How Much Solar Do I Need?

Perhaps one of the most frequently asked questions by new or prospective owners is how much solar they will need to keep their trailer powered while camping without an electric connection. It is a reasonable question, and most of us have pondered it at some point along the way. I have learned a lot about solar, mostly from reading, watching videos, and by my own mistakes (still a lot to learn, too!) and thought it might be helpful to put together an easy to understand post (read that, “non-technical, engineer friends) for people who are pondering this question. Consider this an introductory level post for people who are brand new to thinking about these things.

If you already camp or have a really good idea of what kind of camping you are going to do, it is easy to expedite the process of understanding your needs. If you are new to camping, and are not really sure, than I recommend that you get a season under your belt before spending money. Let’s assume for this post that you have a reasonable idea of how you like to camp.

Solar Basics

Solar basics are a good place to start. Solar does not keep your equipment powered, your battery does. Solar recharges your battery. The basics needed for a solar connection are:

1. Solar panel array,
2. Cables from the solar array to your solar controller,
3. Solar controller (charger), and
4. Cables from your solar controller to your battery.

Managing Usable Battery Capacity

Managing your batteries is the key to camping off grid. There are three ways you can manage your batteries for off-grid camping:

1. You can reduce power consumption.
2. You can increase your battery capacity.
3. You can recharge your batteries.

Which ever method you choose, it is essential to understand how your usage of the various equipment and outlets impacts your battery charge level, much like counting calories impacts our weight. This can seem daunting, so I have created a spreadsheet to help you do that for the T@b 320. I hope to have the chance to create a similar one when I am at uCamp, this year.

Battery capacity plays a large role in determining your solar needs, as well. It can be a surprise to people that nuCamp does not supply the battery for the T@b 320, the dealer does. As a result, the battery your dealer installs will vary in capacity from owner to owner, but most install a battery somewhere in the 70-100ah capacity range. You should anticipate only 1/2 of that capacity for lead acid and AGM batteries is usable capacity. That leaves you with, 35-50ah, depending upon on your battery.

Examples:

• 100ah battery has a usable battery capacity of about 50ah,
• 70ah battery has a usable capacity of about 35ah

Letting your lead acid or AGM battery dip to below a 50% state of charge can lead to quickly ruining your batteries. These types of batteries are simply not made to go below 50%. If you take a shower, run the fan, and watch an hour of TV, you are quickly running out of usable battery capacity. That is where a larger battery capacity can help. There are 2 common ways to increase your usable capacity and a less common, less tested newer way to increase your capacity.

The first is to replace your battery with a larger 12v battery. For some, this will be easiest. You can upgrade to a slightly larger battery, or even go with a significantly larger (150ah) Battery. Make sure you measure where you want to put the battery and the compare to the battery measurements, carefully to ensure you have enough space for a larger battery. Some people choose to alter their battery location or the front propane cover (tub) to allow for a larger battery.

A second way is to replace your battery with dual 6v golf cart batteries and wire them so that together, they are equal 12v (wired in series.) This can seem odd to people who are new to RVs, but it is a common practice because golf cart batteries are better suited for more frequent discharge and recharging than the typical deep cycle marine battery that is issued by RV dealers. Golf cart battereis are avilable in either lead acid or AGM. I recently changed to the AGM batteries. They are a little pricier but are maintenance free, more resistant to the drain that can occur to lead acid batteries in the cold, and pretty close to the same size as their lead acid counterparts. It should be noted that size of 6v batteries can vary by brand. Measure carefully before purchasing new batteries. If you want to see how other owners have installed their golf cart battieres, simply do a search on the forums or the Facebook groups to see a variety of photos. My batteries combine for 225ah, or a total usable battery capacity of around 112 ah.

Below is a video of how I originally set up my dual golf cart batteries. I have since moved my new AGM batteries to the Boondock diamond plate tub. The factory slightly altered the tub to fit the batteries for me.

The third, less tested way to expand your usable battery capacity is to upgrade to lithium. This will likely cause you to also have to upgrade your converter in order to charge your batteries. The attraction of lithium batteries are that they are light weight and their ability to be depleted to near zero without damaging the battery. The cons are the cost and there is some indication from early adopters that they did not get the battery life from lithium that was advertised. There have been improvements in both lifespan and cost with lithium, so I am watching some of the recent adopters and awaiting their reports. Whether you choose AGM or lithium, you should seriously consider a standalone charger, like a Noco Genius 7200. A smart charger will allow your battery to reach the proper charge where the converter in the T@b is meant to re-charge lead acid batteries. There is even some debate that lead acid batteries will perform better when a smart charger is used to help achieve the proper voltage for charging. I will forgo a more technical discussion about proper charging voltage, here, as this is a beginner level post.

