About our solar power rig

How Mr and Mrs Squirrel camp for many days off the grid.

No two people have the same idea of what constitutes a nice camping experience, and some will cheerfully sit within yards of a generator not minding having to raise their voices to be heard over it. To us, the constant noise cuts one off from the environment as effectively as sitting inside a screen room or in an RV. But unlike sitting inside that screen room or RV, which affects only the experience of those choosing to sit there, noise affects everyone within earshot. I consider running a generator in camp to be as rude as requiring neighbors to listen to your choice of music, hour after hour.

There are no really quiet generators. Without other sources of constant sound, like freeways or a river to mask the noise, even the little Honda 1000W generator will infuse an quiet area with a constant, almost subliminal but always audible background of noise. 

When a generator is finally shut off one breathes a sigh of relief, as if a weight had been taken off one's chest.

Getting Power: the Solar Power Setup

We like our comfort when we camp. Just because we're off the grid doesn't mean we can't use a refrigerator, some electric lighting, a little music, or operate our laptop computers or watch DVDs at night! But we don't like camping in places where there are hookups and we especially don't like to listen to noisy generators. Silent, non-polluting solar power and energy-efficient appliances work for us.

Our solar rig consists of six main parts:

Two 45-watt solar panels [1] which convert sunlight into electricity. We keep them stored where the upper bunk mattress used to be. We like sleeping on the lower bunk. 

A solar panel controller [2, below] in the van which regulates the voltage coming from the panels so it can be used for battery charging and to operate our electrical appliances during sunlight hours. 

The power from the solar panels is brought to the controller using low-resistance 6-gauge wire [3] and heavy-duty electrical connectors designed for high current [4]. A 100 ampere-hour (Ah) deep-cycle battery [5] which powers everything at night), and a battery monitor [6, below] which displays the battery's state of charge.

Conserving Power: Our energy budget.

Solar is silent and non-polluting but it doesn't provide as much power as a generator or household current. During the day we can't use more than the panels can provide, and at night we can only use as much power as our one auxiliary deep-cycle has stored in it. We had to decide what appliances are important to use, find the ones that use as little power as possible, and figure out how much power it will take to run it all.

Refrigerator. Keeping food cold is important to avoid spoilage, but most RV and dormitory refrigerators use a lot of power. We replaced our van's original refrigerator with an efficient Norcold DC0040 12-volt model [7]. Over a 24-hour period, I reckon this refrigerator uses 20Ah.

Our laptop computer [8] pulls 3 amps. If we run it for two hours, it needs 6Ah per day.

At night we frequenly watch a DVD on a small DVD player (keeping the sound low so as not to bother the neighbors). Our little Philips player draws about 2.5 amps, and a film is usually about two hours, so that's another 5Ah.

For lighting I we have a couple 8-watt 12-volt dc fluorescent fixtures [9] and a couple of 12-volt halogen "reading lights" [9]. Each light draws an amp or so when on, but we don't use them a lot -- generally one light at a time, and no lighting if we're watching a DVD. We probably use less than 1Ah for lighting per night.

Adding all that up, we use less than 35Ah per 24-hour period. During the day we might listen to soft music when it won't bother our neighbors. Our van's stereo draws about an amp per hour.

How well does it work?

It works great! I check the auxiliary battery with the monitor in the morning, and see that our nighttime power consumption is usually around 20Ah (20% of the 100Ah battery). When the sun hits the panels in the morning, the controller kicks in and starts pumping current into the battery. I usually see more than 6 amps going into the battery at first. The controller slowly tapers the current into the battery as it becomes fully-charged. Before noon, the battery is fully-charged.

During the warmest part of the day, the refrigerator runs more, but with full sun on the panels they provide plenty of power to run everything we've got plus keep the battery at full charge.

When the sun goes back down, the relay in the controller clicks to indicate that the panels have gone offline, and the battery becomes the sole provider of the van's power. Since our dusk-to-dawn power requirement is never more than 20Ah, we still have 80Ah in the battery in the morning. By not discharging the battery very deeply, the battery's life is prolonged and we have some margin in case we have a day or two of overcast weather and the panels can't put out much power (they need full sun, no shading at all).

Tips.

