Microgrid

This is a project that i just finished that is relevant.

Associated spreadsheet unfortunately not live but at the optimized state for NPV.     

1.1.   Scope

The scope of this project is a one house system, through other houses could be easily added, and only looks at electricity production. Only current off the shelf technologies are looked at, no prototypes or possible systems are included.

1.2.   Background

This project is looking at the optimisation of a microgrid that is only powered by diesel fuel or solar PVs.

Batteries are used as an energy storage medium and hot water is produced by the diesel generator but this

hasn’t been modelled.

Fixed into the system is the battery (specifically chosen) bank, load, generator model & type along with

Solar panel model.  What can be changed is the number of solar panels.

Left out are other renewables; wind is ignored because it is inefficient at a small scale while Melbourne’s

wind resources aren’t sufficient to make it worthwhile and Biomass isn’t suitable to a suburban or urban

location.

Optimization is aimed at an improvement over connecting to the grid, specifically around NPV rather

than total price.

1.3.   System Architecture

Generator: Two machines joined together, an ICE to provide torque and an electric generator to turn the torque into electricity which is then feed into the battery

PV: Converts the energy in sunlight into electricity

Battery: Stores excess electricity produced by the generator or PV panels and allows it to be used at a later time than when it was produced, normally night-time.

2.      REFERENCES

1. Lilley, B; Satzow, A; Jones T; (2009) ‘A Value proposition for Distributed Energy In Australia’  CSIRO.

1.  WholeSaleSolar (2013). "Deep Cycle Battery Banks." Retrieved 10/10, 2013.

1. Winaico (2013). "Technological leader: WINAICO QUANTUM." Retrieved 10/9/2013, 2013.

1. Decker, K. D. (2009). "Small windmills put to the test." Retrieved 10/10, 2013, from http://www.lowtechmagazine.com/2009/04/small-windmills-test-results.html.

3.      Discussion
3.1.   Some Advantages and Disadvantages of Islanded Microgrids

The reason we are looking at microgrids is because they offer advantages that are useful for a wide range of people in pursuit of various goals. Below is a sample of those advantages.

Advantages:

• Lower transmission losses

• Which leads to lower distribution costs

• Linked is the lower technical complexity

• Can be easily automated

• Is more disaster proof

• Can be set up to link to the grid and detach when necessary

• Lacks diseconomies of scale

Like anything, microgrids also have their disadvantages that make them unsuitable for all uses. Below is a list of some of those disadvantages.

Disadvantages:

• Can’t aggregate supply and demand from a large area

• Some energy sources aren’t suitable (large wind turbines)

• Requires battery or similar storage (instead of it being optional)

• The initial cost and F.I.T

• Lacks economies of scale

• Isn’t reliable unless well built

3.2.   Some Requirements

Since this system is designed to be owned and operated by the average Australian, its requirements are geared towards that sort of situation. Price is important, along with usability and it’s a functioning investment that needs to provide some sort of return.

Requirements:

The system shall be modifiable/future proof. Say any component can be replaced within another model with performance indicators within a 10% range

The total running costs of the system, including maintenance, fuel and repairs, shall be at the same price or lower than electricity from the grid

The set-up costs of the system shall be affordable ($10-30,000) and at or less than connecting to the grid

The technical skills require for running the system shall be readily obtainable by the clients

The system shall have a high reliability (about 99.9999%)

The system shall be islanded

The system shall provide hot water and electricity at an equal or greater rate than the client’s need, when they need it.

The system shall have a minimum of overnight storage (16Kwh) for winter months

3.3.   Introduction to Optimisation

Each of the various element falls under a different category: those that can be changed (variables), limits to the model (models), the outputs of the model and options.

Variables include:

• Size of the batteries

• Load management of the batteries

• Size of the PV panels

• Generator chosen and fuel choice

• Generator run time

• Cost of electricity

Constraints

• The price has to be less than simply connecting to the grid

• Number of houses that can be connected

• Roof space

• Load (24KWhr)

• Spread of sunlight throughout the year

• System life cycle (20 years) 

What’s being optimised

• Price of electricity needs to be as low as possible

• CO₂ emissions need to be minimised 

What can be changed to improve the design

• The batteries cycling is a separate optimisation between total capacity and lifespan

• Size of the PV’s and battery capacit 

3.4.   Basic Relationships

Microgrid relationships:

• CO₂ emissions are directly proportional to generator run time

• Alternate generators and fuels will also affect CO₂ emissions

• Size of the solar panels is inversely proportional to generator run time

• If there are enough solar panels, increased battery size can lower generator runtime

• Solar panels increase initial cost of the system

• Diesel use affects running cost

• The cost of fuel can fluctuate, while solar panels costs are locked in

• An increase in battery size increases cost

• Generator run time affects how many houses can be connected

• The cost of electricity is setup cost/lifetime plus maintenance costs

• Increase in storage (batteries or fuel tanks) reduces risk

• Risk here refers to the chances that no electricity will be provided when needed

• Battery load management affects battery lifespan

• Life cycle cost is simply the capital costs + maintenance cost divided by lifespan

• Load is serviced from the battery, there is no direct way for generated electricity to service load

3.5.   Mathematical Relationships

PV power produced = #PV x PV% x Solar exposure x PV area

Excess Power = PV power – Load

Storage = Previous days storage + excess power: range 0<Storage<Max Storage

Fuel consumption = g/Kwh of diesel / generator %

Fuel use = Fuel consumption x deficit of storage

Fuel cost = total fuel use x fuel price

Capital cost = Battery price + generator + PV panel prices

Total cost = Capital cost + lifecycle x Fuel cost + replacement battery

Cost per Kwh = Total cost / (lifecycle x load x 365)

CO₂ production = Total fuel use x CO₂ production

Improvement over grid = Cost per Kwh – Comparison cost for grid

NPV = inflation^year*(cost/(1 + discount rate)^year)

• Two forms, one for grid electricity and the other for off grid 

 3.6 Assumptions

The generator is 90% efficient

            -which means the engine has to produce 1.11 of the required load

We have unlimited roof space

Maintenance costs are negligible

No transmission loses

Batteries are 100% efficient, no electricity is lost by storage

The density of diesel is 0.832kg/L

Engine consumption is .204kg/Kwh

            -therefore consumption is 0.245L/Kwh

The price of diesel is $1.5/L

CO₂ production is 2.68/Kg

We are using the Winaico Quantum panels

            -Efficiency is 17.46%

            -Area is 1.663m²              

                -$290 per Panel

Meteorology data is for the botanic gardens, 2012 data

Projects lifecycle is 20 years

Load is 24kWh, spread evenly over a day

Assume batteries are fully charged at the beginning

Assume 27c kWh for comparison with the grid (based on recent electricity bill)

Any battery deficit is recharged by the generator that day

Components don’t lose performance over time

            -batteries just have to be replaced

For a battery bank, I have chosen a specific model 12 Surrette 6v, 400 Ah S530 from whole sale solar

-Price $4497, load 28.8 Kwh and a lifespan of 10 years, warranty 7 years

-Assume that it will last all 10 years then die without losing performance

3.7 Flow chart of calculation      

    

3.8 key data from optimised state    

Optimal #PV: 43 panels

Set up cost: $10967.12

NPV improvement over grid: $38,892.70

NPV cost: $28,229

3.9 Interpretation of spread sheet & Discussion

If optimising for NPV, 43 solar panels is the optimal choice as it has the lowest NPV. Importantly, lowering the load decreases the advantage of going off grid, at 15Kwh it is better to stay connected to the grid. This suggests that adding more houses to the microgrid will further increase the advantage of going off grid, especially if those house have a low electricity usage. In that case this model simulates 3 houses of 8 Kwh load each fairly well and as long as the battery is about one days storage this approach is accurate.

Importantly, this model shows that reducing the battery size as much as possible is the optimal solution. But since calculations are done at a daily basis, when the battery gets below a day’s storage the model will be inaccurate because night-time electricity use isn’t accounted for. If calculations were done an hourly basis, then the day/night cycle can be taken into account and the variation of load over the day can be simulated, then battery storage can be lowered below a day’s storage without the model losing accuracy. This is the prime reason I choose an off the shelf battery, optimising the exact size by buying individual batteries isn’t an option supported by the current model.

The main component missing from the model is heat storage and hot water for space heating. This is actually a separate task that then informs the main model. It is also where the optimum number of attached houses (and thus final load) is likely to come from, more houses means a bigger heat storage tank but also more heat loses in moving the heat around. Having heat storage also allows the excess power produced in the summer months to be used rather than wasted, it can simply power an electric heating element or heat pump.

