What is the difference between kW and kWh?

kW is power, a rate, like the speed on a speedometer. kWh is energy, an amount, like the miles on the odometer. Your array is rated in kW DC, your inverter in kW AC, your battery in usable kWh plus continuous kW, and your utility bills you in kWh. A proposal that mixes these up is worth a very careful second read.

How much does shade actually cost?

More than most people expect on a plain string, and much less with module-level electronics. One module at 40 percent shade in a twelve-module string can cost the whole string over 20 percent; with microinverters the same shade costs about 4 percent.

Will a battery run my whole house?

One 13.5 kWh, 5 kW module will run a well-chosen protected panel for 12 to 30 hours. It will not start a large air conditioning compressor without a soft starter, and it will not carry electric heat. Whole-house backup means two or three modules.

What incentives are available?

The federal residential clean energy credit is currently 30 percent of eligible cost, Colorado exempts qualifying renewable energy components from state sales tax, and Boulder County and several municipalities run efficiency rebates. Amounts and eligibility change. Talk to a qualified tax professional; we are not tax advisers.

Boulder County, since 2016

Your house loses heat before your roof makespower.

We test the envelope, size the mechanicals from a real load calculation, then design an array against what is left. Most people end up with a smaller system and a lower bill than they walked in expecting.

Book an energy audit (720) 555-0185

595Boulder County homes since 2016
1,480kWh per installed kW DC, modelled yearly
4.8from 236 reviews (sample)

kW is the rate. kWh is the amount. We keep them apart on every page.

A home in Boulder County with a rooftop solar array on a sunny afternoon

A family at home in a bright living room

12.6to 5.1 ACH50 on a 1958 ranch

01
NABCEP PV Installation Professional
On every crew, on every job. Not a company certificate hanging in an office.
02
BPI Building Analyst
Required for the rebate programmes we file on your behalf, and for the audit to mean anything.
03
Colorado master electrician
Licence EC.0102938 (sample). Every interconnection and load calculation signed in-house.
04
$2M general liability
Plus workers compensation on all eleven employees. Certificates sent with every contract.
05
10 year workmanship warranty
Roof penetrations, racking, wiring and labour. Separate from the manufacturer warranties.
06
Production guarantee
If first-year output falls more than 10 percent below model for reasons within our control, we make it right (sample terms).

The order of operations

Generate what a tight house needs, not what a leaky one wastes

Solar is the third thing we do, not the first. Doing it in the other order costs more and removes less.

First, the envelope

A house that leaks cannot be fixed with panels

Across the pre-1990 Boulder County housing stock we typically measure 8 to 14 air changes an hour at 50 pascals. Current code for new construction is 3.0. That gap is the back bedroom nobody sleeps in, and it is far cheaper to close than it is to generate around.

Blower door before and after, with both numbers on the invoice
Attic air sealing first, then blown cellulose to R-60
Two inches of closed-cell foam at the rim joist
Mechanical ventilation specified below 3 ACH50

Insulation and air sealing

An installer working in a residential attic space

Then the machines

Sized from a load calculation, not a rule of thumb

Rule-of-thumb sizing overshoots nearly every house we test, commonly by 30 to 40 percent. A room-by-room Manual J against Boulder County's 2 degree F design temperature routinely drops a heat pump a full size, which saves thousands and runs better.

Capacity quoted at 5 degrees F, not at the 47 degree rating
Balance point stated in writing before you sign
Duct static pressure and leakage measured first
NEC 220.83 load calculation for the panel, alongside any charger

Cold-climate heat pumps

An outdoor heat pump unit installed beside a home

Eight things, one crew

What we actually install, and what each one is for

The roof, the attic, the mechanicals and the panel are all ours. There is nobody to point at when something does not line up.

All eight solutions

Energy audits work by GreenLeaf Home Energy

Whole-home energy audit

Blower door, thermal scan, combustion safety and a room-by-room Manual J load, in one visit, with the numbers written down.

Audit fee: $395 for homes to 2,500 sq ft
Time on site: 3 to 4 hours
Typical ACH50 before: 8 to 14 for pre-1990 Boulder County homes

Read the detail

Insulation and air sealing

Seal first, then insulate. Attic to R-60, rim joists closed, and the ACH50 re-tested so you can see it moved.

