How Much Battery Capacity Do I Need?
This first section is to help you decide how much battery capacity you want to include in your build. Successful vans can range anywhere from 100 amp-hrs to over 800 amp-hrs. Its a very important decision to get right as it can make many thousands of dollars of difference in the cost of both the batteries and the rest of the electrical system. Making wrong assumptions can also lead to a van conversion that just does not work very well.
A lot of people going into a van conversion find the idea of an all electric van appealing. This is possible these days, but before you decide to go this way, you want to really really understand all of the impacts this will have on your electrical system.
Loads That Only Run On Electricity
The first step in getting to your electrical system is to estimate your electrical loads – your whole system design will be based on this. Your battery size, how much solar, and the type and size of some of the equipment all depend on a good estimate of your loads.
The first step in estimating your loads is deciding which things in the van are going to be powered by electricity.
In order to get started down this path, lets first look at all those things that can only be powered by electricity. When you add up all the things that are needed and can only be powered by electricity, you have the minimum amount of electricity you will need per day. The table below shows things that need to run off electricity and a rough estimate of how many amp-hours of electricity they use per day. I give my estimate and what its based on and a blank column for you to fill in your estimate. You can use my estimate as a base for yours, or find other data. For example, I show the roof fan running 2 hours a day and you might want to run yours 4 hours a day, so just double my estimate.
|How Estimate d||Your Refined|
|Lights||2.2||3 LEDs @ 3Watts each|
for 3 hrs
|Strip Lights||2||8 ft of LED strip lights|
|Roof Fan||2||Maxxfan speed 5 (1 amp)|
|Water Pump||1||Shurflo pump 7.5 amps|
|CO & LP|
|1||0.04 amp 24 hrs|
|Fire Detector||0||Use a 10 yr Li battery detector|
|Charging Phone||2.5||2 full cell phone charges|
at 15 watt-hr each
|7||Full charge 70 watt-hr 80%|
|2||14 inch 12 V DC/DVD|
0.9 amp 2 hours
|Fridge||40||Test of Norcold 3 cuft|
|Sub Total||60||amp-hr per day for the basics|
|Loads that don’t|
apply to everyone
|Furnace Blower||11||1.8 amps 50% duty cycle|
for 12 hours of use
Cold weather in winter only
|Air Conditioning||See Below|
So, about 60 amp-hr of basics that pretty much will only run on electricity.
Make adjustments as needed. You may not use a laptop, so take off 7 amp-hr if not. Or, you may use a 400 watt gaming PC 6 hours a day, and that would add 200 amp-hours!
If operating in winter with a furnace add 11 or so amp-hrs.
The biggest load is the Fridge at 40 amp-hrs. There are alternatives here – one could use an ice chest, or one could use a propane fridge. But, I think most people these days are choosing from the large selection of RV size compressor fridges. Having lived with propane fridges on a couple past RVs, I think the small electric fridge for RVs is the best invention to come along the last 40 years in the RV world – yes, more important than Li batteries
So, go through the table above and refine the amp-hr numbers for your own use and add any loads that are not shown that need to run on electricity. This then is your base electric use.
Optional Electric Loads
Next we go through the other loads where you have a choice of running them on electricity or some other way (usually fossil fuel).
Cooking can be done without electricity using Propane or Butane. Or, with electricity using electric resistance burners or with an inductive cooktop.
Cooking on a Propane or Butane cooktop uses no electricity and most people like cooking with gas. This is probably why its so popular with camper vanners.
Cooking with an induction cooktop is becoming more popular in the camper van world. Its a nice way to cook and is not prohibitive on energy use. The cost of a good dual burner inductive cooktop is around $135, so not excessive. I’ve used the data from this Transit Van Forum post to estimate the energy use for a day of induction cooking at about 110 amp-hours including 10% inverter losses. This is a day with three coffees, oatmeal, and full cooked super, so its probably a little heavier than normal use, but not excessive.
Most of the dual burner induction cooktops use 1800 watts on full power, so you will want an inverter about this large.
So, adding an inductive cooker almost triples your electricity use per day (60 amp-hrs to 170 amp-hrs). Its a lot, but if you really like inductive cooking, it could be worth it.
It is also possible to cook on a regular electric hot plate, but for the same amount of cooking, this is likely to 30% ish more energy than the inductive. I think most people would choose the inductive cooking instead..
