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We have solar and the bill still went up
This page is about the half of that sentence a heating contractor can actually speak to. It contains no tariffs, no export values and no savings figures, and that is deliberate.
Three things to hold on to.
One: solar changes where the electricity comes from, not how much the house needs. A system that is oversized, badly charged, or leaking a third of its air into a 140-degree attic uses exactly the same amount of electricity whether the roof is generating or not. The panels make that less visible, not less expensive.
Two: we will not tell you anything about your tariff. Not what your exports are worth, not which rate plan you are on, not what a kilowatt-hour costs you at four in the afternoon. Those change, they are your utility’s to state, and a heating contractor guessing about them has cost people real money. Everything on this page is about when and how much your system runs, which is ours.
Three: we do not install or service solar. If the question is whether the array is performing, that is a solar contractor and your own production data. We will not have a view.
Pick what you have and what you want to know. Everything below is written out in full.
Storage sizing depends on your generation, your consumption profile, your tariff and what you want the battery to do — bill management, backup, or both. Those are different answers and they need somebody who works with your production data and your utility’s terms. A heating contractor with an opinion about it is guessing with your money.
There is exactly one thing we can tell you that is relevant, and it is worth knowing. Air conditioning is a large, concentrated load. A compressor starting draws far more than it draws while running, and some storage set-ups handle that starting surge better than others. If backup during an outage is part of what you want, whether the battery and inverter can actually start your outdoor unit is a specific question to put to the storage installer — in writing, naming your equipment.
And one practical point that is free. If a battery is being considered partly because the house uses a lot in the afternoon, it is worth finding out why it uses a lot first. Reducing the load is cheaper than storing electricity to feed it, and in this housing stock the load is usually reducible.
We are glad to give a storage installer the measurements they need. We will not stand in for one.
Solar panels only
The commonest set-up here, and the one where the disappointment usually has a mechanical explanation.
What to look at, in order. First, duct leakage, because in a two-storey house with attic ducts it is the largest single avoidable load and it is invisible. Second, the charge, because a system that is over or under charged runs longer for the same effect. Third, the schedule, because a thermostat set to recover hard at five is buying the most expensive part of the afternoon. Fourth, whether the system is oversized, which shortens run times and hurts comfort without reducing consumption much.
What we will not do is tell you how any of that interacts with your billing. We will tell you how much your system runs and when, and that is a genuinely useful number to take to somebody who does understand your tariff.
Solar and a battery
Then the mechanical question sharpens, because with storage the size and shape of the load matters more than the total.
A system that runs long and steady at a lower output is easier on storage than one that starts hard, runs for eight minutes and stops — which is another reason oversizing is worse than people think. Equipment that can modulate suits a house with a battery particularly well, though that is a replacement decision rather than something to act on today.
The one question worth asking your storage installer, in writing and naming your equipment: can the battery and inverter start the outdoor unit during a backup event? A compressor start is a large momentary draw and the answer is not always yes.
And the boring answer still applies. A leaking duct system wastes stored electricity exactly as efficiently as it wastes grid electricity.
Solar, on a time-of-use plan
Then when the system runs matters as well as how much, and that is a question we can answer in mechanical terms without going anywhere near your rates.
Pre-cooling is the technique and it is genuinely useful in this climate. Cooling the house a little further during the part of the day that suits your plan, then letting it drift back up during the part that does not, shifts consumption without making anybody uncomfortable. How well it works depends on the house: a well-insulated house with good windows holds what you put into it for hours, and a leaky one gives it back in forty minutes.
Which is the honest catch. Pre-cooling works in proportion to how well the building holds temperature, so the houses that would benefit most from shifting are often the ones least able to. That is measurable, and it is worth knowing before you rearrange your day around a thermostat schedule.
What we will not do is tell you which hours are the expensive ones. Your utility states that and it changes.
No solar yet, considering it
Then there is one piece of advice worth more than anything else on this page: reduce the load before you size the array.
An array is sized against how much electricity the house uses. Fix a leaking duct system, correct a charge and sort out the thermostat schedule first, and the house needs less — which means a smaller array does the same job. Do it the other way round and you have paid for panels to feed a problem, and you will still have the problem.
What that looks like in practice: a duct leakage test and a service before you get solar quotes. It is a small amount of money, it takes a morning, and in a house of this type it frequently changes the size of the array being proposed.
It is also worth doing any planned equipment replacement before the array is sized rather than after, for the same reason.
Solar that came with the house
The situation with the most unknowns, and two of them are not ours.
Not ours: whether the array is owned, leased or on a power purchase agreement, and what that means for you. And whether it is performing as it should, which needs the production data and a solar contractor.