Attic air sealing and R-60: $2,800 to $5,400
Dense-pack walls: $3.10 to $4.60 per sq ft of wall
Rim joist foam: $950 to $1,700

Read the detail

Heat pumps work by GreenLeaf Home Energy

Cold-climate heat pumps

Sized from a real Manual J and specified at 5 degrees F, not at the 47 degree rating on the brochure.

Ducted cold-climate system: $14,500 to $24,000 installed
Ductless multi-zone: $9,800 to $19,500 installed
Capacity retained at 5 degrees F: 70 to 80 percent of the 47 degree rating

Read the detail

Rooftop solar work by GreenLeaf Home Energy

Rooftop solar for Boulder County homes

Arrays between 5 and 12 kW DC, sized from twelve months of your own kWh rather than from your roof area.

Typical array size: 5.0 to 11.5 kW DC
Modelled specific yield: 1,480 kWh per kW DC per year
Installed price before incentives: $2.75 to $3.40 per watt DC

Read the detail

Battery storage work by GreenLeaf Home Energy

Home battery storage

Usable kWh for outages and for shifting load out of the 3 to 7 pm peak, wired to a protected loads panel you actually chose.

Usable energy per module: 13.5 kWh
Continuous power: 5.0 kW per module
Surge: 10 kW for 10 seconds

Read the detail

EV chargers work by GreenLeaf Home Energy

EV charger installation

Level 2 at 48 A continuous means 11.5 kW and a 60 A circuit. We do the load calculation before we quote the conduit.

Charger power: 7.7 kW at 32 A, 9.6 kW at 40 A, 11.5 kW at 48 A
Breaker required: 40 A, 50 A or 60 A
Typical install: $1,350 to $2,600

Read the detail

Niche arithmetic, not a brochure

One shaded module, three inverter topologies, three very different numbers

Modules in series share a current, so a string runs at the pace of its weakest active substring. Move the sliders. Then try 40 percent shade against 70 percent and watch which one hurts the string more.

Set the array

Array size, kW DC

Power, not energy. The kWh comes out below.

Modules in the series string12 modules

Modules affected by shade1 module

Shade on each affected module40 percent of its cells

Try 40 percent, then 70 percent. The heavier shade costs the string less, because a fully shaded substring bypasses out of the circuit while partial shade drags the current of every module in series with it.

Modelled first-year production

String inverter, no optimisers0 kWh0 percent lost
String plus DC optimisers0 kWh0 percent lost
Microinverters0 kWh0 percent lost

What we would recommend

Extra hardware cost, optimisers: -
Extra hardware cost, microinverters: -
Simple payback on that extra cost: -

Model: 1,480 kWh per installed kW DC per year for an unshaded Boulder array; three bypass diodes per module; string output is the mean module voltage factor multiplied by the lowest active substring current; module-level output is the mean of each module's own product. Conversion efficiency 97.8 percent string, 97.5 percent optimiser, 96.8 percent microinverter. Extra cost $0.11 and $0.14 per watt DC. Energy valued at $0.135 per kWh. All sample figures.

The three ways to wire a roof

String, optimisers or microinverters, side by side

There is no universally right answer. On a clean single-plane roof the plain string wins on cost and simplicity; under two cottonwoods it loses badly.

Efficiency and cost figures are sample ranges for this demo site. The right answer depends on your roof, which is what the simulator above is for.
	String inverter, no optimisers	String inverter with DC optimisers	Microinverters
Maximum power point tracking	One or two per inverter, shared by a whole string	Per module, in a DC-DC converter under each panel	Per module, converting to AC on the roof
Behaviour under partial shade	Severe. A partly shaded module drags the current of every module in series with it	Low. Each module runs at its own maximum power point	Low. Modules are electrically independent
Rapid shutdown, NEC 690.12	Needs a separate rapid shutdown device at each module	Built into the optimiser	Inherent. No high-voltage DC exists on the roof
Monitoring granularity	String total only. You see a number, not a culprit	Per module, in the portal	Per module, in the portal
DC voltage on the roof	Up to 600 V DC on the roof	Clamped to roughly 1 V per module when shut down	No DC beyond the module leads
Conversion efficiency	97.5 to 98.3 percent CEC weighted	97.0 to 98.0 percent CEC weighted, after optimiser conversion loss	96.5 to 97.5 percent CEC weighted
Warranty	12 years standard, extendable to 20	25 years on the optimiser, 12 on the inverter	25 years
Components on the roof	Lowest. Racking, modules, rapid shutdown	One optimiser per module plus a central inverter	Highest. One inverter per module, all of it on the roof
Cost, relative	Baseline	About $0.08 to $0.14 per watt more	About $0.10 to $0.18 per watt more
Best for	Clean, unshaded, single-plane roofs where every module sees the same sky	Mixed planes, some shade, homeowners who want per-module data and one inverter to service	Complex roofs, several small planes, arrays that will grow later, tree-heavy lots