Anything that uses electricity for heating, like electric blankets, a Mr. Coffee, microwave ovens or similar are not suitable for a small solar power system -- they draw too much power. A Mr. Coffee, for example, is rated by the manufacturer as a 900-watt appliance, which is not outrageous for household 120-volt current, but on a 12-volt circuit, 900 watts requires 95 amperes - more than any 12-volt circuit or portable bank of solar panels could ever provide. If a Mr Coffee is left on for one hour, it would draw 95 ampere-hours out of the battery. But we love coffee, so we boil water on our gas stove and make drip coffee or use a French press coffee (it's better than anything a Mr Coffee can make anyway), and we heat our van in the morning with a little LPG catalytic heater that requires no electricity.

Using an inverter -- a device which converts 12VDC to household 120VAC current -- doesn't help because it has to draw even more than 900 watts out of the battery due to conversion inefficiency. Solar panels and batteries just don't have what it takes to support electric heating devices.

Lighting takes a lot of power, too. Incandescent lamps (including halogen) are about as inefficient as you can get. 12-volt LED and fluorescent lamps are much more efficient, meaning more light per watt. Cold cathode fluorescent lamps are supposed to be the most efficient of all, but they are costly.

Since we only use 20% of the battery capacity in the night, we could clearly use a smaller battery, but I like the margin in case we get a couple days of no sun. Also the less a battery is discharged, the longer it lasts, so a large battery will last more years. If you want to run more energy-hungry appliances, a larger battery could be used but make sure that the panels can provide enough power during the day to replace what was lost during the night and still have enough excess left over to run any appliances you need during sunlight hours.

For battery maintenance,  I check the water level in the battery every few weeks to make sure that it's not running dry, and use the "equalizer" function of the charger once every couple months to maintain battery health, and that's about it.

How much power do various appliances require? Here's a Handy Online Ampere-Hour Calculator: http://www.altavistaaudio.com/Westy/Vanagon/battcalc.html 

If you have any questions, e-mail us: camping.elliott(at)gmail.com


Equipment Notes (probably more than you want to know)

1. The two smallish 45-watt solar panels are easier for me to handle than a single large panel. I place the panels out in the sun, braced upright with cheap camera monopods behind as third legs and move them as needed to face the sun. Some people put panels on top of their campers or vans. We'd never do that because we prefer to park in the shade when it gets hot, and it gets hot a lot here in the southwest US; and we'd need to turn the van all day long to follow the sun. BP Solar, Kyocera, and Sharp all make fine solar panels.

2. With anything more than a 5-watt panel, a controller is needed to prevent damage to the battery from overcharging. The Blue Sky 2000E solar controller is an MPPT (maximum power point) type controller which uses a microprocessor to constantly calculate how best to use the panels for the highest efficiency, while safely charging the battery and at the same time providing power to operate electrical appliances. MMPT controllers squeeze every last drop of power from the panels -- we routinely see at least an amp more current from the controller than the panels are putting into the controller. This is possible because the optimum voltage for panels is around 17 volts while the optimum voltage to charge the battery and run the appliances is around 14 volts. The controller converts the higher-voltage, lower-current power into lower-voltage higher current power. Several companies make small MMPT controllers for marine and recreational use.  http://www.blueskyenergyinc.com/sb2000e.htm 

3. It's important to use fat wire between the panels and the controller. Every ohm of resistance in the wire means power forever lost. We use 6-gauge Ancor marine-grade wire, www.westmarine.com, p/n 290882, or for less money, get some booster (jumper cables) in 6-gauge size and cut off the clamps. That said, even a 40-foot run of 8-gauge wire will only incur a 4% loss of power at 10 amps.

4. Low-voltage systems are high current systems and need high-current connectors so that all the panel current reaches the controller. We use Anderson Powerpole PP75 connectors, http://www.andersonpower.com/products/standard-powerpole.html , (order kit PP-75-6-KIT from http://www.connex-electronics.com). Soldering is required to assemble these connectors to the wire.

5. Our battery is a Trojan SCS225 deep-cycle. It has a 130Ah (ampere-hour) rating which means that it can supply 6.5 amps continuously for 20 hours (or roughly 13 amps for 10 hours, or 1 amp for 130 hours -- it's all amps times hours, roughly). Deep-cycle batteries last a lot longer if you never go below 50% of their capacity, before recharging. Regular car-starting batteries are not well-adapted for light, constant usage with repeated discharge/charge cycles.

