While completing my MSEE degree, I got an idea for how to design sustainable energy generation systems. To give some background, the electric power system delivers electricity to homes and buildings to power televisions, refrigerators, computers, and every other device that plugs into an outlet. A sustainable energy generation system is an off-grid (stand-alone) electric power system that can independently provide reliable electric power to a home/building from renewable energy resources. The main challenge in designing sustainable energy generation systems, i.e. solar and battery storage, is determining how much solar and how much storage are required to reliably supply power year-round.

By considering oversized PV, I pioneered an algorithm that approximates the energy storage requirements for increasingly oversized PV. The result was a graph of all possible configurations of oversized PV and storage, and I found an inverse relationship between PV and storage. Here is an animation of what this looks like.

This relationship is important to optimize for the cheapest system. Since PV and energy storage have different costs, the algorithm computes the price for each system and determines the most cost-effective configuration shown by the red “x”. This data represents the results for a residential home; however, this solution is scalable to any size.

After graduating, I founded OffGrid, an organization to design sustainable energy generation systems. My work involved working on the design, patent application, and funding opportunities. Unfortunately, I was unable to secure funding for this organization and found a job a few months after. I uploaded the algorithm on GitHub and released all potential proprietary rights, pertaining to the system, into the public domain. AMA

My Proof is a technical document with more information about the system and a link to the algorithm.

Comments: 235 • Responses: 24  • Date: 

lt0202301 karma

On page 6 of your paper you assume a 90% efficient ESS with no time-varying leakage, then proceed with a model of a system that requires energy storage times of days, weeks, even months or years. This is not a valid assumption for the math you're doing. Lithium ion ESSs (and other types) have time energy shifting capabilities, but they all suffer from energy loss across this time. Lithium ion batteries not stored at a ~40-60% SOC suffer chemical degradation, affecting their potential max SOC. The depth of discharge, the cycling behavior, even temperature affects how well an ESS behaves. I don't see any of this taken into account in your work. You could potentially keep the stored energy at the levels you discuss by keeping individual cells at 40-60% and having a BMS both for the individual batteries AND for the group, but there is no mention of that in your paper, and your work doesn't really model that type of system.

Simply put, you model a system with unrealistic assumptions that cannot be matched by a real world system. The math seems reasonable, but this cannot be applied to a real world system until you take into account losses and the battery effects.

Could you please comment? I'm not trying to knock this down, I'm trying to understand what I may have missed.

LiveWithEarth113 karma

The section you are referring to (Section IV) is a thought experiment to describe the importance of the correlation between power supply and power demand. You are absolutely right. I do need to take time-varying leakage into account, which I didn't because I haven't done the research to figure out how to modify the algorithm. However, after I do take this into consideration, it's just going to give me different results. I'm confident the inverse relationship will still be present because as the PV system size increases the need to store energy for long periods of time decreases.

At the end of the introduction, I state

Future work includes incorporating probability distributions of the power supply and power demand into the algorithm to design off-grid systems that meet statistical requirements (e.g., there is an 80% chance that PV size X and storage capacity Y will reliably supply electric power year-round for this building for this year), incorporating time-varying energy losses, and mixing renewable energy resources and energy storage systems to optimize for the cheapest cost (e.g., PV size X, wind energy size Y, and energy storage Z is the optimal system).

Edit: I created this diagram to show how I believe the graph will change by including time-varying leakage. https://imgur.com/0n2AzIe. Time-varying leakage is practically negligible for the points at the end of the graph because for these configurations the system stores energy during the day for nighttime use, so energy is stored for less than 24 hours.

lt0202120 karma

However, after I do take this into consideration, it just going to give me different results.

This is like saying "My model of a ball bouncing in a bounded box shows that the ball will bounce forever! Once I take friction and gravity into account, it is just going to give me different results." You have to be realistic with your assumptions, otherwise you can draw unrealistic and nonsensical conclusions from the data.