Ours, and worth doing early: establishing what the heating and cooling system actually is and what condition it is in. A house bought with solar frequently comes with equipment nobody has told you anything about — its age, whether it was ever commissioned, what the ductwork is doing. That is the half of the electricity story you can still change.
One specific thing to check. If there is an array on the roof and the equipment is near the end of its life, the practicalities of replacing that equipment — access, working around the array, whether anything has to be isolated — are worth understanding before it becomes urgent in August.
Why the bill did not drop
There are only really four mechanical explanations, and they are all measurable.
The house uses more than anybody assumed. Duct leakage into a hot attic is the big one in this housing stock, and it is completely invisible. A leakage test gives you a number.
The system runs longer than it should. A charge that is wrong in either direction, a dirty coil, a blocked filter or restricted ductwork all make a system work longer for the same result.
It runs at the wrong times. A schedule written for a different household, or a recovery set to pull the house down hard at five.
Or the load simply grew. More people at home, a car charger, a home office, a second fridge in the garage. None of that is the panels’ fault.
What is not on this list is anything about your tariff, and we would ask you to notice that a lot of the people happy to explain your bill to you also have something to sell.
When to run the air conditioning
Mechanically, there are two honest principles and they are both about the building rather than the meter.
A system works less hard earlier in the day. Cooling a house when it is 85 outside takes less out of the equipment than cooling it when it is 102, because the difference the machine has to work against is smaller. That is physics and it is true regardless of what anybody is charging.
And a house holds what you put into it, for a while. How long depends on insulation, glazing and air leakage. That is what makes shifting consumption possible at all, and it is measurable.
Between those two: cooling earlier and letting it drift later usually costs less energy and shifts what remains. How much of that is worth to you depends entirely on your plan, which is not ours.
One caution. Do not let a thermostat sit at a setback all afternoon in a house that cannot hold temperature. You will be uncomfortable for six hours and then the system will run flat out anyway, which is the worst of both.
Whether to add a battery
See the note above, which is the whole of our position: not our trade, and we will not size or recommend one.
The only thing we would add is the order of operations. If the reason a battery is being considered is that the house uses a great deal in the afternoon, it is worth establishing why before deciding to store electricity to feed it. Reducing the load is almost always cheaper than storing energy for it, and in the houses around here the load is usually reducible by a meaningful amount.
Whether to go all-electric
This one is genuinely ours, at least the heating part of it, and there are three things worth knowing before anybody quotes.
The panel. A heat pump replacing a gas furnace adds electrical load to a service that may already be carrying solar equipment, and possibly a car charger. Whether the panel can take it is the first question and it is the one that most often changes the cost. We check it before quoting rather than after.
The ductwork. A heat pump moves more air for the same effect than a gas furnace does. Ductwork that was marginal with gas can be genuinely inadequate with a heat pump, and that has to be established in advance rather than discovered in the first cold week.
And the winter. This is a mild climate for heat pumps and they work well here. But the backup electric heat is the expensive part, and how the controls stage it decides whether your winter bill is reasonable or alarming. That is a commissioning decision, not an equipment one.
What we will not do is tell you whether it will save you money against gas. That depends on your rates for both fuels, which is exactly the thing we will not guess at.
Do this next
Get a duct leakage test and a proper charge check, in that order. Those two explain most disappointing solar outcomes in this housing stock, and neither requires anybody to know anything about your tariff.
Do this next
Ask your storage installer, in writing, whether the system can start your outdoor unit during a backup event. And get the duct leakage measured, because storage wastes just as efficiently as the grid does.
Do this next
Find out whether your house can actually hold temperature before you build a schedule around it. Pre-cooling works in proportion to how well the building holds what you put into it, and that is measurable.
Do this next
Reduce the load before the array is sized. A duct test and a service before you collect solar quotes. It is a morning’s work and it frequently changes the size of what is proposed.
Do this next
Find out what the heating and cooling system actually is and what state it is in. That is the half of the electricity story you can still change, and it is the half nobody told you about at the sale.
What this page will not tell you
Nothing about tariffs. No rate plans, no export values, no peak hours, no cost per kilowatt-hour. They change, they are your utility’s to state, and we have watched people be given confident wrong answers about them by tradespeople.
Nothing about whether your array is performing. That is a solar contractor with your production data.
And no savings figure for anything we do. Sealing ducts in a house with attic ductwork helps, sometimes a great deal. By how much depends on how leaky it was, which is why we measure before and after and give you both numbers instead of a percentage.
The measurement, not the opinion
A visit, the duct leakage measured with a number, the charge and airflow checked, and a written note of how much your system runs and when. Whatever you do with it afterwards, the figures are yours.