An increasing number of motorhomes have solar panels providing power for free. What's not to like? A free, green power source wherever you go.
If only it was that simple! Mostly, you don't want the power when the sun is shining. You're more likely to want to use power after the best of the daylight has gone, which means you are using power stored in your batteries. And that's the snag.
Basically, there are two basic types of battery: lead-acid and lithium-ion. The former have been around for a very long time. They're readily available and reasonably inexpensive. The problem is that they don't last very long. A typical "leisure" battery sold for motorhome use has a capacilty of about 100Ah (this means that it can give 5 amps of current for 20 hours, though not 100 amps for one hour). Unfortunately, you can't use all this capacity.
Each time you discharge a lead-acid battery you use some of its life up. How far you discharge the battery makes a big difference to how much life is used up. Typically a leisure battery has about 100 charge cycles if you discharge it to 20% capacity remaining, or 200 charge cycles if you discharge it to half empty.
Given that the battery probably costs about £100, that means that each discharge to 20% costs £1 and each discharge to 50% costs 50p.
The limitations of how batteries are charged in a motorhome probably mean that your battery only gets charged to 85% full, which means that you can only use 65% of its capacity for your £1, or 35% for your 50p.
The maths are little different if you have lithium-ion batteries. These cost between five and ten times as much as lead-acid batteries of the same capacity, but they last much longer and are less damaged by being discharged to quite low levels. They generally last five to ten times as long as their lead-acid equivalent, so the cost per cycle is not a lot different. They are lighter and do charge more quickly, and can generally be charged to nearer full capacity, but they can be damaged by being overcharged.
Assuming you are getting 65% or 65Ah from your battery, and that it is running at 12.5v. That means that you are getting 0.812 KWh for your £1. Compare that to LPG. Right now, LPG retails at about 85p per litre in some places, rising to 99p in some areas. The energy stored in a litre of propane is about 7KWh. That means that a £1 cycle of a lead acid battery gives as much power as less than 10p worth of LPG.
Of course, that does depend on having refillable LPG storage. Swapping bottles is vastly more expensive - in the UK, at least.
If only it was that simple! Mostly, you don't want the power when the sun is shining. You're more likely to want to use power after the best of the daylight has gone, which means you are using power stored in your batteries. And that's the snag.
Basically, there are two basic types of battery: lead-acid and lithium-ion. The former have been around for a very long time. They're readily available and reasonably inexpensive. The problem is that they don't last very long. A typical "leisure" battery sold for motorhome use has a capacilty of about 100Ah (this means that it can give 5 amps of current for 20 hours, though not 100 amps for one hour). Unfortunately, you can't use all this capacity.
Each time you discharge a lead-acid battery you use some of its life up. How far you discharge the battery makes a big difference to how much life is used up. Typically a leisure battery has about 100 charge cycles if you discharge it to 20% capacity remaining, or 200 charge cycles if you discharge it to half empty.
Given that the battery probably costs about £100, that means that each discharge to 20% costs £1 and each discharge to 50% costs 50p.
The limitations of how batteries are charged in a motorhome probably mean that your battery only gets charged to 85% full, which means that you can only use 65% of its capacity for your £1, or 35% for your 50p.
The maths are little different if you have lithium-ion batteries. These cost between five and ten times as much as lead-acid batteries of the same capacity, but they last much longer and are less damaged by being discharged to quite low levels. They generally last five to ten times as long as their lead-acid equivalent, so the cost per cycle is not a lot different. They are lighter and do charge more quickly, and can generally be charged to nearer full capacity, but they can be damaged by being overcharged.
Assuming you are getting 65% or 65Ah from your battery, and that it is running at 12.5v. That means that you are getting 0.812 KWh for your £1. Compare that to LPG. Right now, LPG retails at about 85p per litre in some places, rising to 99p in some areas. The energy stored in a litre of propane is about 7KWh. That means that a £1 cycle of a lead acid battery gives as much power as less than 10p worth of LPG.
Of course, that does depend on having refillable LPG storage. Swapping bottles is vastly more expensive - in the UK, at least.