You should put your data sources "power_supply_san_diego" and "power_demand_commercial_building" on GitHub so that people can actually run your program. Based on line 80, "power_supply = circshift(power_supply,4380);", it looks like you're simulation's time step is only an hour. After line 117, you'd want something like "energy_stored(i) = energy_stored(i-1)*EnergyLossOverAnHourAtThisSOC(energy_stored(i));", and you'll want to throw in a function that gives you the energy loss. That said, this still doesn't take into account the cycling and DOD effects on the battery, which absolutely CANNOT be dismissed, because it has a non-trivial effect on the battery's max SOC over time. You also work in total stored energy, not SOC (multiplied by the rated battery max capacity), which makes this whole thing... weird.

I'm not saying this is bad work. This is a great start. I think if you include battery aging effects (which you could learn about here as a start) and the PV ratings, this could be some great and novel work. Keep up it up. Don't let any of my words or anyone else's discourage you.

LiveWithEarth84 karma

To continue with your example, my model of a ball bouncing takes into account friction, and if I include air resistance (time-varying leakage), it is going to give me different results.

The power data is on GitHub. It's the file called example_power_data.mat.

lt020286 karma

The power data is on GitHub. It's the file called example_power_data.mat.

Oops! I simply missed that, sorry.

... if I include air resistance (time-varying leakage), it is going to give me different results.

Good analogy. My point is simply that you draw a conclusion (the optimal curve) from your "ideal" model, but that that shape (the curve) may not even exist when time-varying leakage is taken into account. For example, the curve could change over time, which would be quite interesting to see. As such, your results may be a different paradigm entirely, and not just "different". I think I'm just trying to say that "different results" is not a strong enough term, that's all :).

To be clear, I'm not intending to be hostile at all. I'm intrigued by your work, and wouldn't be critical of it if it wasn't worth the time. I can't go into details because of an NDA, but for the last few months I've been programming in MATLAB on work related to energy storage systems. I'll probably play with your code tonight or this weekend and see what happens when some simplified PV and battery aging effects are implemented just for fun :).

LiveWithEarth42 karma

I created this diagram to show how I believe the graph will change by including time-varying leakage. https://imgur.com/0n2AzIe. Time-varying leakage is practically negligible for the points at the end of the graph because for these configurations the system stores energy during the day for nighttime use, so energy is stored for about 12 hours.

lt020231 karma

I think you're right. It would look something like that, and because the ends don't really change much at the extremes, there will still be an inflection point worth studying.

Nobody is going to buy a stand-alone renewable + ESS system if they don't intend to use it until end of life. I think that your curve will change significantly over time (especially over the years), and that that "optimal" inflection point therefore changes with it. With some further math, one could optimize the system financially as it evolves through time to find the best system mix.

Basically, you've neatly demonstrated a method of handling two dimensions. It just gets much more interesting and produces useful results when you introduce the third dimension (time) and the associated effects (e.g. battery aging). That could be some novel work.

Again, not arguing with you. I really want to see the results of the introduction of time and how that changes the curve :).

LiveWithEarth25 karma

Thanks for the feedback and for sharing what you know about energy storage systems. I will look into time-varying leakage and try to incorporate it into the algorithm to see how the curve actually changes.

musicalmindz7 karma

Good catch! Probably insignificant but there's also loss along transmission between solar and batteries no?

LiveWithEarth1 karma

If the situation involves long distances, the algorithm can be modified to incorporate transmission losses and any other type of energy losses.

_Mardoxx65 karma

What makes this special? Looks like rudamentary maths to me.

LiveWithEarth56 karma

I searched online, through academic publications, and the patent database, and I did not find the relationship between solar and energy storage published anywhere.

Dfizzle234 karma

I take it that this calculation would only benefit areas with high solar irradiance. A >$50k system would not be feasible where solar isn’t a significant renewable source.

Also, out of curiosity, what is the installed capacity of your optimal PV system? That’s something good to know because it should be important to know how large of a rooftop/field is needed to achieve this.

