Solar In A Box

The Pitch

Do you own a flat screen TV? If you live in America and are middle class, there is a pretty good chance you do.

Do you own a solar power system? Probably not.

In 2006, Americans purchased more than 17 million flat screen TVs. During that same time, we bought less less than 5,000 residential solar power systems.

I don't think this is because Americans care more about TV than the environment.

I think it is because flat screen TVs are easy and solar power systems are hard.

You can easily walk into a Wal-Mart store and purchase a flat screen TV and bring it home and plug it in.

Solar power systems today require a huge investment of time, effort, and money to install.

If you could buy an inexpensive solar power system at Wal-Mart and bring it home and plug it in, I think that millions of Americans would.

 

The Concept

Create an off-the-shelf, mass-produced renewable electricity generation system that you can buy at the store, bring home, and plug in. The components of the system are simple, cheap, and modular.

System diagram

The Hub

200 Watt Base Module
A 200 Watt hub with one outlet and one solar panel.
Perfect for powering a desktop computer.

The hub is the base of the system. You plug the hub into a normal wall outlet and then you connect a load (appliance, computer, lights)  into the hub. Both connections use normal household 3-prong plugs. You also connect the solar panel(s) into a special jack on the hub. When the sun is shining, the hub converts the DC energy coming from the solar panel into AC energy that your stuff can use. When the sun is not making enough power for your load (because it is cloudy or nighttime), the hub seamlessly supplies the extra power from your house mains so you always get continuous power.

The hub above has a display that shows the amount of power the load is using and the amount of power that is being supplied by the solar panels.

A 1000 Watt hub with 6 outlets and connections for 4 solar panels 
A 1000 Watt hub with 6 outlets and connections for 4 solar panels.
This could support a small air conditioner or several appliances.

Hubs come in many different sizes from 200 Watts to 2,000 Watts.  Bigger hubs have multiple energy source jacks, so you can buy extra panels and plug them in at anytime to expand the system.

The hub is in constant digital communication with the connected power sources. The communication link runs over the same wires that carry the power. Because the hub is able to read information from the connected solar panels, it can make adjustments based on what size and type of panel is attached and run at maximum efficiency. If the communication link is ever broken because the wires are damaged or disconnected, the power source instantly stops sending power down the lines. This makes the system fail-safe.

Power Sources 

A Solar-In-A-Box solar panel is just a standard solar panel with the addition of an inexpensive module that makes it compatible with the system. This module is responsible for maintaining the communication link with the attached hub. When a panel is first connected, the module tells the hub some information that the hub needs to operate the panel at its maximum efficiency. Then the hub sends a signal to module telling it to start sending power down the connection. The module only sends power down the wire when it is connected to a functioning hub. 

But as a consumer, you do not need to know about any of these details. You'd just buy any compatible power source and plug it in to any hub.

These modules could also easily be incorporated into any power source cable of supplying DC power, making that source able to plug directly into a hub.  This would include a variety of different sizes and types of solar panels and also windmills, small hydroelectric turbines, even a stationary bike with a generator. (Check out my solid-state windmill design with NO moving parts- look ma, no rotor!).

 

Prototype solar mount
A prototype solar panel mount I built. It is cheap,
very stable and durable, UPS ground shippable, can be assembled in about 5 minutes.
You adjust the azimuth (the height of the sun in the sky) along the rear support leg.
You adjust the direction by picking it up and turning it. More pictures here.

 

The Numbers

Solar panels cost between $4 and $5 US per watt in 200 watt per panel sizes.

A low end 350 Watt consumer UPS costs less than $40. I believe a hub of similar size would cost about the same if not less.

So, today a small but expandable 200 watt Solar In A Box system would cost less than $1000 retail. That's about $4-$5 per watt installed.

A net metered system in my area typically costs about $10-$12 per watt installed.

In my area, state-funded rebates pay for about $4 per installed watt for grid-tied solar systems.