String inverter, no optimisers
Maximum power point tracking
One or two per inverter, shared by a whole string
Behaviour under partial shade
Severe. A partly shaded module drags the current of every module in series with it
Rapid shutdown, NEC 690.12
Needs a separate rapid shutdown device at each module
Monitoring granularity
String total only. You see a number, not a culprit
DC voltage on the roof
Up to 600 V DC on the roof
Conversion efficiency
97.5 to 98.3 percent CEC weighted
Warranty
12 years standard, extendable to 20
Components on the roof
Lowest. Racking, modules, rapid shutdown
Cost, relative
Baseline
Best for
Clean, unshaded, single-plane roofs where every module sees the same sky
String inverter with DC optimisers
Maximum power point tracking
Per module, in a DC-DC converter under each panel
Behaviour under partial shade
Low. Each module runs at its own maximum power point
Rapid shutdown, NEC 690.12
Built into the optimiser
Monitoring granularity
Per module, in the portal
DC voltage on the roof
Clamped to roughly 1 V per module when shut down
Conversion efficiency
97.0 to 98.0 percent CEC weighted, after optimiser conversion loss
Warranty
25 years on the optimiser, 12 on the inverter
Components on the roof
One optimiser per module plus a central inverter
Cost, relative
About $0.08 to $0.14 per watt more
Best for
Mixed planes, some shade, homeowners who want per-module data and one inverter to service
Microinverters
Maximum power point tracking
Per module, converting to AC on the roof
Behaviour under partial shade
Low. Modules are electrically independent
Rapid shutdown, NEC 690.12
Inherent. No high-voltage DC exists on the roof
Monitoring granularity
Per module, in the portal
DC voltage on the roof
No DC beyond the module leads
Conversion efficiency
96.5 to 97.5 percent CEC weighted
Warranty
25 years
Components on the roof
Highest. One inverter per module, all of it on the roof
Cost, relative
About $0.10 to $0.18 per watt more
Best for
Complex roofs, several small planes, arrays that will grow later, tree-heavy lots

The full shading guide Tilt and orientation tables

Three to four hours, then five days

What actually happens on audit day

No score out of a hundred. Measured readings, a room-by-room load, and every recommendation costed and ranked by payback.

The conversation before the instruments

Forty minutes on the history of the house: when it was built, what has been done to it, which rooms are cold, which bills look wrong, what smells or sounds are new. Most of the good hypotheses come from here.

Blower door

We seal the house, mount a calibrated fan in an exterior door and depressurise to 50 pascals. The airflow needed to hold that pressure gives CFM50, which converts to air changes per hour against the conditioned volume.

Thermal sweep under pressure

With outside air being actively pulled in, leaks light up on the camera. Top plates, rim joists, recessed lights, the attic hatch, the flue chase and the band above the garage.

Ducts and combustion

Duct leakage measured where ductwork leaves the thermal envelope, static pressure checked at the air handler, and a combustion safety and carbon monoxide test on every atmospherically vented appliance. Anything unsafe is reported on the day.

Manual J

Room by room, against Boulder County's 99 percent winter design temperature of about 2 degrees F. This is what decides the heat pump size, and it is why our proposals are routinely a size smaller than everyone else's.

The report

Within five business days. Measured readings, not a score. Every recommended measure carries a cost, a modelled saving in therms or kWh, and a simple payback, ranked so you can draw a line wherever your budget is.

