Tiny home solar

[Kyle5585]

Hi all!

My fiance and I are building a tiny home and we hope to be largely grid independent within a few years. (Currently we live in AZ and running an AC unit during the summer on solar alone isn't plausible with the size of system we will be able to build) From the research I have done so far and the roof space available to me, we should be able to build a system in the 1200w range. I want to fully understand the system and its capabilities. I do have a pretty good understanding of electrical systems in general, but solar adds an extra level of complexity. I have a few questions to get things started.

A. Math: Where can I go to learn the math that I will need to analyze my systems capabilities and an appliances load/efficiency? I'm a hands on learner, so having images to help conceptualize things is immensely helpful!

B. The solar distributor we talked to said that we would only be able to place panels on one side of the home. To put panels on the other side we would need to buy more components to make it possible. I don't entirely understand why this is. I was hoping someone might be able to explain why. If we were able to put panels on moth sides, we could double the number of panels we have. I realize we would never have simultaneous exposure on both sides, but you would be more likely to have exposure during all parts of the day?

C. The appliance we have been struggling with most is our refrigerator. As my fiance loves to cook we have designed a fairly large kitchen space to accommodate her hobby. Most of the refrigerators we find are either too small, IE dorm fridges, or they draw a lot of power. We don't expect a full size fridge, as we are going tiny, but something at about 24w, 22d, and 60h would be perfect.

D. Batteries: I have read a lot and I am struggling with which way to go. Either Lithium ion (battleborn) or AGM batteries. All things equal the Lithium ion seems like the obvious choice, but it was not highly recommended to us by the solar store we went to. We would save weight, be able to use more of our capacity, and they would last much longer. Am I missing something here? We plan on having 4-6 batteries in our bank if we went with AGM, half that with LI.

Thanks!

 

[SolarfortheOuachitas]

I bought a Haier refrigerator/freezer at Lowe’s for my off-grid cabin kitchen and the size is similar to what you are looking for. There are other good brands of similar size.

It works okay and runs about 50% of the time. If you do the load consumption math on it or any other frig it’ll help you figure out how much storage and array size and balance of system components you’ll need.

There are a variety of good DIY solar books out there and I purchased my book recommendations from the solar DIY sites that I visit.

AGM batteries have worked well for me because the technology is established and they are readily available. Sams Club sells them at good prices.

Everybody lives differently, but I’ve used dorm fridges before and when I went to a larger (but still relatively small) fridge, I found that I still throw food away that hides in the nooks and crannies.

The fun news is that a solar powered cold beer tastes great!

 

[Dzl]

Hi all!

My fiance and I are building a tiny home and we hope to be largely grid independent within a few years. (Currently we live in AZ and running an AC unit during the summer on solar alone isn't plausible with the size of system we will be able to build) From the research I have done so far and the roof space available to me, we should be able to build a system in the 1200w range. I want to fully understand the system and its capabilities. I do have a pretty good understanding of electrical systems in general, but solar adds an extra level of complexity. I have a few questions to get things started.

Hi!

A. Math: Where can I go to learn the math that I will need to analyze my systems capabilities and an appliances load/efficiency? I'm a hands on learner, so having images to help conceptualize things is immensely helpful!

What specific math would you like to learn? I know of a few resources, but it depends what you are looking for (fundamentals? practical solar stuff? more advanced stuff?)

A few fundamentals that are very helpful.

V = IR: Voltage = Current x Resistance (this is Ohm's law)

P = IV: Power = Current x Voltage

Connect in series: Voltages added together, current limited to lowest current component
Connect in parallel: Amps added together, voltage limited to lowest voltage component

I.E.
2 x 10A, 20V, 200W panels:
In series = 10A 40V 400W
In parallel = 20A 20V 400W

Voltage = Electrical 'pressure' or a 'pushing force' and measures the difference between two points
Amps = Electrical 'current' or a 'flow rate
Amp-hours and Amps are different things (Amp-hours (Ah) are a unit of capacity/stored energy)
Watt-hours = Amp-hours x Voltage

There is a relationship between your Daily loads, max loads, battery bank size, inverter size, and PV array size. They should be sized proportionally to one another.

B. The solar distributor we talked to said that we would only be able to place panels on one side of the home. To put panels on the other side we would need to buy more components to make it possible. I don't entirely understand why this is. I was hoping someone might be able to explain why. If we were able to put panels on moth sides, we could double the number of panels we have. I realize we would never have simultaneous exposure on both sides, but you would be more likely to have exposure during all parts of the day?

This is east and west facing orientation?