The Video

Here is an inspirational video I made for Sundance Channel's One Big Idea promotion...

 

It is only a minute long and I only had a couple of hours to make it, but it would have been worth the effort if Sundance liked it.

 

FAQ

Q: What makes a Solar-In-A-Box hub different from  existing solar power inverters?

There are two types of solar inverters available today - grid-tied and non-grid-tied.

Grid-tied inverters take the electricity generated by the solar panels and feed it back into the electrical grid. This is a very complicated process because the inverter must be exactly in sync with the electrical power being generated by the local utility.  The grid-tied inverter must also meet very stringent regulatory requirements because it could potentially effect a large number of people. The existing grid-tied inverters are fantastically engineered to meet all these difficult requirements, but all this extra functionality makes them expensive to produce. Because they feed power backwards, they must be hard-wired into a dedicated breaker on your electrical system. This usually has to be done by a qualified electrician.

Non-grid-tied inverters are not attached to the grid at all so they are much simpler and cheaper than grid-tied inverters. Because they are not connected to the grid, they typically must rely on batteries to supply power when a cloud goes by or at night. Batteries are big and expensive and inefficient.

The Solar-In-A-Box hub is the best of both worlds. Because it only sends power to the directly connected load and never back into the grid, it does not need all the extra complication that a grid-tied inverter needs. When the solar panels are not supplying electricity, the hub can draw power from the grid as needed, avoiding the need for batteries.

Q: Is this net metering?

No. With net metering, when you make more power than you need you send the excess power back to the grid and that turns your meter backwards. Then, some other time when you need more power than you are generating (at night) you draw from the grid and your meter runs forward again.

With Solar-In-A-Box, you never send electricity back into the grid. You use any available solar power when it is generated, and use grid power when solar power is not available. This means that Solar-In-A-Box typically does not reduce the amount of electricity you buy at night, but only during the day when the sun is shinning (unless you also plug a windmill power source into your hub).

Q: Is this better than net metering?

Theoretically, net metering is perfect - if you make more solar power than you can use, you can share it with everyone else on the grid. This typically happens on hot, sunny days which is exactly when the grid really needs some extra power. Even better, the power you are making is put on the edge of the grid where you and your neighbors live, so it doesn't have to travel over long transmission lines to get to where it is needed most (lots of power is lost during transmission). Then, later that night when you need some power to watch TV, you can take back some of what you gave at a time when there is not as much demand on the grid.

Unfortunately, there are some complications. The biggest one is that net metering depends on you sending power to your local electric company. This means dealing with lots of regulation and bureaucracy. In practice, this makes grid-tied solar systems difficult and expensive to install. You are not even allowed to do net metering in some states. I wish it were not true, but it is- and there is no realistic way to change it in the near future.

Because Solar-In-Box never sends power back into the electric grid, the whole system works just like any other electrical product you'd connect to your electric company. There are no special regulations or agreements, you just plug it in.

I think net metering would be the cure to all our woes in an ideal world. Alas, we need practical solutions that can actually work in the world we live in today. Solar-in-a-box is all about doing something now that has a real and practical impact.

Q: What happens if my solar panels are making more power than my load is using?

Because the Solar-In-A-Box hub can not send excess back into the grid, any solar power that is not used is lost. To make sure you efficiently use all the solar power that is being generated, you need to plug in appropriate sized loads into the hub. Ideally, you'd want to to plug in enough stuff to a hub to use slightly more electricity than the solar panels can produce, this way you'll always use all the power generated. Loads that use a constant amount of power during times when the sun is shining are perfect (think computers, air conditioners). You don't get any benefit by connecting something that you only use at night.

Q: Why hasn't anyone done this before?

I don't know. Maybe they have, but since I can't find any Solar-In-A-Box systems at my local Walmart, I have to assume that if they did try it, they didn't succeed.

UPDATE (8/7/07): An Uninterruptible Solar Power Supply design just won an honorable mention in a Circuit Cellar design contest. You can see the technical details here. It is a little different from Solar-In-A-Box in that...