The audit in full Book one

Nothing hidden in a change order

Everything in the price, written on the quote

Twelve months of your own kWh, pulled with written authorisation
Per-plane roof survey: azimuth, pitch, annual solar access, covering and remaining life
Structural check against dead load plus Boulder's ground snow load
Per-module shade profile and a modelled loss figure for all three inverter topologies
NEC 220.83 load calculation and the 120 percent busbar check on your service panel
Permit drawings and the permit itself, city or county

Utility interconnection application and the meter exchange
Rapid shutdown to NEC 690.12, labelled to the inspector's checklist
Flashed mounting feet into rafters, wind zone specification for the corridor towns
Commissioning readings: string voltage, current under load, insulation resistance
Two years of monitoring and the monthly variance report, included
Ten year workmanship warranty on penetrations, racking, wiring and labour

Anything we find that is not in the quote gets priced and agreed before we do it. Most of our change orders are downward, because the audit usually finds the house needs less than people assumed.

A GreenLeaf crew installing modules on a Boulder County roof — 10year workmanship warranty on both trades

Martin Acres, 1958 ranch

The same attic, before and after forty hours

Drag the handle. The array on this house ended up at 6.8 kW DC instead of the 11 kW the homeowners walked in asking for.

The attic after air sealing and blown cellulose to R-60

The same attic before air sealing, with open top plates and bare framing

BeforeAfter

01
12.6 ACH50 before
Open top plates above every interior partition, eleven uncapped can lights, an uninsulated attic hatch and an effectively open rim joist along the north wall.
02
Two days of sealing
Foam, caulk and gasket at the ceiling plane. No insulation added until the camera stopped showing cold air moving.
03
R-60 blown cellulose
Baffles at every soffit bay, depth markers set, material verified in three places.
04
5.1 ACH50 after
Retested with the same calibrated fan. Both numbers went on the invoice, which is the only way either of them means anything.

Sample amounts, not tax advice

Money that comes back off the price

Six programmes currently reach Boulder County homes. Some reduce the contract price at the point of sale, some are rebates you claim afterwards, and some are credits against income tax you only see at filing. They are not interchangeable, and we say which is which on every quote.

Read all six in detail

Every figure on this page is a sample for a demo site. Eligibility, percentages and expiry dates change, often mid-year. We are not tax advisers; take the numbers to one.

01
Federal residential clean energy credit
30 percent of eligible cost
Solar, battery storage of 3 kWh or more, and certain associated electrical work
A credit against federal income tax, not a rebate. It reduces what you owe; it is not a cheque. Eligibility, percentage and expiry are set by federal law and change. Talk to a qualified tax professional.
02
Federal energy efficient home improvement credit
Up to $2,000 for a qualifying heat pump, up to $1,200 for envelope measures
Cold-climate heat pumps, insulation, air sealing, and a credit toward the audit itself
Annual caps apply and reset each tax year, which is a genuine argument for splitting a large project across two years. Not tax advice.
03
Colorado sales and use tax exemption
State sales tax waived on qualifying components
Renewable energy generation equipment and certain storage components
Applied at the point of sale by us, so it shows up as a lower line on your contract rather than as a claim you file.
04
Colorado heat pump tax credit
Sample figure: 10 percent of the installed cost of a qualifying system
Air source and ground source heat pumps and heat pump water heaters
Administered through the installer at point of sale in most cases. Amounts step down over time. Sample figure only.
05
Boulder County EnergySmart
Sample figure: $400 to $2,400 depending on measure
Audits, air sealing, insulation, heat pumps and heat pump water heaters
Requires a pre-work audit from a certified auditor. Ours qualifies, and we prepare the paperwork as part of the report.
06
Utility efficiency rebates
Sample figure: $150 to $1,500 depending on measure and utility
Insulation, air sealing, heat pumps, heat pump water heaters and smart thermostats
Boulder, Lafayette, Louisville and Superior sit in Xcel Energy territory; Longmont has its own municipal programme with different amounts and forms.

Sample offers for this demo site

Four ways the price comes down before any incentive

These are ours, not a programme's. They come off the contract, and they stack with whatever rebates and credits you separately qualify for.