LiveWithEarth3 karma

The higher the solar irradiance the better. The algorithm requires the solar irradiance data of the region (expected power supply) and the expected power demand of the building. This data is used to obtain the optimal results which will depend on the region and power consumption of the building.

xrandx18 karma

I'm a retired EE that spent my career in low voltage and have been out of the game for a long time, so I can't really keep up with the technical nomenclature anymore, but I'm curious...How does your algorithm account for the decreased efficiency and storage capacity of batteries over time? Are you simply relying on scheduled maintenance or do you actually account for it over time with a margin of error or other mechanism?

LiveWithEarth4 karma

The algorithm requires the expected time-series power demand of the building and the expected time-series power supply of the PVs. Using this data, the algorithm simulates the time-series stored energy for increasingly oversized PV. The result is used to determine the energy storage requirements.

Currently, the algorithm doesn't account for decreased efficiency over time, but that is something which can be incorporated into the algorithm.

prankerbankr11 karma

Barely skimmed the doc cause low on time... But first question: why is the graph for such large quantities of power generation? Is there a graph for if I had a single house? So x axis scale being 0-20kW and y axis scale being 0-50kWh?

LiveWithEarth3 karma

I expressed the PV system in terms of expected annual generation. I did this to compare the expected annual generation to the expected annual consumption of the building which was 10MWh. As you can see from the graph, the smallest PV system size would require an expected annual generation greater than 10MWh because the energy storage system has losses.

wolfkeeper2 karma

Your graph is confusing, you would probably have done better to express the system size as a multiple of the expected annual consumption, such as 1.5 instead of 15 MWh.

LiveWithEarth1 karma

That is actually how I initially labeled the PV system size. I called it the power scaling factor, but decided against it. Didn't want to complicate things.

AskMeAboutMySmell10 karma

So, why'd you do it?

Also, what is your favorite food?

LiveWithEarth22 karma

Because I believe achieving sustainable energy is the most important issue our society will face. And as I was learning more and more about sustainability, I realized no one (nor any organization/company) was even trying to solve the root problem. So I tried and made a leap forward.

Torta is a Mexican cuisine and my favorite food.

savanik2 karma

What do you think the root problem in sustainability really is?

LiveWithEarth6 karma

There are two main problems to achieve sustainable energy. The first is figuring out what the system will be (how much solar, wind, hydro, energy storage, etc,.) such that the system provides reliable power year round.

The second problem will be figuring out how to put the sustainable energy system into place. Currently, the consensus is to keep adding more and more renewable energy until we reach 100%; however, I don't think this is the best approach. I think we should upgrade sections of the electric grid one-by-one with sustainable energy generation systems such that the sustainable system is electrically isolated from the original grid. By continuing this process, as more and more sections are upgraded, the original grid gets smaller and smaller until eventually it's all upgraded.

lt02023 karma

The first is figuring out what the system will be (how much solar, wind, hydro, energy storage, etc,.) such that the system provides reliable power year round.

This is literally what almost every power utility company is working on right now. (e.g. here.)

how to put the sustainable energy system into place. ... I don't think (adding more and more renewable energy until we reach 100%) is the best approach.

Why not? We (in the US) have an established grid with FERC and NERC regulating it, with other regulatory bodies (like MISO or ERCOT) sustaining it. Separating out new grids adds completely unnecessary complications to the system, which is already very complicated as we have to deal with buying/selling/transmitting power between systems. Why is electrically isolating oneself from the current fully functioning grid a better choice?

LiveWithEarth2 karma

We still haven’t perfected how to design nor maintain sustainable energy generation systems, and I think by adding more and more renewables to the grid is like trying to build the whole thing at once. It might be possible. But I see it as a huge experiment, with a high likelihood of failing and causing widespread blackouts.

The existing grid started off small and grew into what it is today. My recommendation is to work backwards. Start with what we have today and slowly reduce the size of the original grid by upgrading one piece at a time. Start by upgrading a small town, and from this experience, we will learn more about how to maintain and design these systems. Then, slowly upgrade sections one at a time.