The next consideration is perhaps the most important and this is how you camp. Let’s think of this in terms of personas.

How do you camp?

Sam is a weekend warrior. Sam likes to go off-roading and spends most weekends in the nearby mountains and desert roads a couple of hours from home. Most camping trips are 2-3 days.

Let’s start by looking at Sam. The best two choices for Sam are either larger battery capacity or solar. There is no need for both. A larger battery capacity and keeping an eye on battery usage will get Sam through the weekend without the hassle of setting up solar. Conversely, Sam could probably keep the battery that came with the T@b and top off the battery as needed. a portable panel will save Sam money and allow Sam to park the T@b in the shade an place solar panels in the sun. The challenge with the latter set-up is that if the days turn out to be mostly cloudy, Sam may have to become miserly without battery use. If I were Sam, I would start with a larger battery capacity and see if that does not meet my needs.

Barb is a road warrior. Barb takes cross country trips and only stays at each campsite between 1-2 days. Did someone say Walmart? Barb drives long days and pulls into a Walmart to overnight park before heading out the next day.

Next up is Barb. Barb is on the go! Barb will probably benefit from a combination of a larger battery capacity and reasonable permanent panel installed on the T@b. The larger battery capacity will give Barb the flexibility for long days of driving where her tow vehicle will mostly keep up but she would like to to charge before she checks out or after she checks into campgrounds along the way and also save time by using a permanently mounted solar panel while charging. This set-up also allows Barb to park her T@b in the shade and use her larger battery capacity to keep her powered up in warm weather or park in the sun and use solar in cooler weather.

Pat is a parks warrior. Pat will travel from the east to the west, but does tends to find a spot and stay for 3+ days. Pat might spend a week in Rocky Mountain National Park and then a week in Moab before heading home. Pat might use a combination of campsites with electric and free overnight parking along the way, as well.

Lastly, we have Pat. Sense Pat spends a lot of time in one spot while camping, a portable solar set-up will buy Pat a lot of time. However, if Pat runs into a patch of cloudy or stormy weather, Pat may wish that there was a larger battery bank in the T@b.

You might be thinking at this point, “She still has not told me how much solar I need.” Most T@b owners are pretty happy with between 150-200 watts of solar. Some get by with 100w and that might be a place to start if you are unsure, but I only recommend that little for folks who use their T@b more like a tent and who live in an area that is sunny more often than it is not.

The question that usually follows the how much solar, is whether portable or permanent are best. I have touched on the advantages of each, when looking at the personas. Portable panels allow you to park your trailer in the shade and place the panels in the sun. A permanent mounted solar panel on your T@b, saves you time, especially for quicker stops. Some prefer the permament mount to avoid theft of their solar array. I was not a fan of early installations as I thought it killed the look of the adorable T@b but more recent, cleaner looking installations have swayed my thinking.

Up until recently, I had given up on the permanent mounts because poor design caused frequent cell failures. However, nuCamp is installing a really nice panel and solar controiller right now and I am considering this solution, myself. This design seems to be much smarter and are early reports are positive.

A Few Personal Recommendations

Battery Monitoring: Victron BMV 712 – a battery monitor with a shunt gives you real time state of charge. Typical cigarette style monitors and even the monitor that comes with the T@b do not give you that information. They are giving you only what the voltage is at that moment, based on what is currently charging or be drawn from the batteries. So, if you are running the fan, it looks like your battery is lower than it actually is. Any shunted battery monitor will work but I am partial to Victron because of their fantastic bluetooth enabled app and their frequent firmware upgrades, delivering improved metrics.

Solar Controller: Victron MPPT controllers. You will find great debates about whether MPPT controllers are worth the extra expense. In the case of Victron, the answer is, yes. Not only can you customize the charge to match your battery specs, you can monitor the data with the same Bluetooth app I mentioned above, for the Victron Battery Moniitor. In addition, Victron has some smart capabilities that mitigate the risk of compromised charges due to partial shading of solar cells.

Solar Panels: There are a few good ones, but Renogy beats Zamp, hands down when it conmes to value vs. cost. They have excellent customer service and are continiously rolling out new products. nuCamp is using a Sunflare 190w panel. The Sunflare design is meant for an RV type of application and the design is promising. A side note: you are pretty much only looking for monocrystaline panels. Polycrystaline are panels are less efficient.

Concluding Thoughts

I hope you can tell from this post that there is no one right solution for all people but given you enough information to help you begin to determine which solution is right for you. There is a ton of information out there on the internet but little is written in non-technical jargon. You do not have to be an engineer to master your power management and establish the right solution for you!