So what can we do with the audit information?
That sample household is my humble abode. Here's what I did.
I am beginning this Think Engine ESCo business and so I need reliability and some measure of energy independence from the Guyana Power & Light (GPL) electric utility. I am using savings as capital, but it is very limited. Therefore I have to achieve this in under a million Guyana dollars.
I consider what must be continuously operational other than keeping body and soul together. The answer is easy: my communication system.
Laptop computer must be able to operate at any time; wireless internet and weather station must be able to operate all the time; and I will want to access or back up data in a cloud which must be continuously available.
Consulting the data fom the Energy Auditing page, these would require about 1.5 kWh per day. 300 W of solar panels with 5 hours of sunshine a day would provide that [300 W = 0.3 kW, 0.3 kW × 5 h = 1.5 kWh].
I therefore buy 2 solar panels @ 150 W each to get the 300 W. This requires 200 Ah of battery, which requires a charge controller. Inverter and wiring are also necessary.
The appliances I intend to operate all run at 110-120 V alternating current (AC) so I need an inverter to convert the direct current (DC) from the battery to AC.
I need the battery to store the DC current coming from the solar panels. Here's how I calculate the battery size.
A battery is rated by its capacity in ampere hours (Ah). One Ah means a battery can give a current of 1 A for 1 h. 200 Ah means that the battery can give 200 A in one hour, or 100 A for 2 h, or 50 A for 4 h or 20 A for 10 h or 5A for 40 h or 1 A for 200 h.
I choose a 12 V 200 Ah deep-cycle AGM battery which can store 12 V × 200 Ah = 2 400 Wh = 2.4 kWh, so it can certainly supply the 1.5 kWh I need.
Why did I not choose a smaller and therefor less costly battery? 1.5 kWh can indeed be obtained from a 12 V 125 Ah battery, but it would be exhausted too near the reversible equilibrium concentration of the chemicals in the reaction that powers the ability of the lead-acid battery to charge and discharge. This shortens the life of the battery. There are other kinds of battery available, e.g., lithium-ion batteries which do not have this problem, but are still too expensive on this scale, or sodium-sulphur batteries, which do not have that problem and are cheap, but which must operate at too high a temperature with very corrosive materials to feel safe with.
So, even though I choose a deep-cycle battery, not the ordinary vehicle battery, the chemistry will only allow me long battery life with low battery use.
These are necessary to avoid overcharging the batteries.
A good voltmeter should be sufficient to indicate the state of charge.
Next, relating voltage to state of charge of battery.
And after that, inverters.
Most of the scheming I had to do in the previous column, and of course the expense, could be avoided if I lived in a country with the technological capacity of the USA. Note well, I do not say live in the USA, because here in Guyana we are closer to the equator and have more intense sunshine than on mainland USA.
What is happening in the USA, is that a householder can connect his solar power to the electric utility grid in a special way called a grid-tie. He works out a power purchase agreement (PPA) with the utility, buys as many solar panels as he can afford with microinverters and connects them to the grid. When the sun shines he sells any excess electricity to the utility. When the sun does not shine (at night, or in winter), he uses electricity from the grid. Only if the grid goes down during non-sunshine periods would he need battery storage, and can therefore invest in batteries that last longer, because the infrequency of the back-up will have the batteries just as infrequently cycling deep.
WHAT ABOUT INDUSTRIAL ENERGY?
The same principles apply. The details are just more and often much larger. Therefore more time is involved in accounting and measuring safely.
But there is one big difference: household energy is used to achieve convenience and comfort; whereas industrial energy is used primarily to produce something; convenience and comfort are important only in so far as they contribute economically to production.
An obvious consequence of the larger amounts of energy consumed is that any inefficiencies that one might have overlooked on the household scale, can no longer be overlooked. And the generation, transmission and distribution of electrical energy on the larger scale usually means using the cheaper but more technical 3-phase system.
Next: matching energy and production.
Obviously we do not live in the USA so we can not access that kind of enlightenment. Should we forget about it?
Suppose you want to go solar (for whatever reason, but usually because you cannot get reliable electricity) then if you have capital you can invest in as much as you need. The only question is: is it worth it? And suppose you don't have capital?! ...