I believe the new sustainable energy generation systems should be electrically isolated from the original grid to release our dependence on it. As more and more sustainable energy generation systems are built, the original grid gets smaller and smaller. Neighboring sustainable systems could be connected to increase reliability. The final result would be a decentralized system made of many sustainable systems. Each sustainable system is responsible for its own region but can ask for power from other systems that have extra power or stored energy. We could call this type of arrangement a ‘decentralized backbone’.

R0binSage6 karma

As an inventor/Dreamer, is there a duty to release such things to the public domain?

LiveWithEarth11 karma

Absolutely!

Nikola Tesla is my biggest ideal. He practically gave away his patent rights to many AC power technologies. He didn't care about money. All he cared about was developing technology for humanity. Similarly, I felt releasing the patent rights was the best way for this system to succeed.

tentric11 karma

I think that has more to do with the fact that he got into some sketchy employment arrangements..

LiveWithEarth7 karma

From what I've read, he tore up his contract with Westinghouse because the money Westinghouse owed Tesla would have bankrupted the company.

Tynach3 karma

I truly wish more people thought like you. Thank you.

I really wish there was more I could say. I don't usually comment just to thank someone for having done something already, but.. I felt strongly about it to feel like I needed to.

LiveWithEarth1 karma

I really appreciate your comment :)

shewolfromulus4 karma

Hello, first off I wanted to say thanks for your work in sustainable energy.

Any advice for a student at a community college struggling to get through the prerequisites for Environmental Engineering? I am hoping to transfer next year to a university and finish my bachelor's of Environmental Engineering, however I am second guessing my decision to do this major. I don't know many people in the field or even what type of job I want or if id even enjoy it. I just know that I'm very interested in sustainability and want to make sure we don't screw up the environment any more than we already have. The decision to change my major or keep going with Environmental Engineering has really been weighing on me.
Any words of wisdom or advice?

LiveWithEarth1 karma

I was at a community college for 4 years which was the best choice for me because it gave me the opportunity to figure out what I wanted to study. Once you transfer to a university and begin to take environmental engineering course, I think you will get a much better idea about the field. My advice is to focus on your interest in sustainability and start looking for internships in the field. Also, while your major is important, the major you choose will not limit your career prospects. Good luck!

PSiggS3 karma

In an ideal future what role do you see power companies having? Also, it is very admirable to selflessly give away your intellectual property for the greater good. Props to you.

LiveWithEarth2 karma

I don't think power companies will play a significant role in terms of influencing sustainable energy. They will mainly be influenced by policies or economics. Thanks for your comment :)

RomeoDog3d3 karma

Do you think Tesla can rebuild porte rico power on budget and make it better ?

LiveWithEarth3 karma

Using the existing power plants in Puerto Rico with solar and batteries would be more economical than supporting the entire island with just solar and batteries. At the moment, the integration of solar and batteries do not compete economically with power plants, but I'm sure many years from now it will.

forestdude1 karma

Why would the storage requirements change along with the size of the system? Regardless of system size, when the sun goes down the system is no longer generating. I would think the nightime energy demands should stay relatively flat which to me means the storage requirements should stay relatively flat?

Simplistic example, but if our non generating period demands are 100kwh and a power wall has a capacity of 10kwh, we need 10 power walls regardless of whether or not the pv system charging the power wall is rated at 15kw or 150kw.

There is definitely some optimization, but I would assume that storage requirements are relatively static?

LiveWithEarth1 karma

Here is another way to view the problem. The main challenge for designing sustainable energy generation systems (i.e. solar and batteries) is the seasonal imbalance between the power supply of the PVs and the power demand of the building. Majority of PV generation occurs during the summer when the sun shines brighter and for longer periods. The standard PV size doesn’t produce enough energy during the winter days to power the building and charge the batteries for the nighttime. A sustainable system, with the standard PV system size, would need to store all the excess energy during the summer and use it to offset the energy shortage during the winter. This would require a lot of storage.

By increasing the solar power beyond the standard size produces more energy throughout the year and reduces the need for seasonal storage. The algorithm I developed computes how much storage is required as the the PV system increases.