  1. If the solar panel is not supplying enough power to support the load, the Uninterruptible Solar Power Supply simply switches from solar to full grid power. This means that typically you will need to oversize the panel in relation to the size of the load. The solar panel is typically the system's most expensive component, so it is nice to fully utilize all of its capacity. The Solar-In-A-Box hub would dynamically mix power coming from both sources to optimally use all available solar power at any given moment.
  2. The Uninterruptible Solar Power Supply does not appear to do maximum power point tracking on the solar panel, so the solar panel does not run as efficiently as it could. This would be pretty easy to add, though.
  3. The Uninterruptible Solar Power Supply is only a component, not a system. You'd want to sell it complete with matched solar panels, easy to connect cables, and a UL listing.
  4. The Uninterruptible Solar Power Supply is built and actually works, whereas Solar-In-A-Box is, at this point, just an idea. A existing and functional system is infinitely more useful than a concept. :)

The Uninterruptible Solar Power Supply and Solar-In-A-Box do share one huge attribute in common; both avoid all the problems of gird-tie systems by using all the generated power locally. I think this is a key and novel concept.

UPDATE (9/22/08): Shane sent me a link to this SWEA plug in inverter that superficially looks like a Solar-In-A-Box hub unit. Unfortunately is nothing like a Solar-In-A-Box. It is totally illegal and dangerous. Because it back-feeds power into the plug, it can overload the circuit it is plugged into and cause a fire. It would not take much work for them to fix it, though. Then if they can just bring the price (way) down, it would be great.

UPDATE (7/24/09): Found the Blue Link PV Generator which they say to can just plug directly into a dedicated GFI outlet. My guess is that they mean an outlet on a dedicated branch circuit which is connected to a dedicated breaker. Even so, I can't see how this could be safe or legal. 

Q: Do you have a patent for this idea?

No, and I don't want to. I'd be very happy if lots of people started making their own Solar-In-A-Box compatible components. The competition would drive down prices, and different manufactures could offer a wide range of sizes and features.

APC might want to make a hub with a built-in battery so it would work even during a power failure. Dell might want to make a hub that was built into a computer where the power supply would normally go so the computer could automatically wake up when there was extra power and do power intensive tasks. GE could build a hub into a refrigerator that would use surplus power to make ice.

There are lots of innovation opportunities for power source manufacturers too. While Sharp might make a large but inexpensive standard solar panel that plugs into a hub, Green And Gold might want to produce a Solar-In-Box version of their hyper-efficient and space-saving SunCube DC for apartment dwellers who have small south-facing terraces. Southwest Windpower could even release a Solar-In-A-Box compatible windmill  that would work for people with more wind than sun. Heck, you could even connect a micro-turbine to your hub and run the dehumidifier in your basement off of power from the stream out back.

All of these components would work seamlessly together, so you could buy exactly what you need and just plug it in.

Q: But with Solar-In-A-Box, people are still using power from the gird. Shouldn't we be getting people off the grid?

Solar-In-A-Box is about finding a practical and realistic solution to reduce our environmental impact today. The goal is to make something that normal people can actually afford, buy, and use now to make a difference.

It turns out that you do not need to move everyone off the gird to make a huge difference in our environmental impact. Sunny days is when demand on the grid peaks, and this is when power companies are forced to use the worse pollution producing sources for power. By reducing the demand at these peak times just a little, you can prevent huge amounts of pollution from being produced. By making Solar-In-A-Box cheap and easy, you make it possible for huge numbers of people to participate. Even if only a small percentage of us could use Solar-In-A-Box to cut our peak demand by a small amount, the net impact would be huge.

Also, because the total installed cost of a Solar-In-A-Box system can potentially be so much lower than a grid tied system, people will be able to save more money overall that they would with a grid-tied system, and many, many more people will be able to do so since the barriers (cost, effort) are so much lower.

