Solar for camping - Will this work?

Re: Solar for camping - Will this work?

Short answer is the panels are not very good and a few people here have found that the panels do not output near their rated current.

You can get two poly-crystalline panels that are about 1/2 the size of the 4 panels that will output more energy into your battery/system.

Some other issues... A car battery is a terrible deep cycle battery. Take them down more than 15% cycling and you will probably end up killing the battery fairly quickly (may last a camping season).

Next, powering the laptops... You should measure the power (AC or DC) that they will need to use per day based on typical usage. It may range from 18 watts to 60 watts per laptop depending on size/speed/power save settings.

A Kill-a-Watt meter is great for AC measurements. A DC Amp*Hour/Watt*Hour meter for the DC side.

Next, selecting the way to power your laptops... You can use DC power adapters or an AC inverter... Both have their advantages and disadvantages.

DC laptop adapters are not usually very rugged and may not work well with the 10.5-15.5 volts that a deep cycle battery system may present to a laptop computer adapter... There have been a few reports of failed DC adapters on solar RE systems (probably from high voltage during recharging/equalization). In theory, a DC adapter may be more efficient than using an AC Inverter + AC power brick--but you should measure the actual DC current/wattage to confirm.

For the AC inverter--Choosing the correct size (smaller inverters waste less energy with smaller AC devices) is important. Also, there are TSW (True Sine Wave) type inverters (good and expensive) and MSW (Modified Square Wave--cheap and may cause issues with some AC loads). Small AC wall wart transformers, some electronic power supplies, and some AC motors do not like MSW inverters very well (the devices can overheat). It is difficult to predict which will work OK with MSW and which will not--The old 80/20 rule--80% will probably work OK, 20% may not--but which is which is difficult to guess... If the remote project is critical--you should pony up the money for a good True Sine Wave inverter.

Here are a couple articles that talk about your inverter options:

All About Inverters
Choosing an inverter for water pumping

Here is a really nice 300 12 volt TSW inverter--May be overkill for your application.

Morningstar SureSine, 300 Watt Sine Wave Inverter 115VAC

Lastly, there is a good chance that the 40 AH 12 volt battery is a bit small / wrong type for your application. We really need you estimated loads (watts and hours of operation per day) to recommend the right size battery bank. Too small of battery and you can use all its power within an hour or so--and kill it in days/weeks.

And too small of solar array can mean a week or longer to recharge your battery bank.

In general, first choose the smallest/most power efficient laptops you can find that will meet your needs. And run them only long enough to do the job.

Next, size the battery bank, inverter, and solar array to meet your needs over time based on the location and season. You can run from 2 hours of sun to 6+ hours of sun per day--A huge difference in output from your solar panels. Also, figure that your solar/battery system will be about 50% efficient. For example a reasonably sunny region and not winter time:

• 45 watts * 4 hours of sun per day * 0.50 eff = 90 Watt*Hours per day

A typical laptop/net book will run on around 20-60 watts average power:

• 90 WH / 20 Watts = 4.5 hours per day
• 90 WH / 60 Watts = 1.5 hours per day

-Bill