Another Lithium And Solar Upgrade

[MarkBry]

I’m new to the forum and new to Airstreams. This is my second post. As a new 30 Classic owner, a new tow vehicle, and a solo camper I’ve had my hands full. I’ve just finished part one of my systems upgrade plan. I replaced the two AGM batteries that came with my unit and installed three 300ah Relion lithium batteries. I disconnected the installed charger and installed 60a charger/inverter. (Progressive Dynamics makes a unit having a smart 60a charger and 3k sine wave inverter. ) i debated installing the batteries in the existing box or inside behind a couch against the forward bulkhead. The batteries are in the original box for now. I have installed 4 175 watt panels made by a one off supplier using Gamaca solar cells. I wound up replacing the solar controller mainly to keep the new smart stuff able to talk to each other. I connected the four arrays in series and therefore able to use the existing cables leading down trom the roof. I have a nice display that acts as a control and monitor for the charger, battery state, inverter, and solar controller. The display is currently not installed and just sitting on the couch. I need to figure out how to get a cable to the wall location port between galley and dinette. I have had a new battery box fabricated for me which is slightly larger to allow me to add insulation and a mounting board for most of the new gear. I have three main fuses and three main disconnects that will be mounted there also, batteries, solar charger, and vehicle alternator. I plan to get my new box and mounting board installed in the morning as a friend has agreed to assist. I will then be able to remount my battery shunt and the other components in a neat and organized way. After that I’ll need to run three cables, mount the display, order plastic labels, redraw my schematic, and clean up. Ill also have to figure out what i need to add to take care of a charge coming from the tow vehicle.

A quick check this afternoon was both disappointing and gratifying. The bad part is that I was only making 191 watts from my 700 watt array. The good part is that everything was working. I’m told not to worry but i also need to find out what the extra weight I’ve added affects towing. I calculated an extra 71# before the new box which will add about 10#.

Once I finish part 1 I can begin to plan part two which was really the main reason for part 1. I am going to replace the ammonia absorption fridge with a residential unit.

[ke6gkv]

sounds like a great system. post some pics. it's nice when someone goes down a different path; all lead to the same goal. may you have many miles of great service with your system/ kurt

[DavidEM]

I would reconsider changing to a home type refrigerator. If you want to change from your absorption (LPG) fridge consider an RV/Boat compressor fridge. These use a very efficient Danfoss inverter/compressor. They also have more insulation (but less cu ft volume) than home type fridges.


An efficient Danfoss 10 cu ft fridge will use about 100 amp hours daily. A 17 cu ft Energy Star home fridge will use twice that.


Your 700 watt solar system can be expected to make 200 amp hours on a sunny day, much less on cloudy one.


David

[MarkBry]

David, exactly right. I plan on using Vitrifrigo I have one of their small units in my sailboat. Their 8.1 cf unit is rated at 65 watts.

How do you figure 200 watts from a 700 watt array. I was hoping for 60% or so on a sunny day. I won’t be able to run another test till later in the week. Yesterday i spent an hour or so looking at voltages, currents, and waveforms. Following that i ran the solar controller for one hour and used the monitor’s avg as a result. Yesterday was partly cloudy and a bit hazy. My test started at 4:30p so the angle of the sun was not optimum. In any case the real test will be what it can do over a period of days.

[MarkBry]

Ah I see now. I did not read you carefully, i should have. You said 200ah/ day. That’s in the ballpark of what I’d expect.

[uncle_bob]

Originally Posted by MarkBry

David, exactly right. I plan on using Vitrifrigo I have one of their small units in my sailboat. Their 8.1 cf unit is rated at 65 watts.

How do you figure 200 watts from a 700 watt array. I was hoping for 60% or so on a sunny day. I won’t be able to run another test till later in the week. Yesterday i spent an hour or so looking at voltages, currents, and waveforms. Following that i ran the solar controller for one hour and used the monitor’s avg as a result. Yesterday was partly cloudy and a bit hazy. My test started at 4:30p so the angle of the sun was not optimum. In any case the real test will be what it can do over a period of days.

Hi

200 amp hours at a charge voltage of 13.5V is 2.7 KWH. You need to be careful watching the units on all the numbers.

There are all sorts of tables that show "equivalent peak hours" of sun for various parts of the country by month. There also are tables that get into efficiency vs angle of the panel vs location ( flat on a roof is only good if you are at the equator ... ).

If you take 2700 / 700 = 3.85 "peak hours" that's not to bad for some parts of the country. If you toss in 30% loss due to the flat angle, you are at around 5 hours. Your system will never be 100% efficient so maybe another 10% there for converter losses and the like.

The fllip side is that the panels probably are just a bit better than their ratings when new and shiny clean. If you wash them regularly ( we all do that every night right ?? ) they may stay at that level. If there is a nice film of dust on them, take off another 10 or 20%

You would *think* that was it ... well they also are impacted by temperature. If it's cold out, they do better. In hot weather / lots of sun, they heat up and do worse.

Lots of factors ...

Bob

[DavidEM]

You can do a lot of looking at solar insolation maps, latitude adjustments, panel efficiencies, flat angle adjustments, math to make all this happen. Or just follow these guidelines:

A flat panel of 100 watts will make 40 amp hours on a sunny day in a low latitude location in the summer. It will make about 20 amp hours in a high latitude location in the winter. So pick one of these or in between for your location and time. Then adjust for the number of sunny days and figure a cloudy day will only produce 5-10 Ahs.

For example in southern California you might get 35 Ahs overall in July, but only 25 Ahs in Florida in July because it is often cloudy there in the summer. Weatherspark.com is a good source of climate data. Just eyeball the cloud cover graph and adjust the sunny day output accordingly.