Q: How do you mount the solar panels?

It is important that the mounting systems do not require any permits to set up. They should also be easy and not require any skill or tools more than, say, setting up a piece of lawn furniture.

A standard solar panel could come with a simple aluminum-tube frame that you could just put down on any sunny spot in your yard. It would come with a handy flat cable that could run in though any window or door. You could move the frame around to get the best sun exposure from season to season, or just to mow the grass under it. It would also have an easy way to adjust the angle of the panel so you could change it a few times a year as the sun rises and falls in the sky. This could give you 20% or more additional power compared to a fixed-angle mount system typically installed on your roof.

Check out this prototype panel mount that I built. It weighs less than 10 pounds, costs less than $30 in parts, takes less than 5 minutes to assemble, does not require a permit, and is very stable and durable.

There could also be a window mount that would hang a panel from a window still. The window would close down on it to secure it, similarly to the way you mount an air conditioner in a window. It would have an integrated cable to get the power from the attached panel into the room.

You could even buy a set of nylon straps to secure some panels to your roof. The kit would include some rubber guards that you would snap onto the edges of the panels to protect your roof surface.

I'm sure that many, many people will come up with many more innovative ways to mount the solar panels that do not require permits. The best will be for sale at WalMart in the Solar-In-A-Box Accessories section. Mass markets fuel innovation.

Q: Where can I buy a Solar-In-A-Box system?

You can't buy one- yet. All of above pictures are (crude) photo-shopped mock ups of what I think a system might look like. For now this is just an idea. I'm hopping that I can get enough people interested that it can become a reality.

The technology is ready. The electronics inside a hub are similar to what you'd find inside a UPS. A UPS converts the AC power from the wall into DC to charge its batteries, then converts the DC from the batteries back into AC to power the outlets. Replace the batteries with a connection for a solar panel and add some software to make it more efficient and you have a hub. You can get 500 Watt consumer UPS for as little as $59 today. A 500 Watt hub should cost about the same and be smaller because there are no batteries inside. One of the existing UPS manufactures would be a perfect candidate for making hubs.

The module that attaches to the back of the solar panel (or any power source) would contain a tiny microcomputer, some components to handle the communications link over the connection and a switch for controlling the power flow though the wire. All these parts are cheap and readily available today. My guess is that this module would only add between $1 and $10 to the cost of the power source depending on the size of the power source and the volume of units produced.

Based on these estimates, I think it would be possible to build a 200 Watt Solar-In-A-Box system for less than $1,000.  That's less than the average flat screen TV. And the cost is heavily dependant on the cost of the solar panels themselves, so mass production and distribution could probably cut that significantly.

If anyone is _seriously_ interested in bringing this product to mass production, I'm happy to build a working prototype. If you work for WalMart, I'll even build you a few!

Q: What about rebates?

Some existing rebate programs might cover the Solar-in-a-Box system as it is, others might need to be updated. A good strategy for incentives would be to pay the rebates directly to retailers who sell the system to reduce the out-of-pocket cost for consumers. There are already programs that work like this for things like energy efficient appliances and light bulbs. But ultimately, I think the Solar-In-A-Box system would make sense even without any rebates at all, rebates would just make it better.

I think it is likely that the Solar-In-A-Box system would qualify for the new 30% Federal Energy Tax Credit up to $2,000.

Q: Why don't you add a charge controller and battery so you can supply power after the sun goes down and harvest the most energy possible?

There are many battery-based, solar powered inverter systems, many of them portable. You can also very easily and cheaply build one of these yourself with a solar panel, charger, car battery, and inverter. The total cost of the parts besides the panel is less than $100.

While these systems can be very useful in some situations where you do not have access to the grid, they are not really a good solution for the general problem of reducing grid loads.

While this would certainly be possible, I think it is counter-productive.

 

Batteries are expensive, heavy, and have limited lifetimes. They give back significantly less power than you put into them.

