diy solar

diy solar

Off grid solar trailer for track days/back up for house.

Gschuld

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Aug 4, 2021
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Sorry, this will be a long post in the interest of not leaving out important details/ factors.

I’m considering a modest “off grid” trailer for use at 6-7 race events per year for vintage motorcycle road racing.

Assuming no power available trackside(normal), I’m contemplating something like:

4 Rolls Surrette 6volt L16 batteries in 24volt configuration.
3 Longi 310 watt solar panels
1 all in one Hybrid solar converter/charger of suitable capacity

My events generally require 3-4 overnight stays in the trailer(6x14, moderately well insulated) and often hot days with some hot evenings and occasional cold evenings. Worst case scenario is 85 degrees plus with humidity overnight. Most events are 10plus hours drive from home.

FWIW, I’m primarily of northern Scandinavian decent, and my body reacts poorly over 85 degrees. In high heat I sweat at a ridiculous rate while most people are far less effected. Cold weather, no problem. It’s a common theme with my extended family.

So I’m lookin at a modern inverter type air conditioning unit at 8000btu, specifically a Midea U MAW08 VIQWT

A technical reviewer reported it consumes on various settings (because inverter AC units can do this)

530 watts at 8000btu
380 watts at 5800btu
285 watts at 4300btu
190 watts at 2800btu
160 watts at 2400btu on its lowest setting (and near silent)

As reference, an experiment I read showed a 24 volt bank of 4 used Trojan L16 320@5hr batteries ran a 2012 vintage Kenmore 253.79081 8000watt window AC on full power for 4 hours off a Xantrex 1000 watt sine wave inverter using 550 watts continuous and reported to consume 30-35% of battery power, and elected not to run it down to 50%

I’m assuming at night, bringing 85 degree OAT down to 70-72 degrees will consume on average closer to the 190watts at 2800btu(greatly depending on quality of insulation). If …that is the case, I should be able to run the AC for around 12 hours off a bank of 4 fully charged Rolls 6v batteries at 24 volts and be only down 30-35 percent from full. Sound reasonable?

I’m hoping the 930 watts of solar can produce around 650-700watts in reality mounted horizontally on the roof of the trailer on a sunny day. Even if the AC consumed 380 watts for 5800btu during the day, the 650-700 watts of solar charging should easily handle this and recharge the batteries to full again by night fall. With some power to spare I’d hope.

Am I in the right ballpark here?


Another aspect of my interest is in the potential use as a plug in solar generator/emergency back up power for the house. Where I live we VERY rarely lose power. Generally only coastal storms(NJ), and big ones. We are currently building a new house with 1800 sqft of living space. Well insulated, top quality energy efficient windows and doors, equipment etc. I understand these all in one hybrid solar charge controller/inverters can be plugged into a house and designated to run certain functions. I’d be looking at refrigerator, some lights(LED), fan for air handler, etc. I’m thinking minimal emergency power needs, not heating/ cooling/ cooking. For short term outages of a few hours.

With those hybrid charge controller/inverters, the loads can feed directly of the solar. If the load becomes too great for the solar output, it automatically switches to grid power, or battery backup if asked.

Its not a typical grid tie system in that excess solar is “sold” back to the electric company, so my understanding is that such a system is not requiring any permits or inspection like a roof mounted grid tie solar setup. So it could be plugged in and unplugged at will.

The overall idea is to have the solar system, and backup batteries, serve a function during the 95% of the time when I am not traveling. And when traveling, grid system takes care of it.

3 310watt panels are not capable of providing much useful power to the house, but it’s something. The critical needs backup service is valuable enough.

I could potentially use a larger capacity hybrid solar charge controller/inverter and lay out the trailer to carry more panels, up to 2400 watts or so at the most with a fold out or sliding panel array. Panel weight starts to add up though at some point.

FWIW, I’m contemplating high end Rolls Surrette L16 batteries over a modern Lithium Iron Phosphate (or other) battery bank for several reasons. One being that there would be few charge/discharge cycles per year. Traveling track events use would be under 30 days (cycles) per year.. Maybe …20 more per year if I do some non race related travel. The rest of the time the batteries will be kept on the power grid tied hybrid charger controller, staying topped up and happy. The reduced discharge % capability is also not a huge concern unless I am well off the mark in my assumptions above.

The weight difference issue is not much of a concern for me. I’m old school and I find lead acid batteries more in my experience level comfort zone. That said, I’m not set either way.

Any thoughts are welcome.

Thanks,

George
 
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I’m hoping the 930 watts of solar can produce around 650-700watts in reality mounted horizontally on the roof of the trailer on a sunny day. Even if the AC consumed 380 watts for 5800btu during the day, the 650-700 watts of solar charging should easily handle this and recharge the batteries to full again by night fall. With some power to spare I’d hope.
lets do some math.

The AC will cycle on and off. Lets assume it runs a total of 12 hrs and you run it on the 190W setting.
190W x 12h = 2280Wh. Lets assume a system efficiency of 90%. This means you need 11160/.9=2533 WH of production to run your AC.

Lets assume an insolation number of 5 (that is kinda the norm for the US) If your panels are producing 700W you will get 700*5 =3500 Wh of production from your panels.

Your batteries are 300Ah at 24V or 9360Wh. Since they are lead acid, you only have 9360/2 = 4680Wh.

At first blush, it looks like production and storage will be sufficient on sunny days, but you might be in a bit of trouble if you hit a couple cloudy days.

If the AC is run at the 280W setting, you need 3360Wh. You might be ok on sunny days, but even one cloudy day is likely to be problematic.

the trailer(6x14, moderately well insulated)
Insulation is critical to making Solar powered AC feasible. Most RVs are notorious for not being well sealed and being poorly insulated. (the insulation problem is caused by the need for thin walls to save space. The poorly sealed problem is partly due to poor construction and partly due to all the movement the different parts of the RV experiences. You definitely want to go through the trailer and seal it up as tight as you can as well as add insulation if you can. In addition to that, find ways to keep everything except the solar panels out of the sun. As an example, if the trailer is parked with the long dimension North-south, less of the trailer will be exposed to the sun. Setting up a canopy that provides you and the side of the trailer some shade will help as well.
 
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