01
Audit fee credited back
The $395 whole-home energy audit comes off any GreenLeaf installation over $6,000 signed within 90 days of the report.
Sample offer. One credit per property. Cannot be combined with the bundle discount below.
Ends 31 December 2026
02
Roof and array in one visit
Book a solar-ready reroof with the array in the same mobilisation and we take $1,200 off the combined price.
Sample offer. Applies to combined contracts over $22,000 with both scopes in one schedule.
Ends 30 April 2027
03
Two years of monitoring included
Every rooftop array we install includes two years of the $196 a year monitoring and maintenance plan at no charge.
Sample offer. Standard on all GreenLeaf rooftop installations, no code needed.
Standing offer
04
Neighbour referral
If a neighbour on your street signs an install within a year of yours, you both get $350 and we get a shorter drive.
Sample offer. Paid on commissioning. Code NEIGHBOUR350 at the time of quote.
Standing offer

Offers shown are sample content for this demonstration website and are not a binding offer of goods or services.

The reason most people call us

Where your household's carbon actually comes from

Electricity, gas and driving, in tonnes of CO2 equivalent a year, and what each upgrade removes. Note the order: sealing first, so the heat pump can be smaller.

Last twelve months

Electricity, kWh a year

On the bill, or your average monthly kWh multiplied by twelve.

Natural gas, therms a year

Heating, hot water and cooking if any of them run on gas.

Petrol or diesel miles a year

Average miles per gallon

Electric miles a year

At about 0.30 kWh a mile, already counted in your electricity if you charge at home.

Where it comes from

0.0metric tonnes of CO2 equivalent a year

Electricity0.0 t
Natural gas0.0 t
Driving0.0 t

What each upgrade removes

Air sealing and R-60, cutting heating by 22 percent: 0.0 t
An array covering 90 percent of today's electricity: 0.0 t
A cold-climate heat pump replacing the gas furnace: 0.0 t
Swapping the petrol miles for electric miles: 0.0 t
All four, in the order we would do them: 0.0 t

Sample emission factors: 0.62 lb CO2e per kWh for the Colorado grid, 11.7 lb per therm of natural gas, 19.6 lb per gallon of petrol. Heat pump modelled at a seasonal coefficient of performance of 2.6, electric driving at 0.30 kWh a mile. The grid factor falls every year, which makes electrification look better over time and is not modelled here.

Every page worth reading, all 30 of them

The index, because a menu is not a map

Tools you can run yourself, the engineering behind them, the money side, and the evidence that we can do the work. No hierarchy games.

What we install

Work out your own numbers

Money and paperwork

Proof and people

Four a year, and that is all

Field notes from Boulder County roofs and attics

What the blower door found, what the monitoring caught, which rebate changed and what it means for a house like yours. Written by the people who did the work, not by a marketing department. No sequences, no drip, no sales calls.

01Seasonal reminders that actually save energy, sent before the season
02Rebate and rate changes in plain language, with the arithmetic
03One measured case study an issue, numbers included

Your house loses heat before your roof makespower.

Credentials and guarantees

NABCEP PV Installation Professional

BPI Building Analyst

Colorado master electrician

$2M general liability

10 year workmanship warranty

Production guarantee

Generate what a tight house needs, not what a leaky one wastes

A house that leaks cannot be fixed with panels

Sized from a load calculation, not a rule of thumb

What we actually install, and what each one is for

Whole-home energy audit

Insulation and air sealing

Cold-climate heat pumps

Rooftop solar for Boulder County homes

Home battery storage

EV charger installation

One shaded module, three inverter topologies, three very different numbers

String, optimisers or microinverters, side by side

String inverter, no optimisers

String inverter with DC optimisers

Microinverters

What actually happens on audit day

The conversation before the instruments

Blower door

Thermal sweep under pressure

Ducts and combustion

Manual J

The report

Everything in the price, written on the quote

The same attic, before and after forty hours

12.6 ACH50 before

Two days of sealing

R-60 blown cellulose

5.1 ACH50 after

Money that comes back off the price

Federal residential clean energy credit

Federal energy efficient home improvement credit

Colorado sales and use tax exemption

Colorado heat pump tax credit

Boulder County EnergySmart

Utility efficiency rebates

Four ways the price comes down before any incentive

Audit fee credited back

Roof and array in one visit

Two years of monitoring included

Neighbour referral

Where your household's carbon actually comes from

The index, because a menu is not a map

What we install

Work out your own numbers

Money and paperwork

Proof and people

Field notes from Boulder County roofs and attics

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