If you plan to camp in the cold you will want to be able to heat the van. Heating in cold weather is a very large van energy use. On one winter trip to Banff we kept track of Propane use over four nights averaging lows of 25F. The average propane use was 2.5 lb per night, or 54,000 BTU. If you convert this to what would have been needed for electric resistance heat (a plug in space heater) assuming 80% propane furnace efficiency, it comes out about 1050 amp-hrs per night. This is for a well insulated van kept to 60F inside with 25F outside at night. So, clearly electric resistance heat to keep the van warm on cold nights is not a good choice. And, some nights get a lot colder than 25F. A 1200 watt electric space heater pulls 100 amp-hrs out of the battery for every hour of operation.
Furnaces that run off the van’s gasoline or diesel fuel supply are also popular, and the story is about the same as for Propane furnaces – not much electrical use.
There are other solutions, like really warm sleeping bags maybe with some help from electric mattress heating pads. How tough are you
Some pioneers have tried using minisplit heat pumps as a way to use electric heating. Good Minisplits are about 3X more efficient than resistance heating, so the 1050 amp-hrs in the example above becomes 350 amp-hrs – still quite high, but maybe for fall camping or for miler climates. The mini splits also provide air conditioning, so that’s a plus. On the negative side, the mini splits are bulky and not easy to install in a van, and the jury is still out on whether they will hold up to the bouncy van environment.
Water heating (for showers etc.) is another high energy demand. How much hot water you might needs depends on how many people and their habits. I’ll use four gallons of hot water demand per day in this example. Four gallons can be heated in a regular small electric water heater. To heat four gallons from 60F up to 120F requires about 50 amp-hours from the battery – a bit more if the water must be kept warm for extended periods. So, a fair bit, but definitely doable. Obviously if you want full blown home showers for a couple people, it could easily be two or three times the 50 amp-hrs.
Propane heaters are readily available in RV sizes – both tank type and tankless. They use little to no electricity.
Another more efficient water heater is use engine coolant to heat water in a small tank using a heat exchanger – the IsoTemp is one such water heater. As long as only hot engine coolant is used as the heat source, there is nothing but waste engine heat used to heat the water. These units also include a backup electric heating element, but from user reports, this is often not needed. On the negative side, its expensive and the installation is a complex.
Our less rigorous solution is just to heat up a bit on wash water in the morning in a pan
Air conditioning in hot weather without a shore power is very challenging. There is a strong desire to be able to put enough solar on the roof and batteries in the van to be able to visit hot climates and be self sufficient. The ability to do this depends on a whole raft of things: how well insulated is your van? Do you have good reflective (preferably outside) window covers? How efficient is your air conditioner? Are you trying to air condition the entire van? What color is your van? hot and how humid is it? How much battery and how much solar do you have?
I will cut to the chase and say that as of 2022 I don’t think its possible even for well insulated vans with efficient AC units and lots of battery and solar to sustain several days of hot humid weather without a place to plug in. I’m talking about Texas like 110F humid weather here. You might well be able to work out something that will work for 85F nights where some AC is needed to sleep, but not for multiple days of 110F. Even if you can put enough battery in the van to do a day of hot humid weather AC, it does not appear to be possible to put enough solar on a van roof to replenish the batteries in a day of good sun. Also good to be aware that a full roof of solar panels on a rack will probably cost you at least 2 MPG.
If anyone has actual experience in this area, we would love to hear it. Please include as much data as possible on the van configuration, type of AC, battery and solar capacity, and the weather conditions.
Other Cooling Solutions:
For less severe cooling needs, there are some good solutions.
I’ve collected a lot of van cooling methods on this page ranging through fans, shades, insulation, evaporative cooling, adapting window ACs, mini-splits, and more – you might find some good ideas.
If you anticipate heavy roof van use for cooling, the MaxxFan on speed 7 (lots of airflow) draws 1.1 amp, so running it 16 hours a day would add about 20 amp-hrs per day.
Good insulation, window sun reflectors, light color paint, sun shades on the outside of the van, parking in the shade all help with the cooling and use no electricity.
For dry climates, evaporative coolers are effective and don’t use much electricity – see the this page for more information, but about 50 amp-hrs would give you about 12 hours of evaporative cooling.
Adding the Amp-Hours up
Use the table below to get an idea what your ONE DAY need in amp-hours of battery is
All of this discussion is assuming you have no plugin available – its just you, your van, and the sun.
|Basics||60||This is the total of things that only run on electrical.|
See the first table on this page, and make your own adjustments.
|50||This is minimal (4 gallon) electric water heating for 2 people .|
Double or triple this if you want generous showers or have more people
|110||This is electricity for using an induction plate for cooking.|
See the section above on induction heating for more detail and
to make adjustments.
|1050||This is electric space heating on a cold night (25F) and keeping the inside of the van at 60F.|
This is not really practical – adjust down for mild weather, or monster sleeping bags in a cold van, or mattress heating pads.
If you have another scheme, please describe in the comments.
