Choosing The Correct Solar Panel For Your Motorhome
BUYING A SOLAR PANEL FOR YOUR MOTORHOME – DOES IT NEED TO BE SO COMPLICATED?
For almost a year, a huge solar panel has been propped against the wall in our hallway. In a snap decision (which is usually the case with me) I spied a solar panel for auction on eBay. I placed my snipe bid and by the next morning I was the proud owner of a shiny new solar panel at a very reasonable price.
A whole list of tasks that needed completing around the motorhome have prevented me from attempting to install this before now – along with an ongoing sense of trepidation about my own ability to fit the thing!
The deal wasn’t totally random. As we had not yet had any experience of staying in the van, we did not know what our electricity consumption would be like. It would have been possible to guesstimate each electrical device we might use and for how long each day, but I didn’t want to go through every possible permutation and work with endless equations for converting watts to amp hours and allowing for the use of both 12 volt and 230 volt appliances via an inverter …. sometimes life is too short and I am not about to turn this post into an Faraday lecture.
I decided to use the simple approach. Our motorhome came supplied with 2 leisure batteries. These only have a capacity of 60 amp hours each, and I think they have been installed for some time so most likely have lost some of their limited capacity and ability to hold a charge – so I will be replacing them.
I only have space for 2 batteries as the starter system for the lorry is 24v working off a further 2 starter batteries – space in the battery locker is limited. I was working on the premise of buying 2 x new 120 amp hour batteries, however on checking their dimensions, they would not fit in the available space. I have had to settle for 2 x 110 amp hour batteries. This will almost double the capacity of the existing set up before even allowing for any depletion in the old batteries.
This will be the limit of our electricity usage – simple as that. We will have to work within our limits rather than trying to get greedy on calculations and installing an unlimited battery bank.
Let’s face it, we would all love an endless supply of tiny electrons running through our cables and I have seen systems online with 6 batteries linked to 6 solar panels powering huge pure sine inverters, running everything from microwave/convection ovens to air conditioning systems.
But at the end of the day, we are all limited either through space to store the batteries, space to mount the solar panels or the high cost of acquiring such systems. The axe has to fall somewhere and in my case it was the available battery space which dictated our limits.
Which brings me back to the solar panel and the not such a rash decision to purchase it. The vast majority of systems I have seen installed seem to have an equal correlation between the battery capacity and the size of the solar panel. In all these cases, the wattage measurement of solar panels is similar to the equivalent amp hour storage capacity of the leisure batteries.
A 100 watt solar panel appears to be a good match for a 100 amp hour battery. This is a very casual rule of thumb approach, and if you feel that you would need a more calculated method of choosing your batteries and solar panel…. there is a good write up here that you can refer to.
We will have 220 amp hours of battery capacity so I had settled myself to acquiring 2 x 100w solar panels. That was until I spied the auction on eBay. It was for a single 250 watt polycrystalline solar panel. It has more than the output I was looking for. Always better to have a little spare in the bank rather than not enough! Polycrystalline panels have a distinctive marbled blue colour and do not have the corners cut off the squares
I know there has been a lot of debate about monocrystalline v polycrystalline panels, but it seems that the differences can be narrowed down to relative size of the panel for equivalent output. A 250w mono panel would have been smaller than our polycrystalline panel, but space on the roof is not an issue.
Also, the output from monocrystalline panels suffer greatly if there are any shade obstructions. Watch this video to see how the entire circuit (even of 2 connected panels) is affected by only a single cell in the shade. I also took the approach of Craig from Our Bumble, when he said that the make of his solar panels was unimportant in his opinion.
And finally the price – polycrystalline panels tend to be cheaper than their mono equivalent. I think the sheer size and output rating of this panel put off most bidders and I managed to snag it for just over £100 including free delivery. An absolute bargain for a 250w panel and as we live in Northern Ireland where the shipping of large items from the UK mainland can be extortionate, the fact that delivery was included free was a major added bonus.
When the panel was delivered, I couldn’t believe the size of it! It was 1.5m x 1m, but even reading the sizes in the auction description does not make you appreciate the actual size of the thing until you see it in front of you in all its glory. I was not going to try and jump onto the roof of the van on a dark, cold and wet night to check if it fitted before deciding to place my bid.
Luckily the real estate available on the roof of the van is not such a problem, unlike the space we had available for batteries. I knew this, so was not overly concerned about placing the bid. But if you plan to do something similar, make sure you have checked the available space on your motorhome roof before hitting the bid or buy button!
This solar panel should recharge our batteries nicely and might even leave some additional power during the day to siphon from the battery bank to recharge laptops and cameras etc. The charge controller even has 2 x USB ports and 2 x 12v outlets for this very purpose.
Next…. read about the installation.
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