipment? Or scavenging power from heat sinks? Or even mini water turbines on shower heads and faucets...? The ideas are endless, but there's no suitable way to implement all of these tiny ideas so that they can actually be of benefit past a science experiment.

That type of ingenuity, and the fact that to offset a little bit of power wouldn't take a lot of money in the DIY world, would really get this idea off the ground on a larger scale. Right now, to even get in the game takes a huge investment. With this 'box' you have a choice between the commercial panel/generator route, or the diy route.

One thing to remember is that this isn't supposed to be a whole-house system; each 'box' is only supposed to offset a few devices, or basically replace only a single wall outlet.

 

[itsmoked]

You want to see realll poco fighting and back peddling and from the company that runs the most gratuitous, pro solar ads on TV, check this very interesting site out.

Note the page on the fight with the power company.
Where the poco makes its real intentions abundantly clear.

http://www.solarwarrior.com/

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[2dye4]

spdracer22

I agree that a "box" with this functionality would open up many opportunities for alt energy. However to make this thing power real loads with the necessary source transfer capability means it will not be cheap. Even the parts cost will be in the range of $200.00. I still think it is a worthwhile project.
Is there a web location for people to gather and pursue projects like this??
I am already working on a block diagram for how I imagine the device to function and will welcome all the eng-tips feedback I can get.
There could be a real market for this device given the fact that it allows alt energy to be utilized without all the usual problems. ( No financial payback, just satisfaction )
Lets get started

 

[spdracer22]

Kieth hits a very, very good point, and one that this proposed system circumvents. Since you're not feeding back to the grid, you don't have to worry about interconnection issues. The poco will only see a drop in consumption, much like they'd see if you simply turned off a few big devices, or swapped them for more efficient models. You're not trying to feed the grid, so they can't do anything about it...

 

[itsmoked]

I think that any battery will add a large undesirable to the scheme.

For starters a 40% energy loss! They have lousy charging efficiencies. Someone lays out $300 for a 40W panel and then from then on it acts like a 25W panel? Yuck. The need to replace the battery every few years.. Yuck. The system costs more. Yuck. The system is heavier. Yuck. Bulkier. Yuck.

I like the aforementioned suggestion of converting the Line power to DC feeding instead a (small)capacitor bank. Next an inverter stepping the solar power up to a slightly higher voltage also charging the capacitor bank. If the solar is available it trumps the line power. An inverter is fed from the capacitor bank.

The user would select a device that always runs or runs a lot during solar hours and plugs it into the inverter's output. This would effectively remove that device or some part of it from the daily utility charge realm without back feeding.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[spdracer22]

So, something like (imagine the |'s are lined up):

AC--->Rectifier--->|
|--->Capacitor--->Inverter--->Load
DC---------------->|

Or:

AC--->Rectifier--->|
|--->Inverter--->Load
DC--->Capacitor--->|

 

[itsmoked]

The first. Not the second.

There's a lot of details that might also go into the Line to CapBank aspect. Another words not just rectifiers.

This is certainly a much higher tech project than a feed the power to the Grid job...

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[spdracer22]

Not sure if this link will work... It's a patent for what seems to be a device similar to what we've been talking about.

http://patft.uspto.gov/netacgi/nph-...XT&s1=7012825.PN.&OS=PN/7012825&RS=PN/7012825

 

[peebee]

As others have mentioned, these things all sure sound like UPS systems. You've almost perfectly described an off-line UPS and a double-conversion UPS in the above. The only one I haven't seen so far in the above is line-interactive.

If you ripped out the battery, and plugged in your DC generator (with sufficient voltage control), you'd be all set. The only head-scratcher I see is, what happens if you have your DC generator connected and there is no load? It's unclear to me what happens to a wind or solar generator if no load is attached.... overvoltages might be a problem....

Seems to me the best way to start tinkering with this would be to go buy a cheap APC UPS. There's some available on ebay for $15-20.

 

[LionelHutz]

I agree about the batteries Keith. But, you are going to need one very large capacitor bank to be able to get better utilization from that 40W panel without them.

I'd think you want a load that draws more power than the renewable source can provide. You use an AC-DC-AC inverter as the basis. Then, you add a DC-DC controller that pushes as much renewable energy as possible into the DC buss of this inverter. The DC buss of this inverter will simultaneously get the extra power it needs from the line. I think maybe this is what you were hinting at Keith in your description?

Switching between the two sources would be a waste of the potential capability of the RE in my opinion.

 

[2dye4]

As for batteries.
How bout a small Ni-Cad pack like used in Hybrid Cars.
It even comes complete with a marketing hype built in.
"Hybrid Solar Power System"
Let the investors form a line to the left.

I have to disagree with Lionel. My main concern is that the line supply system not waste so much power when the alt source is idle as to render the whold think a wash.
Switching to direct line power without processing it during down time is a necessity to avoid the (80-90)% maximum effeciency when the power is processed.

My implementation.
Power Transformer with three isolated 120 VAC windings chosed for effeciency. The AC main is switched into one winding by a relay controlled by the system. The alt source feeds an inverter that connects to winding 2. The output to the load comes from winding 3. This gives you the isolation for safety. When the alt source is available the relay opens the mains winding and supplies via the inverter winding.
The control system has to monitor the available alt energy and decide when it can switch as well as redundant safety measures to make sure the alt source doesn't feed the grid through the transformer. Also zero cross switching of the relay would be nice.

 

[peebee]

2dye4 -- your solution starts to sound like the line-interactive UPS system that was missing in the above.....

 

[LionelHutz]

I hear what you're saying but I still think that you will need to match a load to a much bigger RE system to get significant RE only run time. Then, you're wasting a lot of the potential energy production you paid for. And, last time I checked solar panels were far from cheap and wind doesn't give a nice constant output.

I'd be curious to see some preliminary data comparing the required RE source vs the possible savings achievable when suppling some typical house loads.