The heat storage would be modelled like the battery, except that storage lose is added, a certain amount is needed and if there isn’t enough the diesel generator is run for longer. In most cases, the diesel generator won’t be run that much more than it already is but when it does it will provide extra power. This power can again be used by electric heating elements to store heat for tomorrow. Heat for other uses can be added, but this is more complicated since hot water use for showers varies widely with households. 

Changes

Basically, I have writers block. I have several posts in various stages of writing, one titled 'Thinking about sustainability from the triple bottom line approach' which is almost finished, 'Abundance long after the fall' which is just sets of notes and a handful of others. But I lack the ideas, motivation, time and inspiration to either start or finish them. So I'm changing from weekly posting to whenever I have something (I will still be posting on Mondays).

Part of it is probably that as my parents say I 'lack life experience'. That came from when my Twin and I where talking about peak oil with them and some worse possibilities, when they, to paraphrase, spoke from experience (several recessions) and said 'people adapt and get by'. Basically people muddle through and generally come out the other end, that's what their experience has been. The only time my Dad's mentioned the 70s oil crisis was when I talked to him about the possibility of global food shortages this year, his reply was it be like the 70s and people would just use less (in this context waste less food and eat less meat). He then went on to say when the next oil crisis hits the same response will likely happen again, people will adapt; drive less and use more public transport (already happening), he did acknowledge that it would have been better to keep all the changes from the 70s. I haven't lived through a recession (luckily Australia was largely untouched by the GFC) or any sort of crisis, so I just take their word for it and as a consequence I don't have as much stuff to write about and the required insight I feel I need.

For my long-term plan, that's not really a problem. My long term plan is to basically in about 10 years, once I've got my degree, enough experience to be a professional engineer (instead of just a graduate engineer) and a solid grasp of engineering via practice to start writing about engineering and peak oil. It's an area (one among many) which I feel isn't looked at that much in very deep technical ways, note I'm not including petroleum engineering but the other disciplines (the ones my degree has some founding in) of mechanical and electrical. I'll also look at others as I research/interact/study with those disciplines (aerospace, naval, mining, chemical, agricultural, industrial etc). That's the long term plan, short term is to change from weekly posting to whenever I have something.

Also after reading this I realized that a huge amount of what I've written has probably been interpreted in completely different ways from what I meant because of basic differences in what words mean, as well as not expressing all the important details. In the context of the link above, when I asked what socialism was people just said it was helping the poor (technically right) and so I internalized it as a political platform in favour of things like public housing, redistribution of wealth and other such stuff. It made some things confusing, like calling communism socialism (I assumed it was just the right calling the left communist) but overall it seemed consistent and the ideological components were things I'd never heard of. So quite easily a lot of what I've said has been misinterpreted without me realizing both from the inherent ambiguity of words and my own lack of knowledge of some very complex terms and ideas.

The main example I can think of was when talking about Australia's political system. One of the details I forgot to mention was that one of the reasons our system is designed to be extremist and/or mass movement proof is that one of the original design principles of our government was to allow (mentioned here) England to maintain rule over Australia. In those days the most likely mass movements would have been for independence and secessionist's would have been seen (by the English anyway) as extremists. By not mentioning that I probably made it sound like the designers were noble and forward thinking, when they were probably as conservative and corrupt as other founders were and just had the additional advantage of taking pieces from other working democracies around the world (our system of amendments to the constitution come from Switzerland) instead of having to design a system from scratch. It was just a choice made for short term reasons that turned out to be a good long term decision, the invention of the secret ballot was apparently similar.

The difference in interpretation is fairly important. Put it like this, in America it can be considered a bug that the two parties are similar, in Australia that's more or less what's supposed to happen. Think of how preferential voting works, it allows like minded parties to exist and not completely steal votes off each over, but instead share voters, compulsory voting simply reinforces this and makes the most likely result centrist. The fact that Labor is centre-left, while the Liberal's are centre-right and thus have a fair amount of overlap (both support mixed economies but lean one way or another), is a sign that our system is working the way it was designed to, even if the original rational of preventing us from separating from England is meaningless now. Interestingly enough, this also allows flexibility in the parties approaches, the best example is the carbon tax. The Liberals, being centre-right, leans more towards market based approaches while Labor, being centre-left, leans more towards government based action, yet the carbon tax, which is a market based approach is a supported by Labor and the opposing Liberal idea is direct action, a government based approach.

