How much Solar do you need?

How much is enough?

Lets explore how to determine how much solar you really need

When choosing how much solar you need you must think about what you want your solar to accomplish. Do you want it to strictly maintain you while you are off grid or are you looking for a system that will sustain you as well as charge your battery? In most cases, it is the later of the 2. In determining solar, the best thing to do is look at the size of your battery bank. This will help you in determining the best solar panel option for you.

In addition to looking at the size or your battery bank, you can also take into consideration how many amps you draw in a day to know how much you need to regain and add to stay off grid longer. To find out how many amps you use in a day, you can use this simple formula: Watts ÷ Volts = Amps per hour.

Since I am sure that is as clear as mud, let’s talk a little about a battery bank as we try to make it all a bit clearer. The off-grid camper uses a single group 27 battery. When looking at your battery you will see a stamp that tells you how many amps per 20 hour rate the battery can hold. The diagram to the Right shows that this battery has a 20 Hr. Rate of (75Amp Hours) this means the capacity of the battery at a 20-hour rate is 75amps. This results in drawing 75 amps over 20 hours will completely drain your battery. Our goal with solar power is to keep ahead of the amp draw to lengthen your battery life as well as keep you out longer. This may sound like a lot of amps to have in a day but in the world of deep cycle batteries, once the battery reaches 50% capacity it goes into a deep discharge state, this reduces the life cycle of the battery and if it gets to low it will be hard to regain a full charge and may cause a shorter life span of the battery itself.

Next, we consider how many amps are used in a day, on average most campers in truck campers or trailers under 22’ will use 30-35 amps per day (this usage includes phantom draw from you LP detector and other small draw items). This usage does not include things that are considered to have a “phantom” draw on the unit such as your LP Detector, which can draw at least .5 amps per hour resulting in an additional 10 amps of draw in a 20-hour period. If your battery has 75 amp hours and you are using 45 amps (daily use estimate + LP detector), you have drained half your battery and you have only been out 1 day. Now, you can add an additional battery but that still does not allow you to get out for more than 2 days without needing a generator or power pole hookup.

This is where solar power can come to your rescue. Depending on the method of solar you determined is best for you in our previous segment (hardwired or portable) you have different panel sizes available to you. We use the ZAMP solar brand solar kits so the panels below are based on this brand.

For portable solar panel users; the middle of the road option would be the 120-watt system. These panels can put 6.8 amps back into your battery per hour in ideal conditions meaning, you will add back 40.8 amps in a 6-hour period. Helping to keep you afloat a little longer while off gird, if you want complete sustainability while traveling remote on a single Group 27 battery than the 160-watt system would work best. This panel puts 9.4 amps back into your battery in ideal conditions meaning you are adding back 56 amps to your battery in a 6-hour period.

If the hardwired panel was the best type of panel system for you than you again have options for both a middle of the road option and a best option. The middle of the road option would be a 160-watt hardwired kit, these kits give you an 8.9-amp input which in a 6-hour period results in 53.4 amps going back into your battery bank. The best option for you would be the 200-watt hardwired kit, these give you an amazing 11.2 amps back into your battery per hour which results in 67.2 amps back into your battery in a 6-hour period. With both options, you can see that you are replacing the amps used with the amps replaced in your battery meaning in ideal conditions you can stay out longer than without using solar power.  

No matter which system of solar you choose to use with ZAMP solar you are not limited to only that size panel or even that type of system. ZAMP solar is designed to be combined and expanded upon to help meet your solar needs as they grow with you and your camping adventures.

With solar, you also don’t have to worry about over charging your battery either, each solar controller is designed to adjust the amps into the battery so it will never be over charged. Due to this, we recommend if you are on the fence for which panel to choose, you can always go larger to know you are covered vs smaller and worry about not being able to stay out for long periods of time.

There is a lot to think about when it comes to solar and we know it can be confusing, we are always here to answer any of your solar power needs to help you make the best decision the first time. Feel free to contact our office via email at or by telephone at 319-234-0071 and someone on our staff will be more than happy to sort through which panel is best for you.

Join us in our last segment on solar panels to learn more about the ZAMP solar brand and why we feel it is the best solar panel option currently on the market.

This Post Has 2 Comments

  1. How are you defining ‘ideal conditions’? A panel mounted flat to the roof of a vehicle/tent obviously is not in an ideal position to catch incoming solar energy. Also just as obvious, a fixed mount panel, even if angled toward the sun, is not going to track the sun as it moves across the sky. Are these factors accounted for? How efficient will a flat mounted panel really be?

    1. Thanks for your question. You are correct! A flat roof mount solar panel on the roof is not in the 100% sun tracking position but it does utilize a huge wasted space that is always up there. Traveling further north into Canada and Alaska, it gets even worse as the angle of the sun gets lower. Another thing to consider is mounting it to the roof makes it almost theft proof and requires little maintenance.
      In my own experience, I use a roof mounted solar panel as a charger while I am storing the camper, with my electric driven roof lift system, my battery has always 100% when I am ready to go. My roof panel does help when I camp for the day and move on. I watch the solar controller as the afternoon passes and watch the charging amps drop from 6-7 amps to 4 and lower.
      When I set up my base camp for 4-5 days, I take Zamp’s portable suitcase 120 watt with me and add that to the roof panel. That setup keeps my frig and MaxAir fan running all day and furnace, if I need to at, night. With the portable unit, I can track the sun to maximize the wattage output. Usually 3-4 times a day keeps it near peak.
      The only drawback to the setting up the portable unit is the theft factor. Unfortunately, we all have to deal with in today’s society. A bike cable lock helps keep people honest.
      I know there is a sun tracking roof mount available but it is too heavy and expensive for most truck camper and RTT customers to consider.
      I would think that, compared to solar setup that can track the seasonal sun changes, the output to a roof mounted panel is 50-60% less efficient. That is just my opinion without ANY scientific data to back me up. But I do know my roof mounted Zamp is much lighter and affordable for my camping adventures.
      I am no solar expert but I am always learning and have found that Zamp Solar has a great customer service department and my factory rep is always available when I have questions like yours I need to answer.

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