But don’t underestimate how miserable you might be on a cold night with just an electric space heater and limited battery.
|20 to 50||Cooling for climates where a lot of high fan use, or evaporative cooling will work.|
See the cooling section above.
This does not cover mechanical (compressor) AC
|600?||This is moderately hot and humid (90F ish) with the cooling done with a compressor AC unit. Lots of ideas on this page…|
|Effective cooling in genuinely hot and humid weather (110F) for multiple days does not seem to be feasible yet. You may be able to add enough battery inside the van, but there is not enough real estate on the roof for the solar panels to recharge the batteries.|
Please comment if you have a solution or ideas.
Start with the 60 amp-hrs of basics (or your adjusted number), then, if you decide to use electricity for cooking, water heating, space heating, or cooling add the amount from the table for each.
For example, if you decide to go with inductive cooking, but leave space and water heating to propane, butane or gasoline, then your ONE DAY total would be 60 amp-hr + 110 amp-hrs = 170 amp-hours.
This is your one day total – you will use this much from the battery in one day IF you get no charging (sun not shinning and no driving). Most people are not happy with having only one day of batteries. At a minimum something like a day and half provides some margin for emergencies or odd circumstances. You probably don’t want to be down to no usable battery when you wake up in the morning. Many people will want the ability to stay at a remote location for a couple of days, in which case you will want at least twice your one day total – probably a bit more. This lets you stay a couple days without running the engine and no solar charging (cloudy days). If you have solar, and the weather is sunny, that will extend the time. There are some who want to be able to stay a week in a remote location.
See the solar section for estimating how much solar you will need to keep your batteries up.
Here is an example for a dedicated, long term boon docker
Assume a 20 lb propane tank, 180 amp-hours usable of battery, and 300 watts of solar.
- Use electricity only for the things that require it: 60 amp-hours per day
- Use Propane (or gasoline from the van tank) for space heating: 0 to 3 lb propane per day
- Use Propane for cooking: 0 amp-hours per day; 0.4 lb of propane per day
- Use Propane or excess solar for water heating: 0 amp-hours per day; 0.2 lbs propane per day
Limits on boon dock time:
Battery limit: with no solar 3 days; with good solar, no limit
Propane limit: with no space heating 33 days; with cold weather space heating 18 days (25F nights)
Water would add another limiting factor, but it looks like with enough water and 300 watts solar, 18 days would be workable.
Not to beat this to death, but during this 18 days, the batteries provide a maximum of 1200 watt-hours of energy, solar provides about 13,000 watt-hours of energy, and propane provides 431,000 watt-hours of energy.
You can work through the same kinds of examples for your van configuration. One thing that I guess is obvious is that vans that use electricity for all energy needs will likely have short boon-docking limits – the exception might be vans with lots of solar and in mild climates.
Energy Storage Density
Just for fun, here is the comparison for storing energy in the form of Propane to storing energy in LiFePo4 batteries.
Comparing a 20 lb propane cylinder to a 100 amp-hr LiFePo4 battery…
|Item“||20 lb propane|
|431,000 watt-hrs||1200 watt-hrs|
|36 lbs||28.2 lb|
|1.2 CF||0.37 CF|
In rough terms, a 20 lb propane cylinder is about 4 times the volume and 1.3 times heavier than the LiFePo4 battery, but has 359 times as much stored energy. I guess this is why electric cars are hard.
The case for the batteries plus propane van
This van plan uses a couple of golf cart batteries or a couple 100 amp-hr LiFePo4 batteries for about 2200 watt-hours of electrical storage. It uses a 20lb propane cylinder (a standard BBQ cylinder) that is housed in a locker vented to the outside. The propane provides 431,000 watt-hours of energy storage for heating processes.
The basic philosophy is to use batteries that are not so great at storing energy when you have to, and use the propane, which is very good at energy storage when you can. Luckily the things that can only be done with electricity don’t require a whole lot of energy.
The batteries are used to power: lights, roof fan, water pump, gas detectors, charging phones, charging laptop, TV/DVD, and fridge – basically everything that can only be powered by electricity. These add up to about 700 watt-hours a day, so the battery pack could power them for two or three days without any charging.
The propane is used to provide energy for heating processes: cooking, water heating and space heating. These are processes with high energy demands, so the high energy density of the propane is helpful. These turn out to be very demanding energy users – they can add up to 18,000 or more watt-hours per day.
I know that I’m coming across as anti solar in the above. Not really true – my house is powered by DIY solar, water is heated by solar DIY thermal, space heating in part from DIY solar thermal, and I do what is probably the largest DIY solar site out there. Its just that its harder to make it work well on a van, especially when you consider the MPG penalty for large solar roof racks.