 

But, more importantly, the best thing about solar power is that you get power when there is the most demand for power, during peak hours on sunny days.

 

Using a battery would essentially be shifting power generated during peak times to off-peak times, and losing some of the power in the process because batteries are not very efficient.

 

I think the best use for a Solar-In-A-Box system is to trim peak demand on the grid. This can have a surprisingly high environmental impact because as demand on the grid increases, the efficiency of grid power generation and distribution drops very quickly.

 

The grid is actually a very efficient source of power when demand is low (like at night). Lots of cheap and clean power comes from distant hydroelectric sources. Large modern power plants are also pretty efficient power generators.

 

But when the grid has reached it limit on hot, sunny summer days the power companies are forced to turn to very high cost and high impact power sources to meet the marginal extra demand. These small, quick responding sources are typically much less efficient than the baseline sources.

By trimming peak demand, you can greatly reduce the need to activate these inefficient power sources.

 

You can make sure all of the solar power generated by your Solar-In-A-Box system is used by sizing the system correctly. As long as there is enough load connected to the Solar-In-A-Box inverter to use its full output, none will be wasted.

 

Q: Will the unit do MPPT (maximum power point tracking) on the solar module, for 30% more energy capture? 

 

Yes, MPPT is not hard to do in software and there will already be a little computer inside the inverter to handle the communications link to the power sources.. Each solar panel will download its power curve function to the inverter when it is connected, so the inverter can keep each panel at its MPP even if you mix and match different panels on the same system.

 

Q: Sounds like it will not supply power to the grid so you've avoided UL1741 & IEEE 1547 which are big headaches.

 

The only regulatory approval needed for a Solar-In-A-Box system is a UL listing. This approval is secured ONCE by the manufacturer for the system design, not by each purchaser for each unit. This makes it into an appliance that anyone can bring home and plug in and there is nothing the power company or your local town can do to stop you.

Q: Why not connect the inverter directly into the service panel?

Typically you need a permit and a licensed electrician to do work on the service panel. At very least you need to know what you are doing, so it is not a practical (or safe) do-it-yourself project.

The magic behind the Solar-In-A-Box is that it connects to a normal plug. In the USA, as long as an appliance plus into a normal plug and it us UL listed, it does not trigger any code or permitting requirements. That means that anyone can just plug it in anytime they want without needing approvals from their town inspector or a licensed electrician.

Anyone who can plug in a flat screen TV can install a Solar-In-A-Box system.

Q: How does Solar-In-A-Box scale? It seems like if I got lots and lots of them I would have wires everywhere.

I agree that Solar-In-A-Box is not scalable, but I don't think this is relevant. Solar-In-A-Box is meant to solve a very specific problem- getting people to install a solar system who would not otherwise be able to do so. I'd much rather have 1,000,000 relatively small Solar-In-A-Box systems installed around the grid than 5,000 scalable systems.

Q: I have central air conditioning, how could I use Solar-in-Box to power it?

Although air conditioners are the perfect load for a solar system because they often use the most energy at the same time the sun is brightest, central air systems are not a good fit for a Solar-In-A-Box system because they are typically wired directly into a service panel.

But on that note, I've also been thinking a lot about efficient cooling (I don't have air conditioning and it has been pretty hot). I think you could build an amazingly efficient heat-pump system that was basically a ductless-mini split  that could be plugged in and installed in or though a window or a small hole in the wall. These systems are amazingly efficient and quiet. Since it could be plugged in, you could plug it into a Solar in a box hub. The reason that mini-splits are not user installable now is that they must be filled with refrigerant after the hoses that connect the inside and outside parts are connected. This requires some fancy equipment and training because you must be very careful not to let any air into the system or let any refrigerant out of the system.
I think the trick would be to adapt the pump already inside the compressor unit so that it could automatically create the necessary vacuum once the pipes were connected, and even pump down the refrigerant anytime you wanted to unhook the pipes later.