Not an expert, but I would speculate the reason they say you would need more components to accomplish this is because with a dual orientation array you would want the maximum power point to be at the sub-array or panel level so would need to use dual MPPT's or micro-inverters, to keep the shaded side from pulling down the power output of the sunny side. Generally speaking, the issue may be that solar panel power outputs don't just simply add up, lower output panels can and usually do bottleneck the more productive parts of an array. The specifics of this will depend on series and parallel wiring and the charge controller used. It may also be that your solar installer is thinking of the additional wiring, connectors, mounting hardware, etc, and the larger or more complicated components that may be needed, and the effect that woudl have on cost amortization.

C. The appliance we have been struggling with most is our refrigerator. As my fiance loves to cook we have designed a fairly large kitchen space to accommodate her hobby. Most of the refrigerators we find are either too small, IE dorm fridges, or they draw a lot of power. We don't expect a full size fridge, as we are going tiny, but something at about 24w, 22d, and 60h would be perfect.

Fridges draw less power in practice than the amperage in the specs. This is due to duty cycle, once your fridge/freezer has reached its operating temperature, it cycles on/off to maintain that temp, generally speaking its on less than 50% of the time.

If you look at the energy star rating, it will give you a kWh per year figure, divide by 365 to get a ballpark of how much power it will use per day. An 'inverter' type fridge, will be more efficient, they are common outside the US, I'm not sure how easy they are to find in the US or if they are marketed using that term or something else.

One last hint, I believe you can go to energy star's website and search for fridges through it, you can sort by efficiency and I think capacity.

D. Batteries: I have read a lot and I am struggling with which way to go. Either Lithium ion (battleborn) or AGM batteries. All things equal the Lithium ion seems like the obvious choice, but it was not highly recommended to us by the solar store we went to. We would save weight, be able to use more of our capacity, and they would last much longer. Am I missing something here? We plan on having 4-6 batteries in our bank if we went with AGM, half that with LI.

Would you mind sharing why the store did not recommend/encourage you to use lifepo4?
It is the new kid on the block, and many are slow to accept it, we are still in the era of lead acid, but that is changing fast. There are pros and cons to both chemistries, I think lifepo4 wins out in most comparisons, but there are cases where lead acid makes more sense, and of course the upfront cost is substantially lower.

Going with BattleBorn is going to be fairly expensive, even compared to other lifepo4 options. The benefit is you get the simplicity, the warranty, the support, and the reputation. But they ain't cheap.

I suspect it won't be long before someone comes in telling you you would be crazy not to build your own DIY battery using 280Ah raw cells from an Alibaba reseller. For the price of ~1-2 Battleborn batteries you can get double the capacity of the 3 you planned to buy. This is all true, and its one valid approach for sure, one that I recommend with some caveats.

In exchange for the huge cost savings, here are the trade-offs, you are buying straight from a Chinese grey market reseller, returns are usually not an option, warranty cannot be relied on or expected, factory support is not available, cells are not matched or are loosely matched, origin and condition cannot be easily verified, and you are ultimately responsible for putting in the time and research to protecting yourself and your investment. All that said, its totally possible, and not that difficult to properly buy, build, and protect your system, and you have the experience and experiences of others here to lean on and learn from, and the cost savings is substantial. Some people have been burned buying from the grey market, many more people have received questionable quality or condition cells, but most people who bought through known resellers have received reasonable quality cells and reasonable quality service for the price (so long as you don't go in expecting the American "the customer is always right" type of service and handholding).

These two paths (battleborn and 280Ah raw cells) represent the (high and low budget) extremes. You can buy quality matched cells from official resellers with factory or distributor support and warranty, or somewhat cheaper drop-in battleborn alternatives. Both will fall somewhere in between the two extremes in terms of price.

After laying out all the risks/negatives of building with raw cells, more specifically grey market cells. I would advocate that you at least consider the DIY route, if it sounds like something you would be willing to spend the time to do right. Will has some good beginner videos on how to simply build a battery with raw cells.

 

[Brett Jepp]

This is my first post in this forum, being creative has saved me from the need to build a really large expensive solar setup.
I have been living off grid in utah where the summers are quite hot as well. In my location it typically reaches 95f or so during summer months and it is really dry here.

We run most things off the 12v system.

All lighting, water pump, electronics charging, and even the fridge.

The fridge is a dometic DMC2841. Its a DC compressor fridge and runs solely off the 12v system. Since it is built in I was able to add an extra 4” of insulation around it to reduce cycle frequency and duration.

For cooling I built a window hanging swamp(evaporative) cooler that keeps my tiny home down between 70-75 degrees inside. It run on 12v and is very power efficient only drawing 4-5 amps while running. The fan speed is also variable. It is built from wood and fiberglass, and runs on 300mm computer fans and a small 12v fountain pump.
If interested I did a video about the swamp cooler build. And have recommendations for the parts to use.

All of this is powered with 600 watts of solar and a 400ah lead acid battery bank.

Hope this helps, or is at least of some interest.

Brett