David

[MarkBry]

Good answers and great perspectives, thank you, all leading to my having some homework in front of me. Guess Im glad I went with a third battery. My expected use will be on the low side I think. I am solo so normally only one user.

[AirMiles]

Agree with Uncle_Bob that there are a lot of factors that affect solar production. I just upgraded to 600W. I posted my first 30 day period of continuous use here: https://www.airforums.com/forums/f44...ml#post2299311 There were only a few days in that 30 day period that my system produced more than 1kWh. Sure it was a cloudy/overcast period between Sept-October, but that is what happens in real life. I also posted many thirty-day periods with my 400W solar array throughout the "Solar Show and Tell" thread. Here is an example: https://www.airforums.com/forums/f44...ml#post2133206 This had average to good sun conditions and a peak day of 1.5kWh from 400W of solar in July.

Based on my experience, I can produce about 100AH per day with 600W of solar, but if you need 100AH for just your refrigerator, 700W is going to struggle to keep the batteries charged. You can study about eight different thirty-day periods of my real-life solar production with 400W by searching the above linked thread.

[MarkBry]

AirMiles, units of measure. The fridge I picked out specs out at 65 watts and I rounded up to 100 watts not ah. Looking at my battery bank at 900 ah i should have 700 usable ah. Figuring another 100 watts to make coffee and have reading lights I’m figuring maybe 200 watt per hour will be consumed. 200 x 24 = 4800 watts per day. 4800 watts at 13.7v is about 350ah for a day. If I could do as well as you and add 100ah a day I would burn about 250 ah a day. So, my 700ah should last 3 days. In reality it will likely be 2-4 days.

[AirMiles]

Originally Posted by MarkBry

AirMiles, units of measure. The fridge I picked out specs out at 65 watts and I rounded up to 100 watts not ah. Looking at my battery bank at 900 ah i should have 700 usable ah. Figuring another 100 watts to make coffee and have reading lights I’m figuring maybe 200 watt per hour will be consumed. 200 x 24 = 4800 watts per day. 4800 watts at 13.7v is about 350ah for a day. If I could do as well as you and add 100ah a day I would burn about 250 ah a day. So, my 700ah should last 3 days. In reality it will likely be 2-4 days.

Ok, I now I understand you are just trying to go several days, not continuously, without shore power. I try to avoid using shore power or a generator and am successful 97% of the time. My 27' Globetrotter has a three-way refrigerator that I sometimes run on DC while the sun is shining. I am unable to continuously use the DC refrigerator. My refrigerator use 14A at 12V while running and runs nearly continuously. 14A x 24 = 336AH per day. Even if it cycled at 50%, that's 168AH. There's no way for me to run my DC refrigerator on 600W of solar. My experience is to expect between 300% and 400% of panel wattage on good solar days. That would be 2100W to 2800W per day for your 700W of solar panels. Really bad days that cause me to use my generator can be as low as 100W per day! Just thought I'd share my real-world usage which could be used to estimate the output from your solar array.

[Hermes]

AirMiles makes great points. When I installed our solar system it was a relief not to have to worry about our electrical capacity anymore.
We camp in all seasons at different latitudes depending on the season, and it can happen that you will be in a misty, cloudy period which can last 10 days or more! If I had a fridge pulling 65-100 amps per day in those conditions, then power management would become a concern again.
We cook with propane and our furnace runs on propane, we can't avoid it. The propane consumption of the fridge is low. Propane is relatively cheap (getting cheaper) and available all over the continent (and you can always strap an extra tank in the back of the pickup if you are going for a long haul in a remote area). We also have a Honda generator (propane/gas) if needed (rarely).
It's a matter of your camping profile.

[dhroberts]

Originally Posted by uncle_bob

Hi

200 amp hours at a charge voltage of 13.5V is 2.7 KWH. You need to be careful watching the units on all the numbers.

There are all sorts of tables that show "equivalent peak hours" of sun for various parts of the country by month. There also are tables that get into efficiency vs angle of the panel vs location ( flat on a roof is only good if you are at the equator ... ).

If you take 2700 / 700 = 3.85 "peak hours" that's not to bad for some parts of the country. If you toss in 30% loss due to the flat angle, you are at around 5 hours. Your system will never be 100% efficient so maybe another 10% there for converter losses and the like.

The fllip side is that the panels probably are just a bit better than their ratings when new and shiny clean. If you wash them regularly ( we all do that every night right ?? ) they may stay at that level. If there is a nice film of dust on them, take off another 10 or 20%

You would *think* that was it ... well they also are impacted by temperature. If it's cold out, they do better. In hot weather / lots of sun, they heat up and do worse.

Lots of factors ...

Bob

Bob, what is the 2700 used in your calculation?

[uncle_bob]

Originally Posted by dhroberts

Bob, what is the 2700 used in your calculation?

Hi

200 x 13.5 = 2700 = 2,700 = 2.7 K

That's where the 2700 ( or 2.7 K) comes from.

Since you are multiplying volts times amps, the result is watts. Thus it is

200 A x 13.5 V = 2700W = 2.7 KW

Getting to the next layer, it's amp hours rather than simple amps

200 AH x 13.5V = 2700W = 2.7 KWH

so the hours carry over to the right side and it is 2.7 KWH

======

KWH is the normal measure of power consumed when you are looking at shore power sort of things. It also makes sense for any situation where you have multiple voltages involved. KWH are always the same, regardless of voltage.

Solar *is* something that is at a different voltage. Your solar panels put out a range of voltages depending on the amount of light and the load on them. They are rated in watts rather than amps. Trying to work out solar panels in amps or amp hours gets tangled up. It's much easier to do it in watts or watt hours ( = KWH).

Bob