6. Xantrex battery monitor, http://www.xantrex.com/web/id/96/p/1/pt/7/product.asp A very cool gadget -- it monitors energy going in and coming out of the battery and displays how much capacity is available, like a fuel gauge.

 7. Our Norcold DC0040 12-volt refrigerator uses the efficient Danfoss compressor system for maximum cooling with minimum energy consumption. This model draws 2.5 amps when running, so if it ran for 24 hours a day, it would use 60 amp hours (2.5A x 24 hours = 60Ah). But it doesn't run full-time, it cycles on every ten minutes and during a hot day it might run five minutes per ten minute cycle, and on cold nights maybe only a minute per cycle. So that's about 1.25 Ah per hour during the day, and a lot lower at night. Engel also makes refrigerators with the Danfoss system. Most RV and small house or dormitory refrigerators use a lot more power. Check the specs. Our van's original Dometic was a fine unit, and performed up to snuff, but simply wasn't capable of keeping our foods as cold as I'd like when the outside temps got over 90F.

8. We use out laptop computer's DC (cigarette lighter) power supply. Laptops run on DC internally, not the 120-volt AC current you find in your house. Using its DC power supply is more efficient than converting the 12 volt battery voltage to 120 VAC with an inverter [10], then using the laptop's ac-to-dc power supply to take it back to DC.

9. The fluorescent lamps are 8-watt 12-volt dc fluorescent fixtures. I forget the brand/model but the Thin-Lite 190-Series available from many marine and RV suppliers are similar. The halogen reading lamps are 10W West Marine model # 144217. For room general lighting we use Dietz oil lamps. They provide a nice warm glow, and throw off some heat. For reading in bed, I use one of those LED headlamps that you wear on your head. My wife snoozes, I read, and no power is being taken from the battery.

10. Inverter.

Inverters are used to convert 12-volt DC into household-type 120-volt AC for appliances that can't run on 12 volt DC power. There are dozens of brands and types. "Modified Sine Wave" types are suitable for almost all appliances. "Pure Sine Wave" types are a lot more expensive and only needed for very sensitive electronics, or older TV's and VCRs. Inverters are not very efficient, losing maybe 10% of the energy in the conversion process, so to conserve power try to find appliances designed to run directly from the battery's 12 volts. We use our inverter, a 800-watt modified sine wave model, to run our coffee bean grinder and a small immersion blender (for gazpacho), and that's about it. Inverters need to be connected to the battery with fat wire because they use more than 10 amps from the battery for every amp they are delivering to the appliance. Use the Handy Online Ampere-Hour Calculator mentioned above to calculate how much battery power your inverter needs when running appliances.

Recommendation for less sunny climes.

We do most of our camping in the U.S. southwest area, in spring and summer, where there is a lot of sunlight. But overcast weather, camping in winter, or even shade from trees will reduce the amount of sunlight available for conversion to electricity. A worst-case scenario might include camping north of the Arctic Circle in winter, where you won't see sun for weeks. That's no place for solar. In between that worst-case and our cheerful sunny camping, you'll need a system with greater tolerance for reduced sunlight. A friend in New Mexico (Larry Chase, www.roadhaus.com ) with more experience with solar than we provided these more conservative design suggestions:

1) Assume no more than 6 hrs of efficient solar production per day during summer.
2) Derate solar panel specs by 10-15%.
3) Increase calculated estimated usage by 25%.
4) Put panel in sun and van in shade.
5) Keep the connection cord as short as possible (longer length = less efficiency).
6) Use a properly rated gauge for that connection cord to reduce losses. The heavier the wire gauge, the more power gets to your battery.
7) Use efficient appliances, including efficient coolers from Engle, Norcold, or Vitrifrigo.
Solar is silent and non-polluting. We like that when camping. Otherwise, we might as well camp in a downtown parking lot. The key is to find efficient appliances, calculate your anticipated 24-hour ampere-hour needs, get a big enough battery to provide your after dark power needs , then get enough solar panel power to run it all, based on your latitude (less sunlight at higher latitudes) and expected hours per day of sunlight.

More Reading.

Boatowner’s Illustrated Electrical Handbook", by Charlie Wing, ISBN-10: 0071446443