Frequently Asked Questions - Solar

What size solar panel do I use for my trolling motor batteries?

We don’t recommend solar for recharging in a trolling application, only battery maintenance. The amps involved are too substantial. For maintenance, a 2.5 watt solar maintainer per deep cycle battery (12 volt or 24 volt systems) works (no controller), or for 24 volt systems, a 10 watt 24 volt unbreakable solar panel and a 24 volt controller also works. We have seen boathouse situations with large solar arrays on the roof that work, but due to the complexity and cost we look for another solution.

How about solar charging my golf cart?

Similar answer to above: due to the amps involved, it generally doesn’t work. Golf carts are usually 36 volt or 48 volt systems, and the complexity and cost to get any substantial amps becomes prohibitive, not to mention the physical size if mounting on the cart is the intent. Once again, a maintenance level can be achieved, or the Solargizers from Pulsetech in 24 volt and 36 volt are applicable.

What size panel will MAINTAIN a single car size battery, or a deep cycle marine?

A 2.5 watt Solar Maintainer is appropriately sized for maintenance levels on these batteries. It is not large enough to overcharge, and doesn’t require a controller, but is large enough for a maintenance level charge. These and the 1 watt and 5 watt have a built in diode to prevent feedback through the panel at night, one of the functions of a solar controller. If there is any sort of drain on the battery like an onboard computer, bilge pump, alarm, etc., a larger panel sized to compensate for the drain is required.

Can I series or parallel connect solar panels?

Yes, panels can be series connected for elevated voltages, i.e. two 12 volt panels for 24 volts, three panels for 36 volts, etc. Solar panels can be parallel connected for increased amp production, as long as the combined peak output doesn’t exceed the capacity of the controller. This can be handy when increasing the consumption on an existing system (just add another panel).

Can I run my device straight off of a solar panel, without a battery?

Sometimes. Some devices which are not voltage sensitive, and do not involve a surge when starting can be run off of an appropriate solar panel. This includes SOME motors, some lights, and some small electronics. Some solar controllers will not show current at their output unless they are connected to a viable battery, so this must be considered when diagnosing a solar setup.

What do batteries do in a solar setup?

Batteries act as a buffer and/or storage container. Devices with a surge when starting, such as SOME motors, compressors, some electronics, some lights, and some battery chargers and inverters require a surge of amps. A battery can supply this, and then the solar panel(s) recharge the battery and possibly carry some or all of the load. This would be the buffer application. Since solar only generates electricity during daylight hours (and the peak ones at that), a battery pack can store this energy for use at night or another time. Generally, the battery pack is sized for worst case scenarios (i.e. winter hours), and several days capacity, or more.

Are there solar panels for portable or rough service or vandal prone areas?

Yes, there are unbreakable panels, which are essentially a sheet of stainless steel with the solar material bonded to it, which have no glass front, and will tolerate dropping, impact, and vandalism. And there are flexible and folding solar panels, some military grade, up to 55 watts for camping, backpacking, scientific investigations, etc., where permanent installation or daily use is not intended. Then there are UniSolar panels, which are similar to the stainless units mentioned above, but have an aluminum frame like a standard panel, and are available up to 64 watts. Unfortunately, the UniSolar panels are sometimes built in sporadic batches, and not always available.

Do I need a solar controller?

Except for a few small panels, appropriately suited to the battery size, yes. A solar panel will put out power whenever it is exposed to the sun. If a battery is full, it will attempt to pass current, and may overcharge the battery. A controller regulates the output, similar to a battery charger, and backs off the current when the battery is full, and just maintains the charge. It also prevents feedback through the panel at night, which will occur if not blocked. The 1, 2, and 5 watt BSP panels we carry have blocking diodes built in to prevent the feedback, if they are used without a controller.

What type of batteries are best for a solar panel system?

All the lead acid battery types are used, such as flooded, AGM, and Gel, and sometimes other chemistries (like nicad) in specialty applications. Cost per amp hour, the flooded (wet) batteries are hard to beat, but require routine maintenance, which if neglected can cost more than the initial savings. The sealed AGM and Gel batteries are more expensive, but reduce maintenance and internal discharge factors. Most controllers will deal with flooded and AGM batteries, but some are not suitable for Gel batteries, as they require a different charge voltage, which if exceeded, will damage the batteries. As for longevity, quality batteries properly maintained will give roughly equal life among the three types.

What information do I need to size solar to a particular application?

You need the daily power consumption (24 hours) in watts or amps, the geographical location, and any mitigating factors like intermittent use, seasonal use, etc. From this, we can size a battery for 2 to 7 days capacity, and select enough solar to meet the geographical/seasonal situation. The power consumption may be a compilation of several components, some of them not constant (i.e. a radio transmitter operating 90% of the time in standby mode). But the key to a successful system is accurate and realistic power consumption numbers. A small error or omission even in milliamps can result in a dead or damaged battery.

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