Solar Scams

A dear friend of mine, knowing of my interest in solar power generation, asked me about an emergency power backup system being sold by Solutions From Science [sic]. She was quite interested in this offering because it was a seemingly reasonable alternative to a gas generator. In particular, she was attracted by the elimination of the storage of gas and the fumes from a running generator.

I took a look at the system which was being offered and sent her the following in an email:

Hi Friend,

I'm glad your forwarded this link to me as I was quite curious.

Executive Summary

It would be a waste of money and you would not be happy with this system's performance.

Analysis

This is basically a very low power solar panel (90 watts, barely enough to power a light bulb when in full sunlight). This panel is going to charge a battery capable of providing 1,800 watts.

They don't say how long that battery can provide those 1,800 watts which is one concern. Normally, a company will specify a battery's capacity in terms of watt-hours, or how many watts it can provide for how many hours. If we guess that the battery can provide 1,800 watts for an hour before it is completely depleted then we can estimate how long it can power certain appliances:

• A 22 cu. ft. Energy Star refrigerator typically uses 500 kWh per year, or 1.37 kWh per day. With 1,800 watt-hours available that refrigerator would run for about 31 hours.
• A washing machine uses anywhere from 1.9 kWh to 4.5 kWh per load. So the battery wouldn't even be able to do one load.

Actually, though, it's very bad to completely deplete a battery. Usually, a battery should never be discharged below 20%. I doubt that they're being honest about the battery capacity.

One other interesting question is: How long would it take to recharge the battery? Let's guess that we experience a power outage in the winter (since they seem to inject fear of power loss in a winter storm) but that there's no storm or even a single cloud in the sky. The normal 'peak' sun hours in winter is usually given as 4 hours. Let's say that we've used the maximum recommended capacity of the battery (80%) which means we need to put back into the battery a fresh 1,440 watt-hours. The efficiency of a charge controller is usually about 85%. So let's calculate how many hours it would take to recharge the battery:

• total hours to recharge = watt-hours required to charge the battery / (output of the solar panel x efficiency)
• total hours to recharge = 1440 / (90 x 0.85)
• total hours to recharge = 18.8 hours

• total days to recharge = 18.8 / 4
• total days to recharge = 4.7 days

So this says that at best you would have to charge that battery for five days just to do one load of wash.

This is also saying that the best power you could possibly get out of this system in the winter would be a measly 306 watts per day! This is barely enough to provide light.

This system is clearly a scam. You would probably be better off picking up a small diesel generator and barrel of fuel.

I hope these words are helpful.

Mike

It's disgusting how some people prey on other's fears.