The last point is fairly important since I feel there are some very important points I should talk about, but due to what they are and insufficient knowledge, understanding and so my ability to clearly explain them on my part any misinterpretation could easily change what I mean entirely, such as the when I talk about current civilization but don't necessarily include the growth part. The important points all come back in one way or another to my feeling/instinct that all the thinkers in the overshoot/ sustainability sphere (and this includes me) have all missed at least one major trend, fact, insight etc, though the minimum is more like 5 missed things. Like how renewable energy  is actually driving down electricity prices, due to solar there won't be summer peak in Australia in a decade or so is one cause, or the fact that new renewables are cheaper than new coal plants while also causing coal plants to work less. Just reflect on that, without a carbon price unsubsidized wind is 14% cheaper than a new brown coal plant, the description of brown coal I've heard is dirt that can be burnt, it is dirt cheap ($4 a ton or so) and yet wind is cheaper while large scale solar isn't far behind, this is a monumental change. And solar has disadvantages, PV cells can use low grade silicon, a partnership between ANU and origin energy just made a solar cell that needs 10% of the silicon while the silicon can be low grade and radiation damaged (these ones, though I got the details here). But the supply chains are appropriated from other sectors, such as computers which require high quality silicon, also this affects the glass, if it was optimized for PVs about 15% more light would be let through. However despite this they won't be able to save our current industrial society, but they will improve the one that follows. What I mean by that phrase is probably fairly ambiguous (to any one reading).

To put that in context, if the energy problem was the only crisis (it's not) facing industrial civilization, then the path we're on now will solve it and deliver sustainability. Not without some crises and hardship, but on it's own it isn't something on the scale of the fall of Rome and with it all but a few surviving fragments of classical civilization. It even makes climate change a threat of a different nature, it's inevitable that Australia will stop burning coal well before the massive reserves are anywhere near depleted and so it will be burnt overseas if at all. So not all the fossil fuels in the ground will necessarily be burnt, brown coal doesn't really have an export market and probably isn't worthwhile shipping. All the oil may be burnt, because it's hard to replace transport, but for electricity any scramble to shore up supplies in the future will be renewables because they're cheaper and easy to use. Now you could bring up that renewables are subsidized currently, except they receive less than fossil fuels, or the lack of rare earths and limits to mining, expect that Japan just found a huge reserve of rare earths and solar doesn't use rare earths. Just a quick aside about mining, first using sea mining isn't a good idea for iron, aluminum, copper or most other common metals, but rare earths are far more valuable and you only require small quantities so its a good way to go (also that reserve is way better than normal ones, less radioactivity), secondly this book mentions that we are nowhere near the entropic limits to mining, partly because mining projects are optimized around money (Net Present Value) rather than energy, and thirdly recycling is far cheaper in energy and capital terms but takes more labor (perfect for future societies) while not being utilized to its fullest extend, recycling of rare earths is only just starting. A better criticism would be to talk about powering transport and such, since mostly petrol does that (but not coal) and for electrification electric cars get a lot of focus, unfortunate since there not where to start (trains and ships are due to their size and energy efficiency). 

That specific point is also built into a really obvious point. Historical analysis is all well and good, but it assumes that this time around your dealing with something which has enough in the way of similarities that comparisons can be made. So you could have a pattern repeat a 100 times, it's reasonable to assume that that cycle will repeat, but if something fundamental has changed then chances are that cycle won't repeat (though it could have similarities). It also requires that the right parallels are drawn, most people use Greek democracy as what ours is based of but wisely Western civilization choose to base it's democracy of Rome's model (by way of Machiavelli) which is why it's far more stable (Greek democracies were short lived and unstable). There's an obvious difference this time round, we're the first technic civilization and so won't respond in the exact same way and our problems won't follow the same pattern as previous civilizations. They'll probably have many similarities though. One difference is the point above and while that doesn't avert all the problems and stop some sort of crisis, it's a big enough difference. So at some point I'll look at how current technic societies differ from non-technic and where they're similar (both have cities, literacy, hierarchies etc) along with the different kinds of technological process (along a specific line).

But I'm not going to touch those topics in any substantive way until I've gotten better at writing and have gained some experience in the technical world (and thus where we differ) that I can draw upon. Besides, what I've written up to now is more an experiment and there to simply get my ideas down, I already think a fair bit of what I've written is wrong. In ten years when I have the experience I might choose to go down a completely different path, I might have a completely different view, or something could have happened by then. It is the future, all we can do is guess, but plans are nice things to have.