pros and cons

Whenever I hear someone use the phrase solar generator, I invariably find myself asking them what it is exactly that they mean by solar generator. Some people use the phrase solar generator to simply refer to solar power generation from solar panels. There is an abundance of information on this and other sites about solar panels and grid-connected residential solar power systems and so I will not repeat this information here.

 

What does require explanation is when the phrase solar generator is used to describe an all in one power generation and storage solution. A class of product has become common on the market recently that refer to themselves as solar generators. This articles examines these products and provides some warning for those that are considering purchasing them.

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What exactly is a solar generator and how do they work?

Products known as solar generators usually contain:

  • Solar panels 
  • A battery charger to allow the electricity generated by the solar panels to charge the battery 
  • Solar batteries 
  • An inverter to convert the power stored in the battery to AC power that can be used to power the electrical devices you wish to use.

 

diagram

 

What is a typical voltage for a solar generator to operate at?

Solar generators are typically built for the voltage of the battery bank. Standard voltages are generally 12V, 24 volts or 48 volts.

What does the charge controller or solar battery charger do in a solar generator?

The role of the battery charger or solar charge controller is to do two things.

  • It is to convert the electricity received from the solar panels to the voltage required by the battery bank; and
  • To regulate the flow of power from the solar to the battery bank so as not to damage the batteries. Solar batteries need to be treated carefully in terms of the rates at which they are charged and discharged so as not to damage them.

What does the battery do in a solar generator?

At the risk of being overly simplistic, the role of the battery is to store power so that it is available when you need to use it. Solar is an intermittent energy generation source and so it may not be generating electricity right at the moment you need to use electricity. Even if it is generating solar power it may not be generating enough to power the electrical devices that you want to use.

What does an inverter do in making a solar generator work?

The electricity that is produced by the solar panels and stored in the battery is produced and stored as DC (direct current electricity). However, most of the household appliances that we want to run require AC power at either 110 volts or 240 volts, depending on where you are.

Inverters in a solar generator are usually pure sine wave inverters. So the inverter performs two functions in a solar power generation system:

  • It converts the DC power to AC power;
  • It steps up the voltage from either 12V, 24V or 48V to the required voltage of either 11 volts or 240 volts.

Why are there more portable solar generators than fixed solar powered generators?

The evolution of the portable solar generator has come about because in most fixed locations, such as peoples homes and businesses, people have access to grid power at a relatively affordable cost.

Because the public grid supplies energy 24x7 and battery storage for solar power is expensive it has not been cost effective to have fixed solar generators (solar panels and battery storage) in most areas connected to the grid.

man with portable generator

Source: Goal Zero

However, there has for 30-40 years been an off-grid solar industry to supply the power needs of people who live or holiday in areas not served by the grid. These off-grid power systems are essentially larger versions of what have been packaged up today as solar generators.

 

How much electricity do solar generators give you?

A quick look around the internet shows that most of the products being solar as solar generators are sold with energy storage capability of between .1 and 2 kWh. To put this in context according to the Energy Information Administration the average American household uses around 30 kWh’s per day of electricity. So if your thinking of going out bush and living like a king...think again.

You can see the range of solar generators from an online store here: https://www.goalzero.com.au.

 

There are also a lot of solar generators sold on websites like eBay. If we take the goal zero Yeti solar generator (a product we have no affiliation with) we see it has the following specifications:

 

goal-zero-generator 

 

SpecificationData
Product Code GZ39005
Charge by Wall 18hrs
Vehicle charge via optional DC to DC charger (20A) 5 hrs
Charge by 1 x Boulder 90 20hrs
Battery Capacity 18-22V, 100Wh
Solar Type Monocrystalline, 17-18% efficient
Kit Weight 52.5kg
Cell Type Monocrystalline
MC4 Connectors 14-22V, up to 6A (90W max)
Weight of Panel 9.8 kg
Dimensions of Panel 950 x 680 x 35mm
Certs CE, FCC, ROHS

 

What can a solar generator power and for how long?

If we stick with the example above (which I think is a good example because at around $2,500 this solar generator is about the largest most people would consider buying and other cheaper models actually produce and store less energy) this unit contains 100 Wh of energy full charged. This is .1 kWh. To give you a reference a standard refrigerator uses between 1-2 kWh per day and so this unit could run a full sized fridge for 1-2 hours.