UPDATE: It looks like just such a DC powered mini-split air conditioner now exists! This one uses batteries, which will undoubtily make it more expensive & heavy than if it also had the ability to pull AC from the grid when nessisarry, but it would be great if you live off the grid and really want some AC.

While you are designing a new air conditioning system, why not use the exhausted heat to generate free hot water? I'd also include a heat recovery unit so you could efficiently bring in conditioned fresh air. Finally, why not collect the condensate into a tank and have free, pure, cold drinking water? All the technology exists today, just in discreet components. All that is needed is a bit of integration engineering to bring them all together into one mass-produced and affordable machine that you could buy at WalMart. You'd save a huge amount of energy and money and be more comfortable. Depending on how hot it gets this summer, I'm going to try to build a prototype of a super-efficient DIY mini-split system for myself, so check back.

Anyway, none of this helps you with your existing central air conditioner. Maybe you could consider shifting your usage time by making ice at night. If you got a time-of-day meter from your electric utility, this could save you money as well.

Q: If I send you $1,000 will you send me a 200W Solar-In-A-Box?

Unfortunately I don't have time to start building and sending Solar-In-A-Box systems one at a time. I guess if enough people really want it, I'll put up an Instructable on how to build a prototype yourself, but I think it misses the point. The whole point of Solar-In-A-Box is to make solar energy into a mass produced product rather than a fringe project. 

Q: Can I plug my air conditioner into a Solar-In-A-Box?

If you want to run air conditioning from solar, there are much more efficient ways to do it then plugging a standard unit into a Solar-in-a-Box system
 
Solar panels make Direct Current (DC). Part of the work the Solar-IN-A-Box system does is convert this DC current into Alternating Current (AC) which is the type that comes out of a normal wall socket.

Most air conditioning units use AC to run a motor(s) that drives a compressor and fan. To convert the DC from the panels into AC to run a motor is inefficient. Much better is to use the DC coming out of the panels directly to run the motor.
 
There are DC powered air conditioners available for boats and RVs. You could, for example, just buy something like this…
 
http://www.dcbreeze.com/
 
…and connect it to 3-5 200W solar panels (depending on where you live) and you’d have a zero-power system that would give you cold air whenever sun was hitting the panels.
 
Alternately, you could get one of the new super-efficient split systems like this…
 
http://www.fujitsugeneral.com/wallmounted.htm
 
...and with a bit of hacking, you could connect the DC from a solar array directly into the air conditioner and bypass the inverter. These systems already use DC motors because it makes them run more efficiently, the inverter converts the AC in your house mains into DC.

I think either of these systems would be a great product to sell – as would a ready-to-go solar powered window-mount unit. Ideally this unit would operate like the more expensive split systems and have separate (DC driven) motors for the outdoor compressor and the indoor fan.  This would make it very quiet and efficient compared to a normal window unit. 

UPDATE 11/3/2010 : Here is a company that has done just that...

http://www.securusair.com/techspecs.html

 

Questions

If you have any questions or suggestions, you can reach me at...

Email address for questions

Updates

5/1/07 - Initial upload.

5/2/07 - Added rough draft content.

5/4/07 - Added more rough content, fixed spelling errors.

5/7/07 - More Q & A.

7/1/07 - Spelling edits. Added video link. Added DiggIt button.

8/7/07 - Added info and links for Lindsay Meek's Uninterruptible Solar Power Supply project.

1/3/08 - Added a picture of prototype panel mount. Added a link to pictures of the prototype mount on Flickr to the QA section on mounts.

6/17/08 - Added QA about air conditioners.

7/24/09 - Added links to the applicable DG standards and a link to Synergy Systems.

2/2/10 - Looks like we getting closer to the solar appliance. If they add a "Hub" type module, then you'd have a pure consumer plug-and-play product.

6/1/10 - Added a link to the new DC powered air conditioner. Thanks Mike!

11/3/10 - Added a link to the Securus solar air conditioner (via Mat-a-watt).

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