However, applications like charging a phone or a CFL or LED light only use very small amounts of energy and so these appliances can work for quite a long period of time. Here is how long the maker of the above generator claims that the above generator could run each of the following applications for if the battery started fully charged, the solar was generating and the below load was the only load drawing on the generator:

 

DeviceCharges
Light-A-Life 410-420hrs
MP3 Player 410-420
Action Cam 300-320
GPS 150-410
Smartphone 125-250
Camera 85-250
Camp Fridge 40-85hrs
Tablet 30-80
Cordless Tools 20-65
Laptop 12-25
CPAP 6-85hrs
Large Fridge 6-25hrs
Television 4-13hrs
Power Tools 1-5hrs
 

Some of these claims seem optimistic. I am not sure how a unit with 100 Wh’s (.1 kWh or one-tenth of a kilowatt hour) of capacity could run a fridge that uses around .05 -.1 kWh’s of power per hour for 6-25 hours.

 

How big are solar generators, are they really portable?

At 52KG (about 115 pounds) it could be argued that claiming that this solar generator is portable is a stretch but the reality is that most solar generators are permanently attached to moving structures such as boats, caravans and camping trailers. So in reality generators become portable by virtue of what they are mounted on.

 

What are are advantages of solar generators?

In a word, they are quiet and don’t require fuel. Diesel generators are noisy and require refueling so if you have very minimal electrical requirements (i.e one light, phone charging and a very small and very efficient camp fridge) then they can be useful. Low recurring electrical loads in very remote locations are the strength of solar generators. But for a serious power source, or as a power station for a remote community they are not really as good as a diesel generator.

Silent operation can be an advantage when hunting or fishing and I know a bloke in Australia who has a goal zero yeti 400 for camping to provide a 12 volt power supply capable of 100 watt hours. Another advantage of a solar generator over a diesel or petrol generator is that you don’t have to worry about stale fuel where the generator may stand idle for a long time.

 

What are the disadvantages of most portable solar generators?

The three key disadvantages of solar generators are typically:

  • They are very slow to charge the battery storage capacity that they do have; They can only store a very small amount of electricity in their battery. This disadvantage comes from the use of lead acid batteries and the energy storage device in the generator and the fact that lead acid batteries are very heavy. Storing large amounts of energy using lead-acid batteries would make the solar generators difficult to transport.
  • They can only release energy in the form of ac output at a defined rate. The rate at which the battery in a unit can be charged and the rate at which it can be discharged are controlled by the battery charger and the inverter and are usually only enough to service the type of electrical load associated with a light and a camp fridge. It is probably not possible to use electrical appliances that have large start up loads like air-conditioners using a solar generator.
  • They are expensive relative to a fuel powered generator with the same power output and even compared to a fuel powered generator with 10 times more electricity production capacity.
  • They offer a limited amount of battery backup with a maximum draw of 1500 watts (1.5 kw) being common

 

Are solar generators suitable for backup power for grid failures?

Solar generators will almost always be unsuitable for applications for backup power when there are power outages on the grid because typically appliances connected to the grid will be drawing much more power than what a solar generator could supply instantaneously.

 

So when all is said and done would I use a solar generator for my boat, caravan or camper?

The short answer is …...no. I would have my car or boat motor charging a battery while it is running and then run from that battery when I am stationary for a long time. Alternators from an engine can produce far more power than solar and you can use quite cheap batteries that offer much more storage capacity and that will allow you to run more appliances for a longer time.

Having said this I have seen great applications for solar generators where there is a very low power need in a very remote location. One such example I came across was a trough monitoring camera on a remote ranch in the Australia outback. The solar generator simply needed to provide a charge to a camera broadcasting pictures of water in troughs over a 2,000 square mile farm. In fact off-grid solar really got its start in telecommunications repeating stations.

As a rough rule of thumb if you can charge something with a USB it is probably an application that can be powered by a solar powered generator. The remote nature of outback ranches in Australia is why many solar charge controllers and solar generator kits originated in Australia.

 

Will Lithium-Ion battery technology make future solar generator kits more attractive?

I think the answer is yes. Lithium-Ion batteries offer far higher energy density than lead-acid batteries that have traditionally been used in solar generators.

 

However, what has slowed the adoption of Lithium-Ion battery technology in solar generator kits has been the development of the electronics to support the way that Lithium-Ion batteries require a battery management system that treats the batteries differently than what solar charge controllers and sine wave inverters have traditionally treated lead-acid batteries. However, makers of solar battery chargers and solar inverters are teaming up at increasing rates with makers of Lithium-Ion batteries and Li-Ion battery management systems to integrate their electronics into seamless packages. I would expect solar generators to be released over 2018 and 2019 with Li-Ion batteries are much larger energy storage capacity.

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